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tclThreadAlloc.c

/*
 * tclThreadAlloc.c --
 *
 *    This is a very fast storage allocator for used with threads (designed
 *    avoid lock contention).  The basic strategy is to allocate memory in
 *    fixed size blocks from block caches.
 * 
 * The Initial Developer of the Original Code is America Online, Inc.
 * Portions created by AOL are Copyright (C) 1999 America Online, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclThreadAlloc.c,v 1.4.2.6 2005/04/07 11:27:17 vasiljevic Exp $ 
 */

#include "tclInt.h"

#if defined(TCL_THREADS) && defined(USE_THREAD_ALLOC) && !defined(TCL_MEM_DEBUG)

#ifdef WIN32
#include "tclWinInt.h"
#else
extern Tcl_Mutex *TclpNewAllocMutex(void);
extern void *TclpGetAllocCache(void);
extern void TclpSetAllocCache(void *);
#endif

/*
 * If range checking is enabled, an additional byte will be allocated
 * to store the magic number at the end of the requested memory.
 */

#ifndef RCHECK
#ifdef  NDEBUG
#define RCHECK          0
#else
#define RCHECK          1
#endif
#endif

/*
 * The following define the number of Tcl_Obj's to allocate/move
 * at a time and the high water mark to prune a per-thread cache.
 * On a 32 bit system, sizeof(Tcl_Obj) = 24 so 800 * 24 = ~16k.
 *
 */
 
#define NOBJALLOC  800
#define NOBJHIGH  1200

/*
 * The following defines the number of buckets in the bucket
 * cache and those block sizes from (1<<4) to (1<<(3+NBUCKETS))
 */

#define NBUCKETS    11
#define MAXALLOC    16284

/*
 * The following union stores accounting information for
 * each block including two small magic numbers and
 * a bucket number when in use or a next pointer when
 * free.  The original requested size (not including
 * the Block overhead) is also maintained.
 */
 
typedef struct Block {
    union {
      struct Block *next;       /* Next in free list. */
      struct {
          unsigned char magic1; /* First magic number. */
          unsigned char bucket; /* Bucket block allocated from. */
          unsigned char unused; /* Padding. */
          unsigned char magic2; /* Second magic number. */
        } b_s;
    } b_u;
    size_t b_reqsize;           /* Requested allocation size. */
} Block;
#define b_next          b_u.next
#define b_bucket  b_u.b_s.bucket
#define b_magic1  b_u.b_s.magic1
#define b_magic2  b_u.b_s.magic2
#define MAGIC           0xef

/*
 * The following structure defines a bucket of blocks with
 * various accounting and statistics information.
 */

typedef struct Bucket {
    Block *firstPtr;
    int nfree;
    int nget;
    int nput;
    int nwait;
    int nlock;
    int nrequest;
} Bucket;

/*
 * The following structure defines a cache of buckets and objs.
 */

typedef struct Cache {
    struct Cache  *nextPtr;
    Tcl_ThreadId   owner;
    Tcl_Obj       *firstObjPtr;
    int            nobjs;
    int                nsysalloc;
    Bucket         buckets[NBUCKETS];
} Cache;

/*
 * The following array specifies various per-bucket 
 * limits and locks.  The values are statically initialized
 * to avoid calculating them repeatedly.
 */

struct binfo {
    size_t blocksize;   /* Bucket blocksize. */
    int maxblocks;      /* Max blocks before move to share. */
    int nmove;          /* Num blocks to move to share. */
    Tcl_Mutex *lockPtr; /* Share bucket lock. */
} binfo[NBUCKETS] = {
    {   16, 1024, 512, NULL},
    {   32,  512, 256, NULL},
    {   64,  256, 128, NULL},
    {  128,  128,  64, NULL},
    {  256,   64,  32, NULL},
    {  512,   32,  16, NULL},
    { 1024,   16,   8, NULL},
    { 2048,    8,   4, NULL},
    { 4096,    4,   2, NULL},
    { 8192,    2,   1, NULL},
    {16284,    1,   1, NULL},
};

/*
 * Static functions defined in this file.
 */

static void LockBucket(Cache *cachePtr, int bucket);
static void UnlockBucket(Cache *cachePtr, int bucket);
static void PutBlocks(Cache *cachePtr, int bucket, int nmove);
static int  GetBlocks(Cache *cachePtr, int bucket);
static Block *Ptr2Block(char *ptr);
static char *Block2Ptr(Block *blockPtr, int bucket, unsigned int reqsize);
static void MoveObjs(Cache *fromPtr, Cache *toPtr, int nmove);

/*
 * Local variables defined in this file and initialized at
 * startup.
 */

static Tcl_Mutex *listLockPtr;
static Tcl_Mutex *objLockPtr;
static Cache     sharedCache;
static Cache    *sharedPtr = &sharedCache;
static Cache    *firstCachePtr = &sharedCache;


/*
 *----------------------------------------------------------------------
 *
 *  GetCache ---
 *
 *    Gets per-thread memory cache, allocating it if necessary.
 *
 * Results:
 *    Pointer to cache.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static Cache *
GetCache(void)
{
    Cache *cachePtr;

    /*
     * Check for first-time initialization.
     */

    if (listLockPtr == NULL) {
      Tcl_Mutex *initLockPtr;
      int i;

      initLockPtr = Tcl_GetAllocMutex();
      Tcl_MutexLock(initLockPtr);
      if (listLockPtr == NULL) {
          listLockPtr = TclpNewAllocMutex();
          objLockPtr = TclpNewAllocMutex();
          for (i = 0; i < NBUCKETS; ++i) {
              binfo[i].lockPtr = TclpNewAllocMutex();
          }
      }
      Tcl_MutexUnlock(initLockPtr);
    }

    /*
     * Get this thread's cache, allocating if necessary.
     */

    cachePtr = TclpGetAllocCache();
    if (cachePtr == NULL) {
      cachePtr = calloc(1, sizeof(Cache));
      if (cachePtr == NULL) {
          panic("alloc: could not allocate new cache");
      }
      Tcl_MutexLock(listLockPtr);
      cachePtr->nextPtr = firstCachePtr;
      firstCachePtr = cachePtr;
      Tcl_MutexUnlock(listLockPtr);
      cachePtr->owner = Tcl_GetCurrentThread();
      TclpSetAllocCache(cachePtr);
    }
    return cachePtr;
}


/*
 *----------------------------------------------------------------------
 *
 *  TclFreeAllocCache --
 *
 *    Flush and delete a cache, removing from list of caches.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
TclFreeAllocCache(void *arg)
{
    Cache *cachePtr = arg;
    Cache **nextPtrPtr;
    register int   bucket;

    /*
     * Flush blocks.
     */

    for (bucket = 0; bucket < NBUCKETS; ++bucket) {
      if (cachePtr->buckets[bucket].nfree > 0) {
          PutBlocks(cachePtr, bucket, cachePtr->buckets[bucket].nfree);
      }
    }

    /*
     * Flush objs.
     */

    if (cachePtr->nobjs > 0) {
      Tcl_MutexLock(objLockPtr);
      MoveObjs(cachePtr, sharedPtr, cachePtr->nobjs);
      Tcl_MutexUnlock(objLockPtr);
    }

    /*
     * Remove from pool list.
     */

    Tcl_MutexLock(listLockPtr);
    nextPtrPtr = &firstCachePtr;
    while (*nextPtrPtr != cachePtr) {
      nextPtrPtr = &(*nextPtrPtr)->nextPtr;
    }
    *nextPtrPtr = cachePtr->nextPtr;
    cachePtr->nextPtr = NULL;
    Tcl_MutexUnlock(listLockPtr);
    free(cachePtr);
}


/*
 *----------------------------------------------------------------------
 *
 *  TclpAlloc --
 *
 *    Allocate memory.
 *
 * Results:
 *    Pointer to memory just beyond Block pointer.
 *
 * Side effects:
 *    May allocate more blocks for a bucket.
 *
 *----------------------------------------------------------------------
 */

char *
TclpAlloc(unsigned int reqsize)
{
    Cache         *cachePtr = TclpGetAllocCache();
    Block         *blockPtr;
    register int   bucket;
    size_t           size;

    if (cachePtr == NULL) {
      cachePtr = GetCache();
    }
    
    /*
     * Increment the requested size to include room for 
     * the Block structure.  Call malloc() directly if the
     * required amount is greater than the largest block,
     * otherwise pop the smallest block large enough,
     * allocating more blocks if necessary.
     */

    blockPtr = NULL;     
    size = reqsize + sizeof(Block);
#if RCHECK
    ++size;
#endif
    if (size > MAXALLOC) {
      bucket = NBUCKETS;
      blockPtr = malloc(size);
      if (blockPtr != NULL) {
          cachePtr->nsysalloc += reqsize;
      }
    } else {
      bucket = 0;
      while (binfo[bucket].blocksize < size) {
          ++bucket;
      }
      if (cachePtr->buckets[bucket].nfree || GetBlocks(cachePtr, bucket)) {
          blockPtr = cachePtr->buckets[bucket].firstPtr;
          cachePtr->buckets[bucket].firstPtr = blockPtr->b_next;
          --cachePtr->buckets[bucket].nfree;
          ++cachePtr->buckets[bucket].nget;
          cachePtr->buckets[bucket].nrequest += reqsize;
      }
    }
    if (blockPtr == NULL) {
      return NULL;
    }
    return Block2Ptr(blockPtr, bucket, reqsize);
}


/*
 *----------------------------------------------------------------------
 *
 *  TclpFree --
 *
 *    Return blocks to the thread block cache.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    May move blocks to shared cache.
 *
 *----------------------------------------------------------------------
 */

void
TclpFree(char *ptr)
{
    if (ptr != NULL) {
      Cache  *cachePtr = TclpGetAllocCache();
      Block *blockPtr;
      int bucket;

      if (cachePtr == NULL) {
          cachePtr = GetCache();
      }
 
      /*
       * Get the block back from the user pointer and
       * call system free directly for large blocks.
       * Otherwise, push the block back on the bucket and
       * move blocks to the shared cache if there are now
       * too many free.
       */

      blockPtr = Ptr2Block(ptr);
      bucket = blockPtr->b_bucket;
      if (bucket == NBUCKETS) {
          cachePtr->nsysalloc -= blockPtr->b_reqsize;
          free(blockPtr);
      } else {
          cachePtr->buckets[bucket].nrequest -= blockPtr->b_reqsize;
          blockPtr->b_next = cachePtr->buckets[bucket].firstPtr;
          cachePtr->buckets[bucket].firstPtr = blockPtr;
          ++cachePtr->buckets[bucket].nfree;
          ++cachePtr->buckets[bucket].nput;
          if (cachePtr != sharedPtr &&
                cachePtr->buckets[bucket].nfree > binfo[bucket].maxblocks) {
            PutBlocks(cachePtr, bucket, binfo[bucket].nmove);
          }
      }
    }
}


/*
 *----------------------------------------------------------------------
 *
 *  TclpRealloc --
 *
 *    Re-allocate memory to a larger or smaller size.
 *
 * Results:
 *    Pointer to memory just beyond Block pointer.
 *
 * Side effects:
 *    Previous memory, if any, may be freed.
 *
 *----------------------------------------------------------------------
 */

char *
TclpRealloc(char *ptr, unsigned int reqsize)
{
    Cache *cachePtr = TclpGetAllocCache();
    Block *blockPtr;
    void *new;
    size_t size, min;
    int bucket;

    if (ptr == NULL) {
      return TclpAlloc(reqsize);
    }

    if (cachePtr == NULL) {
      cachePtr = GetCache();
    }

    /*
     * If the block is not a system block and fits in place,
     * simply return the existing pointer.  Otherwise, if the block
     * is a system block and the new size would also require a system
     * block, call realloc() directly.
     */

    blockPtr = Ptr2Block(ptr);
    size = reqsize + sizeof(Block);
#if RCHECK
    ++size;
#endif
    bucket = blockPtr->b_bucket;
    if (bucket != NBUCKETS) {
      if (bucket > 0) {
          min = binfo[bucket-1].blocksize;
      } else {
          min = 0;
      }
      if (size > min && size <= binfo[bucket].blocksize) {
          cachePtr->buckets[bucket].nrequest -= blockPtr->b_reqsize;
          cachePtr->buckets[bucket].nrequest += reqsize;
          return Block2Ptr(blockPtr, bucket, reqsize);
      }
    } else if (size > MAXALLOC) {
      cachePtr->nsysalloc -= blockPtr->b_reqsize;
      cachePtr->nsysalloc += reqsize;
      blockPtr = realloc(blockPtr, size);
      if (blockPtr == NULL) {
          return NULL;
      }
      return Block2Ptr(blockPtr, NBUCKETS, reqsize);
    }

    /*
     * Finally, perform an expensive malloc/copy/free.
     */

    new = TclpAlloc(reqsize);
    if (new != NULL) {
      if (reqsize > blockPtr->b_reqsize) {
          reqsize = blockPtr->b_reqsize;
      }
      memcpy(new, ptr, reqsize);
      TclpFree(ptr);
    }
    return new;
}


/*
 *----------------------------------------------------------------------
 *
 * TclThreadAllocObj --
 *
 *    Allocate a Tcl_Obj from the per-thread cache.
 *
 * Results:
 *    Pointer to uninitialized Tcl_Obj.
 *
 * Side effects:
 *    May move Tcl_Obj's from shared cached or allocate new Tcl_Obj's
 *    if list is empty.
 *
 *----------------------------------------------------------------------
 */

Tcl_Obj *
TclThreadAllocObj(void)
{
    register Cache *cachePtr = TclpGetAllocCache();
    register int nmove;
    register Tcl_Obj *objPtr;
    Tcl_Obj *newObjsPtr;

    if (cachePtr == NULL) {
      cachePtr = GetCache();
    }

    /*
     * Get this thread's obj list structure and move
     * or allocate new objs if necessary.
     */
     
    if (cachePtr->nobjs == 0) {
      Tcl_MutexLock(objLockPtr);
      nmove = sharedPtr->nobjs;
      if (nmove > 0) {
          if (nmove > NOBJALLOC) {
            nmove = NOBJALLOC;
          }
          MoveObjs(sharedPtr, cachePtr, nmove);
      }
      Tcl_MutexUnlock(objLockPtr);
      if (cachePtr->nobjs == 0) {
          cachePtr->nobjs = nmove = NOBJALLOC;
          newObjsPtr = malloc(sizeof(Tcl_Obj) * nmove);
          if (newObjsPtr == NULL) {
            panic("alloc: could not allocate %d new objects", nmove);
          }
          while (--nmove >= 0) {
            objPtr = &newObjsPtr[nmove];
            objPtr->internalRep.otherValuePtr = cachePtr->firstObjPtr;
            cachePtr->firstObjPtr = objPtr;
          }
      }
    }

    /*
     * Pop the first object.
     */

    objPtr = cachePtr->firstObjPtr;
    cachePtr->firstObjPtr = objPtr->internalRep.otherValuePtr;
    --cachePtr->nobjs;
    return objPtr;
}


/*
 *----------------------------------------------------------------------
 *
 * TclThreadFreeObj --
 *
 *    Return a free Tcl_Obj to the per-thread cache.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    May move free Tcl_Obj's to shared list upon hitting high
 *    water mark.
 *
 *----------------------------------------------------------------------
 */

void
TclThreadFreeObj(Tcl_Obj *objPtr)
{
    Cache *cachePtr = TclpGetAllocCache();

    if (cachePtr == NULL) {
      cachePtr = GetCache();
    }

    /*
     * Get this thread's list and push on the free Tcl_Obj.
     */
     
    objPtr->internalRep.otherValuePtr = cachePtr->firstObjPtr;
    cachePtr->firstObjPtr = objPtr;
    ++cachePtr->nobjs;
    
    /*
     * If the number of free objects has exceeded the high
     * water mark, move some blocks to the shared list.
     */
     
    if (cachePtr->nobjs > NOBJHIGH) {
      Tcl_MutexLock(objLockPtr);
      MoveObjs(cachePtr, sharedPtr, NOBJALLOC);
      Tcl_MutexUnlock(objLockPtr);
    }
}


/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetMemoryInfo --
 *
 *    Return a list-of-lists of memory stats.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    List appended to given dstring.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_GetMemoryInfo(Tcl_DString *dsPtr)
{
    Cache *cachePtr;
    char buf[200];
    int n;

    Tcl_MutexLock(listLockPtr);
    cachePtr = firstCachePtr;
    while (cachePtr != NULL) {
      Tcl_DStringStartSublist(dsPtr);
      if (cachePtr == sharedPtr) {
          Tcl_DStringAppendElement(dsPtr, "shared");
      } else {
          sprintf(buf, "thread%d", (int) cachePtr->owner);
          Tcl_DStringAppendElement(dsPtr, buf);
      }
      for (n = 0; n < NBUCKETS; ++n) {
          sprintf(buf, "%d %d %d %d %d %d %d",
            (int) binfo[n].blocksize,
            cachePtr->buckets[n].nfree,
            cachePtr->buckets[n].nget,
            cachePtr->buckets[n].nput,
            cachePtr->buckets[n].nrequest,
            cachePtr->buckets[n].nlock,
            cachePtr->buckets[n].nwait);
          Tcl_DStringAppendElement(dsPtr, buf);
      }
      Tcl_DStringEndSublist(dsPtr);
          cachePtr = cachePtr->nextPtr;
    }
    Tcl_MutexUnlock(listLockPtr);
}


/*
 *----------------------------------------------------------------------
 *
 * MoveObjs --
 *
 *    Move Tcl_Obj's between caches.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static void
MoveObjs(Cache *fromPtr, Cache *toPtr, int nmove)
{
    register Tcl_Obj *objPtr = fromPtr->firstObjPtr;
    Tcl_Obj *fromFirstObjPtr = objPtr;

    toPtr->nobjs += nmove;
    fromPtr->nobjs -= nmove;

    /*
     * Find the last object to be moved; set the next one
     * (the first one not to be moved) as the first object
     * in the 'from' cache.
     */

    while (--nmove) {
      objPtr = objPtr->internalRep.otherValuePtr;
    }
    fromPtr->firstObjPtr = objPtr->internalRep.otherValuePtr;    

    /*
     * Move all objects as a block - they are already linked to
     * each other, we just have to update the first and last.
     */

    objPtr->internalRep.otherValuePtr = toPtr->firstObjPtr;
    toPtr->firstObjPtr = fromFirstObjPtr;
}


/*
 *----------------------------------------------------------------------
 *
 *  Block2Ptr, Ptr2Block --
 *
 *    Convert between internal blocks and user pointers.
 *
 * Results:
 *    User pointer or internal block.
 *
 * Side effects:
 *    Invalid blocks will abort the server.
 *
 *----------------------------------------------------------------------
 */

static char *
Block2Ptr(Block *blockPtr, int bucket, unsigned int reqsize) 
{
    register void *ptr;

    blockPtr->b_magic1 = blockPtr->b_magic2 = MAGIC;
    blockPtr->b_bucket = bucket;
    blockPtr->b_reqsize = reqsize;
    ptr = ((void *) (blockPtr + 1));
#if RCHECK
    ((unsigned char *)(ptr))[reqsize] = MAGIC;
#endif
    return (char *) ptr;
}

static Block *
Ptr2Block(char *ptr)
{
    register Block *blockPtr;

    blockPtr = (((Block *) ptr) - 1);
    if (blockPtr->b_magic1 != MAGIC
#if RCHECK
      || ((unsigned char *) ptr)[blockPtr->b_reqsize] != MAGIC
#endif
      || blockPtr->b_magic2 != MAGIC) {
      panic("alloc: invalid block: %p: %x %x %x\n",
          blockPtr, blockPtr->b_magic1, blockPtr->b_magic2,
          ((unsigned char *) ptr)[blockPtr->b_reqsize]);
    }
    return blockPtr;
}


/*
 *----------------------------------------------------------------------
 *
 *  LockBucket, UnlockBucket --
 *
 *    Set/unset the lock to access a bucket in the shared cache.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Lock activity and contention are monitored globally and on
 *    a per-cache basis.
 *
 *----------------------------------------------------------------------
 */

static void
LockBucket(Cache *cachePtr, int bucket)
{
#if 0
    if (Tcl_MutexTryLock(binfo[bucket].lockPtr) != TCL_OK) {
      Tcl_MutexLock(binfo[bucket].lockPtr);
      ++cachePtr->buckets[bucket].nwait;
      ++sharedPtr->buckets[bucket].nwait;
    }
#else
    Tcl_MutexLock(binfo[bucket].lockPtr);
#endif
    ++cachePtr->buckets[bucket].nlock;
    ++sharedPtr->buckets[bucket].nlock;
}


static void
UnlockBucket(Cache *cachePtr, int bucket)
{
    Tcl_MutexUnlock(binfo[bucket].lockPtr);
}


/*
 *----------------------------------------------------------------------
 *
 *  PutBlocks --
 *
 *    Return unused blocks to the shared cache.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

static void
PutBlocks(Cache *cachePtr, int bucket, int nmove)
{
    register Block *lastPtr, *firstPtr;
    register int n = nmove;

    /*
     * Before acquiring the lock, walk the block list to find
     * the last block to be moved.
     */

    firstPtr = lastPtr = cachePtr->buckets[bucket].firstPtr;
    while (--n > 0) {
      lastPtr = lastPtr->b_next;
    }
    cachePtr->buckets[bucket].firstPtr = lastPtr->b_next;
    cachePtr->buckets[bucket].nfree -= nmove;

    /*
     * Aquire the lock and place the list of blocks at the front
     * of the shared cache bucket.
     */

    LockBucket(cachePtr, bucket);
    lastPtr->b_next = sharedPtr->buckets[bucket].firstPtr;
    sharedPtr->buckets[bucket].firstPtr = firstPtr;
    sharedPtr->buckets[bucket].nfree += nmove;
    UnlockBucket(cachePtr, bucket);
}


/*
 *----------------------------------------------------------------------
 *
 *  GetBlocks --
 *
 *    Get more blocks for a bucket.
 *
 * Results:
 *    1 if blocks where allocated, 0 otherwise.
 *
 * Side effects:
 *    Cache may be filled with available blocks.
 *
 *----------------------------------------------------------------------
 */

static int
GetBlocks(Cache *cachePtr, int bucket)
{
    register Block *blockPtr;
    register int n;
    register size_t size;

    /*
     * First, atttempt to move blocks from the shared cache.  Note
     * the potentially dirty read of nfree before acquiring the lock
     * which is a slight performance enhancement.  The value is
     * verified after the lock is actually acquired.
     */
     
    if (cachePtr != sharedPtr && sharedPtr->buckets[bucket].nfree > 0) {
      LockBucket(cachePtr, bucket);
      if (sharedPtr->buckets[bucket].nfree > 0) {

          /*
           * Either move the entire list or walk the list to find
           * the last block to move.
           */

          n = binfo[bucket].nmove;
          if (n >= sharedPtr->buckets[bucket].nfree) {
            cachePtr->buckets[bucket].firstPtr =
                sharedPtr->buckets[bucket].firstPtr;
            cachePtr->buckets[bucket].nfree =
                sharedPtr->buckets[bucket].nfree;
            sharedPtr->buckets[bucket].firstPtr = NULL;
            sharedPtr->buckets[bucket].nfree = 0;
          } else {
            blockPtr = sharedPtr->buckets[bucket].firstPtr;
            cachePtr->buckets[bucket].firstPtr = blockPtr;
            sharedPtr->buckets[bucket].nfree -= n;
            cachePtr->buckets[bucket].nfree = n;
            while (--n > 0) {
                blockPtr = blockPtr->b_next;
            }
            sharedPtr->buckets[bucket].firstPtr = blockPtr->b_next;
            blockPtr->b_next = NULL;
          }
      }
      UnlockBucket(cachePtr, bucket);
    }
    
    if (cachePtr->buckets[bucket].nfree == 0) {

      /*
       * If no blocks could be moved from shared, first look for a
       * larger block in this cache to split up.
       */

      blockPtr = NULL;
      n = NBUCKETS;
      size = 0; /* lint */
      while (--n > bucket) {
          if (cachePtr->buckets[n].nfree > 0) {
            size = binfo[n].blocksize;
            blockPtr = cachePtr->buckets[n].firstPtr;
            cachePtr->buckets[n].firstPtr = blockPtr->b_next;
            --cachePtr->buckets[n].nfree;
            break;
          }
      }

      /*
       * Otherwise, allocate a big new block directly.
       */

      if (blockPtr == NULL) {
          size = MAXALLOC;
          blockPtr = malloc(size);
          if (blockPtr == NULL) {
            return 0;
          }
      }

      /*
       * Split the larger block into smaller blocks for this bucket.
       */

      n = size / binfo[bucket].blocksize;
      cachePtr->buckets[bucket].nfree = n;
      cachePtr->buckets[bucket].firstPtr = blockPtr;
      while (--n > 0) {
          blockPtr->b_next = (Block *) 
            ((char *) blockPtr + binfo[bucket].blocksize);
          blockPtr = blockPtr->b_next;
      }
      blockPtr->b_next = NULL;
    }
    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * TclFinalizeThreadAlloc --
 *
 *    This procedure is used to destroy all private resources used in
 *    this file.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
TclFinalizeThreadAlloc()
{
    int i;
    for (i = 0; i < NBUCKETS; ++i) {
        TclpFreeAllocMutex(binfo[i].lockPtr); 
        binfo[i].lockPtr = NULL;
    }

    TclpFreeAllocMutex(objLockPtr);
    objLockPtr = NULL;

    TclpFreeAllocMutex(listLockPtr);
    listLockPtr = NULL;

    TclpFreeAllocCache(NULL);
}

#else /* ! defined(TCL_THREADS) && ! defined(USE_THREAD_ALLOC) */

/*
 *----------------------------------------------------------------------
 *
 * TclFinalizeThreadAlloc --
 *
 *    This procedure is used to destroy all private resources used in
 *    this file.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
TclFinalizeThreadAlloc()
{
    Tcl_Panic("TclFinalizeThreadAlloc called when threaded memory allocator not in use.");
}

#endif /* TCL_THREADS */

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