text: /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
   * Copyright by The HDF Group.                                               *
   * Copyright by the Board of Trustees of the University of Illinois.         *
   * All rights reserved.                                                      *
   *                                                                           *
   * This file is part of HDF5.  The full HDF5 copyright notice, including     *
   * terms governing use, modification, and redistribution, is contained in    *
   * the COPYING file, which can be found at the root of the source code       *
   * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
   * If you do not have access to either file, you may request a copy from     *
   * help@hdfgroup.org.                                                        *
   * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
  
  /*-------------------------------------------------------------------------
   *
   * Created:             H5ACmpio.c
   *                      Jun 20 2015
   *                      Quincey Koziol
   *
   * Purpose:             Functions in this file implement support for parallel
   *                      I/O cache functionality
   *
   *-------------------------------------------------------------------------
   */
  
  /****************/
  /* Module Setup */
  /****************/
  
  #include "H5ACmodule.h" /* This source code file is part of the H5AC module */
  #define H5F_FRIEND      /*suppress error about including H5Fpkg	  */
  
  /***********/
  /* Headers */
  /***********/
  #include "H5private.h"   /* Generic Functions			*/
  #include "H5ACpkg.h"     /* Metadata cache			*/
  #include "H5Cprivate.h"  /* Cache                                */
  #include "H5CXprivate.h" /* API Contexts                         */
  #include "H5Eprivate.h"  /* Error handling		  	*/
  #include "H5Fpkg.h"      /* Files				*/
  #include "H5MMprivate.h" /* Memory management                    */
  
  #ifdef H5_HAVE_PARALLEL
  
  /****************/
  /* Local Macros */
  /****************/
  
  /******************/
  /* Local Typedefs */
  /******************/
  
  /****************************************************************************
   *
   * structure H5AC_slist_entry_t
   *
   * The dirty entry list maintained via the d_slist_ptr field of H5AC_aux_t
   * and the cleaned entry list maintained via the c_slist_ptr field of
   * H5AC_aux_t are just lists of the file offsets of the dirty/cleaned
   * entries.  Unfortunately, the slist code makes us define a dynamically
   * allocated structure to store these offsets in.  This structure serves
   * that purpose.  Its fields are as follows:
   *
   * addr:	file offset of a metadata entry.  Entries are added to this
   *		list (if they aren't there already) when they are marked
   *		dirty in an unprotect, inserted, or moved.  They are
   *		removed when they appear in a clean entries broadcast.
   *
   ****************************************************************************/
  typedef struct H5AC_slist_entry_t {
      haddr_t addr;
  } H5AC_slist_entry_t;
  
  /* User data for address list building callbacks */
  typedef struct H5AC_addr_list_ud_t {
      H5AC_aux_t *aux_ptr;      /* 'Auxiliary' parallel cache info */
      haddr_t *   addr_buf_ptr; /* Array to store addresses */
      unsigned    u;            /* Counter for position in array */
  } H5AC_addr_list_ud_t;
  
  /********************/
  /* Local Prototypes */
  /********************/
  
  static herr_t H5AC__broadcast_candidate_list(H5AC_t *cache_ptr, unsigned *num_entries_ptr,
                                               haddr_t **haddr_buf_ptr_ptr);
  static herr_t H5AC__broadcast_clean_list(H5AC_t *cache_ptr);
  static herr_t H5AC__construct_candidate_list(H5AC_t *cache_ptr, H5AC_aux_t *aux_ptr, int sync_point_op);
  static herr_t H5AC__copy_candidate_list_to_buffer(const H5AC_t *cache_ptr, unsigned *num_entries_ptr,
                                                    haddr_t **haddr_buf_ptr_ptr);
  static herr_t H5AC__propagate_and_apply_candidate_list(H5F_t *f);
  static herr_t H5AC__propagate_flushed_and_still_clean_entries_list(H5F_t *f);
  static herr_t H5AC__receive_haddr_list(MPI_Comm mpi_comm, unsigned *num_entries_ptr,
                                         haddr_t **haddr_buf_ptr_ptr);
  static herr_t H5AC__receive_candidate_list(const H5AC_t *cache_ptr, unsigned *num_entries_ptr,
                                             haddr_t **haddr_buf_ptr_ptr);
  static herr_t H5AC__receive_and_apply_clean_list(H5F_t *f);
  static herr_t H5AC__tidy_cache_0_lists(H5AC_t *cache_ptr, unsigned num_candidates,
                                         haddr_t *candidates_list_ptr);
  static herr_t H5AC__rsp__dist_md_write__flush(H5F_t *f);
  static herr_t H5AC__rsp__dist_md_write__flush_to_min_clean(H5F_t *f);
  static herr_t H5AC__rsp__p0_only__flush(H5F_t *f);
  static herr_t H5AC__rsp__p0_only__flush_to_min_clean(H5F_t *f);
  
  /*********************/
  /* Package Variables */
  /*********************/
  
  /* Declare a free list to manage the H5AC_aux_t struct */
  H5FL_DEFINE(H5AC_aux_t);
  
  /*****************************/
  /* Library Private Variables */
  /*****************************/
  
  /*******************/
  /* Local Variables */
  /*******************/
  
  /* Declare a free list to manage the H5AC_slist_entry_t struct */
  H5FL_DEFINE_STATIC(H5AC_slist_entry_t);
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__set_sync_point_done_callback
   *
   * Purpose:     Set the value of the sync_point_done callback.  This
   *		callback is used by the parallel test code to verify
   *		that the expected writes and only the expected writes
   *		take place during a sync point.
   *
   * Return:      Non-negative on success/Negative on failure
   *
   * Programmer:  John Mainzer
   *              5/9/10
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__set_sync_point_done_callback(H5C_t *cache_ptr,
                                     void (*sync_point_done)(unsigned num_writes, haddr_t *written_entries_tbl))
  {
      H5AC_aux_t *aux_ptr;
  
      FUNC_ENTER_PACKAGE_NOERR
  
      /* Sanity checks */
      HDassert(cache_ptr);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
  
      aux_ptr->sync_point_done = sync_point_done;
  
      FUNC_LEAVE_NOAPI(SUCCEED)
  } /* H5AC__set_sync_point_done_callback() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__set_write_done_callback
   *
   * Purpose:     Set the value of the write_done callback.  This callback
   *              is used to improve performance of the parallel test bed
   *              for the cache.
   *
   * Return:      Non-negative on success/Negative on failure
   *
   * Programmer:  John Mainzer
   *              5/11/06
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__set_write_done_callback(H5C_t *cache_ptr, void (*write_done)(void))
  {
      H5AC_aux_t *aux_ptr;
  
      FUNC_ENTER_PACKAGE_NOERR
  
      /* Sanity checks */
      HDassert(cache_ptr);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
  
      aux_ptr->write_done = write_done;
  
      FUNC_LEAVE_NOAPI(SUCCEED)
  } /* H5AC__set_write_done_callback() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC_add_candidate()
   *
   * Purpose:     Add the supplied metadata entry address to the candidate
   *		list.  Verify that each entry added does not appear in
   *		the list prior to its insertion.
   *
   *		This function is intended for used in constructing list
   *		of entried to be flushed during sync points.  It shouldn't
   *		be called anywhere else.
   *
   * Return:      Non-negative on success/Negative on failure
   *
   * Programmer:  John Mainzer
   *              3/17/10
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC_add_candidate(H5AC_t *cache_ptr, haddr_t addr)
  {
      H5AC_aux_t *        aux_ptr;
      H5AC_slist_entry_t *slist_entry_ptr = NULL;
      herr_t              ret_value       = SUCCEED; /* Return value */
  
      FUNC_ENTER_NOAPI(FAIL)
  
      /* Sanity checks */
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
      HDassert(aux_ptr->candidate_slist_ptr != NULL);
  
      /* Construct an entry for the supplied address, and insert
       * it into the candidate slist.
       */
      if (NULL == (slist_entry_ptr = H5FL_MALLOC(H5AC_slist_entry_t)))
          HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "Can't allocate candidate slist entry")
      slist_entry_ptr->addr = addr;
  
      if (H5SL_insert(aux_ptr->candidate_slist_ptr, slist_entry_ptr, &(slist_entry_ptr->addr)) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTINSERT, FAIL, "can't insert entry into dirty entry slist")
  
  done:
      /* Clean up on error */
      if (ret_value < 0)
          if (slist_entry_ptr)
              slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC_add_candidate() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__broadcast_candidate_list()
   *
   * Purpose:     Broadcast the contents of the process 0 candidate entry
   *		slist.  In passing, also remove all entries from said
   *		list.  As the application of this will be handled by
   *		the same functions on all processes, construct and
   *		return a copy of the list in the same format as that
   *		received by the other processes.  Note that if this
   *		copy is returned in *haddr_buf_ptr_ptr, the caller
   *		must free it.
   *
   *		This function must only be called by the process with
   *		MPI_rank 0.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 7/1/05
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__broadcast_candidate_list(H5AC_t *cache_ptr, unsigned *num_entries_ptr, haddr_t **haddr_buf_ptr_ptr)
  {
      H5AC_aux_t *aux_ptr       = NULL;
      haddr_t *   haddr_buf_ptr = NULL;
      int         mpi_result;
      unsigned    num_entries;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->mpi_rank == 0);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
      HDassert(aux_ptr->candidate_slist_ptr != NULL);
      HDassert(num_entries_ptr != NULL);
      HDassert(*num_entries_ptr == 0);
      HDassert(haddr_buf_ptr_ptr != NULL);
      HDassert(*haddr_buf_ptr_ptr == NULL);
  
      /* First broadcast the number of entries in the list so that the
       * receivers can set up buffers to receive them.  If there aren't
       * any, we are done.
       */
      num_entries = (unsigned)H5SL_count(aux_ptr->candidate_slist_ptr);
      if (MPI_SUCCESS != (mpi_result = MPI_Bcast(&num_entries, 1, MPI_UNSIGNED, 0, aux_ptr->mpi_comm)))
          HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_result)
  
      if (num_entries > 0) {
          size_t   buf_size        = 0;
          unsigned chk_num_entries = 0;
  
          /* convert the candidate list into the format we
           * are used to receiving from process 0, and also load it
           * into a buffer for transmission.
           */
          if (H5AC__copy_candidate_list_to_buffer(cache_ptr, &chk_num_entries, &haddr_buf_ptr) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't construct candidate buffer.")
          HDassert(chk_num_entries == num_entries);
          HDassert(haddr_buf_ptr != NULL);
  
          /* Now broadcast the list of candidate entries */
          buf_size = sizeof(haddr_t) * num_entries;
          if (MPI_SUCCESS !=
              (mpi_result = MPI_Bcast((void *)haddr_buf_ptr, (int)buf_size, MPI_BYTE, 0, aux_ptr->mpi_comm)))
              HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_result)
      } /* end if */
  
      /* Pass the number of entries and the buffer pointer
       * back to the caller.  Do this so that we can use the same code
       * to apply the candidate list to all the processes.
       */
      *num_entries_ptr   = num_entries;
      *haddr_buf_ptr_ptr = haddr_buf_ptr;
  
  done:
      if (ret_value < 0)
          if (haddr_buf_ptr)
              haddr_buf_ptr = (haddr_t *)H5MM_xfree((void *)haddr_buf_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__broadcast_candidate_list() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__broadcast_clean_list_cb()
   *
   * Purpose:     Skip list callback for building array of addresses for
   *              broadcasting the clean list.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  Quincey Koziol, 6/12/15
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__broadcast_clean_list_cb(void *_item, void H5_ATTR_UNUSED *_key, void *_udata)
  {
      H5AC_slist_entry_t * slist_entry_ptr = (H5AC_slist_entry_t *)_item;   /* Address of item */
      H5AC_addr_list_ud_t *udata           = (H5AC_addr_list_ud_t *)_udata; /* Context for callback */
      haddr_t              addr;
  
      FUNC_ENTER_STATIC_NOERR
  
      /* Sanity checks */
      HDassert(slist_entry_ptr);
      HDassert(udata);
  
      /* Store the entry's address in the buffer */
      addr                          = slist_entry_ptr->addr;
      udata->addr_buf_ptr[udata->u] = addr;
      udata->u++;
  
      /* now release the entry */
      slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
      /* and also remove the matching entry from the dirtied list
       * if it exists.
       */
      if (NULL !=
          (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(udata->aux_ptr->d_slist_ptr, (void *)(&addr))))
          slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
      FUNC_LEAVE_NOAPI(SUCCEED)
  } /* H5AC__broadcast_clean_list_cb() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__broadcast_clean_list()
   *
   * Purpose:     Broadcast the contents of the process 0 cleaned entry
   *		slist.  In passing, also remove all entries from said
   *		list, and also remove any matching entries from the dirtied
   *		slist.
   *
   *		This function must only be called by the process with
   *		MPI_rank 0.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 7/1/05
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__broadcast_clean_list(H5AC_t *cache_ptr)
  {
      haddr_t *   addr_buf_ptr = NULL;
      H5AC_aux_t *aux_ptr;
      int         mpi_result;
      unsigned    num_entries = 0;
      herr_t      ret_value   = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->mpi_rank == 0);
      HDassert(aux_ptr->c_slist_ptr != NULL);
  
      /* First broadcast the number of entries in the list so that the
       * receives can set up a buffer to receive them.  If there aren't
       * any, we are done.
       */
      num_entries = (unsigned)H5SL_count(aux_ptr->c_slist_ptr);
      if (MPI_SUCCESS != (mpi_result = MPI_Bcast(&num_entries, 1, MPI_UNSIGNED, 0, aux_ptr->mpi_comm)))
          HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_result)
  
      if (num_entries > 0) {
          H5AC_addr_list_ud_t udata;
          size_t              buf_size;
  
          /* allocate a buffer to store the list of entry base addresses in */
          buf_size = sizeof(haddr_t) * num_entries;
          if (NULL == (addr_buf_ptr = (haddr_t *)H5MM_malloc(buf_size)))
              HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "memory allocation failed for addr buffer")
  
          /* Set up user data for callback */
          udata.aux_ptr      = aux_ptr;
          udata.addr_buf_ptr = addr_buf_ptr;
          udata.u            = 0;
  
          /* Free all the clean list entries, building the address list in the callback */
          /* (Callback also removes the matching entries from the dirtied list) */
          if (H5SL_free(aux_ptr->c_slist_ptr, H5AC__broadcast_clean_list_cb, &udata) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, "Can't build address list for clean entries")
  
          /* Now broadcast the list of cleaned entries */
          if (MPI_SUCCESS !=
              (mpi_result = MPI_Bcast((void *)addr_buf_ptr, (int)buf_size, MPI_BYTE, 0, aux_ptr->mpi_comm)))
              HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_result)
      } /* end if */
  
      /* if it is defined, call the sync point done callback.  Note
       * that this callback is defined purely for testing purposes,
       * and should be undefined under normal operating circumstances.
       */
      if (aux_ptr->sync_point_done)
          (aux_ptr->sync_point_done)(num_entries, addr_buf_ptr);
  
  done:
      if (addr_buf_ptr)
          addr_buf_ptr = (haddr_t *)H5MM_xfree((void *)addr_buf_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__broadcast_clean_list() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__construct_candidate_list()
   *
   * Purpose:     In the parallel case when the metadata_write_strategy is
   *		H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED, process 0 uses
   *		this function to construct the list of cache entries to
   *		be flushed.  This list is then propagated to the other
   *		caches, and then flushed in a distributed fashion.
   *
   *		The sync_point_op parameter is used to determine the extent
   *		of the flush.
   *
   * Return:      Non-negative on success/Negative on failure
   *
   * Programmer:  John Mainzer
   *              3/17/10
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__construct_candidate_list(H5AC_t *cache_ptr, H5AC_aux_t H5_ATTR_NDEBUG_UNUSED *aux_ptr,
                                 int sync_point_op)
  {
      herr_t ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(cache_ptr != NULL);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
      HDassert((sync_point_op == H5AC_SYNC_POINT_OP__FLUSH_CACHE) || (aux_ptr->mpi_rank == 0));
      HDassert(aux_ptr->d_slist_ptr != NULL);
      HDassert(aux_ptr->c_slist_ptr != NULL);
      HDassert(H5SL_count(aux_ptr->c_slist_ptr) == 0);
      HDassert(aux_ptr->candidate_slist_ptr != NULL);
      HDassert(H5SL_count(aux_ptr->candidate_slist_ptr) == 0);
      HDassert((sync_point_op == H5AC_SYNC_POINT_OP__FLUSH_TO_MIN_CLEAN) ||
               (sync_point_op == H5AC_SYNC_POINT_OP__FLUSH_CACHE));
  
      switch (sync_point_op) {
          case H5AC_SYNC_POINT_OP__FLUSH_TO_MIN_CLEAN:
              if (H5C_construct_candidate_list__min_clean((H5C_t *)cache_ptr) < 0)
                  HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5C_construct_candidate_list__min_clean() failed.")
              break;
  
          case H5AC_SYNC_POINT_OP__FLUSH_CACHE:
              if (H5C_construct_candidate_list__clean_cache((H5C_t *)cache_ptr) < 0)
                  HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL,
                              "H5C_construct_candidate_list__clean_cache() failed.")
              break;
  
          default:
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "unknown sync point operation.")
              break;
      } /* end switch */
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__construct_candidate_list() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__copy_candidate_list_to_buffer_cb
   *
   * Purpose:     Skip list callback for building array of addresses for
   *              broadcasting the candidate list.
   *
   * Return:	Return SUCCEED on success, and FAIL on failure.
   *
   * Programmer:  Quincey Koziol, 6/12/15
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__copy_candidate_list_to_buffer_cb(void *_item, void H5_ATTR_UNUSED *_key, void *_udata)
  {
      H5AC_slist_entry_t * slist_entry_ptr = (H5AC_slist_entry_t *)_item;   /* Address of item */
      H5AC_addr_list_ud_t *udata           = (H5AC_addr_list_ud_t *)_udata; /* Context for callback */
  
      FUNC_ENTER_STATIC_NOERR
  
      /* Sanity checks */
      HDassert(slist_entry_ptr);
      HDassert(udata);
  
      /* Store the entry's address in the buffer */
      udata->addr_buf_ptr[udata->u] = slist_entry_ptr->addr;
      udata->u++;
  
      /* now release the entry */
      slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
      FUNC_LEAVE_NOAPI(SUCCEED)
  } /* H5AC__copy_candidate_list_to_buffer_cb() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__copy_candidate_list_to_buffer
   *
   * Purpose:     Allocate buffer(s) and copy the contents of the candidate
   *		entry slist into it (them).  In passing, remove all
   *		entries from the candidate slist.  Note that the
   *		candidate slist must not be empty.
   *
   *		If MPI_Offset_buf_ptr_ptr is not NULL, allocate a buffer
   *		of MPI_Offset, copy the contents of the candidate
   *		entry list into it with the appropriate conversions,
   *		and return the base address of the buffer in
   *		*MPI_Offset_buf_ptr.  Note that this is the buffer
   *		used by process 0 to transmit the list of entries to
   *		be flushed to all other processes (in this file group).
   *
   *		Similarly, allocate a buffer of haddr_t, load the contents
   *		of the candidate list into this buffer, and return its
   *		base address in *haddr_buf_ptr_ptr.  Note that this
   *		latter buffer is constructed unconditionally.
   *
   *		In passing, also remove all entries from the candidate
   *		entry slist.
   *
   * Return:	Return SUCCEED on success, and FAIL on failure.
   *
   * Programmer:  John Mainzer, 4/19/10
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__copy_candidate_list_to_buffer(const H5AC_t *cache_ptr, unsigned *num_entries_ptr,
                                      haddr_t **haddr_buf_ptr_ptr)
  {
      H5AC_aux_t *        aux_ptr = NULL;
      H5AC_addr_list_ud_t udata;
      haddr_t *           haddr_buf_ptr = NULL;
      size_t              buf_size;
      unsigned            num_entries = 0;
      herr_t              ret_value   = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
      HDassert(aux_ptr->candidate_slist_ptr != NULL);
      HDassert(H5SL_count(aux_ptr->candidate_slist_ptr) > 0);
      HDassert(num_entries_ptr != NULL);
      HDassert(*num_entries_ptr == 0);
      HDassert(haddr_buf_ptr_ptr != NULL);
      HDassert(*haddr_buf_ptr_ptr == NULL);
  
      num_entries = (unsigned)H5SL_count(aux_ptr->candidate_slist_ptr);
  
      /* allocate a buffer(s) to store the list of candidate entry
       * base addresses in
       */
      buf_size = sizeof(haddr_t) * num_entries;
      if (NULL == (haddr_buf_ptr = (haddr_t *)H5MM_malloc(buf_size)))
          HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "memory allocation failed for haddr buffer")
  
      /* Set up user data for callback */
      udata.aux_ptr      = aux_ptr;
      udata.addr_buf_ptr = haddr_buf_ptr;
      udata.u            = 0;
  
      /* Free all the candidate list entries, building the address list in the callback */
      if (H5SL_free(aux_ptr->candidate_slist_ptr, H5AC__copy_candidate_list_to_buffer_cb, &udata) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, "Can't build address list for candidate entries")
  
      /* Pass the number of entries and the buffer pointer
       * back to the caller.
       */
      *num_entries_ptr   = num_entries;
      *haddr_buf_ptr_ptr = haddr_buf_ptr;
  
  done:
      if (ret_value < 0)
          if (haddr_buf_ptr)
              haddr_buf_ptr = (haddr_t *)H5MM_xfree((void *)haddr_buf_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__copy_candidate_list_to_buffer() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__log_deleted_entry()
   *
   * Purpose:     Log an entry which has been deleted.
   *
   *		Only called for mpi_rank 0. We must make sure that the entry
   *              doesn't appear in the cleaned or dirty entry lists.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 6/29/05
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__log_deleted_entry(const H5AC_info_t *entry_ptr)
  {
      H5AC_t *            cache_ptr;
      H5AC_aux_t *        aux_ptr;
      H5AC_slist_entry_t *slist_entry_ptr = NULL;
      haddr_t             addr;
  
      FUNC_ENTER_PACKAGE_NOERR
  
      /* Sanity checks */
      HDassert(entry_ptr);
      addr      = entry_ptr->addr;
      cache_ptr = entry_ptr->cache_ptr;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->mpi_rank == 0);
      HDassert(aux_ptr->d_slist_ptr != NULL);
      HDassert(aux_ptr->c_slist_ptr != NULL);
  
      /* if the entry appears in the dirtied entry slist, remove it. */
      if (NULL != (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->d_slist_ptr, (void *)(&addr))))
          slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
      /* if the entry appears in the cleaned entry slist, remove it. */
      if (NULL != (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->c_slist_ptr, (void *)(&addr))))
          slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
      FUNC_LEAVE_NOAPI(SUCCEED)
  } /* H5AC__log_deleted_entry() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__log_dirtied_entry()
   *
   * Purpose:     Update the dirty_bytes count for a newly dirtied entry.
   *
   *		If mpi_rank isn't 0, this simply means adding the size
   *		of the entries to the dirty_bytes count.
   *
   *		If mpi_rank is 0, we must first check to see if the entry
   *		appears in the dirty entries slist.  If it is, do nothing.
   *		If it isn't, add the size to the dirty_bytes count, add the
   *		entry to the dirty entries slist, and remove it from the
   *		cleaned list (if it is present there).
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 6/29/05
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__log_dirtied_entry(const H5AC_info_t *entry_ptr)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_PACKAGE
  
      /* Sanity checks */
      HDassert(entry_ptr);
      HDassert(entry_ptr->is_dirty == FALSE);
      cache_ptr = entry_ptr->cache_ptr;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
  
      if (aux_ptr->mpi_rank == 0) {
          H5AC_slist_entry_t *slist_entry_ptr;
          haddr_t             addr = entry_ptr->addr;
  
          /* Sanity checks */
          HDassert(aux_ptr->d_slist_ptr != NULL);
          HDassert(aux_ptr->c_slist_ptr != NULL);
  
          if (NULL == H5SL_search(aux_ptr->d_slist_ptr, (void *)(&addr))) {
              /* insert the address of the entry in the dirty entry list, and
               * add its size to the dirty_bytes count.
               */
              if (NULL == (slist_entry_ptr = H5FL_MALLOC(H5AC_slist_entry_t)))
                  HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "Can't allocate dirty slist entry .")
              slist_entry_ptr->addr = addr;
  
              if (H5SL_insert(aux_ptr->d_slist_ptr, slist_entry_ptr, &(slist_entry_ptr->addr)) < 0)
                  HGOTO_ERROR(H5E_CACHE, H5E_CANTINSERT, FAIL, "can't insert entry into dirty entry slist.")
  
              aux_ptr->dirty_bytes += entry_ptr->size;
  #if H5AC_DEBUG_DIRTY_BYTES_CREATION
              aux_ptr->unprotect_dirty_bytes += entry_ptr->size;
              aux_ptr->unprotect_dirty_bytes_updates += 1;
  #endif    /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
          } /* end if */
  
          /* the entry is dirty.  If it exists on the cleaned entries list,
           * remove it.
           */
          if (NULL !=
              (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->c_slist_ptr, (void *)(&addr))))
              slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
      } /* end if */
      else {
          aux_ptr->dirty_bytes += entry_ptr->size;
  #if H5AC_DEBUG_DIRTY_BYTES_CREATION
          aux_ptr->unprotect_dirty_bytes += entry_ptr->size;
          aux_ptr->unprotect_dirty_bytes_updates += 1;
  #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
      }  /* end else */
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__log_dirtied_entry() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__log_cleaned_entry()
   *
   * Purpose:     Treat this operation as a 'clear' and remove the entry
   * 		from both the cleaned and dirtied lists if it is present.
   *		Reduces the dirty_bytes count by the size of the entry.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  Quincey Koziol
   *              7/23/16
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__log_cleaned_entry(const H5AC_info_t *entry_ptr)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
  
      FUNC_ENTER_PACKAGE_NOERR
  
      /* Sanity check */
      HDassert(entry_ptr);
      HDassert(entry_ptr->is_dirty == FALSE);
      cache_ptr = entry_ptr->cache_ptr;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
  
      if (aux_ptr->mpi_rank == 0) {
          H5AC_slist_entry_t *slist_entry_ptr;
          haddr_t             addr = entry_ptr->addr;
  
          /* Sanity checks */
          HDassert(aux_ptr->d_slist_ptr != NULL);
          HDassert(aux_ptr->c_slist_ptr != NULL);
  
          /* Remove it from both the cleaned list and the dirtied list.  */
          if (NULL !=
              (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->c_slist_ptr, (void *)(&addr))))
              slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
          if (NULL !=
              (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->d_slist_ptr, (void *)(&addr))))
              slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
      } /* end if */
  
      /* Decrement the dirty byte count */
      aux_ptr->dirty_bytes -= entry_ptr->size;
  
      FUNC_LEAVE_NOAPI(SUCCEED)
  } /* H5AC__log_cleaned_entry() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__log_flushed_entry()
   *
   * Purpose:     Update the clean entry slist for the flush of an entry --
   *		specifically, if the entry has been cleared, remove it
   * 		from both the cleaned and dirtied lists if it is present.
   *		Otherwise, if the entry was dirty, insert the indicated
   *		entry address in the clean slist if it isn't there already.
   *
   *		This function is only used in PHDF5, and should only
   *		be called for the process with mpi rank 0.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 6/29/05
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__log_flushed_entry(H5C_t *cache_ptr, haddr_t addr, hbool_t was_dirty, unsigned flags)
  {
      hbool_t             cleared;
      H5AC_aux_t *        aux_ptr;
      H5AC_slist_entry_t *slist_entry_ptr = NULL;
      herr_t              ret_value       = SUCCEED; /* Return value */
  
      FUNC_ENTER_PACKAGE
  
      /* Sanity check */
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->mpi_rank == 0);
      HDassert(aux_ptr->c_slist_ptr != NULL);
  
      /* Set local flags */
      cleared = ((flags & H5C__FLUSH_CLEAR_ONLY_FLAG) != 0);
  
      if (cleared) {
          /* If the entry has been cleared, must remove it from both the
           * cleaned list and the dirtied list.
           */
          if (NULL !=
              (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->c_slist_ptr, (void *)(&addr))))
              slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
          if (NULL !=
              (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->d_slist_ptr, (void *)(&addr))))
              slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
      } /* end if */
      else if (was_dirty) {
          if (NULL == H5SL_search(aux_ptr->c_slist_ptr, (void *)(&addr))) {
              /* insert the address of the entry in the clean entry list. */
              if (NULL == (slist_entry_ptr = H5FL_MALLOC(H5AC_slist_entry_t)))
                  HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "Can't allocate clean slist entry .")
              slist_entry_ptr->addr = addr;
  
              if (H5SL_insert(aux_ptr->c_slist_ptr, slist_entry_ptr, &(slist_entry_ptr->addr)) < 0)
                  HGOTO_ERROR(H5E_CACHE, H5E_CANTINSERT, FAIL, "can't insert entry into clean entry slist.")
          } /* end if */
      }     /* end else-if */
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__log_flushed_entry() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__log_inserted_entry()
   *
   * Purpose:     Update the dirty_bytes count for a newly inserted entry.
   *
   *		If mpi_rank isn't 0, this simply means adding the size
   *		of the entry to the dirty_bytes count.
   *
   *		If mpi_rank is 0, we must also add the entry to the
   *		dirty entries slist.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 6/30/05
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__log_inserted_entry(const H5AC_info_t *entry_ptr)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_PACKAGE
  
      /* Sanity checks */
      HDassert(entry_ptr);
      cache_ptr = entry_ptr->cache_ptr;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
  
      if (aux_ptr->mpi_rank == 0) {
          H5AC_slist_entry_t *slist_entry_ptr;
  
          HDassert(aux_ptr->d_slist_ptr != NULL);
          HDassert(aux_ptr->c_slist_ptr != NULL);
  
          /* Entry to insert should not be in dirty list currently */
          if (NULL != H5SL_search(aux_ptr->d_slist_ptr, (const void *)(&entry_ptr->addr)))
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Inserted entry already in dirty slist.")
  
          /* insert the address of the entry in the dirty entry list, and
           * add its size to the dirty_bytes count.
           */
          if (NULL == (slist_entry_ptr = H5FL_MALLOC(H5AC_slist_entry_t)))
              HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "Can't allocate dirty slist entry .")
          slist_entry_ptr->addr = entry_ptr->addr;
          if (H5SL_insert(aux_ptr->d_slist_ptr, slist_entry_ptr, &(slist_entry_ptr->addr)) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTINSERT, FAIL, "can't insert entry into dirty entry slist.")
  
          /* Entry to insert should not be in clean list either */
          if (NULL != H5SL_search(aux_ptr->c_slist_ptr, (const void *)(&entry_ptr->addr)))
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Inserted entry in clean slist.")
      } /* end if */
  
      aux_ptr->dirty_bytes += entry_ptr->size;
  
  #if H5AC_DEBUG_DIRTY_BYTES_CREATION
      aux_ptr->insert_dirty_bytes += entry_ptr->size;
      aux_ptr->insert_dirty_bytes_updates += 1;
  #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__log_inserted_entry() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__log_moved_entry()
   *
   * Purpose:     Update the dirty_bytes count for a moved entry.
   *
   *		WARNING
   *
   *		At present, the way that the move call is used ensures
   *		that the moved entry is present in all caches by
   *		moving in a collective operation and immediately after
   *		unprotecting the target entry.
   *
   *		This function uses this invariant, and will cause arcane
   *		failures if it is not met.  If maintaining this invariant
   *		becomes impossible, we will have to rework this function
   *		extensively, and likely include a bit of IPC for
   *		synchronization.  A better option might be to subsume
   *		move in the unprotect operation.
   *
   *		Given that the target entry is in all caches, the function
   *		proceeds as follows:
   *
   *		For processes with mpi rank other 0, it simply checks to
   *		see if the entry was dirty prior to the move, and adds
   *		the entries size to the dirty bytes count.
   *
   *		In the process with mpi rank 0, the function first checks
   *		to see if the entry was dirty prior to the move.  If it
   *		was, and if the entry doesn't appear in the dirtied list
   *		under its old address, it adds the entry's size to the
   *		dirty bytes count.
   *
   *		The rank 0 process then removes any references to the
   *		entry under its old address from the cleands and dirtied
   *		lists, and inserts an entry in the dirtied list under the
   *		new address.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 6/30/05
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__log_moved_entry(const H5F_t *f, haddr_t old_addr, haddr_t new_addr)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      hbool_t     entry_in_cache;
      hbool_t     entry_dirty;
      size_t      entry_size;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_PACKAGE
  
      /* Sanity checks */
      HDassert(f);
      HDassert(f->shared);
      cache_ptr = (H5AC_t *)f->shared->cache;
      HDassert(cache_ptr);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
  
      /* get entry status, size, etc here */
      if (H5C_get_entry_status(f, old_addr, &entry_size, &entry_in_cache, &entry_dirty, NULL, NULL, NULL, NULL,
                               NULL, NULL) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't get entry status.")
      if (!entry_in_cache)
          HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "entry not in cache.")
  
      if (aux_ptr->mpi_rank == 0) {
          H5AC_slist_entry_t *slist_entry_ptr;
  
          HDassert(aux_ptr->d_slist_ptr != NULL);
          HDassert(aux_ptr->c_slist_ptr != NULL);
  
          /* if the entry appears in the cleaned entry slist, under its old
           * address, remove it.
           */
          if (NULL !=
              (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->c_slist_ptr, (void *)(&old_addr))))
              slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, slist_entry_ptr);
  
          /* if the entry appears in the dirtied entry slist under its old
           * address, remove it, but don't free it. Set addr to new_addr.
           */
          if (NULL !=
              (slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->d_slist_ptr, (void *)(&old_addr))))
              slist_entry_ptr->addr = new_addr;
          else {
              /* otherwise, allocate a new entry that is ready
               * for insertion, and increment dirty_bytes.
               *
               * Note that the fact that the entry wasn't in the dirtied
               * list under its old address implies that it must have
               * been clean to start with.
               */
              HDassert(!entry_dirty);
              if (NULL == (slist_entry_ptr = H5FL_MALLOC(H5AC_slist_entry_t)))
                  HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "Can't allocate dirty slist entry .")
              slist_entry_ptr->addr = new_addr;
  
              aux_ptr->dirty_bytes += entry_size;
  
  #if H5AC_DEBUG_DIRTY_BYTES_CREATION
              aux_ptr->move_dirty_bytes += entry_size;
              aux_ptr->move_dirty_bytes_updates += 1;
  #endif    /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
          } /* end else */
  
          /* insert / reinsert the entry in the dirty slist */
          if (H5SL_insert(aux_ptr->d_slist_ptr, slist_entry_ptr, &(slist_entry_ptr->addr)) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTINSERT, FAIL, "can't insert entry into dirty entry slist.")
      } /* end if */
      else if (!entry_dirty) {
          aux_ptr->dirty_bytes += entry_size;
  
  #if H5AC_DEBUG_DIRTY_BYTES_CREATION
          aux_ptr->move_dirty_bytes += entry_size;
          aux_ptr->move_dirty_bytes_updates += 1;
  #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
      }  /* end else-if */
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__log_moved_entry() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__propagate_and_apply_candidate_list
   *
   * Purpose:     Prior to the addition of support for multiple metadata
   *		write strategies, in PHDF5, only the metadata cache with
   *		mpi rank 0 was allowed to write to file.  All other
   *		metadata caches on processes with rank greater than 0
   *		were required to retain dirty entries until they were
   *		notified that the entry was clean.
   *
   *		This constraint is relaxed with the distributed
   *		metadata write strategy, in which a list of candidate
   *		metadata cache entries is constructed by the process 0
   *		cache and then distributed to the caches of all the other
   *		processes.  Once the listed is distributed, many (if not
   *		all) processes writing writing a unique subset of the
   *		entries, and marking the remainder clean.  The subsets
   *		are chosen so that each entry in the list of candidates
   *		is written by exactly one cache, and all entries are
   *		marked as being clean in all caches.
   *
   *		While the list of candidate cache entries is prepared
   *		elsewhere, this function is the main routine for distributing
   *		and applying the list.  It must be run simultaniously on
   *		all processes that have the relevant file open.  To ensure
   *		proper synchronization, there is a barrier at the beginning
   *		of this function.
   *
   *		At present, this function is called under one of two
   *		circumstances:
   *
   *		1) Dirty byte creation exceeds some user specified value.
   *
   *		   While metadata reads may occur independently, all
   *		   operations writing metadata must be collective.  Thus
   *		   all metadata caches see the same sequence of operations,
   *                 and therefore the same dirty data creation.
   *
   *		   This fact is used to synchronize the caches for purposes
   *                 of propagating the list of candidate entries, by simply
   *		   calling this function from all caches whenever some user
   *		   specified threshold on dirty data is exceeded.  (the
   *		   process 0 cache creates the candidate list just before
   *		   calling this function).
   *
   *		2) Under direct user control -- this operation must be
   *		   collective.
   *
   *              The operations to be managed by this function are as
   * 		follows:
   *
   *		All processes:
   *
   *		1) Participate in an opening barrier.
   *
   *		For the process with mpi rank 0:
   *
   *		1) Load the contents of the candidate list
   *		   (candidate_slist_ptr) into a buffer, and broadcast that
   *		   buffer to all the other caches.  Clear the candidate
   *		   list in passing.
   *
   *		If there is a positive number of candidates, proceed with
   *		the following:
   *
   *		2) Apply the candidate entry list.
   *
   *		3) Particpate in a closing barrier.
   *
   *		4) Remove from the dirty list (d_slist_ptr) and from the
   *		   flushed and still clean entries list (c_slist_ptr),
   *                 all addresses that appeared in the candidate list, as
   *		   these entries are now clean.
   *
   *
   *		For all processes with mpi rank greater than 0:
   *
   *		1) Receive the candidate entry list broadcast
   *
   *		If there is a positive number of candidates, proceed with
   *		the following:
   *
   *		2) Apply the candidate entry list.
   *
   *		3) Particpate in a closing barrier.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              3/17/10
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__propagate_and_apply_candidate_list(H5F_t *f)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      haddr_t *   candidates_list_ptr = NULL;
      int         mpi_result;
      unsigned    num_candidates = 0;
      herr_t      ret_value      = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(f != NULL);
      cache_ptr = f->shared->cache;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
  
      /* to prevent "messages from the future" we must synchronize all
       * processes before we write any entries.
       */
      if (MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)))
          HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_result)
  
      if (aux_ptr->mpi_rank == 0) {
          if (H5AC__broadcast_candidate_list(cache_ptr, &num_candidates, &candidates_list_ptr) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't broadcast candidate slist.")
  
          HDassert(H5SL_count(aux_ptr->candidate_slist_ptr) == 0);
      } /* end if */
      else {
          if (H5AC__receive_candidate_list(cache_ptr, &num_candidates, &candidates_list_ptr) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't receive candidate broadcast.")
      } /* end else */
  
      if (num_candidates > 0) {
          herr_t result;
  
          /* all processes apply the candidate list.
           * H5C_apply_candidate_list() handles the details of
           * distributing the writes across the processes.
           */
  
          /* Enable writes during this operation */
          aux_ptr->write_permitted = TRUE;
  
          /* Apply the candidate list */
          result = H5C_apply_candidate_list(f, cache_ptr, num_candidates, candidates_list_ptr,
                                            aux_ptr->mpi_rank, aux_ptr->mpi_size);
  
          /* Disable writes again */
          aux_ptr->write_permitted = FALSE;
  
          /* Check for error on the write operation */
          if (result < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't apply candidate list.")
  
          /* this code exists primarily for the test bed -- it allows us to
           * enforce posix semantics on the server that pretends to be a
           * file system in our parallel tests.
           */
          if (aux_ptr->write_done)
              (aux_ptr->write_done)();
  
          /* to prevent "messages from the past" we must synchronize all
           * processes again before we go on.
           */
          if (MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)))
              HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_result)
  
          /* if this is process zero, tidy up the dirtied,
           * and flushed and still clean lists.
           */
          if (aux_ptr->mpi_rank == 0)
              if (H5AC__tidy_cache_0_lists(cache_ptr, num_candidates, candidates_list_ptr) < 0)
                  HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't tidy up process 0 lists.")
      } /* end if */
  
      /* if it is defined, call the sync point done callback.  Note
       * that this callback is defined purely for testing purposes,
       * and should be undefined under normal operating circumstances.
       */
      if (aux_ptr->sync_point_done)
          (aux_ptr->sync_point_done)(num_candidates, candidates_list_ptr);
  
  done:
      if (candidates_list_ptr)
          candidates_list_ptr = (haddr_t *)H5MM_xfree((void *)candidates_list_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__propagate_and_apply_candidate_list() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__propagate_flushed_and_still_clean_entries_list
   *
   * Purpose:     In PHDF5, if the process 0 only metadata write strategy
   *		is selected, only the metadata cache with mpi rank 0 is
   *		allowed to write to file.  All other metadata caches on
   *		processes with rank greater than 0 must retain dirty
   *		entries until they are notified that the entry is now
   *		clean.
   *
   *		This function is the main routine for handling this
   *		notification procedure.  It must be called
   *		simultaniously on all processes that have the relevant
   *		file open.  To this end, it is called only during a
   *		sync point, with a barrier prior to the call.
   *
   *		Note that any metadata entry writes by process 0 will
   *		occur after the barrier and just before this call.
   *
   *		Typically, calls to this function will be triggered in
   *		one of two ways:
   *
   *		1) Dirty byte creation exceeds some user specified value.
   *
   *		   While metadata reads may occur independently, all
   *		   operations writing metadata must be collective.  Thus
   *		   all metadata caches see the same sequence of operations,
   *                 and therefore the same dirty data creation.
   *
   *		   This fact is used to synchronize the caches for purposes
   *                 of propagating the list of flushed and still clean
   *		   entries, by simply calling this function from all
   *		   caches whenever some user specified threshold on dirty
   *		   data is exceeded.
   *
   *		2) Under direct user control -- this operation must be
   *		   collective.
   *
   *              The operations to be managed by this function are as
   * 		follows:
   *
   *		For the process with mpi rank 0:
   *
   *		1) Load the contents of the flushed and still clean entries
   *		   list (c_slist_ptr) into a buffer, and broadcast that
   *		   buffer to all the other caches.
   *
   *		2) Clear the flushed and still clean entries list
   *                 (c_slist_ptr).
   *
   *
   *		For all processes with mpi rank greater than 0:
   *
   *		1) Receive the flushed and still clean entries list broadcast
   *
   *		2) Mark the specified entries as clean.
   *
   *
   *		For all processes:
   *
   *		1) Reset the dirtied bytes count to 0.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              July 5, 2005
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__propagate_flushed_and_still_clean_entries_list(H5F_t *f)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(f != NULL);
      cache_ptr = f->shared->cache;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY);
  
      if (aux_ptr->mpi_rank == 0) {
          if (H5AC__broadcast_clean_list(cache_ptr) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't broadcast clean slist.")
          HDassert(H5SL_count(aux_ptr->c_slist_ptr) == 0);
      } /* end if */
      else if (H5AC__receive_and_apply_clean_list(f) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't receive and/or process clean slist broadcast.")
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__propagate_flushed_and_still_clean_entries_list() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__receive_haddr_list()
   *
   * Purpose:     Receive the list of entry addresses from process 0,
   *		and return it in a buffer pointed to by *haddr_buf_ptr_ptr.
   *		Note that the caller must free this buffer if it is
   *		returned.
   *
   *		This function must only be called by the process with
   *		MPI_rank greater than 0.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  Quincey Koziol, 6/11/2015
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__receive_haddr_list(MPI_Comm mpi_comm, unsigned *num_entries_ptr, haddr_t **haddr_buf_ptr_ptr)
  {
      haddr_t *haddr_buf_ptr = NULL;
      int      mpi_result;
      unsigned num_entries;
      herr_t   ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(num_entries_ptr != NULL);
      HDassert(*num_entries_ptr == 0);
      HDassert(haddr_buf_ptr_ptr != NULL);
      HDassert(*haddr_buf_ptr_ptr == NULL);
  
      /* First receive the number of entries in the list so that we
       * can set up a buffer to receive them.  If there aren't
       * any, we are done.
       */
      if (MPI_SUCCESS != (mpi_result = MPI_Bcast(&num_entries, 1, MPI_UNSIGNED, 0, mpi_comm)))
          HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_result)
  
      if (num_entries > 0) {
          size_t buf_size;
  
          /* allocate buffers to store the list of entry base addresses in */
          buf_size = sizeof(haddr_t) * num_entries;
          if (NULL == (haddr_buf_ptr = (haddr_t *)H5MM_malloc(buf_size)))
              HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "memory allocation failed for haddr buffer")
  
          /* Now receive the list of candidate entries */
          if (MPI_SUCCESS !=
              (mpi_result = MPI_Bcast((void *)haddr_buf_ptr, (int)buf_size, MPI_BYTE, 0, mpi_comm)))
              HMPI_GOTO_ERROR(FAIL, "MPI_Bcast failed", mpi_result)
      } /* end if */
  
      /* finally, pass the number of entries and the buffer pointer
       * back to the caller.
       */
      *num_entries_ptr   = num_entries;
      *haddr_buf_ptr_ptr = haddr_buf_ptr;
  
  done:
      if (ret_value < 0)
          if (haddr_buf_ptr)
              haddr_buf_ptr = (haddr_t *)H5MM_xfree((void *)haddr_buf_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__receive_haddr_list() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__receive_and_apply_clean_list()
   *
   * Purpose:     Receive the list of cleaned entries from process 0,
   *		and mark the specified entries as clean.
   *
   *		This function must only be called by the process with
   *		MPI_rank greater than 0.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 7/4/05
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__receive_and_apply_clean_list(H5F_t *f)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      haddr_t *   haddr_buf_ptr = NULL;
      unsigned    num_entries   = 0;
      herr_t      ret_value     = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity check */
      HDassert(f != NULL);
      cache_ptr = f->shared->cache;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->mpi_rank != 0);
  
      /* Retrieve the clean list from process 0 */
      if (H5AC__receive_haddr_list(aux_ptr->mpi_comm, &num_entries, &haddr_buf_ptr) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "can't receive clean list")
  
      if (num_entries > 0)
          /* mark the indicated entries as clean */
          if (H5C_mark_entries_as_clean(f, num_entries, haddr_buf_ptr) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't mark entries clean.")
  
      /* if it is defined, call the sync point done callback.  Note
       * that this callback is defined purely for testing purposes,
       * and should be undefined under normal operating circumstances.
       */
      if (aux_ptr->sync_point_done)
          (aux_ptr->sync_point_done)(num_entries, haddr_buf_ptr);
  
  done:
      if (haddr_buf_ptr)
          haddr_buf_ptr = (haddr_t *)H5MM_xfree((void *)haddr_buf_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__receive_and_apply_clean_list() */
  
  /*-------------------------------------------------------------------------
   *
   * Function:    H5AC__receive_candidate_list()
   *
   * Purpose:     Receive the list of candidate entries from process 0,
   *		and return it in a buffer pointed to by *haddr_buf_ptr_ptr.
   *		Note that the caller must free this buffer if it is
   *		returned.
   *
   *		This function must only be called by the process with
   *		MPI_rank greater than 0.
   *
   *		Return SUCCEED on success, and FAIL on failure.
   *
   * Return:      Non-negative on success/Negative on failure.
   *
   * Programmer:  John Mainzer, 3/17/10
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__receive_candidate_list(const H5AC_t *cache_ptr, unsigned *num_entries_ptr, haddr_t **haddr_buf_ptr_ptr)
  {
      H5AC_aux_t *aux_ptr;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->mpi_rank != 0);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
      HDassert(num_entries_ptr != NULL);
      HDassert(*num_entries_ptr == 0);
      HDassert(haddr_buf_ptr_ptr != NULL);
      HDassert(*haddr_buf_ptr_ptr == NULL);
  
      /* Retrieve the candidate list from process 0 */
      if (H5AC__receive_haddr_list(aux_ptr->mpi_comm, num_entries_ptr, haddr_buf_ptr_ptr) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "can't receive clean list")
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__receive_candidate_list() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__rsp__dist_md_write__flush
   *
   * Purpose:     Routine for handling the details of running a sync point
   *		that is triggered by a flush -- which in turn must have been
   *		triggered by either a flush API call or a file close --
   *		when the distributed metadata write strategy is selected.
   *
   *		Upon entry, each process generates it own candidate list,
   *              being a sorted list of all dirty metadata entries currently
   *		in the metadata cache.  Note that this list must be idendical
   *		across all processes, as all processes see the same stream
   *		of dirty metadata coming in, and use the same lists of
   *		candidate entries at each sync point.  (At first glance, this
   *		argument sounds circular, but think of it in the sense of
   *		a recursive proof).
   *
   *		If this this list is empty, we are done, and the function
   *		returns
   *
   *		Otherwise, after the sorted list dirty metadata entries is
   *		constructed, each process uses the same algorithm to assign
   *		each entry on the candidate list to exactly one process for
   *		flushing.
   *
   *		At this point, all processes participate in a barrier to
   *		avoid messages from the past/future bugs.
   *
   *		Each process then flushes the entries assigned to it, and
   *		marks all other entries on the candidate list as clean.
   *
   *		Finally, all processes participate in a second barrier to
   *		avoid messages from the past/future bugs.
   *
   *		At the end of this process, process 0 and only process 0
   *		must tidy up its lists of dirtied and cleaned entries.
   *		These lists are not used in the distributed metadata write
   *		strategy, but they must be maintained should we shift
   *		to a strategy that uses them.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              April 28, 2010
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__rsp__dist_md_write__flush(H5F_t *f)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      haddr_t *   haddr_buf_ptr = NULL;
      int         mpi_result;
      unsigned    num_entries = 0;
      herr_t      ret_value   = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(f != NULL);
      cache_ptr = f->shared->cache;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
  
      /* first construct the candidate list -- initially, this will be in the
       * form of a skip list.  We will convert it later.
       */
      if (H5C_construct_candidate_list__clean_cache(cache_ptr) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't construct candidate list.")
  
      if (H5SL_count(aux_ptr->candidate_slist_ptr) > 0) {
          herr_t result;
  
          /* convert the candidate list into the format we
           * are used to receiving from process 0.
           */
          if (H5AC__copy_candidate_list_to_buffer(cache_ptr, &num_entries, &haddr_buf_ptr) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't construct candidate buffer.")
  
          /* Initial sync point barrier
           *
           * When flushing from within the close operation from a file,
           * it's possible to skip this barrier (on the second flush of the cache).
           */
          if (!H5CX_get_mpi_file_flushing())
              if (MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)))
                  HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_result)
  
          /* Enable writes during this operation */
          aux_ptr->write_permitted = TRUE;
  
          /* Apply the candidate list */
          result = H5C_apply_candidate_list(f, cache_ptr, num_entries, haddr_buf_ptr, aux_ptr->mpi_rank,
                                            aux_ptr->mpi_size);
  
          /* Disable writes again */
          aux_ptr->write_permitted = FALSE;
  
          /* Check for error on the write operation */
          if (result < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't apply candidate list.")
  
          /* this code exists primarily for the test bed -- it allows us to
           * enforce posix semantics on the server that pretends to be a
           * file system in our parallel tests.
           */
          if (aux_ptr->write_done)
              (aux_ptr->write_done)();
  
          /* final sync point barrier */
          if (MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)))
              HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_result)
  
          /* if this is process zero, tidy up the dirtied,
           * and flushed and still clean lists.
           */
          if (aux_ptr->mpi_rank == 0)
              if (H5AC__tidy_cache_0_lists(cache_ptr, num_entries, haddr_buf_ptr) < 0)
                  HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Can't tidy up process 0 lists.")
      } /* end if */
  
      /* if it is defined, call the sync point done callback.  Note
       * that this callback is defined purely for testing purposes,
       * and should be undefined under normal operating circumstances.
       */
      if (aux_ptr->sync_point_done)
          (aux_ptr->sync_point_done)(num_entries, haddr_buf_ptr);
  
  done:
      if (haddr_buf_ptr)
          haddr_buf_ptr = (haddr_t *)H5MM_xfree((void *)haddr_buf_ptr);
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__rsp__dist_md_write__flush() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__rsp__dist_md_write__flush_to_min_clean
   *
   * Purpose:     Routine for handling the details of running a sync point
   *		triggered by the accumulation of dirty metadata (as
   *		opposed to a flush call to the API) when the distributed
   *		metadata write strategy is selected.
   *
   *		After invocation and initial sanity checking this function
   *		first checks to see if evictions are enabled -- if they
   *		are not, the function does nothing and returns.
   *
   *		Otherwise, process zero constructs a list of entries to
   *		be flushed in order to bring the process zero cache back
   *		within its min clean requirement.  Note that this list
   *		(the candidate list) may be empty.
   *
   *              Then, all processes participate in a barrier.
   *
   *		After the barrier, process 0 broadcasts the number of
   *		entries in the candidate list prepared above, and all
   *		other processes receive this number.
   *
   *		If this number is zero, we are done, and the function
   *		returns without further action.
   *
   *		Otherwise, process 0 broadcasts the sorted list of
   *		candidate entries, and all other processes receive it.
   *
   *		Then, each process uses the same algorithm to assign
   *		each entry on the candidate list to exactly one process
   *		for flushing.
   *
   *		Each process then flushes the entries assigned to it, and
   *		marks all other entries on the candidate list as clean.
   *
   *		Finally, all processes participate in a second barrier to
   *		avoid messages from the past/future bugs.
   *
   *		At the end of this process, process 0 and only process 0
   *		must tidy up its lists of dirtied and cleaned entries.
   *		These lists are not used in the distributed metadata write
   *		strategy, but they must be maintained should we shift
   *		to a strategy that uses them.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              April 28, 2010
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__rsp__dist_md_write__flush_to_min_clean(H5F_t *f)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      hbool_t     evictions_enabled;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(f != NULL);
      cache_ptr = f->shared->cache;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
  
      /* Query if evictions are allowed */
      if (H5C_get_evictions_enabled((const H5C_t *)cache_ptr, &evictions_enabled) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "H5C_get_evictions_enabled() failed.")
  
      if (evictions_enabled) {
          /* construct candidate list -- process 0 only */
          if (aux_ptr->mpi_rank == 0)
              if (H5AC__construct_candidate_list(cache_ptr, aux_ptr, H5AC_SYNC_POINT_OP__FLUSH_TO_MIN_CLEAN) <
                  0)
                  HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't construct candidate list.")
  
          /* propagate and apply candidate list -- all processes */
          if (H5AC__propagate_and_apply_candidate_list(f) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't propagate and apply candidate list.")
      } /* evictions enabled */
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__rsp__dist_md_write__flush_to_min_clean() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__rsp__p0_only__flush
   *
   * Purpose:     Routine for handling the details of running a sync point
   *		that is triggered a flush -- which in turn must have been
   *		triggered by either a flush API call or a file close --
   *		when the process 0 only metadata write strategy is selected.
   *
   *              First, all processes participate in a barrier.
   *
   *		Then process zero flushes all dirty entries, and broadcasts
   *		they number of clean entries (if any) to all the other
   *		caches.
   *
   *		If this number is zero, we are done.
   *
   *		Otherwise, process 0 broadcasts the list of cleaned
   *		entries, and all other processes which are part of this
   *		file group receive it, and mark the listed entries as
   *		clean in their caches.
   *
   *		Since all processes have the same set of dirty
   *		entries at the beginning of the sync point, and all
   *		entries that will be written are written before
   *		process zero broadcasts the number of cleaned entries,
   *		there is no need for a closing barrier.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              April 28, 2010
   *
   * Changes:     None.
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__rsp__p0_only__flush(H5F_t *f)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      int         mpi_result;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(f != NULL);
      cache_ptr = f->shared->cache;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY);
  
      /* To prevent "messages from the future" we must
       * synchronize all processes before we start the flush.
       * Hence the following barrier.
       *
       * However, when flushing from within the close operation from a file,
       * it's possible to skip this barrier (on the second flush of the cache).
       */
      if (!H5CX_get_mpi_file_flushing()) {
  
          if (MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)))
  
              HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_result)
      }
  
      /* Flush data to disk, from rank 0 process */
      if (aux_ptr->mpi_rank == 0) {
          herr_t result;
  
          /* Enable writes during this operation */
          aux_ptr->write_permitted = TRUE;
  
          /* Flush the cache */
          result = H5C_flush_cache(f, H5AC__NO_FLAGS_SET);
  
          /* Disable writes again */
          aux_ptr->write_permitted = FALSE;
  
          /* Check for error on the write operation */
          if (result < 0)
  
              HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't flush.")
  
          /* this code exists primarily for the test bed -- it allows us to
           * enforce POSIX semantics on the server that pretends to be a
           * file system in our parallel tests.
           */
          if (aux_ptr->write_done) {
  
              (aux_ptr->write_done)();
          }
      } /* end if */
  
      /* Propagate cleaned entries to other ranks. */
      if (H5AC__propagate_flushed_and_still_clean_entries_list(f) < 0)
  
          HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't propagate clean entries list.")
  
  done:
  
      FUNC_LEAVE_NOAPI(ret_value)
  
  } /* H5AC__rsp__p0_only__flush() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__rsp__p0_only__flush_to_min_clean
   *
   * Purpose:     Routine for handling the details of running a sync point
   *		triggered by the accumulation of dirty metadata (as
   *		opposed to a flush call to the API) when the process 0
   *		only metadata write strategy is selected.
   *
   *		After invocation and initial sanity checking this function
   *		first checks to see if evictions are enabled -- if they
   *		are not, the function does nothing and returns.
   *
   *              Otherwise, all processes participate in a barrier.
   *
   *		After the barrier, if this is process 0, the function
   *		causes the cache to flush sufficient entries to get the
   *		cache back within its minimum clean fraction, and broadcast
   *		the number of entries which have been flushed since
   *		the last sync point, and are still clean.
   *
   *		If this number is zero, we are done.
   *
   *		Otherwise, process 0 broadcasts the list of cleaned
   *		entries, and all other processes which are part of this
   *		file group receive it, and mark the listed entries as
   *		clean in their caches.
   *
   *		Since all processes have the same set of dirty
   *		entries at the beginning of the sync point, and all
   *		entries that will be written are written before
   *		process zero broadcasts the number of cleaned entries,
   *		there is no need for a closing barrier.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              April 28, 2010
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__rsp__p0_only__flush_to_min_clean(H5F_t *f)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      hbool_t     evictions_enabled;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_STATIC
  
      /* Sanity checks */
      HDassert(f != NULL);
      cache_ptr = f->shared->cache;
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY);
  
      /* Query if evictions are allowed */
      if (H5C_get_evictions_enabled((const H5C_t *)cache_ptr, &evictions_enabled) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "H5C_get_evictions_enabled() failed.")
  
      /* Flush if evictions are allowed -- following call
       * will cause process 0 to flush to min clean size,
       * and then propagate the newly clean entries to the
       * other processes.
       *
       * Otherwise, do nothing.
       */
      if (evictions_enabled) {
          int mpi_result;
  
          /* to prevent "messages from the future" we must synchronize all
           * processes before we start the flush.  This synchronization may
           * already be done -- hence the do_barrier parameter.
           */
          if (MPI_SUCCESS != (mpi_result = MPI_Barrier(aux_ptr->mpi_comm)))
              HMPI_GOTO_ERROR(FAIL, "MPI_Barrier failed", mpi_result)
  
          if (0 == aux_ptr->mpi_rank) {
              herr_t result;
  
              /* here, process 0 flushes as many entries as necessary to
               * comply with the currently specified min clean size.
               * Note that it is quite possible that no entries will be
               * flushed.
               */
  
              /* Enable writes during this operation */
              aux_ptr->write_permitted = TRUE;
  
              /* Flush the cache */
              result = H5C_flush_to_min_clean(f);
  
              /* Disable writes again */
              aux_ptr->write_permitted = FALSE;
  
              /* Check for error on the write operation */
              if (result < 0)
                  HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5C_flush_to_min_clean() failed.")
  
              /* this call exists primarily for the test code -- it is used
               * to enforce POSIX semantics on the process used to simulate
               * reads and writes in t_cache.c.
               */
              if (aux_ptr->write_done)
                  (aux_ptr->write_done)();
          } /* end if */
  
          if (H5AC__propagate_flushed_and_still_clean_entries_list(f) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't propagate clean entries list.")
      } /* end if */
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__rsp__p0_only__flush_to_min_clean() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__run_sync_point
   *
   * Purpose:     Top level routine for managing a sync point between all
   *		meta data caches in the parallel case.  Since all caches
   *		see the same sequence of dirty metadata, we simply count
   *		bytes of dirty metadata, and run a sync point whenever the
   *		number of dirty bytes of metadata seen since the last
   *		sync point exceeds a threshold that is common across all
   *		processes.  We also run sync points in response to
   *		HDF5 API calls triggering either a flush or a file close.
   *
   *		In earlier versions of PHDF5, only the metadata cache with
   *		mpi rank 0 was allowed to write to file.  All other
   *		metadata caches on processes with rank greater than 0 were
   *		required to retain dirty entries until they were notified
   *		that the entry is was clean.
   *
   *		This function was created to make it easier for us to
   *		experiment with other options, as it is a single point
   *		for the execution of sync points.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              March 11, 2010
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__run_sync_point(H5F_t *f, int sync_point_op)
  {
      H5AC_t *    cache_ptr;
      H5AC_aux_t *aux_ptr;
      herr_t      ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_PACKAGE
  
      /* Sanity checks */
      HDassert(f != NULL);
  
      cache_ptr = f->shared->cache;
  
      HDassert(cache_ptr != NULL);
  
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
  
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert((sync_point_op == H5AC_SYNC_POINT_OP__FLUSH_TO_MIN_CLEAN) ||
               (sync_point_op == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED));
  
  #if H5AC_DEBUG_DIRTY_BYTES_CREATION
      HDfprintf(stdout, "%d:H5AC_propagate...:%u: (u/uu/i/iu/r/ru) = %zu/%u/%zu/%u/%zu/%u\n", aux_ptr->mpi_rank,
                aux_ptr->dirty_bytes_propagations, aux_ptr->unprotect_dirty_bytes,
                aux_ptr->unprotect_dirty_bytes_updates, aux_ptr->insert_dirty_bytes,
                aux_ptr->insert_dirty_bytes_updates, aux_ptr->rename_dirty_bytes,
                aux_ptr->rename_dirty_bytes_updates);
  #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
  
      /* clear collective access flag on half of the entries in the
         cache and mark them as independent in case they need to be
         evicted later. All ranks are guaranteed to mark the same entries
         since we don't modify the order of the collectively accessed
         entries except through collective access. */
      if (H5C_clear_coll_entries(cache_ptr, TRUE) < 0)
          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "H5C_clear_coll_entries() failed.")
  
      switch (aux_ptr->metadata_write_strategy) {
          case H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY:
              switch (sync_point_op) {
                  case H5AC_SYNC_POINT_OP__FLUSH_TO_MIN_CLEAN:
                      if (H5AC__rsp__p0_only__flush_to_min_clean(f) < 0)
                          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL,
                                      "H5AC__rsp__p0_only__flush_to_min_clean() failed.")
                      break;
  
                  case H5AC_SYNC_POINT_OP__FLUSH_CACHE:
                      if (H5AC__rsp__p0_only__flush(f) < 0)
                          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "H5AC__rsp__p0_only__flush() failed.")
                      break;
  
                  default:
                      HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "unknown flush op");
                      break;
              } /* end switch */
              break;
  
          case H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED:
              switch (sync_point_op) {
                  case H5AC_SYNC_POINT_OP__FLUSH_TO_MIN_CLEAN:
                      if (H5AC__rsp__dist_md_write__flush_to_min_clean(f) < 0)
                          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL,
                                      "H5AC__rsp__dist_md_write__flush_to_min_clean() failed.")
                      break;
  
                  case H5AC_SYNC_POINT_OP__FLUSH_CACHE:
                      if (H5AC__rsp__dist_md_write__flush(f) < 0)
                          HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "H5AC__rsp__dist_md_write__flush() failed.")
                      break;
  
                  default:
                      HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "unknown flush op");
                      break;
              } /* end switch */
              break;
  
          default:
              HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Unknown metadata write strategy.")
              break;
      } /* end switch */
  
      /* reset the dirty bytes count */
      aux_ptr->dirty_bytes = 0;
  
  #if H5AC_DEBUG_DIRTY_BYTES_CREATION
      aux_ptr->dirty_bytes_propagations += 1;
      aux_ptr->unprotect_dirty_bytes         = 0;
      aux_ptr->unprotect_dirty_bytes_updates = 0;
      aux_ptr->insert_dirty_bytes            = 0;
      aux_ptr->insert_dirty_bytes_updates    = 0;
      aux_ptr->rename_dirty_bytes            = 0;
      aux_ptr->rename_dirty_bytes_updates    = 0;
  #endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */
  
  done:
  
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__run_sync_point() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__tidy_cache_0_lists()
   *
   * Purpose:     In the distributed metadata write strategy, not all dirty
   *		entries are written by process 0 -- thus we must tidy
   *		up the dirtied, and flushed and still clean lists
   *		maintained by process zero after each sync point.
   *
   *		This procedure exists to tend to this issue.
   *
   *		At this point, all entries that process 0 cleared should
   *		have been removed from both the dirty and flushed and
   *		still clean lists, and entries that process 0 has flushed
   *		should have been removed from the dirtied list and added
   *		to the flushed and still clean list.
   *
   *		However, since the distributed metadata write strategy
   *		doesn't make use of these lists, the objective is simply
   *		to maintain these lists in consistent state that allows
   *		them to be used should the metadata write strategy change
   *		to one that uses these lists.
   *
   *		Thus for our purposes, all we need to do is remove from
   *		the dirtied and flushed and still clean lists all
   *		references to entries that appear in the candidate list.
   *
   * Return:      Success:        non-negative
   *
   *              Failure:        negative
   *
   * Programmer:  John Mainzer
   *              4/20/10
   *
   *-------------------------------------------------------------------------
   */
  static herr_t
  H5AC__tidy_cache_0_lists(H5AC_t *cache_ptr, unsigned num_candidates, haddr_t *candidates_list_ptr)
  {
      H5AC_aux_t *aux_ptr;
      unsigned    u;
  
      FUNC_ENTER_STATIC_NOERR
  
      /* Sanity checks */
      HDassert(cache_ptr != NULL);
      aux_ptr = (H5AC_aux_t *)H5C_get_aux_ptr(cache_ptr);
      HDassert(aux_ptr != NULL);
      HDassert(aux_ptr->magic == H5AC__H5AC_AUX_T_MAGIC);
      HDassert(aux_ptr->metadata_write_strategy == H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED);
      HDassert(aux_ptr->mpi_rank == 0);
      HDassert(num_candidates > 0);
      HDassert(candidates_list_ptr != NULL);
  
      /* clean up dirtied and flushed and still clean lists by removing
       * all entries on the candidate list.  Cleared entries should
       * have been removed from both the dirty and cleaned lists at
       * this point, flushed entries should have been added to the
       * cleaned list.  However, for this metadata write strategy,
       * we just want to remove all references to the candidate entries.
       */
      for (u = 0; u < num_candidates; u++) {
          H5AC_slist_entry_t *d_slist_entry_ptr;
          H5AC_slist_entry_t *c_slist_entry_ptr;
          haddr_t             addr;
  
          addr = candidates_list_ptr[u];
  
          /* addr may be either on the dirtied list, or on the flushed
           * and still clean list.  Remove it.
           */
          if (NULL !=
              (d_slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->d_slist_ptr, (void *)&addr)))
              d_slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, d_slist_entry_ptr);
          if (NULL !=
              (c_slist_entry_ptr = (H5AC_slist_entry_t *)H5SL_remove(aux_ptr->c_slist_ptr, (void *)&addr)))
              c_slist_entry_ptr = H5FL_FREE(H5AC_slist_entry_t, c_slist_entry_ptr);
      } /* end for */
  
      FUNC_LEAVE_NOAPI(SUCCEED)
  } /* H5AC__tidy_cache_0_lists() */
  
  /*-------------------------------------------------------------------------
   * Function:    H5AC__flush_entries
   *
   * Purpose:     Flush the metadata cache associated with the specified file,
   *              only writing from rank 0, but propagating the cleaned entries
   *              to all ranks.
   *
   * Return:      Non-negative on success/Negative on failure if there was a
   *              request to flush all items and something was protected.
   *
   * Programmer:  Quincey Koziol
   *              Aug 22 2009
   *
   *-------------------------------------------------------------------------
   */
  herr_t
  H5AC__flush_entries(H5F_t *f)
  {
      herr_t ret_value = SUCCEED; /* Return value */
  
      FUNC_ENTER_PACKAGE
  
      /* Sanity checks */
      HDassert(f);
      HDassert(f->shared->cache);
  
      /* Check if we have >1 ranks */
      if (H5C_get_aux_ptr(f->shared->cache))
          if (H5AC__run_sync_point(f, H5AC_SYNC_POINT_OP__FLUSH_CACHE) < 0)
              HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "Can't run sync point.")
  
  done:
      FUNC_LEAVE_NOAPI(ret_value)
  } /* H5AC__flush_entries() */
  #endif /* H5_HAVE_PARALLEL */
  