text: /* GLIB sliced memory - fast concurrent memory chunk allocator
   * Copyright (C) 2005 Tim Janik
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the
   * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   * Boston, MA 02111-1307, USA.
   */
  /* MT safe */
  
  #include "config.h"
  
  #include "gslice.h"
  
  #if     defined HAVE_POSIX_MEMALIGN && defined POSIX_MEMALIGN_WITH_COMPLIANT_ALLOCS
  #  define HAVE_COMPLIANT_POSIX_MEMALIGN 1
  #endif
  
  #ifdef HAVE_COMPLIANT_POSIX_MEMALIGN
  #define _XOPEN_SOURCE 600       /* posix_memalign() */
  #endif
  #include <stdlib.h>             /* posix_memalign() */
  #include <string.h>
  #include <errno.h>
  #include "gmem.h"               /* gslice.h */
  #include "gthreadprivate.h"
  #include "glib.h"
  #include "galias.h"
  #ifdef HAVE_UNISTD_H
  #include <unistd.h>             /* sysconf() */
  #endif
  #ifdef G_OS_WIN32
  #include <windows.h>
  #include <process.h>
  #endif
  
  #include <stdio.h>              /* fputs/fprintf */
  
  
  /* the GSlice allocator is split up into 4 layers, roughly modelled after the slab
   * allocator and magazine extensions as outlined in:
   * + [Bonwick94] Jeff Bonwick, The slab allocator: An object-caching kernel
   *   memory allocator. USENIX 1994, http://citeseer.ist.psu.edu/bonwick94slab.html
   * + [Bonwick01] Bonwick and Jonathan Adams, Magazines and vmem: Extending the
   *   slab allocator to many cpu's and arbitrary resources.
   *   USENIX 2001, http://citeseer.ist.psu.edu/bonwick01magazines.html
   * the layers are:
   * - the thread magazines. for each (aligned) chunk size, a magazine (a list)
   *   of recently freed and soon to be allocated chunks is maintained per thread.
   *   this way, most alloc/free requests can be quickly satisfied from per-thread
   *   free lists which only require one g_private_get() call to retrive the
   *   thread handle.
   * - the magazine cache. allocating and freeing chunks to/from threads only
   *   occours at magazine sizes from a global depot of magazines. the depot
   *   maintaines a 15 second working set of allocated magazines, so full
   *   magazines are not allocated and released too often.
   *   the chunk size dependent magazine sizes automatically adapt (within limits,
   *   see [3]) to lock contention to properly scale performance across a variety
   *   of SMP systems.
   * - the slab allocator. this allocator allocates slabs (blocks of memory) close
   *   to the system page size or multiples thereof which have to be page aligned.
   *   the blocks are divided into smaller chunks which are used to satisfy
   *   allocations from the upper layers. the space provided by the reminder of
   *   the chunk size division is used for cache colorization (random distribution
   *   of chunk addresses) to improve processor cache utilization. multiple slabs
   *   with the same chunk size are kept in a partially sorted ring to allow O(1)
   *   freeing and allocation of chunks (as long as the allocation of an entirely
   *   new slab can be avoided).
   * - the page allocator. on most modern systems, posix_memalign(3) or
   *   memalign(3) should be available, so this is used to allocate blocks with
   *   system page size based alignments and sizes or multiples thereof.
   *   if no memalign variant is provided, valloc() is used instead and
   *   block sizes are limited to the system page size (no multiples thereof).
   *   as a fallback, on system without even valloc(), a malloc(3)-based page
   *   allocator with alloc-only behaviour is used.
   *
   * NOTES:
   * [1] some systems memalign(3) implementations may rely on boundary tagging for
   *     the handed out memory chunks. to avoid excessive page-wise fragmentation,
   *     we reserve 2 * sizeof (void*) per block size for the systems memalign(3),
   *     specified in NATIVE_MALLOC_PADDING.
   * [2] using the slab allocator alone already provides for a fast and efficient
   *     allocator, it doesn't properly scale beyond single-threaded uses though.
   *     also, the slab allocator implements eager free(3)-ing, i.e. does not
   *     provide any form of caching or working set maintenance. so if used alone,
   *     it's vulnerable to trashing for sequences of balanced (alloc, free) pairs
   *     at certain thresholds.
   * [3] magazine sizes are bound by an implementation specific minimum size and
   *     a chunk size specific maximum to limit magazine storage sizes to roughly
   *     16KB.
   * [4] allocating ca. 8 chunks per block/page keeps a good balance between
   *     external and internal fragmentation (<= 12.5%). [Bonwick94]
   */
  
  /* --- macros and constants --- */
  #define LARGEALIGNMENT          (256)
  #define P2ALIGNMENT             (2 * sizeof (gsize))                            /* fits 2 pointers (assumed to be 2 * GLIB_SIZEOF_SIZE_T below) */
  #define ALIGN(size, base)       ((base) * (gsize) (((size) + (base) - 1) / (base)))
  #define NATIVE_MALLOC_PADDING   P2ALIGNMENT                                     /* per-page padding left for native malloc(3) see [1] */
  #define SLAB_INFO_SIZE          P2ALIGN (sizeof (SlabInfo) + NATIVE_MALLOC_PADDING)
  #define MAX_MAGAZINE_SIZE       (256)                                           /* see [3] and allocator_get_magazine_threshold() for this */
  #define MIN_MAGAZINE_SIZE       (4)
  #define MAX_STAMP_COUNTER       (7)                                             /* distributes the load of gettimeofday() */
  #define MAX_SLAB_CHUNK_SIZE(al) (((al)->max_page_size - SLAB_INFO_SIZE) / 8)    /* we want at last 8 chunks per page, see [4] */
  #define MAX_SLAB_INDEX(al)      (SLAB_INDEX (al, MAX_SLAB_CHUNK_SIZE (al)) + 1)
  #define SLAB_INDEX(al, asize)   ((asize) / P2ALIGNMENT - 1)                     /* asize must be P2ALIGNMENT aligned */
  #define SLAB_CHUNK_SIZE(al, ix) (((ix) + 1) * P2ALIGNMENT)
  #define SLAB_BPAGE_SIZE(al,csz) (8 * (csz) + SLAB_INFO_SIZE)
  
  /* optimized version of ALIGN (size, P2ALIGNMENT) */
  #if     GLIB_SIZEOF_SIZE_T * 2 == 8  /* P2ALIGNMENT */
  #define P2ALIGN(size)   (((size) + 0x7) & ~(gsize) 0x7)
  #elif   GLIB_SIZEOF_SIZE_T * 2 == 16 /* P2ALIGNMENT */
  #define P2ALIGN(size)   (((size) + 0xf) & ~(gsize) 0xf)
  #else
  #define P2ALIGN(size)   ALIGN (size, P2ALIGNMENT)
  #endif
  
  /* special helpers to avoid gmessage.c dependency */
  static void mem_error (const char *format, ...) G_GNUC_PRINTF (1,2);
  #define mem_assert(cond)    do { if (G_LIKELY (cond)) ; else mem_error ("assertion failed: %s", #cond); } while (0)
  
  /* --- structures --- */
  typedef struct _ChunkLink      ChunkLink;
  typedef struct _SlabInfo       SlabInfo;
  typedef struct _CachedMagazine CachedMagazine;
  struct _ChunkLink {
    ChunkLink *next;
    ChunkLink *data;
  };
  struct _SlabInfo {
    ChunkLink *chunks;
    guint n_allocated;
    SlabInfo *next, *prev;
  };
  typedef struct {
    ChunkLink *chunks;
    gsize      count;                     /* approximative chunks list length */
  } Magazine;
  typedef struct {
    Magazine   *magazine1;                /* array of MAX_SLAB_INDEX (allocator) */
    Magazine   *magazine2;                /* array of MAX_SLAB_INDEX (allocator) */
  } ThreadMemory;
  typedef struct {
    gboolean always_malloc;
    gboolean bypass_magazines;
    gboolean debug_blocks;
    gsize    working_set_msecs;
    guint    color_increment;
  } SliceConfig;
  typedef struct {
    /* const after initialization */
    gsize         min_page_size, max_page_size;
    SliceConfig   config;
    gsize         max_slab_chunk_size_for_magazine_cache;
    /* magazine cache */
    GMutex       *magazine_mutex;
    ChunkLink   **magazines;                /* array of MAX_SLAB_INDEX (allocator) */
    guint        *contention_counters;      /* array of MAX_SLAB_INDEX (allocator) */
    gint          mutex_counter;
    guint         stamp_counter;
    guint         last_stamp;
    /* slab allocator */
    GMutex       *slab_mutex;
    SlabInfo    **slab_stack;                /* array of MAX_SLAB_INDEX (allocator) */
    guint        color_accu;
  } Allocator;
  
  /* --- g-slice prototypes --- */
  static gpointer     slab_allocator_alloc_chunk       (gsize      chunk_size);
  static void         slab_allocator_free_chunk        (gsize      chunk_size,
                                                        gpointer   mem);
  static void         private_thread_memory_cleanup    (gpointer   data);
  static gpointer     allocator_memalign               (gsize      alignment,
                                                        gsize      memsize);
  static void         allocator_memfree                (gsize      memsize,
                                                        gpointer   mem);
  static inline void  magazine_cache_update_stamp      (void);
  static inline gsize allocator_get_magazine_threshold (Allocator *allocator,
                                                        guint      ix);
  
  /* --- g-slice memory checker --- */
  static void     smc_notify_alloc  (void   *pointer,
                                     size_t  size);
  static int      smc_notify_free   (void   *pointer,
                                     size_t  size);
  
  /* --- variables --- */
  static GPrivate   *private_thread_memory = NULL;
  static gsize       sys_page_size = 0;
  static Allocator   allocator[1] = { { 0, }, };
  static SliceConfig slice_config = {
    FALSE,        /* always_malloc */
    FALSE,        /* bypass_magazines */
    FALSE,        /* debug_blocks */
    15 * 1000,    /* working_set_msecs */
    1,            /* color increment, alt: 0x7fffffff */
  };
  static GMutex     *smc_tree_mutex = NULL; /* mutex for G_SLICE=debug-blocks */
  
  /* --- auxillary funcitons --- */
  void
  g_slice_set_config (GSliceConfig ckey,
                      gint64       value)
  {
    g_return_if_fail (sys_page_size == 0);
    switch (ckey)
      {
      case G_SLICE_CONFIG_ALWAYS_MALLOC:
        slice_config.always_malloc = value != 0;
        break;
      case G_SLICE_CONFIG_BYPASS_MAGAZINES:
        slice_config.bypass_magazines = value != 0;
        break;
      case G_SLICE_CONFIG_WORKING_SET_MSECS:
        slice_config.working_set_msecs = value;
        break;
      case G_SLICE_CONFIG_COLOR_INCREMENT:
        slice_config.color_increment = value;
      default: ;
      }
  }
  
  gint64
  g_slice_get_config (GSliceConfig ckey)
  {
    switch (ckey)
      {
      case G_SLICE_CONFIG_ALWAYS_MALLOC:
        return slice_config.always_malloc;
      case G_SLICE_CONFIG_BYPASS_MAGAZINES:
        return slice_config.bypass_magazines;
      case G_SLICE_CONFIG_WORKING_SET_MSECS:
        return slice_config.working_set_msecs;
      case G_SLICE_CONFIG_CHUNK_SIZES:
        return MAX_SLAB_INDEX (allocator);
      case G_SLICE_CONFIG_COLOR_INCREMENT:
        return slice_config.color_increment;
      default:
        return 0;
      }
  }
  
  gint64*
  g_slice_get_config_state (GSliceConfig ckey,
                            gint64       address,
                            guint       *n_values)
  {
    guint i = 0;
    g_return_val_if_fail (n_values != NULL, NULL);
    *n_values = 0;
    switch (ckey)
      {
        gint64 array[64];
      case G_SLICE_CONFIG_CONTENTION_COUNTER:
        array[i++] = SLAB_CHUNK_SIZE (allocator, address);
        array[i++] = allocator->contention_counters[address];
        array[i++] = allocator_get_magazine_threshold (allocator, address);
        *n_values = i;
        return g_memdup (array, sizeof (array[0]) * *n_values);
      default:
        return NULL;
      }
  }
  
  static void
  slice_config_init (SliceConfig *config)
  {
    /* don't use g_malloc/g_message here */
    gchar buffer[1024];
    const gchar *val = _g_getenv_nomalloc ("G_SLICE", buffer);
    const GDebugKey keys[] = {
      { "always-malloc", 1 << 0 },
      { "debug-blocks",  1 << 1 },
    };
    gint flags = !val ? 0 : g_parse_debug_string (val, keys, G_N_ELEMENTS (keys));
    *config = slice_config;
    if (flags & (1 << 0))         /* always-malloc */
      config->always_malloc = TRUE;
    if (flags & (1 << 1))         /* debug-blocks */
      config->debug_blocks = TRUE;
  }
  
  static void
  g_slice_init_nomessage (void)
  {
    /* we may not use g_error() or friends here */
    mem_assert (sys_page_size == 0);
    mem_assert (MIN_MAGAZINE_SIZE >= 4);
  
  #ifdef G_OS_WIN32
    {
      SYSTEM_INFO system_info;
      GetSystemInfo (&system_info);
      sys_page_size = system_info.dwPageSize;
    }
  #else
    sys_page_size = sysconf (_SC_PAGESIZE); /* = sysconf (_SC_PAGE_SIZE); = getpagesize(); */
  #endif
    mem_assert (sys_page_size >= 2 * LARGEALIGNMENT);
    mem_assert ((sys_page_size & (sys_page_size - 1)) == 0);
    slice_config_init (&allocator->config);
    allocator->min_page_size = sys_page_size;
  #if HAVE_COMPLIANT_POSIX_MEMALIGN || HAVE_MEMALIGN
    /* allow allocation of pages up to 8KB (with 8KB alignment).
     * this is useful because many medium to large sized structures
     * fit less than 8 times (see [4]) into 4KB pages.
     * we allow very small page sizes here, to reduce wastage in
     * threads if only small allocations are required (this does
     * bear the risk of incresing allocation times and fragmentation
     * though).
     */
    allocator->min_page_size = MAX (allocator->min_page_size, 4096);
    allocator->max_page_size = MAX (allocator->min_page_size, 8192);
    allocator->min_page_size = MIN (allocator->min_page_size, 128);
  #else
    /* we can only align to system page size */
    allocator->max_page_size = sys_page_size;
  #endif
    if (allocator->config.always_malloc)
      {
        allocator->contention_counters = NULL;
        allocator->magazines = NULL;
        allocator->slab_stack = NULL;
      }
    else
      {
        allocator->contention_counters = g_new0 (guint, MAX_SLAB_INDEX (allocator));
        allocator->magazines = g_new0 (ChunkLink*, MAX_SLAB_INDEX (allocator));
        allocator->slab_stack = g_new0 (SlabInfo*, MAX_SLAB_INDEX (allocator));
      }
  
    allocator->magazine_mutex = NULL;     /* _g_slice_thread_init_nomessage() */
    allocator->mutex_counter = 0;
    allocator->stamp_counter = MAX_STAMP_COUNTER; /* force initial update */
    allocator->last_stamp = 0;
    allocator->slab_mutex = NULL;         /* _g_slice_thread_init_nomessage() */
    allocator->color_accu = 0;
    magazine_cache_update_stamp();
    /* values cached for performance reasons */
    allocator->max_slab_chunk_size_for_magazine_cache = MAX_SLAB_CHUNK_SIZE (allocator);
    if (allocator->config.always_malloc || allocator->config.bypass_magazines)
      allocator->max_slab_chunk_size_for_magazine_cache = 0;      /* non-optimized cases */
    /* at this point, g_mem_gc_friendly() should be initialized, this
     * should have been accomplished by the above g_malloc/g_new calls
     */
  }
  
  static inline guint
  allocator_categorize (gsize aligned_chunk_size)
  {
    /* speed up the likely path */
    if (G_LIKELY (aligned_chunk_size && aligned_chunk_size <= allocator->max_slab_chunk_size_for_magazine_cache))
      return 1;           /* use magazine cache */
  
    /* the above will fail (max_slab_chunk_size_for_magazine_cache == 0) if the
     * allocator is still uninitialized, or if we are not configured to use the
     * magazine cache.
     */
    if (!sys_page_size)
      g_slice_init_nomessage ();
    if (!allocator->config.always_malloc &&
        aligned_chunk_size &&
        aligned_chunk_size <= MAX_SLAB_CHUNK_SIZE (allocator))
      {
        if (allocator->config.bypass_magazines)
          return 2;       /* use slab allocator, see [2] */
        return 1;         /* use magazine cache */
      }
    return 0;             /* use malloc() */
  }
  
  void
  _g_slice_thread_init_nomessage (void)
  {
    /* we may not use g_error() or friends here */
    if (!sys_page_size)
      g_slice_init_nomessage();
    else
      {
        /* g_slice_init_nomessage() has been called already, probably due
         * to a g_slice_alloc1() before g_thread_init().
         */
      }
    private_thread_memory = g_private_new (private_thread_memory_cleanup);
    allocator->magazine_mutex = g_mutex_new();
    allocator->slab_mutex = g_mutex_new();
    if (allocator->config.debug_blocks)
      smc_tree_mutex = g_mutex_new();
  }
  
  static inline void
  g_mutex_lock_a (GMutex *mutex,
                  guint  *contention_counter)
  {
    gboolean contention = FALSE;
    if (!g_mutex_trylock (mutex))
      {
        g_mutex_lock (mutex);
        contention = TRUE;
      }
    if (contention)
      {
        allocator->mutex_counter++;
        if (allocator->mutex_counter >= 1)        /* quickly adapt to contention */
          {
            allocator->mutex_counter = 0;
            *contention_counter = MIN (*contention_counter + 1, MAX_MAGAZINE_SIZE);
          }
      }
    else /* !contention */
      {
        allocator->mutex_counter--;
        if (allocator->mutex_counter < -11)       /* moderately recover magazine sizes */
          {
            allocator->mutex_counter = 0;
            *contention_counter = MAX (*contention_counter, 1) - 1;
          }
      }
  }
  
  static inline ThreadMemory*
  thread_memory_from_self (void)
  {
    ThreadMemory *tmem = g_private_get (private_thread_memory);
    if (G_UNLIKELY (!tmem))
      {
        static ThreadMemory *single_thread_memory = NULL;   /* remember single-thread info for multi-threaded case */
        if (single_thread_memory && g_thread_supported ())
          {
            g_mutex_lock (allocator->slab_mutex);
            if (single_thread_memory)
              {
                /* GSlice has been used before g_thread_init(), and now
                 * we are running threaded. to cope with it, use the saved
                 * thread memory structure from when we weren't threaded.
                 */
                tmem = single_thread_memory;
                single_thread_memory = NULL;      /* slab_mutex protected when multi-threaded */
              }
            g_mutex_unlock (allocator->slab_mutex);
          }
        if (!tmem)
  	{
            const guint n_magazines = MAX_SLAB_INDEX (allocator);
  	  tmem = g_malloc0 (sizeof (ThreadMemory) + sizeof (Magazine) * 2 * n_magazines);
  	  tmem->magazine1 = (Magazine*) (tmem + 1);
  	  tmem->magazine2 = &tmem->magazine1[n_magazines];
  	}
        /* g_private_get/g_private_set works in the single-threaded xor the multi-
         * threaded case. but not *across* g_thread_init(), after multi-thread
         * initialization it returns NULL for previously set single-thread data.
         */
        g_private_set (private_thread_memory, tmem);
        /* save single-thread thread memory structure, in case we need to
         * pick it up again after multi-thread initialization happened.
         */
        if (!single_thread_memory && !g_thread_supported ())
          single_thread_memory = tmem;            /* no slab_mutex created yet */
      }
    return tmem;
  }
  
  static inline ChunkLink*
  magazine_chain_pop_head (ChunkLink **magazine_chunks)
  {
    /* magazine chains are linked via ChunkLink->next.
     * each ChunkLink->data of the toplevel chain may point to a subchain,
     * linked via ChunkLink->next. ChunkLink->data of the subchains just
     * contains uninitialized junk.
     */
    ChunkLink *chunk = (*magazine_chunks)->data;
    if (G_UNLIKELY (chunk))
      {
        /* allocating from freed list */
        (*magazine_chunks)->data = chunk->next;
      }
    else
      {
        chunk = *magazine_chunks;
        *magazine_chunks = chunk->next;
      }
    return chunk;
  }
  
  #if 0 /* useful for debugging */
  static guint
  magazine_count (ChunkLink *head)
  {
    guint count = 0;
    if (!head)
      return 0;
    while (head)
      {
        ChunkLink *child = head->data;
        count += 1;
        for (child = head->data; child; child = child->next)
          count += 1;
        head = head->next;
      }
    return count;
  }
  #endif
  
  static inline gsize
  allocator_get_magazine_threshold (Allocator *allocator,
                                    guint      ix)
  {
    /* the magazine size calculated here has a lower bound of MIN_MAGAZINE_SIZE,
     * which is required by the implementation. also, for moderately sized chunks
     * (say >= 64 bytes), magazine sizes shouldn't be much smaller then the number
     * of chunks available per page/2 to avoid excessive traffic in the magazine
     * cache for small to medium sized structures.
     * the upper bound of the magazine size is effectively provided by
     * MAX_MAGAZINE_SIZE. for larger chunks, this number is scaled down so that
     * the content of a single magazine doesn't exceed ca. 16KB.
     */
    gsize chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
    guint threshold = MAX (MIN_MAGAZINE_SIZE, allocator->max_page_size / MAX (5 * chunk_size, 5 * 32));
    guint contention_counter = allocator->contention_counters[ix];
    if (G_UNLIKELY (contention_counter))  /* single CPU bias */
      {
        /* adapt contention counter thresholds to chunk sizes */
        contention_counter = contention_counter * 64 / chunk_size;
        threshold = MAX (threshold, contention_counter);
      }
    return threshold;
  }
  
  /* --- magazine cache --- */
  static inline void
  magazine_cache_update_stamp (void)
  {
    if (allocator->stamp_counter >= MAX_STAMP_COUNTER)
      {
        GTimeVal tv;
        g_get_current_time (&tv);
        allocator->last_stamp = tv.tv_sec * 1000 + tv.tv_usec / 1000; /* milli seconds */
        allocator->stamp_counter = 0;
      }
    else
      allocator->stamp_counter++;
  }
  
  static inline ChunkLink*
  magazine_chain_prepare_fields (ChunkLink *magazine_chunks)
  {
    ChunkLink *chunk1;
    ChunkLink *chunk2;
    ChunkLink *chunk3;
    ChunkLink *chunk4;
    /* checked upon initialization: mem_assert (MIN_MAGAZINE_SIZE >= 4); */
    /* ensure a magazine with at least 4 unused data pointers */
    chunk1 = magazine_chain_pop_head (&magazine_chunks);
    chunk2 = magazine_chain_pop_head (&magazine_chunks);
    chunk3 = magazine_chain_pop_head (&magazine_chunks);
    chunk4 = magazine_chain_pop_head (&magazine_chunks);
    chunk4->next = magazine_chunks;
    chunk3->next = chunk4;
    chunk2->next = chunk3;
    chunk1->next = chunk2;
    return chunk1;
  }
  
  /* access the first 3 fields of a specially prepared magazine chain */
  #define magazine_chain_prev(mc)         ((mc)->data)
  #define magazine_chain_stamp(mc)        ((mc)->next->data)
  #define magazine_chain_uint_stamp(mc)   GPOINTER_TO_UINT ((mc)->next->data)
  #define magazine_chain_next(mc)         ((mc)->next->next->data)
  #define magazine_chain_count(mc)        ((mc)->next->next->next->data)
  
  static void
  magazine_cache_trim (Allocator *allocator,
                       guint      ix,
                       guint      stamp)
  {
    /* g_mutex_lock (allocator->mutex); done by caller */
    /* trim magazine cache from tail */
    ChunkLink *current = magazine_chain_prev (allocator->magazines[ix]);
    ChunkLink *trash = NULL;
    while (ABS (stamp - magazine_chain_uint_stamp (current)) >= allocator->config.working_set_msecs)
      {
        /* unlink */
        ChunkLink *prev = magazine_chain_prev (current);
        ChunkLink *next = magazine_chain_next (current);
        magazine_chain_next (prev) = next;
        magazine_chain_prev (next) = prev;
        /* clear special fields, put on trash stack */
        magazine_chain_next (current) = NULL;
        magazine_chain_count (current) = NULL;
        magazine_chain_stamp (current) = NULL;
        magazine_chain_prev (current) = trash;
        trash = current;
        /* fixup list head if required */
        if (current == allocator->magazines[ix])
          {
            allocator->magazines[ix] = NULL;
            break;
          }
        current = prev;
      }
    g_mutex_unlock (allocator->magazine_mutex);
    /* free trash */
    if (trash)
      {
        const gsize chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
        g_mutex_lock (allocator->slab_mutex);
        while (trash)
          {
            current = trash;
            trash = magazine_chain_prev (current);
            magazine_chain_prev (current) = NULL; /* clear special field */
            while (current)
              {
                ChunkLink *chunk = magazine_chain_pop_head (&current);
                slab_allocator_free_chunk (chunk_size, chunk);
              }
          }
        g_mutex_unlock (allocator->slab_mutex);
      }
  }
  
  static void
  magazine_cache_push_magazine (guint      ix,
                                ChunkLink *magazine_chunks,
                                gsize      count) /* must be >= MIN_MAGAZINE_SIZE */
  {
    ChunkLink *current = magazine_chain_prepare_fields (magazine_chunks);
    ChunkLink *next, *prev;
    g_mutex_lock (allocator->magazine_mutex);
    /* add magazine at head */
    next = allocator->magazines[ix];
    if (next)
      prev = magazine_chain_prev (next);
    else
      next = prev = current;
    magazine_chain_next (prev) = current;
    magazine_chain_prev (next) = current;
    magazine_chain_prev (current) = prev;
    magazine_chain_next (current) = next;
    magazine_chain_count (current) = (gpointer) count;
    /* stamp magazine */
    magazine_cache_update_stamp();
    magazine_chain_stamp (current) = GUINT_TO_POINTER (allocator->last_stamp);
    allocator->magazines[ix] = current;
    /* free old magazines beyond a certain threshold */
    magazine_cache_trim (allocator, ix, allocator->last_stamp);
    /* g_mutex_unlock (allocator->mutex); was done by magazine_cache_trim() */
  }
  
  static ChunkLink*
  magazine_cache_pop_magazine (guint  ix,
                               gsize *countp)
  {
    g_mutex_lock_a (allocator->magazine_mutex, &allocator->contention_counters[ix]);
    if (!allocator->magazines[ix])
      {
        guint magazine_threshold = allocator_get_magazine_threshold (allocator, ix);
        gsize i, chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
        ChunkLink *chunk, *head;
        g_mutex_unlock (allocator->magazine_mutex);
        g_mutex_lock (allocator->slab_mutex);
        head = slab_allocator_alloc_chunk (chunk_size);
        head->data = NULL;
        chunk = head;
        for (i = 1; i < magazine_threshold; i++)
          {
            chunk->next = slab_allocator_alloc_chunk (chunk_size);
            chunk = chunk->next;
            chunk->data = NULL;
          }
        chunk->next = NULL;
        g_mutex_unlock (allocator->slab_mutex);
        *countp = i;
        return head;
      }
    else
      {
        ChunkLink *current = allocator->magazines[ix];
        ChunkLink *prev = magazine_chain_prev (current);
        ChunkLink *next = magazine_chain_next (current);
        /* unlink */
        magazine_chain_next (prev) = next;
        magazine_chain_prev (next) = prev;
        allocator->magazines[ix] = next == current ? NULL : next;
        g_mutex_unlock (allocator->magazine_mutex);
        /* clear special fields and hand out */
        *countp = (gsize) magazine_chain_count (current);
        magazine_chain_prev (current) = NULL;
        magazine_chain_next (current) = NULL;
        magazine_chain_count (current) = NULL;
        magazine_chain_stamp (current) = NULL;
        return current;
      }
  }
  
  /* --- thread magazines --- */
  static void
  private_thread_memory_cleanup (gpointer data)
  {
    ThreadMemory *tmem = data;
    const guint n_magazines = MAX_SLAB_INDEX (allocator);
    guint ix;
    for (ix = 0; ix < n_magazines; ix++)
      {
        Magazine *mags[2];
        guint j;
        mags[0] = &tmem->magazine1[ix];
        mags[1] = &tmem->magazine2[ix];
        for (j = 0; j < 2; j++)
          {
            Magazine *mag = mags[j];
            if (mag->count >= MIN_MAGAZINE_SIZE)
              magazine_cache_push_magazine (ix, mag->chunks, mag->count);
            else
              {
                const gsize chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
                g_mutex_lock (allocator->slab_mutex);
                while (mag->chunks)
                  {
                    ChunkLink *chunk = magazine_chain_pop_head (&mag->chunks);
                    slab_allocator_free_chunk (chunk_size, chunk);
                  }
                g_mutex_unlock (allocator->slab_mutex);
              }
          }
      }
    g_free (tmem);
  }
  
  static void
  thread_memory_magazine1_reload (ThreadMemory *tmem,
                                  guint         ix)
  {
    Magazine *mag = &tmem->magazine1[ix];
    mem_assert (mag->chunks == NULL); /* ensure that we may reset mag->count */
    mag->count = 0;
    mag->chunks = magazine_cache_pop_magazine (ix, &mag->count);
  }
  
  static void
  thread_memory_magazine2_unload (ThreadMemory *tmem,
                                  guint         ix)
  {
    Magazine *mag = &tmem->magazine2[ix];
    magazine_cache_push_magazine (ix, mag->chunks, mag->count);
    mag->chunks = NULL;
    mag->count = 0;
  }
  
  static inline void
  thread_memory_swap_magazines (ThreadMemory *tmem,
                                guint         ix)
  {
    Magazine xmag = tmem->magazine1[ix];
    tmem->magazine1[ix] = tmem->magazine2[ix];
    tmem->magazine2[ix] = xmag;
  }
  
  static inline gboolean
  thread_memory_magazine1_is_empty (ThreadMemory *tmem,
                                    guint         ix)
  {
    return tmem->magazine1[ix].chunks == NULL;
  }
  
  static inline gboolean
  thread_memory_magazine2_is_full (ThreadMemory *tmem,
                                   guint         ix)
  {
    return tmem->magazine2[ix].count >= allocator_get_magazine_threshold (allocator, ix);
  }
  
  static inline gpointer
  thread_memory_magazine1_alloc (ThreadMemory *tmem,
                                 guint         ix)
  {
    Magazine *mag = &tmem->magazine1[ix];
    ChunkLink *chunk = magazine_chain_pop_head (&mag->chunks);
    if (G_LIKELY (mag->count > 0))
      mag->count--;
    return chunk;
  }
  
  static inline void
  thread_memory_magazine2_free (ThreadMemory *tmem,
                                guint         ix,
                                gpointer      mem)
  {
    Magazine *mag = &tmem->magazine2[ix];
    ChunkLink *chunk = mem;
    chunk->data = NULL;
    chunk->next = mag->chunks;
    mag->chunks = chunk;
    mag->count++;
  }
  
  /* --- API functions --- */
  gpointer
  g_slice_alloc (gsize mem_size)
  {
    gsize chunk_size;
    gpointer mem;
    guint acat;
    chunk_size = P2ALIGN (mem_size);
    acat = allocator_categorize (chunk_size);
    if (G_LIKELY (acat == 1))     /* allocate through magazine layer */
      {
        ThreadMemory *tmem = thread_memory_from_self();
        guint ix = SLAB_INDEX (allocator, chunk_size);
        if (G_UNLIKELY (thread_memory_magazine1_is_empty (tmem, ix)))
          {
            thread_memory_swap_magazines (tmem, ix);
            if (G_UNLIKELY (thread_memory_magazine1_is_empty (tmem, ix)))
              thread_memory_magazine1_reload (tmem, ix);
          }
        mem = thread_memory_magazine1_alloc (tmem, ix);
      }
    else if (acat == 2)           /* allocate through slab allocator */
      {
        g_mutex_lock (allocator->slab_mutex);
        mem = slab_allocator_alloc_chunk (chunk_size);
        g_mutex_unlock (allocator->slab_mutex);
      }
    else                          /* delegate to system malloc */
      mem = g_malloc (mem_size);
    if (G_UNLIKELY (allocator->config.debug_blocks))
      smc_notify_alloc (mem, mem_size);
    return mem;
  }
  
  gpointer
  g_slice_alloc0 (gsize mem_size)
  {
    gpointer mem = g_slice_alloc (mem_size);
    if (mem)
      memset (mem, 0, mem_size);
    return mem;
  }
  
  gpointer
  g_slice_copy (gsize         mem_size,
                gconstpointer mem_block)
  {
    gpointer mem = g_slice_alloc (mem_size);
    if (mem)
      memcpy (mem, mem_block, mem_size);
    return mem;
  }
  
  void
  g_slice_free1 (gsize    mem_size,
                 gpointer mem_block)
  {
    gsize chunk_size = P2ALIGN (mem_size);
    guint acat = allocator_categorize (chunk_size);
    if (G_UNLIKELY (!mem_block))
      return;
    if (G_UNLIKELY (allocator->config.debug_blocks) &&
        !smc_notify_free (mem_block, mem_size))
      abort();
    if (G_LIKELY (acat == 1))             /* allocate through magazine layer */
      {
        ThreadMemory *tmem = thread_memory_from_self();
        guint ix = SLAB_INDEX (allocator, chunk_size);
        if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
          {
            thread_memory_swap_magazines (tmem, ix);
            if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
              thread_memory_magazine2_unload (tmem, ix);
          }
        if (G_UNLIKELY (g_mem_gc_friendly))
          memset (mem_block, 0, chunk_size);
        thread_memory_magazine2_free (tmem, ix, mem_block);
      }
    else if (acat == 2)                   /* allocate through slab allocator */
      {
        if (G_UNLIKELY (g_mem_gc_friendly))
          memset (mem_block, 0, chunk_size);
        g_mutex_lock (allocator->slab_mutex);
        slab_allocator_free_chunk (chunk_size, mem_block);
        g_mutex_unlock (allocator->slab_mutex);
      }
    else                                  /* delegate to system malloc */
      {
        if (G_UNLIKELY (g_mem_gc_friendly))
          memset (mem_block, 0, mem_size);
        g_free (mem_block);
      }
  }
  
  void
  g_slice_free_chain_with_offset (gsize    mem_size,
                                  gpointer mem_chain,
                                  gsize    next_offset)
  {
    gpointer slice = mem_chain;
    /* while the thread magazines and the magazine cache are implemented so that
     * they can easily be extended to allow for free lists containing more free
     * lists for the first level nodes, which would allow O(1) freeing in this
     * function, the benefit of such an extension is questionable, because:
     * - the magazine size counts will become mere lower bounds which confuses
     *   the code adapting to lock contention;
     * - freeing a single node to the thread magazines is very fast, so this
     *   O(list_length) operation is multiplied by a fairly small factor;
     * - memory usage histograms on larger applications seem to indicate that
     *   the amount of released multi node lists is negligible in comparison
     *   to single node releases.
     * - the major performance bottle neck, namely g_private_get() or
     *   g_mutex_lock()/g_mutex_unlock() has already been moved out of the
     *   inner loop for freeing chained slices.
     */
    gsize chunk_size = P2ALIGN (mem_size);
    guint acat = allocator_categorize (chunk_size);
    if (G_LIKELY (acat == 1))             /* allocate through magazine layer */
      {
        ThreadMemory *tmem = thread_memory_from_self();
        guint ix = SLAB_INDEX (allocator, chunk_size);
        while (slice)
          {
            guint8 *current = slice;
            slice = *(gpointer*) (current + next_offset);
            if (G_UNLIKELY (allocator->config.debug_blocks) &&
                !smc_notify_free (current, mem_size))
              abort();
            if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
              {
                thread_memory_swap_magazines (tmem, ix);
                if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
                  thread_memory_magazine2_unload (tmem, ix);
              }
            if (G_UNLIKELY (g_mem_gc_friendly))
              memset (current, 0, chunk_size);
            thread_memory_magazine2_free (tmem, ix, current);
          }
      }
    else if (acat == 2)                   /* allocate through slab allocator */
      {
        g_mutex_lock (allocator->slab_mutex);
        while (slice)
          {
            guint8 *current = slice;
            slice = *(gpointer*) (current + next_offset);
            if (G_UNLIKELY (allocator->config.debug_blocks) &&
                !smc_notify_free (current, mem_size))
              abort();
            if (G_UNLIKELY (g_mem_gc_friendly))
              memset (current, 0, chunk_size);
            slab_allocator_free_chunk (chunk_size, current);
          }
        g_mutex_unlock (allocator->slab_mutex);
      }
    else                                  /* delegate to system malloc */
      while (slice)
        {
          guint8 *current = slice;
          slice = *(gpointer*) (current + next_offset);
          if (G_UNLIKELY (allocator->config.debug_blocks) &&
              !smc_notify_free (current, mem_size))
            abort();
          if (G_UNLIKELY (g_mem_gc_friendly))
            memset (current, 0, mem_size);
          g_free (current);
        }
  }
  
  /* --- single page allocator --- */
  static void
  allocator_slab_stack_push (Allocator *allocator,
                             guint      ix,
                             SlabInfo  *sinfo)
  {
    /* insert slab at slab ring head */
    if (!allocator->slab_stack[ix])
      {
        sinfo->next = sinfo;
        sinfo->prev = sinfo;
      }
    else
      {
        SlabInfo *next = allocator->slab_stack[ix], *prev = next->prev;
        next->prev = sinfo;
        prev->next = sinfo;
        sinfo->next = next;
        sinfo->prev = prev;
      }
    allocator->slab_stack[ix] = sinfo;
  }
  
  static gsize
  allocator_aligned_page_size (Allocator *allocator,
                               gsize      n_bytes)
  {
    gsize val = 1 << g_bit_storage (n_bytes - 1);
    val = MAX (val, allocator->min_page_size);
    return val;
  }
  
  static void
  allocator_add_slab (Allocator *allocator,
                      guint      ix,
                      gsize      chunk_size)
  {
    ChunkLink *chunk;
    SlabInfo *sinfo;
    gsize addr, padding, n_chunks, color = 0;
    gsize page_size = allocator_aligned_page_size (allocator, SLAB_BPAGE_SIZE (allocator, chunk_size));
    /* allocate 1 page for the chunks and the slab */
    gpointer aligned_memory = allocator_memalign (page_size, page_size - NATIVE_MALLOC_PADDING);
    guint8 *mem = aligned_memory;
    guint i;
    if (!mem)
      {
        const gchar *syserr = "unknown error";
  #if HAVE_STRERROR
        syserr = strerror (errno);
  #endif
        mem_error ("failed to allocate %u bytes (alignment: %u): %s\n",
                   (guint) (page_size - NATIVE_MALLOC_PADDING), (guint) page_size, syserr);
      }
    /* mask page adress */
    addr = ((gsize) mem / page_size) * page_size;
    /* assert alignment */
    mem_assert (aligned_memory == (gpointer) addr);
    /* basic slab info setup */
    sinfo = (SlabInfo*) (mem + page_size - SLAB_INFO_SIZE);
    sinfo->n_allocated = 0;
    sinfo->chunks = NULL;
    /* figure cache colorization */
    n_chunks = ((guint8*) sinfo - mem) / chunk_size;
    padding = ((guint8*) sinfo - mem) - n_chunks * chunk_size;
    if (padding)
      {
        color = (allocator->color_accu * P2ALIGNMENT) % padding;
        allocator->color_accu += allocator->config.color_increment;
      }
    /* add chunks to free list */
    chunk = (ChunkLink*) (mem + color);
    sinfo->chunks = chunk;
    for (i = 0; i < n_chunks - 1; i++)
      {
        chunk->next = (ChunkLink*) ((guint8*) chunk + chunk_size);
        chunk = chunk->next;
      }
    chunk->next = NULL;   /* last chunk */
    /* add slab to slab ring */
    allocator_slab_stack_push (allocator, ix, sinfo);
  }
  
  static gpointer
  slab_allocator_alloc_chunk (gsize chunk_size)
  {
    ChunkLink *chunk;
    guint ix = SLAB_INDEX (allocator, chunk_size);
    /* ensure non-empty slab */
    if (!allocator->slab_stack[ix] || !allocator->slab_stack[ix]->chunks)
      allocator_add_slab (allocator, ix, chunk_size);
    /* allocate chunk */
    chunk = allocator->slab_stack[ix]->chunks;
    allocator->slab_stack[ix]->chunks = chunk->next;
    allocator->slab_stack[ix]->n_allocated++;
    /* rotate empty slabs */
    if (!allocator->slab_stack[ix]->chunks)
      allocator->slab_stack[ix] = allocator->slab_stack[ix]->next;
    return chunk;
  }
  
  static void
  slab_allocator_free_chunk (gsize    chunk_size,
                             gpointer mem)
  {
    ChunkLink *chunk;
    gboolean was_empty;
    guint ix = SLAB_INDEX (allocator, chunk_size);
    gsize page_size = allocator_aligned_page_size (allocator, SLAB_BPAGE_SIZE (allocator, chunk_size));
    gsize addr = ((gsize) mem / page_size) * page_size;
    /* mask page adress */
    guint8 *page = (guint8*) addr;
    SlabInfo *sinfo = (SlabInfo*) (page + page_size - SLAB_INFO_SIZE);
    /* assert valid chunk count */
    mem_assert (sinfo->n_allocated > 0);
    /* add chunk to free list */
    was_empty = sinfo->chunks == NULL;
    chunk = (ChunkLink*) mem;
    chunk->next = sinfo->chunks;
    sinfo->chunks = chunk;
    sinfo->n_allocated--;
    /* keep slab ring partially sorted, empty slabs at end */
    if (was_empty)
      {
        /* unlink slab */
        SlabInfo *next = sinfo->next, *prev = sinfo->prev;
        next->prev = prev;
        prev->next = next;
        if (allocator->slab_stack[ix] == sinfo)
          allocator->slab_stack[ix] = next == sinfo ? NULL : next;
        /* insert slab at head */
        allocator_slab_stack_push (allocator, ix, sinfo);
      }
    /* eagerly free complete unused slabs */
    if (!sinfo->n_allocated)
      {
        /* unlink slab */
        SlabInfo *next = sinfo->next, *prev = sinfo->prev;
        next->prev = prev;
        prev->next = next;
        if (allocator->slab_stack[ix] == sinfo)
          allocator->slab_stack[ix] = next == sinfo ? NULL : next;
        /* free slab */
        allocator_memfree (page_size, page);
      }
  }
  
  /* --- memalign implementation --- */
  #ifdef HAVE_MALLOC_H
  #include <malloc.h>             /* memalign() */
  #endif
  
  /* from config.h:
   * define HAVE_POSIX_MEMALIGN           1 // if free(posix_memalign(3)) works, <stdlib.h>
   * define HAVE_COMPLIANT_POSIX_MEMALIGN 1 // if free(posix_memalign(3)) works for sizes != 2^n, <stdlib.h>
   * define HAVE_MEMALIGN                 1 // if free(memalign(3)) works, <malloc.h>
   * define HAVE_VALLOC                   1 // if free(valloc(3)) works, <stdlib.h> or <malloc.h>
   * if none is provided, we implement malloc(3)-based alloc-only page alignment
   */
  
  #if !(HAVE_COMPLIANT_POSIX_MEMALIGN || HAVE_MEMALIGN || HAVE_VALLOC)
  static GTrashStack *compat_valloc_trash = NULL;
  #endif
  
  static gpointer
  allocator_memalign (gsize alignment,
                      gsize memsize)
  {
    gpointer aligned_memory = NULL;
    gint err = ENOMEM;
  #if     HAVE_COMPLIANT_POSIX_MEMALIGN
    err = posix_memalign (&aligned_memory, alignment, memsize);
  #elif   HAVE_MEMALIGN
    errno = 0;
    aligned_memory = memalign (alignment, memsize);
    err = errno;
  #elif   HAVE_VALLOC
    errno = 0;
    aligned_memory = valloc (memsize);
    err = errno;
  #else
    /* simplistic non-freeing page allocator */
    mem_assert (alignment == sys_page_size);
    mem_assert (memsize <= sys_page_size);
    if (!compat_valloc_trash)
      {
        const guint n_pages = 16;
        guint8 *mem = malloc (n_pages * sys_page_size);
        err = errno;
        if (mem)
          {
            gint i = n_pages;
            guint8 *amem = (guint8*) ALIGN ((gsize) mem, sys_page_size);
            if (amem != mem)
              i--;        /* mem wasn't page aligned */
            while (--i >= 0)
              g_trash_stack_push (&compat_valloc_trash, amem + i * sys_page_size);
          }
      }
    aligned_memory = g_trash_stack_pop (&compat_valloc_trash);
  #endif
    if (!aligned_memory)
      errno = err;
    return aligned_memory;
  }
  
  static void
  allocator_memfree (gsize    memsize,
                     gpointer mem)
  {
  #if     HAVE_COMPLIANT_POSIX_MEMALIGN || HAVE_MEMALIGN || HAVE_VALLOC
    free (mem);
  #else
    mem_assert (memsize <= sys_page_size);
    g_trash_stack_push (&compat_valloc_trash, mem);
  #endif
  }
  
  static void
  mem_error (const char *format,
             ...)
  {
    const char *pname;
    va_list args;
    /* at least, put out "MEMORY-ERROR", in case we segfault during the rest of the function */
    fputs ("\n***MEMORY-ERROR***: ", stderr);
    pname = g_get_prgname();
    fprintf (stderr, "%s[%ld]: GSlice: ", pname ? pname : "", (long)getpid());
    va_start (args, format);
    vfprintf (stderr, format, args);
    va_end (args);
    fputs ("\n", stderr);
    abort();
    _exit (1);
  }
  
  /* --- g-slice memory checker tree --- */
  typedef size_t SmcKType;                /* key type */
  typedef size_t SmcVType;                /* value type */
  typedef struct {
    SmcKType key;
    SmcVType value;
  } SmcEntry;
  static void             smc_tree_insert      (SmcKType  key,
                                                SmcVType  value);
  static gboolean         smc_tree_lookup      (SmcKType  key,
                                                SmcVType *value_p);
  static gboolean         smc_tree_remove      (SmcKType  key);
  
  
  /* --- g-slice memory checker implementation --- */
  static void
  smc_notify_alloc (void   *pointer,
                    size_t  size)
  {
    size_t adress = (size_t) pointer;
    if (pointer)
      smc_tree_insert (adress, size);
  }
  
  #if 0
  static void
  smc_notify_ignore (void *pointer)
  {
    size_t adress = (size_t) pointer;
    if (pointer)
      smc_tree_remove (adress);
  }
  #endif
  
  static int
  smc_notify_free (void   *pointer,
                   size_t  size)
  {
    size_t adress = (size_t) pointer;
    SmcVType real_size;
    gboolean found_one;
  
    if (!pointer)
      return 1; /* ignore */
    found_one = smc_tree_lookup (adress, &real_size);
    if (!found_one)
      {
        fprintf (stderr, "GSlice: MemChecker: attempt to release non-allocated block: %p size=%" G_GSIZE_FORMAT "\n", pointer, size);
        return 0;
      }
    if (real_size != size && (real_size || size))
      {
        fprintf (stderr, "GSlice: MemChecker: attempt to release block with invalid size: %p size=%" G_GSIZE_FORMAT " invalid-size=%" G_GSIZE_FORMAT "\n", pointer, real_size, size);
        return 0;
      }
    if (!smc_tree_remove (adress))
      {
        fprintf (stderr, "GSlice: MemChecker: attempt to release non-allocated block: %p size=%" G_GSIZE_FORMAT "\n", pointer, size);
        return 0;
      }
    return 1; /* all fine */
  }
  
  /* --- g-slice memory checker tree implementation --- */
  #define SMC_TRUNK_COUNT     (4093 /* 16381 */)          /* prime, to distribute trunk collisions (big, allocated just once) */
  #define SMC_BRANCH_COUNT    (511)                       /* prime, to distribute branch collisions */
  #define SMC_TRUNK_EXTENT    (SMC_BRANCH_COUNT * 2039)   /* key adress space per trunk, should distribute uniformly across BRANCH_COUNT */
  #define SMC_TRUNK_HASH(k)   ((k / SMC_TRUNK_EXTENT) % SMC_TRUNK_COUNT)  /* generate new trunk hash per megabyte (roughly) */
  #define SMC_BRANCH_HASH(k)  (k % SMC_BRANCH_COUNT)
  
  typedef struct {
    SmcEntry    *entries;
    unsigned int n_entries;
  } SmcBranch;
  
  static SmcBranch     **smc_tree_root = NULL;
  
  static void
  smc_tree_abort (int errval)
  {
    const char *syserr = "unknown error";
  #if HAVE_STRERROR
    syserr = strerror (errval);
  #endif
    mem_error ("MemChecker: failure in debugging tree: %s", syserr);
  }
  
  static inline SmcEntry*
  smc_tree_branch_grow_L (SmcBranch   *branch,
                          unsigned int index)
  {
    unsigned int old_size = branch->n_entries * sizeof (branch->entries[0]);
    unsigned int new_size = old_size + sizeof (branch->entries[0]);
    SmcEntry *entry;
    mem_assert (index <= branch->n_entries);
    branch->entries = (SmcEntry*) realloc (branch->entries, new_size);
    if (!branch->entries)
      smc_tree_abort (errno);
    entry = branch->entries + index;
    g_memmove (entry + 1, entry, (branch->n_entries - index) * sizeof (entry[0]));
    branch->n_entries += 1;
    return entry;
  }
  
  static inline SmcEntry*
  smc_tree_branch_lookup_nearest_L (SmcBranch *branch,
                                    SmcKType   key)
  {
    unsigned int n_nodes = branch->n_entries, offs = 0;
    SmcEntry *check = branch->entries;
    int cmp = 0;
    while (offs < n_nodes)
      {
        unsigned int i = (offs + n_nodes) >> 1;
        check = branch->entries + i;
        cmp = key < check->key ? -1 : key != check->key;
        if (cmp == 0)
          return check;                   /* return exact match */
        else if (cmp < 0)
          n_nodes = i;
        else /* (cmp > 0) */
          offs = i + 1;
      }
    /* check points at last mismatch, cmp > 0 indicates greater key */
    return cmp > 0 ? check + 1 : check;   /* return insertion position for inexact match */
  }
  
  static void
  smc_tree_insert (SmcKType key,
                   SmcVType value)
  {
    unsigned int ix0, ix1;
    SmcEntry *entry;
  
    g_mutex_lock (smc_tree_mutex);
    ix0 = SMC_TRUNK_HASH (key);
    ix1 = SMC_BRANCH_HASH (key);
    if (!smc_tree_root)
      {
        smc_tree_root = calloc (SMC_TRUNK_COUNT, sizeof (smc_tree_root[0]));
        if (!smc_tree_root)
          smc_tree_abort (errno);
      }
    if (!smc_tree_root[ix0])
      {
        smc_tree_root[ix0] = calloc (SMC_BRANCH_COUNT, sizeof (smc_tree_root[0][0]));
        if (!smc_tree_root[ix0])
          smc_tree_abort (errno);
      }
    entry = smc_tree_branch_lookup_nearest_L (&smc_tree_root[ix0][ix1], key);
    if (!entry ||                                                                         /* need create */
        entry >= smc_tree_root[ix0][ix1].entries + smc_tree_root[ix0][ix1].n_entries ||   /* need append */
        entry->key != key)                                                                /* need insert */
      entry = smc_tree_branch_grow_L (&smc_tree_root[ix0][ix1], entry - smc_tree_root[ix0][ix1].entries);
    entry->key = key;
    entry->value = value;
    g_mutex_unlock (smc_tree_mutex);
  }
  
  static gboolean
  smc_tree_lookup (SmcKType  key,
                   SmcVType *value_p)
  {
    SmcEntry *entry = NULL;
    unsigned int ix0 = SMC_TRUNK_HASH (key), ix1 = SMC_BRANCH_HASH (key);
    gboolean found_one = FALSE;
    *value_p = 0;
    g_mutex_lock (smc_tree_mutex);
    if (smc_tree_root && smc_tree_root[ix0])
      {
        entry = smc_tree_branch_lookup_nearest_L (&smc_tree_root[ix0][ix1], key);
        if (entry &&
            entry < smc_tree_root[ix0][ix1].entries + smc_tree_root[ix0][ix1].n_entries &&
            entry->key == key)
          {
            found_one = TRUE;
            *value_p = entry->value;
          }
      }
    g_mutex_unlock (smc_tree_mutex);
    return found_one;
  }
  
  static gboolean
  smc_tree_remove (SmcKType key)
  {
    unsigned int ix0 = SMC_TRUNK_HASH (key), ix1 = SMC_BRANCH_HASH (key);
    gboolean found_one = FALSE;
    g_mutex_lock (smc_tree_mutex);
    if (smc_tree_root && smc_tree_root[ix0])
      {
        SmcEntry *entry = smc_tree_branch_lookup_nearest_L (&smc_tree_root[ix0][ix1], key);
        if (entry &&
            entry < smc_tree_root[ix0][ix1].entries + smc_tree_root[ix0][ix1].n_entries &&
            entry->key == key)
          {
            unsigned int i = entry - smc_tree_root[ix0][ix1].entries;
            smc_tree_root[ix0][ix1].n_entries -= 1;
            g_memmove (entry, entry + 1, (smc_tree_root[ix0][ix1].n_entries - i) * sizeof (entry[0]));
            if (!smc_tree_root[ix0][ix1].n_entries)
              {
                /* avoid useless pressure on the memory system */
                free (smc_tree_root[ix0][ix1].entries);
                smc_tree_root[ix0][ix1].entries = NULL;
              }
            found_one = TRUE;
          }
      }
    g_mutex_unlock (smc_tree_mutex);
    return found_one;
  }
  
  #ifdef G_ENABLE_DEBUG
  void
  g_slice_debug_tree_statistics (void)
  {
    g_mutex_lock (smc_tree_mutex);
    if (smc_tree_root)
      {
        unsigned int i, j, t = 0, o = 0, b = 0, su = 0, ex = 0, en = 4294967295u;
        double tf, bf;
        for (i = 0; i < SMC_TRUNK_COUNT; i++)
          if (smc_tree_root[i])
            {
              t++;
              for (j = 0; j < SMC_BRANCH_COUNT; j++)
                if (smc_tree_root[i][j].n_entries)
                  {
                    b++;
                    su += smc_tree_root[i][j].n_entries;
                    en = MIN (en, smc_tree_root[i][j].n_entries);
                    ex = MAX (ex, smc_tree_root[i][j].n_entries);
                  }
                else if (smc_tree_root[i][j].entries)
                  o++; /* formerly used, now empty */
            }
        en = b ? en : 0;
        tf = MAX (t, 1.0); /* max(1) to be a valid divisor */
        bf = MAX (b, 1.0); /* max(1) to be a valid divisor */
        fprintf (stderr, "GSlice: MemChecker: %u trunks, %u branches, %u old branches\n", t, b, o);
        fprintf (stderr, "GSlice: MemChecker: %f branches per trunk, %.2f%% utilization\n",
                 b / tf,
                 100.0 - (SMC_BRANCH_COUNT - b / tf) / (0.01 * SMC_BRANCH_COUNT));
        fprintf (stderr, "GSlice: MemChecker: %f entries per branch, %u minimum, %u maximum\n",
                 su / bf, en, ex);
      }
    else
      fprintf (stderr, "GSlice: MemChecker: root=NULL\n");
    g_mutex_unlock (smc_tree_mutex);
    
    /* sample statistics (beast + GSLice + 24h scripted core & GUI activity):
     *  PID %CPU %MEM   VSZ  RSS      COMMAND
     * 8887 30.3 45.8 456068 414856   beast-0.7.1 empty.bse
     * $ cat /proc/8887/statm # total-program-size resident-set-size shared-pages text/code data/stack library dirty-pages
     * 114017 103714 2354 344 0 108676 0
     * $ cat /proc/8887/status 
     * Name:   beast-0.7.1
     * VmSize:   456068 kB
     * VmLck:         0 kB
     * VmRSS:    414856 kB
     * VmData:   434620 kB
     * VmStk:        84 kB
     * VmExe:      1376 kB
     * VmLib:     13036 kB
     * VmPTE:       456 kB
     * Threads:        3
     * (gdb) print g_slice_debug_tree_statistics ()
     * GSlice: MemChecker: 422 trunks, 213068 branches, 0 old branches
     * GSlice: MemChecker: 504.900474 branches per trunk, 98.81% utilization
     * GSlice: MemChecker: 4.965039 entries per branch, 1 minimum, 37 maximum
     */
  }
  #endif /* G_ENABLE_DEBUG */
  
  #define __G_SLICE_C__
  #include "galiasdef.c"
  