diff options
Diffstat (limited to 'generic')
| -rw-r--r-- | generic/tclAlloc.c | 10 | ||||
| -rw-r--r-- | generic/tclInt.h | 32 | ||||
| -rwxr-xr-x | generic/tclThreadAlloc.c | 914 |
3 files changed, 954 insertions, 2 deletions
diff --git a/generic/tclAlloc.c b/generic/tclAlloc.c index 099da71..fe64c97 100644 --- a/generic/tclAlloc.c +++ b/generic/tclAlloc.c @@ -15,9 +15,16 @@ * See the file "license.terms" for information on usage and redistribution * of this file, and for a DISCLAIMER OF ALL WARRANTIES. * - * RCS: @(#) $Id: tclAlloc.c,v 1.15 2002/02/27 07:08:28 hobbs Exp $ + * RCS: @(#) $Id: tclAlloc.c,v 1.16 2002/04/23 17:03:34 hobbs Exp $ */ +/* + * Windows and Unix use an alternative allocator when building with threads + * that has significantly reduced lock contention. + */ + +#if !defined(TCL_THREADS) || !defined(USE_THREAD_ALLOC) + #include "tclInt.h" #include "tclPort.h" @@ -721,3 +728,4 @@ TclpRealloc(cp, nbytes) } #endif /* !USE_TCLALLOC */ +#endif /* !TCL_THREADS */ diff --git a/generic/tclInt.h b/generic/tclInt.h index a2dc4ac..f87eac9 100644 --- a/generic/tclInt.h +++ b/generic/tclInt.h @@ -12,7 +12,7 @@ * See the file "license.terms" for information on usage and redistribution * of this file, and for a DISCLAIMER OF ALL WARRANTIES. * - * RCS: @(#) $Id: tclInt.h,v 1.84 2002/03/06 15:04:58 msofer Exp $ + * RCS: @(#) $Id: tclInt.h,v 1.85 2002/04/23 17:03:34 hobbs Exp $ */ #ifndef _TCLINT @@ -2244,6 +2244,36 @@ EXTERN int TclCompileWhileCmd _ANSI_ARGS_((Tcl_Interp *interp, TclIncrObjsFreed(); \ } +#elif defined(TCL_THREADS) && defined(USE_THREAD_ALLOC) + +/* + * The TCL_THREADS mode is like the regular mode but allocates Tcl_Obj's + * from per-thread caches. + */ + +EXTERN Tcl_Obj *TclThreadAllocObj _ANSI_ARGS_((void)); +EXTERN void TclThreadFreeObj _ANSI_ARGS_((Tcl_Obj *)); + +# define TclNewObj(objPtr) \ + (objPtr) = TclThreadAllocObj(); \ + (objPtr)->refCount = 0; \ + (objPtr)->bytes = tclEmptyStringRep; \ + (objPtr)->length = 0; \ + (objPtr)->typePtr = NULL + +# define TclDecrRefCount(objPtr) \ + if (--(objPtr)->refCount <= 0) { \ + if (((objPtr)->bytes != NULL) \ + && ((objPtr)->bytes != tclEmptyStringRep)) { \ + ckfree((char *) (objPtr)->bytes); \ + } \ + if (((objPtr)->typePtr != NULL) \ + && ((objPtr)->typePtr->freeIntRepProc != NULL)) { \ + (objPtr)->typePtr->freeIntRepProc(objPtr); \ + } \ + TclThreadFreeObj((objPtr)); \ + } + #else /* not TCL_MEM_DEBUG */ #ifdef TCL_THREADS diff --git a/generic/tclThreadAlloc.c b/generic/tclThreadAlloc.c new file mode 100755 index 0000000..5a8a925 --- /dev/null +++ b/generic/tclThreadAlloc.c @@ -0,0 +1,914 @@ +/* + * 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 1.1 2002/04/23 17:03:34 hobbs Exp $ */ + +#if defined(TCL_THREADS) && defined(USE_THREAD_ALLOC) + +#include "tclInt.h" + +#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); +#ifdef WIN32 + TlsFree((DWORD) cachePtr); +#else + free(cachePtr); +#endif +} + + +/* + *---------------------------------------------------------------------- + * + * 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 = GetCache(); + Block *blockPtr; + register int bucket; + size_t size; + + /* + * 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) +{ + Cache *cachePtr = GetCache(); + Block *blockPtr; + int bucket; + + /* + * 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 = GetCache(); + Block *blockPtr; + void *new; + size_t size, min; + int bucket; + + /* + * 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 = GetCache(); + register int nmove; + register Tcl_Obj *objPtr; + Tcl_Obj *newObjsPtr; + + /* + * 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 = GetCache(); + + /* + * Get this thread's list and push on the free Tcl_Obj. + */ + + objPtr->internalRep.otherValuePtr = cachePtr->firstObjPtr; + cachePtr->firstObjPtr = objPtr; + + /* + * If the number of free objects has exceeded the high + * water mark, move some blocks to the shared list. + */ + + ++cachePtr->nobjs; + 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; + + toPtr->nobjs += nmove; + fromPtr->nobjs -= nmove; + while (--nmove >= 0) { + objPtr = fromPtr->firstObjPtr; + fromPtr->firstObjPtr = objPtr->internalRep.otherValuePtr; + objPtr->internalRep.otherValuePtr = toPtr->firstObjPtr; + toPtr->firstObjPtr = objPtr; + } +} + + +/* + *---------------------------------------------------------------------- + * + * 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; +} + +#endif /* TCL_THREADS */ |