text: /* -----------------------------------------------------------------------------
   *
   * (c) The GHC Team, 1998-2012
   *
   * Storage manager front end
   *
   * Documentation on the architecture of the Storage Manager can be
   * found in the online commentary:
   *
   *   http://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage
   *
   * ---------------------------------------------------------------------------*/
  
  #include "PosixSource.h"
  #include "Rts.h"
  
  #include "Storage.h"
  #include "GCThread.h"
  #include "RtsUtils.h"
  #include "Stats.h"
  #include "BlockAlloc.h"
  #include "Weak.h"
  #include "Sanity.h"
  #include "Arena.h"
  #include "Capability.h"
  #include "Schedule.h"
  #include "RetainerProfile.h"        // for counting memory blocks (memInventory)
  #include "OSMem.h"
  #include "Trace.h"
  #include "GC.h"
  #include "Evac.h"
  #if defined(ios_HOST_OS)
  #include "Hash.h"
  #endif
  
  #include <string.h>
  
  #include "ffi.h"
  
  /*
   * All these globals require sm_mutex to access in THREADED_RTS mode.
   */
  StgIndStatic  *dyn_caf_list        = NULL;
  StgIndStatic  *debug_caf_list      = NULL;
  StgIndStatic  *revertible_caf_list = NULL;
  rtsBool       keepCAFs;
  
  W_ large_alloc_lim;    /* GC if n_large_blocks in any nursery
                          * reaches this. */
  
  bdescr *exec_block;
  
  generation *generations = NULL; /* all the generations */
  generation *g0          = NULL; /* generation 0, for convenience */
  generation *oldest_gen  = NULL; /* oldest generation, for convenience */
  
  /*
   * Array of nurseries, size == n_capabilities
   *
   * nursery[i] belongs to NUMA node (i % n_numa_nodes)
   * This is chosen to be the same convention as capabilities[i], so
   * that when not using nursery chunks (+RTS -n), we just map
   * capabilities to nurseries 1:1.
   */
  nursery *nurseries = NULL;
  uint32_t n_nurseries;
  
  /*
   * When we are using nursery chunks, we need a separate next_nursery
   * pointer for each NUMA node.
   */
  volatile StgWord next_nursery[MAX_NUMA_NODES];
  
  #ifdef THREADED_RTS
  /*
   * Storage manager mutex:  protects all the above state from
   * simultaneous access by two STG threads.
   */
  Mutex sm_mutex;
  #endif
  
  static void allocNurseries (uint32_t from, uint32_t to);
  static void assignNurseriesToCapabilities (uint32_t from, uint32_t to);
  
  static void
  initGeneration (generation *gen, int g)
  {
      gen->no = g;
      gen->collections = 0;
      gen->par_collections = 0;
      gen->failed_promotions = 0;
      gen->max_blocks = 0;
      gen->blocks = NULL;
      gen->n_blocks = 0;
      gen->n_words = 0;
      gen->live_estimate = 0;
      gen->old_blocks = NULL;
      gen->n_old_blocks = 0;
      gen->large_objects = NULL;
      gen->n_large_blocks = 0;
      gen->n_large_words = 0;
      gen->n_new_large_words = 0;
      gen->compact_objects = NULL;
      gen->n_compact_blocks = 0;
      gen->scavenged_large_objects = NULL;
      gen->n_scavenged_large_blocks = 0;
      gen->live_compact_objects = NULL;
      gen->n_live_compact_blocks = 0;
      gen->compact_blocks_in_import = NULL;
      gen->n_compact_blocks_in_import = 0;
      gen->mark = 0;
      gen->compact = 0;
      gen->bitmap = NULL;
  #ifdef THREADED_RTS
      initSpinLock(&gen->sync);
  #endif
      gen->threads = END_TSO_QUEUE;
      gen->old_threads = END_TSO_QUEUE;
      gen->weak_ptr_list = NULL;
      gen->old_weak_ptr_list = NULL;
  }
  
  void
  initStorage (void)
  {
    uint32_t g, n;
  
    if (generations != NULL) {
        // multi-init protection
        return;
    }
  
    initMBlocks();
  
    /* Sanity check to make sure the LOOKS_LIKE_ macros appear to be
     * doing something reasonable.
     */
    /* We use the NOT_NULL variant or gcc warns that the test is always true */
    ASSERT(LOOKS_LIKE_INFO_PTR_NOT_NULL((StgWord)&stg_BLOCKING_QUEUE_CLEAN_info));
    ASSERT(LOOKS_LIKE_CLOSURE_PTR(&stg_dummy_ret_closure));
    ASSERT(!HEAP_ALLOCED(&stg_dummy_ret_closure));
  
    initBlockAllocator();
  
  #if defined(THREADED_RTS)
    initMutex(&sm_mutex);
  #endif
  
    ACQUIRE_SM_LOCK;
  
    /* allocate generation info array */
    generations = (generation *)stgMallocBytes(RtsFlags.GcFlags.generations
                                               * sizeof(struct generation_),
                                               "initStorage: gens");
  
    /* Initialise all generations */
    for(g = 0; g < RtsFlags.GcFlags.generations; g++) {
        initGeneration(&generations[g], g);
    }
  
    /* A couple of convenience pointers */
    g0 = &generations[0];
    oldest_gen = &generations[RtsFlags.GcFlags.generations-1];
  
    /* Set up the destination pointers in each younger gen. step */
    for (g = 0; g < RtsFlags.GcFlags.generations-1; g++) {
        generations[g].to = &generations[g+1];
    }
    oldest_gen->to = oldest_gen;
  
    /* The oldest generation has one step. */
    if (RtsFlags.GcFlags.compact || RtsFlags.GcFlags.sweep) {
        if (RtsFlags.GcFlags.generations == 1) {
            errorBelch("WARNING: compact/sweep is incompatible with -G1; disabled");
        } else {
            oldest_gen->mark = 1;
            if (RtsFlags.GcFlags.compact)
                oldest_gen->compact = 1;
        }
    }
  
    generations[0].max_blocks = 0;
  
    dyn_caf_list = (StgIndStatic*)END_OF_CAF_LIST;
    debug_caf_list = (StgIndStatic*)END_OF_CAF_LIST;
    revertible_caf_list = (StgIndStatic*)END_OF_CAF_LIST;
  
    if (RtsFlags.GcFlags.largeAllocLim > 0) {
        large_alloc_lim = RtsFlags.GcFlags.largeAllocLim * BLOCK_SIZE_W;
    } else {
        large_alloc_lim = RtsFlags.GcFlags.minAllocAreaSize * BLOCK_SIZE_W;
    }
  
    exec_block = NULL;
  
  #ifdef THREADED_RTS
    initSpinLock(&gc_alloc_block_sync);
  #ifdef PROF_SPIN
    whitehole_spin = 0;
  #endif
  #endif
  
    N = 0;
  
    for (n = 0; n < n_numa_nodes; n++) {
        next_nursery[n] = n;
    }
    storageAddCapabilities(0, n_capabilities);
  
    IF_DEBUG(gc, statDescribeGens());
  
    RELEASE_SM_LOCK;
  
    traceEventHeapInfo(CAPSET_HEAP_DEFAULT,
                       RtsFlags.GcFlags.generations,
                       RtsFlags.GcFlags.maxHeapSize * BLOCK_SIZE,
                       RtsFlags.GcFlags.minAllocAreaSize * BLOCK_SIZE,
                       MBLOCK_SIZE,
                       BLOCK_SIZE);
  }
  
  void storageAddCapabilities (uint32_t from, uint32_t to)
  {
      uint32_t n, g, i, new_n_nurseries;
  
      if (RtsFlags.GcFlags.nurseryChunkSize == 0) {
          new_n_nurseries = to;
      } else {
          memcount total_alloc = to * RtsFlags.GcFlags.minAllocAreaSize;
          new_n_nurseries =
              stg_max(to, total_alloc / RtsFlags.GcFlags.nurseryChunkSize);
      }
  
      if (from > 0) {
          nurseries = stgReallocBytes(nurseries,
                                      new_n_nurseries * sizeof(struct nursery_),
                                      "storageAddCapabilities");
      } else {
          nurseries = stgMallocBytes(new_n_nurseries * sizeof(struct nursery_),
                                     "storageAddCapabilities");
      }
  
      // we've moved the nurseries, so we have to update the rNursery
      // pointers from the Capabilities.
      for (i = 0; i < to; i++) {
          capabilities[i]->r.rNursery = &nurseries[i];
      }
  
      /* The allocation area.  Policy: keep the allocation area
       * small to begin with, even if we have a large suggested heap
       * size.  Reason: we're going to do a major collection first, and we
       * don't want it to be a big one.  This vague idea is borne out by
       * rigorous experimental evidence.
       */
      allocNurseries(n_nurseries, new_n_nurseries);
      n_nurseries = new_n_nurseries;
  
      /*
       * Assign each of the new capabilities a nursery.  Remember to start from
       * next_nursery, because we may have already consumed some of the earlier
       * nurseries.
       */
      assignNurseriesToCapabilities(from,to);
  
      // allocate a block for each mut list
      for (n = from; n < to; n++) {
          for (g = 1; g < RtsFlags.GcFlags.generations; g++) {
              capabilities[n]->mut_lists[g] =
                  allocBlockOnNode(capNoToNumaNode(n));
          }
      }
  
  #if defined(THREADED_RTS) && defined(llvm_CC_FLAVOR) && (CC_SUPPORTS_TLS == 0)
      newThreadLocalKey(&gctKey);
  #endif
  
      initGcThreads(from, to);
  }
  
  
  void
  exitStorage (void)
  {
      updateNurseriesStats();
      stat_exit();
  }
  
  void
  freeStorage (rtsBool free_heap)
  {
      stgFree(generations);
      if (free_heap) freeAllMBlocks();
  #if defined(THREADED_RTS)
      closeMutex(&sm_mutex);
  #endif
      stgFree(nurseries);
  #if defined(THREADED_RTS) && defined(llvm_CC_FLAVOR) && (CC_SUPPORTS_TLS == 0)
      freeThreadLocalKey(&gctKey);
  #endif
      freeGcThreads();
  }
  
  /* -----------------------------------------------------------------------------
     Note [CAF management].
  
     The entry code for every CAF does the following:
  
        - calls newCaf, which builds a CAF_BLACKHOLE on the heap and atomically
          updates the CAF with IND_STATIC pointing to the CAF_BLACKHOLE
  
        - if newCaf returns zero, it re-enters the CAF (see Note [atomic
          CAF entry])
  
        - pushes an update frame pointing to the CAF_BLACKHOLE
  
     Why do we build an BLACKHOLE in the heap rather than just updating
     the thunk directly?  It's so that we only need one kind of update
     frame - otherwise we'd need a static version of the update frame
     too, and various other parts of the RTS that deal with update
     frames would also need special cases for static update frames.
  
     newCaf() does the following:
  
        - atomically locks the CAF (see [atomic CAF entry])
  
        - it builds a CAF_BLACKHOLE on the heap
  
        - it updates the CAF with an IND_STATIC pointing to the
          CAF_BLACKHOLE, atomically.
  
        - it puts the CAF on the oldest generation's mutable list.
          This is so that we treat the CAF as a root when collecting
          younger generations.
  
        - links the CAF onto the CAF list (see below)
  
     ------------------
     Note [atomic CAF entry]
  
     With THREADED_RTS, newCaf() is required to be atomic (see
     #5558). This is because if two threads happened to enter the same
     CAF simultaneously, they would create two distinct CAF_BLACKHOLEs,
     and so the normal threadPaused() machinery for detecting duplicate
     evaluation will not detect this.  Hence in lockCAF() below, we
     atomically lock the CAF with WHITEHOLE before updating it with
     IND_STATIC, and return zero if another thread locked the CAF first.
     In the event that we lost the race, CAF entry code will re-enter
     the CAF and block on the other thread's CAF_BLACKHOLE.
  
     ------------------
     Note [GHCi CAFs]
  
     For GHCI, we have additional requirements when dealing with CAFs:
  
        - we must *retain* all dynamically-loaded CAFs ever entered,
          just in case we need them again.
        - we must be able to *revert* CAFs that have been evaluated, to
          their pre-evaluated form.
  
        To do this, we use an additional CAF list.  When newCaf() is
        called on a dynamically-loaded CAF, we add it to the CAF list
        instead of the old-generation mutable list, and save away its
        old info pointer (in caf->saved_info) for later reversion.
  
        To revert all the CAFs, we traverse the CAF list and reset the
        info pointer to caf->saved_info, then throw away the CAF list.
        (see GC.c:revertCAFs()).
  
        -- SDM 29/1/01
  
     -------------------------------------------------------------------------- */
  
  STATIC_INLINE StgInd *
  lockCAF (StgRegTable *reg, StgIndStatic *caf)
  {
      const StgInfoTable *orig_info;
      Capability *cap = regTableToCapability(reg);
      StgInd *bh;
  
      orig_info = caf->header.info;
  
  #ifdef THREADED_RTS
      const StgInfoTable *cur_info;
  
      if (orig_info == &stg_IND_STATIC_info ||
          orig_info == &stg_WHITEHOLE_info) {
          // already claimed by another thread; re-enter the CAF
          return NULL;
      }
  
      cur_info = (const StgInfoTable *)
          cas((StgVolatilePtr)&caf->header.info,
              (StgWord)orig_info,
              (StgWord)&stg_WHITEHOLE_info);
  
      if (cur_info != orig_info) {
          // already claimed by another thread; re-enter the CAF
          return NULL;
      }
  
      // successfully claimed by us; overwrite with IND_STATIC
  #endif
  
      // For the benefit of revertCAFs(), save the original info pointer
      caf->saved_info = orig_info;
  
      // Allocate the blackhole indirection closure
      bh = (StgInd *)allocate(cap, sizeofW(*bh));
      SET_HDR(bh, &stg_CAF_BLACKHOLE_info, caf->header.prof.ccs);
      bh->indirectee = (StgClosure *)cap->r.rCurrentTSO;
  
      caf->indirectee = (StgClosure *)bh;
      write_barrier();
      SET_INFO((StgClosure*)caf,&stg_IND_STATIC_info);
  
      return bh;
  }
  
  StgInd *
  newCAF(StgRegTable *reg, StgIndStatic *caf)
  {
      StgInd *bh;
  
      bh = lockCAF(reg, caf);
      if (!bh) return NULL;
  
      if(keepCAFs)
      {
          // Note [dyn_caf_list]
          // If we are in GHCi _and_ we are using dynamic libraries,
          // then we can't redirect newCAF calls to newRetainedCAF (see below),
          // so we make newCAF behave almost like newRetainedCAF.
          // The dynamic libraries might be used by both the interpreted
          // program and GHCi itself, so they must not be reverted.
          // This also means that in GHCi with dynamic libraries, CAFs are not
          // garbage collected. If this turns out to be a problem, we could
          // do another hack here and do an address range test on caf to figure
          // out whether it is from a dynamic library.
  
          ACQUIRE_SM_LOCK; // dyn_caf_list is global, locked by sm_mutex
          caf->static_link = (StgClosure*)dyn_caf_list;
          dyn_caf_list = (StgIndStatic*)((StgWord)caf | STATIC_FLAG_LIST);
          RELEASE_SM_LOCK;
      }
      else
      {
          // Put this CAF on the mutable list for the old generation.
          if (oldest_gen->no != 0) {
              recordMutableCap((StgClosure*)caf,
                               regTableToCapability(reg), oldest_gen->no);
          }
  
  #ifdef DEBUG
          // In the DEBUG rts, we keep track of live CAFs by chaining them
          // onto a list debug_caf_list.  This is so that we can tell if we
          // ever enter a GC'd CAF, and emit a suitable barf().
          //
          // The saved_info field of the CAF is used as the link field for
          // debug_caf_list, because this field is only used by newDynCAF
          // for revertible CAFs, and we don't put those on the
          // debug_caf_list.
          ACQUIRE_SM_LOCK; // debug_caf_list is global, locked by sm_mutex
          ((StgIndStatic *)caf)->saved_info = (const StgInfoTable*)debug_caf_list;
          debug_caf_list = (StgIndStatic*)caf;
          RELEASE_SM_LOCK;
  #endif
      }
  
      return bh;
  }
  
  // External API for setting the keepCAFs flag. see #3900.
  void
  setKeepCAFs (void)
  {
      keepCAFs = 1;
  }
  
  // An alternate version of newCAF which is used for dynamically loaded
  // object code in GHCi.  In this case we want to retain *all* CAFs in
  // the object code, because they might be demanded at any time from an
  // expression evaluated on the command line.
  // Also, GHCi might want to revert CAFs, so we add these to the
  // revertible_caf_list.
  //
  // The linker hackily arranges that references to newCAF from dynamic
  // code end up pointing to newRetainedCAF.
  //
  StgInd* newRetainedCAF (StgRegTable *reg, StgIndStatic *caf)
  {
      StgInd *bh;
  
      bh = lockCAF(reg, caf);
      if (!bh) return NULL;
  
      ACQUIRE_SM_LOCK;
  
      caf->static_link = (StgClosure*)revertible_caf_list;
      revertible_caf_list = (StgIndStatic*)((StgWord)caf | STATIC_FLAG_LIST);
  
      RELEASE_SM_LOCK;
  
      return bh;
  }
  
  // If we are using loadObj/unloadObj in the linker, then we want to
  //
  //  - retain all CAFs in statically linked code (keepCAFs == rtsTrue),
  //    because we might link a new object that uses any of these CAFs.
  //
  //  - GC CAFs in dynamically-linked code, so that we can detect when
  //    a dynamically-linked object is unloadable.
  //
  // So for this case, we set keepCAFs to rtsTrue, and link newCAF to newGCdCAF
  // for dynamically-linked code.
  //
  StgInd* newGCdCAF (StgRegTable *reg, StgIndStatic *caf)
  {
      StgInd *bh;
  
      bh = lockCAF(reg, caf);
      if (!bh) return NULL;
  
      // Put this CAF on the mutable list for the old generation.
      if (oldest_gen->no != 0) {
          recordMutableCap((StgClosure*)caf,
                           regTableToCapability(reg), oldest_gen->no);
      }
  
      return bh;
  }
  
  /* -----------------------------------------------------------------------------
     Nursery management.
     -------------------------------------------------------------------------- */
  
  static bdescr *
  allocNursery (uint32_t node, bdescr *tail, W_ blocks)
  {
      bdescr *bd = NULL;
      W_ i, n;
  
      // We allocate the nursery as a single contiguous block and then
      // divide it into single blocks manually.  This way we guarantee
      // that the nursery blocks are adjacent, so that the processor's
      // automatic prefetching works across nursery blocks.  This is a
      // tiny optimisation (~0.5%), but it's free.
  
      while (blocks > 0) {
          n = stg_min(BLOCKS_PER_MBLOCK, blocks);
          // allocLargeChunk will prefer large chunks, but will pick up
          // small chunks if there are any available.  We must allow
          // single blocks here to avoid fragmentation (#7257)
          bd = allocLargeChunkOnNode(node, 1, n);
          n = bd->blocks;
          blocks -= n;
  
          for (i = 0; i < n; i++) {
              initBdescr(&bd[i], g0, g0);
  
              bd[i].blocks = 1;
              bd[i].flags = 0;
  
              if (i > 0) {
                  bd[i].u.back = &bd[i-1];
              } else {
                  bd[i].u.back = NULL;
              }
  
              if (i+1 < n) {
                  bd[i].link = &bd[i+1];
              } else {
                  bd[i].link = tail;
                  if (tail != NULL) {
                      tail->u.back = &bd[i];
                  }
              }
  
              bd[i].free = bd[i].start;
          }
  
          tail = &bd[0];
      }
  
      return &bd[0];
  }
  
  STATIC_INLINE void
  assignNurseryToCapability (Capability *cap, uint32_t n)
  {
      ASSERT(n < n_nurseries);
      cap->r.rNursery = &nurseries[n];
      cap->r.rCurrentNursery = nurseries[n].blocks;
      newNurseryBlock(nurseries[n].blocks);
      cap->r.rCurrentAlloc   = NULL;
      ASSERT(cap->r.rCurrentNursery->node == cap->node);
  }
  
  /*
   * Give each Capability a nursery from the pool. No need to do atomic increments
   * here, everything must be stopped to call this function.
   */
  static void
  assignNurseriesToCapabilities (uint32_t from, uint32_t to)
  {
      uint32_t i, node;
  
      for (i = from; i < to; i++) {
          node = capabilities[i]->node;
          assignNurseryToCapability(capabilities[i], next_nursery[node]);
          next_nursery[node] += n_numa_nodes;
      }
  }
  
  static void
  allocNurseries (uint32_t from, uint32_t to)
  {
      uint32_t i;
      memcount n_blocks;
  
      if (RtsFlags.GcFlags.nurseryChunkSize) {
          n_blocks = RtsFlags.GcFlags.nurseryChunkSize;
      } else {
          n_blocks = RtsFlags.GcFlags.minAllocAreaSize;
      }
  
      for (i = from; i < to; i++) {
          nurseries[i].blocks = allocNursery(capNoToNumaNode(i), NULL, n_blocks);
          nurseries[i].n_blocks = n_blocks;
      }
  }
  
  void
  resetNurseries (void)
  {
      uint32_t n;
  
      for (n = 0; n < n_numa_nodes; n++) {
          next_nursery[n] = n;
      }
      assignNurseriesToCapabilities(0, n_capabilities);
  
  #ifdef DEBUG
      bdescr *bd;
      for (n = 0; n < n_nurseries; n++) {
          for (bd = nurseries[n].blocks; bd; bd = bd->link) {
              ASSERT(bd->gen_no == 0);
              ASSERT(bd->gen == g0);
              ASSERT(bd->node == capNoToNumaNode(n));
              IF_DEBUG(sanity, memset(bd->start, 0xaa, BLOCK_SIZE));
          }
      }
  #endif
  }
  
  W_
  countNurseryBlocks (void)
  {
      uint32_t i;
      W_ blocks = 0;
  
      for (i = 0; i < n_nurseries; i++) {
          blocks += nurseries[i].n_blocks;
      }
      return blocks;
  }
  
  //
  // Resize each of the nurseries to the specified size.
  //
  static void
  resizeNurseriesEach (W_ blocks)
  {
      uint32_t i, node;
      bdescr *bd;
      W_ nursery_blocks;
      nursery *nursery;
  
      for (i = 0; i < n_nurseries; i++) {
          nursery = &nurseries[i];
          nursery_blocks = nursery->n_blocks;
          if (nursery_blocks == blocks) continue;
  
          node = capNoToNumaNode(i);
          if (nursery_blocks < blocks) {
              debugTrace(DEBUG_gc, "increasing size of nursery to %d blocks",
                         blocks);
              nursery->blocks = allocNursery(node, nursery->blocks,
                                             blocks-nursery_blocks);
          }
          else
          {
              bdescr *next_bd;
  
              debugTrace(DEBUG_gc, "decreasing size of nursery to %d blocks",
                         blocks);
  
              bd = nursery->blocks;
              while (nursery_blocks > blocks) {
                  next_bd = bd->link;
                  next_bd->u.back = NULL;
                  nursery_blocks -= bd->blocks; // might be a large block
                  freeGroup(bd);
                  bd = next_bd;
              }
              nursery->blocks = bd;
              // might have gone just under, by freeing a large block, so make
              // up the difference.
              if (nursery_blocks < blocks) {
                  nursery->blocks = allocNursery(node, nursery->blocks,
                                                 blocks-nursery_blocks);
              }
          }
          nursery->n_blocks = blocks;
          ASSERT(countBlocks(nursery->blocks) == nursery->n_blocks);
      }
  }
  
  void
  resizeNurseriesFixed (void)
  {
      uint32_t blocks;
  
      if (RtsFlags.GcFlags.nurseryChunkSize) {
          blocks = RtsFlags.GcFlags.nurseryChunkSize;
      } else {
          blocks = RtsFlags.GcFlags.minAllocAreaSize;
      }
  
      resizeNurseriesEach(blocks);
  }
  
  //
  // Resize the nurseries to the total specified size.
  //
  void
  resizeNurseries (W_ blocks)
  {
      // If there are multiple nurseries, then we just divide the number
      // of available blocks between them.
      resizeNurseriesEach(blocks / n_nurseries);
  }
  
  rtsBool
  getNewNursery (Capability *cap)
  {
      StgWord i;
      uint32_t node = cap->node;
      uint32_t n;
  
      for(;;) {
          i = next_nursery[node];
          if (i < n_nurseries) {
              if (cas(&next_nursery[node], i, i+n_numa_nodes) == i) {
                  assignNurseryToCapability(cap, i);
                  return rtsTrue;
              }
          } else if (n_numa_nodes > 1) {
              // Try to find an unused nursery chunk on other nodes.  We'll get
              // remote memory, but the rationale is that avoiding GC is better
              // than avoiding remote memory access.
              rtsBool lost = rtsFalse;
              for (n = 0; n < n_numa_nodes; n++) {
                  if (n == node) continue;
                  i = next_nursery[n];
                  if (i < n_nurseries) {
                      if (cas(&next_nursery[n], i, i+n_numa_nodes) == i) {
                          assignNurseryToCapability(cap, i);
                          return rtsTrue;
                      } else {
                          lost = rtsTrue; /* lost a race */
                      }
                  }
              }
              if (!lost) return rtsFalse;
          } else {
              return rtsFalse;
          }
      }
  }
  
  /* -----------------------------------------------------------------------------
     move_STACK is called to update the TSO structure after it has been
     moved from one place to another.
     -------------------------------------------------------------------------- */
  
  void
  move_STACK (StgStack *src, StgStack *dest)
  {
      ptrdiff_t diff;
  
      // relocate the stack pointer...
      diff = (StgPtr)dest - (StgPtr)src; // In *words*
      dest->sp = (StgPtr)dest->sp + diff;
  }
  
  /* -----------------------------------------------------------------------------
     StgPtr allocate (Capability *cap, W_ n)
  
     Allocates an area of memory n *words* large, from the nursery of
     the supplied Capability, or from the global block pool if the area
     requested is larger than LARGE_OBJECT_THRESHOLD.  Memory is not
     allocated from the current nursery block, so as not to interfere
     with Hp/HpLim.
  
     The address of the allocated memory is returned. allocate() never
     fails; if it returns, the returned value is a valid address.  If
     the nursery is already full, then another block is allocated from
     the global block pool.  If we need to get memory from the OS and
     that operation fails, then the whole process will be killed.
     -------------------------------------------------------------------------- */
  
  StgPtr
  allocate (Capability *cap, W_ n)
  {
      bdescr *bd;
      StgPtr p;
  
      TICK_ALLOC_HEAP_NOCTR(WDS(n));
      CCS_ALLOC(cap->r.rCCCS,n);
      if (cap->r.rCurrentTSO != NULL) {
          // cap->r.rCurrentTSO->alloc_limit -= n*sizeof(W_)
          ASSIGN_Int64((W_*)&(cap->r.rCurrentTSO->alloc_limit),
                       (PK_Int64((W_*)&(cap->r.rCurrentTSO->alloc_limit))
                        - n*sizeof(W_)));
      }
  
      if (n >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
          // The largest number of words such that
          // the computation of req_blocks will not overflow.
          W_ max_words = (HS_WORD_MAX & ~(BLOCK_SIZE-1)) / sizeof(W_);
          W_ req_blocks;
  
          if (n > max_words)
              req_blocks = HS_WORD_MAX; // signal overflow below
          else
              req_blocks = (W_)BLOCK_ROUND_UP(n*sizeof(W_)) / BLOCK_SIZE;
  
          // Attempting to allocate an object larger than maxHeapSize
          // should definitely be disallowed.  (bug #1791)
          if ((RtsFlags.GcFlags.maxHeapSize > 0 &&
               req_blocks >= RtsFlags.GcFlags.maxHeapSize) ||
              req_blocks >= HS_INT32_MAX)   // avoid overflow when
                                            // calling allocGroup() below
          {
              heapOverflow();
              // heapOverflow() doesn't exit (see #2592), but we aren't
              // in a position to do a clean shutdown here: we
              // either have to allocate the memory or exit now.
              // Allocating the memory would be bad, because the user
              // has requested that we not exceed maxHeapSize, so we
              // just exit.
              stg_exit(EXIT_HEAPOVERFLOW);
          }
  
          ACQUIRE_SM_LOCK
          bd = allocGroupOnNode(cap->node,req_blocks);
          dbl_link_onto(bd, &g0->large_objects);
          g0->n_large_blocks += bd->blocks; // might be larger than req_blocks
          g0->n_new_large_words += n;
          RELEASE_SM_LOCK;
          initBdescr(bd, g0, g0);
          bd->flags = BF_LARGE;
          bd->free = bd->start + n;
          cap->total_allocated += n;
          return bd->start;
      }
  
      /* small allocation (<LARGE_OBJECT_THRESHOLD) */
  
      bd = cap->r.rCurrentAlloc;
      if (bd == NULL || bd->free + n > bd->start + BLOCK_SIZE_W) {
  
          if (bd) finishedNurseryBlock(cap,bd);
  
          // The CurrentAlloc block is full, we need to find another
          // one.  First, we try taking the next block from the
          // nursery:
          bd = cap->r.rCurrentNursery->link;
  
          if (bd == NULL) {
              // The nursery is empty: allocate a fresh block (we can't
              // fail here).
              ACQUIRE_SM_LOCK;
              bd = allocBlockOnNode(cap->node);
              cap->r.rNursery->n_blocks++;
              RELEASE_SM_LOCK;
              initBdescr(bd, g0, g0);
              bd->flags = 0;
              // If we had to allocate a new block, then we'll GC
              // pretty quickly now, because MAYBE_GC() will
              // notice that CurrentNursery->link is NULL.
          } else {
              newNurseryBlock(bd);
              // we have a block in the nursery: take it and put
              // it at the *front* of the nursery list, and use it
              // to allocate() from.
              //
              // Previously the nursery looked like this:
              //
              //           CurrentNursery
              //                  /
              //                +-+    +-+
              // nursery -> ... |A| -> |B| -> ...
              //                +-+    +-+
              //
              // After doing this, it looks like this:
              //
              //                      CurrentNursery
              //                            /
              //            +-+           +-+
              // nursery -> |B| -> ... -> |A| -> ...
              //            +-+           +-+
              //             |
              //             CurrentAlloc
              //
              // The point is to get the block out of the way of the
              // advancing CurrentNursery pointer, while keeping it
              // on the nursery list so we don't lose track of it.
              cap->r.rCurrentNursery->link = bd->link;
              if (bd->link != NULL) {
                  bd->link->u.back = cap->r.rCurrentNursery;
              }
          }
          dbl_link_onto(bd, &cap->r.rNursery->blocks);
          cap->r.rCurrentAlloc = bd;
          IF_DEBUG(sanity, checkNurserySanity(cap->r.rNursery));
      }
      p = bd->free;
      bd->free += n;
  
      IF_DEBUG(sanity, ASSERT(*((StgWord8*)p) == 0xaa));
      return p;
  }
  
  /* ---------------------------------------------------------------------------
     Allocate a fixed/pinned object.
  
     We allocate small pinned objects into a single block, allocating a
     new block when the current one overflows.  The block is chained
     onto the large_object_list of generation 0.
  
     NOTE: The GC can't in general handle pinned objects.  This
     interface is only safe to use for ByteArrays, which have no
     pointers and don't require scavenging.  It works because the
     block's descriptor has the BF_LARGE flag set, so the block is
     treated as a large object and chained onto various lists, rather
     than the individual objects being copied.  However, when it comes
     to scavenge the block, the GC will only scavenge the first object.
     The reason is that the GC can't linearly scan a block of pinned
     objects at the moment (doing so would require using the
     mostly-copying techniques).  But since we're restricting ourselves
     to pinned ByteArrays, not scavenging is ok.
  
     This function is called by newPinnedByteArray# which immediately
     fills the allocated memory with a MutableByteArray#.
     ------------------------------------------------------------------------- */
  
  StgPtr
  allocatePinned (Capability *cap, W_ n)
  {
      StgPtr p;
      bdescr *bd;
  
      // If the request is for a large object, then allocate()
      // will give us a pinned object anyway.
      if (n >= LARGE_OBJECT_THRESHOLD/sizeof(W_)) {
          p = allocate(cap, n);
          Bdescr(p)->flags |= BF_PINNED;
          return p;
      }
  
      TICK_ALLOC_HEAP_NOCTR(WDS(n));
      CCS_ALLOC(cap->r.rCCCS,n);
      if (cap->r.rCurrentTSO != NULL) {
          // cap->r.rCurrentTSO->alloc_limit -= n*sizeof(W_);
          ASSIGN_Int64((W_*)&(cap->r.rCurrentTSO->alloc_limit),
                       (PK_Int64((W_*)&(cap->r.rCurrentTSO->alloc_limit))
                        - n*sizeof(W_)));
      }
  
      bd = cap->pinned_object_block;
  
      // If we don't have a block of pinned objects yet, or the current
      // one isn't large enough to hold the new object, get a new one.
      if (bd == NULL || (bd->free + n) > (bd->start + BLOCK_SIZE_W)) {
  
          // stash the old block on cap->pinned_object_blocks.  On the
          // next GC cycle these objects will be moved to
          // g0->large_objects.
          if (bd != NULL) {
              // add it to the allocation stats when the block is full
              finishedNurseryBlock(cap, bd);
              dbl_link_onto(bd, &cap->pinned_object_blocks);
          }
  
          // We need to find another block.  We could just allocate one,
          // but that means taking a global lock and we really want to
          // avoid that (benchmarks that allocate a lot of pinned
          // objects scale really badly if we do this).
          //
          // So first, we try taking the next block from the nursery, in
          // the same way as allocate().
          bd = cap->r.rCurrentNursery->link;
          if (bd == NULL) {
              // The nursery is empty: allocate a fresh block (we can't fail
              // here).
              ACQUIRE_SM_LOCK;
              bd = allocBlockOnNode(cap->node);
              RELEASE_SM_LOCK;
              initBdescr(bd, g0, g0);
          } else {
              newNurseryBlock(bd);
              // we have a block in the nursery: steal it
              cap->r.rCurrentNursery->link = bd->link;
              if (bd->link != NULL) {
                  bd->link->u.back = cap->r.rCurrentNursery;
              }
              cap->r.rNursery->n_blocks -= bd->blocks;
          }
  
          cap->pinned_object_block = bd;
          bd->flags  = BF_PINNED | BF_LARGE | BF_EVACUATED;
  
          // The pinned_object_block remains attached to the capability
          // until it is full, even if a GC occurs.  We want this
          // behaviour because otherwise the unallocated portion of the
          // block would be forever slop, and under certain workloads
          // (allocating a few ByteStrings per GC) we accumulate a lot
          // of slop.
          //
          // So, the pinned_object_block is initially marked
          // BF_EVACUATED so the GC won't touch it.  When it is full,
          // we place it on the large_objects list, and at the start of
          // the next GC the BF_EVACUATED flag will be cleared, and the
          // block will be promoted as usual (if anything in it is
          // live).
      }
  
      p = bd->free;
      bd->free += n;
      return p;
  }
  
  /* -----------------------------------------------------------------------------
     Write Barriers
     -------------------------------------------------------------------------- */
  
  /*
     This is the write barrier for MUT_VARs, a.k.a. IORefs.  A
     MUT_VAR_CLEAN object is not on the mutable list; a MUT_VAR_DIRTY
     is.  When written to, a MUT_VAR_CLEAN turns into a MUT_VAR_DIRTY
     and is put on the mutable list.
  */
  void
  dirty_MUT_VAR(StgRegTable *reg, StgClosure *p)
  {
      Capability *cap = regTableToCapability(reg);
      if (p->header.info == &stg_MUT_VAR_CLEAN_info) {
          p->header.info = &stg_MUT_VAR_DIRTY_info;
          recordClosureMutated(cap,p);
      }
  }
  
  void
  dirty_TVAR(Capability *cap, StgTVar *p)
  {
      if (p->header.info == &stg_TVAR_CLEAN_info) {
          p->header.info = &stg_TVAR_DIRTY_info;
          recordClosureMutated(cap,(StgClosure*)p);
      }
  }
  
  // Setting a TSO's link field with a write barrier.
  // It is *not* necessary to call this function when
  //    * setting the link field to END_TSO_QUEUE
  //    * setting the link field of the currently running TSO, as it
  //      will already be dirty.
  void
  setTSOLink (Capability *cap, StgTSO *tso, StgTSO *target)
  {
      if (tso->dirty == 0) {
          tso->dirty = 1;
          recordClosureMutated(cap,(StgClosure*)tso);
      }
      tso->_link = target;
  }
  
  void
  setTSOPrev (Capability *cap, StgTSO *tso, StgTSO *target)
  {
      if (tso->dirty == 0) {
          tso->dirty = 1;
          recordClosureMutated(cap,(StgClosure*)tso);
      }
      tso->block_info.prev = target;
  }
  
  void
  dirty_TSO (Capability *cap, StgTSO *tso)
  {
      if (tso->dirty == 0) {
          tso->dirty = 1;
          recordClosureMutated(cap,(StgClosure*)tso);
      }
  }
  
  void
  dirty_STACK (Capability *cap, StgStack *stack)
  {
      if (stack->dirty == 0) {
          stack->dirty = 1;
          recordClosureMutated(cap,(StgClosure*)stack);
      }
  }
  
  /*
     This is the write barrier for MVARs.  An MVAR_CLEAN objects is not
     on the mutable list; a MVAR_DIRTY is.  When written to, a
     MVAR_CLEAN turns into a MVAR_DIRTY and is put on the mutable list.
     The check for MVAR_CLEAN is inlined at the call site for speed,
     this really does make a difference on concurrency-heavy benchmarks
     such as Chaneneos and cheap-concurrency.
  */
  void
  dirty_MVAR(StgRegTable *reg, StgClosure *p)
  {
      recordClosureMutated(regTableToCapability(reg),p);
  }
  
  /* -----------------------------------------------------------------------------
   * Stats and stuff
   * -------------------------------------------------------------------------- */
  
  /* -----------------------------------------------------------------------------
   * [Note allocation accounting]
   *
   *   - When cap->r.rCurrentNusery moves to a new block in the nursery,
   *     we add the size of the used portion of the previous block to
   *     cap->total_allocated. (see finishedNurseryBlock())
   *
   *   - When we start a GC, the allocated portion of CurrentNursery and
   *     CurrentAlloc are added to cap->total_allocated. (see
   *     updateNurseriesStats())
   *
   * -------------------------------------------------------------------------- */
  
  //
  // Calculate the total allocated memory since the start of the
  // program.  Also emits events reporting the per-cap allocation
  // totals.
  //
  StgWord
  calcTotalAllocated (void)
  {
      W_ tot_alloc = 0;
      W_ n;
  
      for (n = 0; n < n_capabilities; n++) {
          tot_alloc += capabilities[n]->total_allocated;
  
          traceEventHeapAllocated(capabilities[n],
                                  CAPSET_HEAP_DEFAULT,
                                  capabilities[n]->total_allocated * sizeof(W_));
      }
  
      return tot_alloc;
  }
  
  //
  // Update the per-cap total_allocated numbers with an approximation of
  // the amount of memory used in each cap's nursery.
  //
  void
  updateNurseriesStats (void)
  {
      uint32_t i;
      bdescr *bd;
  
      for (i = 0; i < n_capabilities; i++) {
          // The current nursery block and the current allocate block have not
          // yet been accounted for in cap->total_allocated, so we add them here.
          bd = capabilities[i]->r.rCurrentNursery;
          if (bd) finishedNurseryBlock(capabilities[i], bd);
          bd = capabilities[i]->r.rCurrentAlloc;
          if (bd) finishedNurseryBlock(capabilities[i], bd);
      }
  }
  
  W_ countOccupied (bdescr *bd)
  {
      W_ words;
  
      words = 0;
      for (; bd != NULL; bd = bd->link) {
          ASSERT(bd->free <= bd->start + bd->blocks * BLOCK_SIZE_W);
          words += bd->free - bd->start;
      }
      return words;
  }
  
  W_ genLiveWords (generation *gen)
  {
      return gen->n_words + gen->n_large_words +
          gen->n_compact_blocks * BLOCK_SIZE_W;
  }
  
  W_ genLiveBlocks (generation *gen)
  {
      return gen->n_blocks + gen->n_large_blocks + gen->n_compact_blocks;
  }
  
  W_ gcThreadLiveWords (uint32_t i, uint32_t g)
  {
      W_ a, b, c;
  
      a = countOccupied(gc_threads[i]->gens[g].todo_bd);
      b = gc_threads[i]->gens[g].n_part_words;
      c = gc_threads[i]->gens[g].n_scavd_words;
  
  //    debugBelch("cap %d, g%d, %ld %ld %ld\n", i, g, a, b, c);
      return a + b + c;
  }
  
  W_ gcThreadLiveBlocks (uint32_t i, uint32_t g)
  {
      W_ blocks;
  
      blocks  = countBlocks(gc_threads[i]->gens[g].todo_bd);
      blocks += gc_threads[i]->gens[g].n_part_blocks;
      blocks += gc_threads[i]->gens[g].n_scavd_blocks;
  
      return blocks;
  }
  
  /* Determine which generation will be collected next, and approximate
   * the maximum amount of memory that will be required to do the GC,
   * taking into account data that will be copied, and the space needed
   * to store bitmaps and the mark stack.  Note: blocks_needed does not
   * include the blocks in the nursery.
   *
   * Assume: all data currently live will remain live.  Generationss
   * that will be collected next time will therefore need twice as many
   * blocks since all the data will be copied.
   */
  extern W_
  calcNeeded (rtsBool force_major, memcount *blocks_needed)
  {
      W_ needed = 0, blocks;
      uint32_t g, N;
      generation *gen;
  
      if (force_major) {
          N = RtsFlags.GcFlags.generations - 1;
      } else {
          N = 0;
      }
  
      for (g = 0; g < RtsFlags.GcFlags.generations; g++) {
          gen = &generations[g];
  
          blocks = gen->n_blocks // or: gen->n_words / BLOCK_SIZE_W (?)
                 + gen->n_large_blocks
                 + gen->n_compact_blocks;
  
          // we need at least this much space
          needed += blocks;
  
          // are we collecting this gen?
          if (g == 0 || // always collect gen 0
              blocks > gen->max_blocks)
          {
              N = stg_max(N,g);
  
              // we will collect this gen next time
              if (gen->mark) {
                  //  bitmap:
                  needed += gen->n_blocks / BITS_IN(W_);
                  //  mark stack:
                  needed += gen->n_blocks / 100;
              }
              if (gen->compact) {
                  continue; // no additional space needed for compaction
              } else {
                  needed += gen->n_blocks;
              }
          }
      }
  
      if (blocks_needed != NULL) {
          *blocks_needed = needed;
      }
      return N;
  }
  
  /* ----------------------------------------------------------------------------
     Executable memory
  
     Executable memory must be managed separately from non-executable
     memory.  Most OSs these days require you to jump through hoops to
     dynamically allocate executable memory, due to various security
     measures.
  
     Here we provide a small memory allocator for executable memory.
     Memory is managed with a page granularity; we allocate linearly
     in the page, and when the page is emptied (all objects on the page
     are free) we free the page again, not forgetting to make it
     non-executable.
  
     TODO: The inability to handle objects bigger than BLOCK_SIZE_W means that
           the linker cannot use allocateExec for loading object code files
           on Windows. Once allocateExec can handle larger objects, the linker
           should be modified to use allocateExec instead of VirtualAlloc.
     ------------------------------------------------------------------------- */
  
  #if (defined(arm_HOST_ARCH) || defined(aarch64_HOST_ARCH)) && defined(ios_HOST_OS)
  void sys_icache_invalidate(void *start, size_t len);
  #endif
  
  /* On ARM and other platforms, we need to flush the cache after
     writing code into memory, so the processor reliably sees it. */
  void flushExec (W_ len, AdjustorExecutable exec_addr)
  {
  #if defined(i386_HOST_ARCH) || defined(x86_64_HOST_ARCH)
    /* x86 doesn't need to do anything, so just suppress some warnings. */
    (void)len;
    (void)exec_addr;
  #elif (defined(arm_HOST_ARCH) || defined(aarch64_HOST_ARCH)) && defined(ios_HOST_OS)
    /* On iOS we need to use the special 'sys_icache_invalidate' call. */
    sys_icache_invalidate(exec_addr, ((unsigned char*)exec_addr)+len);
  #elif defined(__GNUC__)
    /* For all other platforms, fall back to a libgcc builtin. */
    unsigned char* begin = (unsigned char*)exec_addr;
    unsigned char* end   = begin + len;
    __clear_cache((void*)begin, (void*)end);
  #else
  #error Missing support to flush the instruction cache
  #endif
  }
  
  #if defined(linux_HOST_OS)
  
  // On Linux we need to use libffi for allocating executable memory,
  // because it knows how to work around the restrictions put in place
  // by SELinux.
  
  AdjustorWritable allocateExec (W_ bytes, AdjustorExecutable *exec_ret)
  {
      void **ret, **exec;
      ACQUIRE_SM_LOCK;
      ret = ffi_closure_alloc (sizeof(void *) + (size_t)bytes, (void**)&exec);
      RELEASE_SM_LOCK;
      if (ret == NULL) return ret;
      *ret = ret; // save the address of the writable mapping, for freeExec().
      *exec_ret = exec + 1;
      return (ret + 1);
  }
  
  // freeExec gets passed the executable address, not the writable address.
  void freeExec (AdjustorExecutable addr)
  {
      AdjustorWritable writable;
      writable = *((void**)addr - 1);
      ACQUIRE_SM_LOCK;
      ffi_closure_free (writable);
      RELEASE_SM_LOCK
  }
  
  #elif defined(ios_HOST_OS)
  
  static HashTable* allocatedExecs;
  
  AdjustorWritable allocateExec(W_ bytes, AdjustorExecutable *exec_ret)
  {
      AdjustorWritable writ;
      ffi_closure* cl;
      if (bytes != sizeof(ffi_closure)) {
          barf("allocateExec: for ffi_closure only");
      }
      ACQUIRE_SM_LOCK;
      cl = writ = ffi_closure_alloc((size_t)bytes, exec_ret);
      if (cl != NULL) {
          if (allocatedExecs == NULL) {
              allocatedExecs = allocHashTable();
          }
          insertHashTable(allocatedExecs, (StgWord)*exec_ret, writ);
      }
      RELEASE_SM_LOCK;
      return writ;
  }
  
  AdjustorWritable execToWritable(AdjustorExecutable exec)
  {
      AdjustorWritable writ;
      ACQUIRE_SM_LOCK;
      if (allocatedExecs == NULL ||
         (writ = lookupHashTable(allocatedExecs, (StgWord)exec)) == NULL) {
          RELEASE_SM_LOCK;
          barf("execToWritable: not found");
      }
      RELEASE_SM_LOCK;
      return writ;
  }
  
  void freeExec(AdjustorExecutable exec)
  {
      AdjustorWritable writ;
      ffi_closure* cl;
      cl = writ = execToWritable(exec);
      ACQUIRE_SM_LOCK;
      removeHashTable(allocatedExecs, (StgWord)exec, writ);
      ffi_closure_free(cl);
      RELEASE_SM_LOCK
  }
  
  #else
  
  AdjustorWritable allocateExec (W_ bytes, AdjustorExecutable *exec_ret)
  {
      void *ret;
      W_ n;
  
      ACQUIRE_SM_LOCK;
  
      // round up to words.
      n  = (bytes + sizeof(W_) + 1) / sizeof(W_);
  
      if (n+1 > BLOCK_SIZE_W) {
          barf("allocateExec: can't handle large objects");
      }
  
      if (exec_block == NULL ||
          exec_block->free + n + 1 > exec_block->start + BLOCK_SIZE_W) {
          bdescr *bd;
          W_ pagesize = getPageSize();
          bd = allocGroup(stg_max(1, pagesize / BLOCK_SIZE));
          debugTrace(DEBUG_gc, "allocate exec block %p", bd->start);
          bd->gen_no = 0;
          bd->flags = BF_EXEC;
          bd->link = exec_block;
          if (exec_block != NULL) {
              exec_block->u.back = bd;
          }
          bd->u.back = NULL;
          setExecutable(bd->start, bd->blocks * BLOCK_SIZE, rtsTrue);
          exec_block = bd;
      }
      *(exec_block->free) = n;  // store the size of this chunk
      exec_block->gen_no += n;  // gen_no stores the number of words allocated
      ret = exec_block->free + 1;
      exec_block->free += n + 1;
  
      RELEASE_SM_LOCK
      *exec_ret = ret;
      return ret;
  }
  
  void freeExec (void *addr)
  {
      StgPtr p = (StgPtr)addr - 1;
      bdescr *bd = Bdescr((StgPtr)p);
  
      if ((bd->flags & BF_EXEC) == 0) {
          barf("freeExec: not executable");
      }
  
      if (*(StgPtr)p == 0) {
          barf("freeExec: already free?");
      }
  
      ACQUIRE_SM_LOCK;
  
      bd->gen_no -= *(StgPtr)p;
      *(StgPtr)p = 0;
  
      if (bd->gen_no == 0) {
          // Free the block if it is empty, but not if it is the block at
          // the head of the queue.
          if (bd != exec_block) {
              debugTrace(DEBUG_gc, "free exec block %p", bd->start);
              dbl_link_remove(bd, &exec_block);
              setExecutable(bd->start, bd->blocks * BLOCK_SIZE, rtsFalse);
              freeGroup(bd);
          } else {
              bd->free = bd->start;
          }
      }
  
      RELEASE_SM_LOCK
  }
  
  #endif /* switch(HOST_OS) */
  
  #ifdef DEBUG
  
  // handy function for use in gdb, because Bdescr() is inlined.
  extern bdescr *_bdescr (StgPtr p);
  
  bdescr *
  _bdescr (StgPtr p)
  {
      return Bdescr(p);
  }
  
  #endif
  