tclThreadAlloc.c Go to the documentation of this file. /* * 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 1.25 2007/12/17 15:28:28 msofer Exp $ */ #include "tclInt.h" #if defined(TCL_THREADS) && defined(USE_THREAD_ALLOC) /* * 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 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 union Block { struct { union { union 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. */ } s; } u; size_t reqSize; /* Requested allocation size. */ } b; unsigned char padding[TCL_ALLOCALIGN]; } Block; #define nextBlock b.u.next #define sourceBucket b.u.s.bucket #define magicNum1 b.u.s.magic1 #define magicNum2 b.u.s.magic2 #define MAGIC 0xEF #define blockReqSize b.reqSize /* * The following defines the minimum and and maximum block sizes and the number * of buckets in the bucket cache. */ #define MINALLOC ((sizeof(Block) + 8 + (TCL_ALLOCALIGN-1)) & ~(TCL_ALLOCALIGN-1)) #define NBUCKETS (11 - (MINALLOC >> 5)) #define MAXALLOC (MINALLOC << (NBUCKETS - 1)) /* * The following structure defines a bucket of blocks with various accounting * and statistics information. */ typedef struct Bucket { Block *firstPtr; /* First block available */ long numFree; /* Number of blocks available */ /* All fields below for accounting only */ long numRemoves; /* Number of removes from bucket */ long numInserts; /* Number of inserts into bucket */ long numWaits; /* Number of waits to acquire a lock */ long numLocks; /* Number of locks acquired */ long totalAssigned; /* Total space assigned to bucket */ } Bucket; /* * The following structure defines a cache of buckets and objs, of which there * will be (at most) one per thread. */ typedef struct Cache { struct Cache *nextPtr; /* Linked list of cache entries */ Tcl_ThreadId owner; /* Which thread's cache is this? */ Tcl_Obj *firstObjPtr; /* List of free objects for thread */ int numObjects; /* Number of objects for thread */ int totalAssigned; /* Total space assigned to thread */ Bucket buckets[NBUCKETS]; /* The buckets for this thread */ } Cache; /* * The following array specifies various per-bucket limits and locks. The * values are statically initialized to avoid calculating them repeatedly. */ static struct { size_t blockSize; /* Bucket blocksize. */ int maxBlocks; /* Max blocks before move to share. */ int numMove; /* Num blocks to move to share. */ Tcl_Mutex *lockPtr; /* Share bucket lock. */ } bucketInfo[NBUCKETS]; /* * Static functions defined in this file. */ static Cache * GetCache(void); static void LockBucket(Cache *cachePtr, int bucket); static void UnlockBucket(Cache *cachePtr, int bucket); static void PutBlocks(Cache *cachePtr, int bucket, int numMove); 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 numMove); /* * 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; unsigned int i; initLockPtr = Tcl_GetAllocMutex(); Tcl_MutexLock(initLockPtr); if (listLockPtr == NULL) { listLockPtr = TclpNewAllocMutex(); objLockPtr = TclpNewAllocMutex(); for (i = 0; i < NBUCKETS; ++i) { bucketInfo[i].blockSize = MINALLOC << i; bucketInfo[i].maxBlocks = 1 << (NBUCKETS - 1 - i); bucketInfo[i].numMove = i < NBUCKETS - 1 ? 1 << (NBUCKETS - 2 - i) : 1; bucketInfo[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) { Tcl_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 unsigned int bucket; /* * Flush blocks. */ for (bucket = 0; bucket < NBUCKETS; ++bucket) { if (cachePtr->buckets[bucket].numFree > 0) { PutBlocks(cachePtr, bucket, cachePtr->buckets[bucket].numFree); } } /* * Flush objs. */ if (cachePtr->numObjects > 0) { Tcl_MutexLock(objLockPtr); MoveObjs(cachePtr, sharedPtr, cachePtr->numObjects); 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->totalAssigned += reqSize; } } else { bucket = 0; while (bucketInfo[bucket].blockSize < size) { ++bucket; } if (cachePtr->buckets[bucket].numFree || GetBlocks(cachePtr, bucket)) { blockPtr = cachePtr->buckets[bucket].firstPtr; cachePtr->buckets[bucket].firstPtr = blockPtr->nextBlock; --cachePtr->buckets[bucket].numFree; ++cachePtr->buckets[bucket].numRemoves; cachePtr->buckets[bucket].totalAssigned += 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; Block *blockPtr; int bucket; if (ptr == NULL) { return; } cachePtr = TclpGetAllocCache(); 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->sourceBucket; if (bucket == NBUCKETS) { cachePtr->totalAssigned -= blockPtr->blockReqSize; free(blockPtr); return; } cachePtr->buckets[bucket].totalAssigned -= blockPtr->blockReqSize; blockPtr->nextBlock = cachePtr->buckets[bucket].firstPtr; cachePtr->buckets[bucket].firstPtr = blockPtr; ++cachePtr->buckets[bucket].numFree; ++cachePtr->buckets[bucket].numInserts; if (cachePtr != sharedPtr && cachePtr->buckets[bucket].numFree > bucketInfo[bucket].maxBlocks) { PutBlocks(cachePtr, bucket, bucketInfo[bucket].numMove); } }  /* *---------------------------------------------------------------------- * * 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 *newPtr; 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->sourceBucket; if (bucket != NBUCKETS) { if (bucket > 0) { min = bucketInfo[bucket-1].blockSize; } else { min = 0; } if (size > min && size <= bucketInfo[bucket].blockSize) { cachePtr->buckets[bucket].totalAssigned -= blockPtr->blockReqSize; cachePtr->buckets[bucket].totalAssigned += reqSize; return Block2Ptr(blockPtr, bucket, reqSize); } } else if (size > MAXALLOC) { cachePtr->totalAssigned -= blockPtr->blockReqSize; cachePtr->totalAssigned += reqSize; blockPtr = realloc(blockPtr, size); if (blockPtr == NULL) { return NULL; } return Block2Ptr(blockPtr, NBUCKETS, reqSize); } /* * Finally, perform an expensive malloc/copy/free. */ newPtr = TclpAlloc(reqSize); if (newPtr != NULL) { if (reqSize > blockPtr->blockReqSize) { reqSize = blockPtr->blockReqSize; } memcpy(newPtr, ptr, reqSize); TclpFree(ptr); } return newPtr; }  /* *---------------------------------------------------------------------- * * 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 Tcl_Obj *objPtr; if (cachePtr == NULL) { cachePtr = GetCache(); } /* * Get this thread's obj list structure and move or allocate new objs if * necessary. */ if (cachePtr->numObjects == 0) { register int numMove; Tcl_MutexLock(objLockPtr); numMove = sharedPtr->numObjects; if (numMove > 0) { if (numMove > NOBJALLOC) { numMove = NOBJALLOC; } MoveObjs(sharedPtr, cachePtr, numMove); } Tcl_MutexUnlock(objLockPtr); if (cachePtr->numObjects == 0) { Tcl_Obj *newObjsPtr; cachePtr->numObjects = numMove = NOBJALLOC; newObjsPtr = malloc(sizeof(Tcl_Obj) * numMove); if (newObjsPtr == NULL) { Tcl_Panic("alloc: could not allocate %d new objects", numMove); } while (--numMove >= 0) { objPtr = &newObjsPtr[numMove]; objPtr->internalRep.otherValuePtr = cachePtr->firstObjPtr; cachePtr->firstObjPtr = objPtr; } } } /* * Pop the first object. */ objPtr = cachePtr->firstObjPtr; cachePtr->firstObjPtr = objPtr->internalRep.otherValuePtr; --cachePtr->numObjects; 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->numObjects; /* * If the number of free objects has exceeded the high water mark, move * some blocks to the shared list. */ if (cachePtr->numObjects > 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. * *---------------------------------------------------------------------- */ MODULE_SCOPE void Tcl_GetMemoryInfo( Tcl_DString *dsPtr) { Cache *cachePtr; char buf[200]; unsigned int n; Tcl_MutexLock(listLockPtr); cachePtr = firstCachePtr; while (cachePtr != NULL) { Tcl_DStringStartSublist(dsPtr); if (cachePtr == sharedPtr) { Tcl_DStringAppendElement(dsPtr, "shared"); } else { sprintf(buf, "thread%p", cachePtr->owner); Tcl_DStringAppendElement(dsPtr, buf); } for (n = 0; n < NBUCKETS; ++n) { sprintf(buf, "%lu %ld %ld %ld %ld %ld %ld", (unsigned long) bucketInfo[n].blockSize, cachePtr->buckets[n].numFree, cachePtr->buckets[n].numRemoves, cachePtr->buckets[n].numInserts, cachePtr->buckets[n].totalAssigned, cachePtr->buckets[n].numLocks, cachePtr->buckets[n].numWaits); 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 numMove) { register Tcl_Obj *objPtr = fromPtr->firstObjPtr; Tcl_Obj *fromFirstObjPtr = objPtr; toPtr->numObjects += numMove; fromPtr->numObjects -= numMove; /* * 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 (--numMove) { 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->magicNum1 = blockPtr->magicNum2 = MAGIC; blockPtr->sourceBucket = bucket; blockPtr->blockReqSize = 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->magicNum1 != MAGIC || blockPtr->magicNum2 != MAGIC) { Tcl_Panic("alloc: invalid block: %p: %x %x", blockPtr, blockPtr->magicNum1, blockPtr->magicNum2); } #if RCHECK if (((unsigned char *) ptr)[blockPtr->blockReqSize] != MAGIC) { Tcl_Panic("alloc: invalid block: %p: %x %x %x", blockPtr, blockPtr->magicNum1, blockPtr->magicNum2, ((unsigned char *) ptr)[blockPtr->blockReqSize]); } #endif 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(bucketInfo[bucket].lockPtr) != TCL_OK) { Tcl_MutexLock(bucketInfo[bucket].lockPtr); ++cachePtr->buckets[bucket].numWaits; ++sharedPtr->buckets[bucket].numWaits; } #else Tcl_MutexLock(bucketInfo[bucket].lockPtr); #endif ++cachePtr->buckets[bucket].numLocks; ++sharedPtr->buckets[bucket].numLocks; } static void UnlockBucket( Cache *cachePtr, int bucket) { Tcl_MutexUnlock(bucketInfo[bucket].lockPtr); }  /* *---------------------------------------------------------------------- * * PutBlocks -- * * Return unused blocks to the shared cache. * * Results: * None. * * Side effects: * None. * *---------------------------------------------------------------------- */ static void PutBlocks( Cache *cachePtr, int bucket, int numMove) { register Block *lastPtr, *firstPtr; register int n = numMove; /* * 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->nextBlock; } cachePtr->buckets[bucket].firstPtr = lastPtr->nextBlock; cachePtr->buckets[bucket].numFree -= numMove; /* * Aquire the lock and place the list of blocks at the front of the shared * cache bucket. */ LockBucket(cachePtr, bucket); lastPtr->nextBlock = sharedPtr->buckets[bucket].firstPtr; sharedPtr->buckets[bucket].firstPtr = firstPtr; sharedPtr->buckets[bucket].numFree += numMove; 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; /* * First, atttempt to move blocks from the shared cache. Note the * potentially dirty read of numFree 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].numFree > 0) { LockBucket(cachePtr, bucket); if (sharedPtr->buckets[bucket].numFree > 0) { /* * Either move the entire list or walk the list to find the last * block to move. */ n = bucketInfo[bucket].numMove; if (n >= sharedPtr->buckets[bucket].numFree) { cachePtr->buckets[bucket].firstPtr = sharedPtr->buckets[bucket].firstPtr; cachePtr->buckets[bucket].numFree = sharedPtr->buckets[bucket].numFree; sharedPtr->buckets[bucket].firstPtr = NULL; sharedPtr->buckets[bucket].numFree = 0; } else { blockPtr = sharedPtr->buckets[bucket].firstPtr; cachePtr->buckets[bucket].firstPtr = blockPtr; sharedPtr->buckets[bucket].numFree -= n; cachePtr->buckets[bucket].numFree = n; while (--n > 0) { blockPtr = blockPtr->nextBlock; } sharedPtr->buckets[bucket].firstPtr = blockPtr->nextBlock; blockPtr->nextBlock = NULL; } } UnlockBucket(cachePtr, bucket); } if (cachePtr->buckets[bucket].numFree == 0) { register size_t size; /* * 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].numFree > 0) { size = bucketInfo[n].blockSize; blockPtr = cachePtr->buckets[n].firstPtr; cachePtr->buckets[n].firstPtr = blockPtr->nextBlock; --cachePtr->buckets[n].numFree; 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 / bucketInfo[bucket].blockSize; cachePtr->buckets[bucket].numFree = n; cachePtr->buckets[bucket].firstPtr = blockPtr; while (--n > 0) { blockPtr->nextBlock = (Block *) ((char *) blockPtr + bucketInfo[bucket].blockSize); blockPtr = blockPtr->nextBlock; } blockPtr->nextBlock = NULL; } return 1; }  /* *---------------------------------------------------------------------- * * TclFinalizeThreadAlloc -- * * This procedure is used to destroy all private resources used in this * file. * * Results: * None. * * Side effects: * None. * *---------------------------------------------------------------------- */ void TclFinalizeThreadAlloc(void) { unsigned int i; for (i = 0; i < NBUCKETS; ++i) { TclpFreeAllocMutex(bucketInfo[i].lockPtr); bucketInfo[i].lockPtr = NULL; } TclpFreeAllocMutex(objLockPtr); objLockPtr = NULL; TclpFreeAllocMutex(listLockPtr); listLockPtr = NULL; TclpFreeAllocCache(NULL); }  #else /* *---------------------------------------------------------------------- * * TclFinalizeThreadAlloc -- * * This procedure is used to destroy all private resources used in this * file. * * Results: * None. * * Side effects: * None. * *---------------------------------------------------------------------- */ void TclFinalizeThreadAlloc(void) { Tcl_Panic("TclFinalizeThreadAlloc called when threaded memory allocator not in use"); } #endif /* TCL_THREADS */  /* * Local Variables: * mode: c * c-basic-offset: 4 * fill-column: 78 * End: */

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