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tclAlloc.c

/* 
 * tclAlloc.c --
 *
 *    This is a very fast storage allocator.  It allocates blocks of a
 *    small number of different sizes, and keeps free lists of each size.
 *    Blocks that don't exactly fit are passed up to the next larger size.
 *    Blocks over a certain size are directly allocated from the system.
 *
 * Copyright (c) 1983 Regents of the University of California.
 * Copyright (c) 1996-1997 Sun Microsystems, Inc.
 * Copyright (c) 1998-1999 by Scriptics Corporation.
 *
 * Portions contributed by Chris Kingsley, Jack Jansen and Ray Johnson.
 *
 * 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 1.9 2000/04/21 04:04:12 hobbs Exp $
 */

#include "tclInt.h"
#include "tclPort.h"

#if USE_TCLALLOC

#ifdef TCL_DEBUG
#   define DEBUG
/* #define MSTATS */
#   define RCHECK
#endif

/*
 * On Unix this will already be defined
 */
#if defined(WIN32) || defined(MAC_TCL)
typedef unsigned long caddr_t;
#endif

/*
 * The overhead on a block is at least 8 bytes.  When free, this space
 * contains a pointer to the next free block, and the bottom two bits must
 * be zero.  When in use, the first byte is set to MAGIC, and the second
 * byte is the size index.  The remaining bytes are for alignment.
 * If range checking is enabled then a second word holds the size of the
 * requested block, less 1, rounded up to a multiple of sizeof(RMAGIC).
 * The order of elements is critical: ov_magic must overlay the low order
 * bits of ov_next, and ov_magic can not be a valid ov_next bit pattern.
 */

union overhead {
    union overhead *ov_next;  /* when free */
    unsigned char ov_padding[8]; /* Ensure the structure is 8-byte aligned. */
    struct {
      unsigned char     ovu_magic0; /* magic number */
      unsigned char     ovu_index;  /* bucket # */
      unsigned char     ovu_unused; /* unused */
      unsigned char     ovu_magic1; /* other magic number */
#ifdef RCHECK
      unsigned short    ovu_rmagic; /* range magic number */
      unsigned long     ovu_size;   /* actual block size */
      unsigned short  ovu_unused2;    /* padding to 8-byte align */
#endif
    } ovu;
#define ov_magic0 ovu.ovu_magic0
#define ov_magic1 ovu.ovu_magic1
#define ov_index  ovu.ovu_index
#define ov_rmagic ovu.ovu_rmagic
#define ov_size         ovu.ovu_size
};


#define MAGIC           0xef        /* magic # on accounting info */
#define RMAGIC          0x5555            /* magic # on range info */

#ifdef RCHECK
#define     RSLOP       sizeof (unsigned short)
#else
#define     RSLOP       0
#endif

#define OVERHEAD (sizeof(union overhead) + RSLOP)

/*
 * nextf[i] is the pointer to the next free block of size 2^(i+3).  The
 * smallest allocatable block is 8 bytes.  The overhead information
 * precedes the data area returned to the user.
 */

#define NBUCKETS  13
#define MAXMALLOC (1<<(NBUCKETS+2))
static      union overhead *nextf[NBUCKETS];

/* 
 * The following structure is used to keep track of all system memory 
 * currently owned by Tcl.  When finalizing, all this memory will
 * be returned to the system.
 */

struct block {
    struct block *nextPtr;    /* Linked list. */
    struct block *prevPtr;    /* Linked list for big blocks, ensures 8-byte 
                         * alignment for suballocated blocks. */
};

static struct block *blockList;           /* Tracks the suballocated blocks. */
static struct block bigBlocks = {   /* Big blocks aren't suballocated. */
    &bigBlocks, &bigBlocks
};

/*
 * The allocator is protected by a special mutex that must be
 * explicitly initialized.  Futhermore, because Tcl_Alloc may be
 * used before anything else in Tcl, we make this module self-initializing
 * after all with the allocInit variable.
 */

#ifdef TCL_THREADS
static Tcl_Mutex *allocMutexPtr;
#endif
static int allocInit = 0;


#ifdef MSTATS

/*
 * nmalloc[i] is the difference between the number of mallocs and frees
 * for a given block size.
 */

static      unsigned int nmalloc[NBUCKETS+1];
#include <stdio.h>
#endif

#if defined(DEBUG) || defined(RCHECK)
#define     ASSERT(p)   if (!(p)) panic(# p)
#define RANGE_ASSERT(p) if (!(p)) panic(# p)
#else
#define     ASSERT(p)
#define RANGE_ASSERT(p)
#endif

/*
 * Prototypes for functions used only in this file.
 */

static void             MoreCore _ANSI_ARGS_((int bucket));


/*
 *-------------------------------------------------------------------------
 *
 * TclInitAlloc --
 *
 *    Initialize the memory system.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Initialize the mutex used to serialize allocations.
 *
 *-------------------------------------------------------------------------
 */

void
TclInitAlloc()
{
    if (!allocInit) {
      allocInit = 1;
#ifdef TCL_THREADS
      allocMutexPtr = Tcl_GetAllocMutex();
#endif
    }
}

/*
 *-------------------------------------------------------------------------
 *
 * TclFinalizeAllocSubsystem --
 *
 *    Release all resources being used by this subsystem, including 
 *    aggressively freeing all memory allocated by TclpAlloc() that 
 *    has not yet been released with TclpFree().
 *    
 *    After this function is called, all memory allocated with 
 *    TclpAlloc() should be considered unusable.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    This subsystem is self-initializing, since memory can be 
 *    allocated before Tcl is formally initialized.  After this call,
 *    this subsystem has been reset to its initial state and is 
 *    usable again.
 *
 *-------------------------------------------------------------------------
 */

void
TclFinalizeAllocSubsystem()
{
    int i;
    struct block *blockPtr, *nextPtr;

    Tcl_MutexLock(allocMutexPtr);
    for (blockPtr = blockList; blockPtr != NULL; blockPtr = nextPtr) {
      nextPtr = blockPtr->nextPtr;
      TclpSysFree(blockPtr);
    }
    blockList = NULL;

    for (blockPtr = bigBlocks.nextPtr; blockPtr != &bigBlocks; ) {
      nextPtr = blockPtr->nextPtr;
      TclpSysFree(blockPtr);
      blockPtr = nextPtr;
    }
    bigBlocks.nextPtr = &bigBlocks;
    bigBlocks.prevPtr = &bigBlocks;

    for (i = 0; i < NBUCKETS; i++) {
      nextf[i] = NULL;
#ifdef MSTATS
      nmalloc[i] = 0;
#endif
    }
#ifdef MSTATS
    nmalloc[i] = 0;
#endif
    Tcl_MutexUnlock(allocMutexPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpAlloc --
 *
 *    Allocate more memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

char *
TclpAlloc(nbytes)
    unsigned int nbytes;      /* Number of bytes to allocate. */
{
    register union overhead *op;
    register long bucket;
    register unsigned amt;
    struct block *bigBlockPtr;

    if (!allocInit) {
      /*
       * We have to make the "self initializing" because Tcl_Alloc
       * may be used before any other part of Tcl.  E.g., see
       * main() for tclsh!
       */
      TclInitAlloc();
    }
    Tcl_MutexLock(allocMutexPtr);
    /*
     * First the simple case: we simple allocate big blocks directly
     */
    if (nbytes + OVERHEAD >= MAXMALLOC) {
      bigBlockPtr = (struct block *) TclpSysAlloc((unsigned) 
            (sizeof(struct block) + OVERHEAD + nbytes), 0);
      if (bigBlockPtr == NULL) {
          Tcl_MutexUnlock(allocMutexPtr);
          return NULL;
      }
      bigBlockPtr->nextPtr = bigBlocks.nextPtr;
      bigBlocks.nextPtr = bigBlockPtr;
      bigBlockPtr->prevPtr = &bigBlocks;
      bigBlockPtr->nextPtr->prevPtr = bigBlockPtr;

      op = (union overhead *) (bigBlockPtr + 1);
      op->ov_magic0 = op->ov_magic1 = MAGIC;
      op->ov_index = 0xff;
#ifdef MSTATS
      nmalloc[NBUCKETS]++;
#endif
#ifdef RCHECK
      /*
       * Record allocated size of block and
       * bound space with magic numbers.
       */
      op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1);
      op->ov_rmagic = RMAGIC;
      *(unsigned short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC;
#endif
      Tcl_MutexUnlock(allocMutexPtr);
      return (void *)(op+1);
    }
    /*
     * Convert amount of memory requested into closest block size
     * stored in hash buckets which satisfies request.
     * Account for space used per block for accounting.
     */
#ifndef RCHECK
    amt = 8;      /* size of first bucket */
    bucket = 0;
#else
    amt = 16;     /* size of first bucket */
    bucket = 1;
#endif
    while (nbytes + OVERHEAD > amt) {
      amt <<= 1;
      if (amt == 0) {
          Tcl_MutexUnlock(allocMutexPtr);
          return (NULL);
      }
      bucket++;
    }
    ASSERT( bucket < NBUCKETS );

    /*
     * If nothing in hash bucket right now,
     * request more memory from the system.
     */
    if ((op = nextf[bucket]) == NULL) {
      MoreCore(bucket);
      if ((op = nextf[bucket]) == NULL) {
          Tcl_MutexUnlock(allocMutexPtr);
          return (NULL);
      }
    }
    /*
     * Remove from linked list
     */
    nextf[bucket] = op->ov_next;
    op->ov_magic0 = op->ov_magic1 = MAGIC;
    op->ov_index = (unsigned char) bucket;
#ifdef MSTATS
    nmalloc[bucket]++;
#endif
#ifdef RCHECK
    /*
     * Record allocated size of block and
     * bound space with magic numbers.
     */
    op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1);
    op->ov_rmagic = RMAGIC;
    *(unsigned short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC;
#endif
    Tcl_MutexUnlock(allocMutexPtr);
    return ((char *)(op + 1));
}

/*
 *----------------------------------------------------------------------
 *
 * MoreCore --
 *
 *    Allocate more memory to the indicated bucket.
 *
 *    Assumes Mutex is already held.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Attempts to get more memory from the system.
 *
 *----------------------------------------------------------------------
 */

static void
MoreCore(bucket)
    int bucket;         /* What bucket to allocat to. */
{
    register union overhead *op;
    register long sz;         /* size of desired block */
    long amt;                 /* amount to allocate */
    int nblks;                /* how many blocks we get */
    struct block *blockPtr;

    /*
     * sbrk_size <= 0 only for big, FLUFFY, requests (about
     * 2^30 bytes on a VAX, I think) or for a negative arg.
     */
    sz = 1 << (bucket + 3);
    ASSERT(sz > 0);

    amt = MAXMALLOC;
    nblks = amt / sz;
    ASSERT(nblks*sz == amt);

    blockPtr = (struct block *) TclpSysAlloc((unsigned) 
          (sizeof(struct block) + amt), 1);
    /* no more room! */
    if (blockPtr == NULL) {
      return;
    }
    blockPtr->nextPtr = blockList;
    blockList = blockPtr;

    op = (union overhead *) (blockPtr + 1);
    
    /*
     * Add new memory allocated to that on
     * free list for this hash bucket.
     */
    nextf[bucket] = op;
    while (--nblks > 0) {
      op->ov_next = (union overhead *)((caddr_t)op + sz);
      op = (union overhead *)((caddr_t)op + sz);
    }
    op->ov_next = (union overhead *)NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * TclpFree --
 *
 *    Free memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
TclpFree(cp)
    char *cp;           /* Pointer to memory to free. */
{   
    register long size;
    register union overhead *op;
    struct block *bigBlockPtr;

    if (cp == NULL) {
      return;
    }

    Tcl_MutexLock(allocMutexPtr);
    op = (union overhead *)((caddr_t)cp - sizeof (union overhead));

    ASSERT(op->ov_magic0 == MAGIC);       /* make sure it was in use */
    ASSERT(op->ov_magic1 == MAGIC);
    if (op->ov_magic0 != MAGIC || op->ov_magic1 != MAGIC) {
      Tcl_MutexUnlock(allocMutexPtr);
      return;
    }

    RANGE_ASSERT(op->ov_rmagic == RMAGIC);
    RANGE_ASSERT(*(unsigned short *)((caddr_t)(op + 1) + op->ov_size) == RMAGIC);
    size = op->ov_index;
    if ( size == 0xff ) {
#ifdef MSTATS
      nmalloc[NBUCKETS]--;
#endif
      bigBlockPtr = (struct block *) op - 1;
      bigBlockPtr->prevPtr->nextPtr = bigBlockPtr->nextPtr;
      bigBlockPtr->nextPtr->prevPtr = bigBlockPtr->prevPtr;
      TclpSysFree(bigBlockPtr);
      Tcl_MutexUnlock(allocMutexPtr);
      return;
    }
    ASSERT(size < NBUCKETS);
    op->ov_next = nextf[size];      /* also clobbers ov_magic */
    nextf[size] = op;
#ifdef MSTATS
    nmalloc[size]--;
#endif
    Tcl_MutexUnlock(allocMutexPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpRealloc --
 *
 *    Reallocate memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

char *
TclpRealloc(cp, nbytes)
    char *cp;                 /* Pointer to alloced block. */
    unsigned int nbytes;      /* New size of memory. */
{   
    int i;
    union overhead *op;
    struct block *bigBlockPtr;
    int expensive;
    unsigned long maxsize;

    if (cp == NULL) {
      return (TclpAlloc(nbytes));
    }

    Tcl_MutexLock(allocMutexPtr);

    op = (union overhead *)((caddr_t)cp - sizeof (union overhead));

    ASSERT(op->ov_magic0 == MAGIC);       /* make sure it was in use */
    ASSERT(op->ov_magic1 == MAGIC);
    if (op->ov_magic0 != MAGIC || op->ov_magic1 != MAGIC) {
      Tcl_MutexUnlock(allocMutexPtr);
      return NULL;
    }

    RANGE_ASSERT(op->ov_rmagic == RMAGIC);
    RANGE_ASSERT(*(unsigned short *)((caddr_t)(op + 1) + op->ov_size) == RMAGIC);
    i = op->ov_index;

    /*
     * If the block isn't in a bin, just realloc it.
     */

    if (i == 0xff) {
      struct block *prevPtr, *nextPtr;
      bigBlockPtr = (struct block *) op - 1;
      prevPtr = bigBlockPtr->prevPtr;
      nextPtr = bigBlockPtr->nextPtr;
      bigBlockPtr = (struct block *) TclpSysRealloc(bigBlockPtr, 
            sizeof(struct block) + OVERHEAD + nbytes);
      if (bigBlockPtr == NULL) {
          Tcl_MutexUnlock(allocMutexPtr);
          return NULL;
      }

      if (prevPtr->nextPtr != bigBlockPtr) {
          /*
           * If the block has moved, splice the new block into the list where
           * the old block used to be. 
           */

          prevPtr->nextPtr = bigBlockPtr;
          nextPtr->prevPtr = bigBlockPtr;
      }

      op = (union overhead *) (bigBlockPtr + 1);
#ifdef MSTATS
      nmalloc[NBUCKETS]++;
#endif
#ifdef RCHECK
      /*
       * Record allocated size of block and update magic number bounds.
       */

      op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1);
      *(unsigned short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC;
#endif
      Tcl_MutexUnlock(allocMutexPtr);
      return (char *)(op+1);
    }
    maxsize = 1 << (i+3);
    expensive = 0;
    if ( nbytes + OVERHEAD > maxsize ) {
      expensive = 1;
    } else if ( i > 0 && nbytes + OVERHEAD < (maxsize/2) ) {
      expensive = 1;
    }

    if (expensive) {
      void *newp;

      Tcl_MutexUnlock(allocMutexPtr);

      newp = TclpAlloc(nbytes);
      if ( newp == NULL ) {
          return NULL;
      }
      maxsize -= OVERHEAD;
      if ( maxsize < nbytes )
          nbytes = maxsize;
      memcpy((VOID *) newp, (VOID *) cp, (size_t) nbytes);
      TclpFree(cp);
      return newp;
    }
    
    /*
     * Ok, we don't have to copy, it fits as-is
     */
#ifdef RCHECK
    op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1);
    *(unsigned short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC;
#endif
    Tcl_MutexUnlock(allocMutexPtr);
    return(cp);
}

/*
 *----------------------------------------------------------------------
 *
 * mstats --
 *
 *    Prints two lines of numbers, one showing the length of the 
 *    free list for each size category, the second showing the 
 *    number of mallocs - frees for each size category.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

#ifdef MSTATS
void
mstats(s)
    char *s;      /* Where to write info. */
{
    register int i, j;
    register union overhead *p;
    int totfree = 0,
      totused = 0;

    Tcl_MutexLock(allocMutexPtr);
    fprintf(stderr, "Memory allocation statistics %s\nTclpFree:\t", s);
    for (i = 0; i < NBUCKETS; i++) {
      for (j = 0, p = nextf[i]; p; p = p->ov_next, j++)
          fprintf(stderr, " %d", j);
      totfree += j * (1 << (i + 3));
    }
    fprintf(stderr, "\nused:\t");
    for (i = 0; i < NBUCKETS; i++) {
      fprintf(stderr, " %d", nmalloc[i]);
      totused += nmalloc[i] * (1 << (i + 3));
    }
    fprintf(stderr, "\n\tTotal small in use: %d, total free: %d\n",
          totused, totfree);
    fprintf(stderr, "\n\tNumber of big (>%d) blocks in use: %d\n", 
          MAXMALLOC, nmalloc[NBUCKETS]);
    Tcl_MutexUnlock(allocMutexPtr);
}
#endif

#else  /* !USE_TCLALLOC */

/*
 *----------------------------------------------------------------------
 *
 * TclpAlloc --
 *
 *    Allocate more memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

char *
TclpAlloc(nbytes)
    unsigned int nbytes;      /* Number of bytes to allocate. */
{
    return (char*) malloc(nbytes);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpFree --
 *
 *    Free memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
TclpFree(cp)
    char *cp;           /* Pointer to memory to free. */
{   
    free(cp);
    return;
}

/*
 *----------------------------------------------------------------------
 *
 * TclpRealloc --
 *
 *    Reallocate memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

char *
TclpRealloc(cp, nbytes)
    char *cp;                 /* Pointer to alloced block. */
    unsigned int nbytes;      /* New size of memory. */
{   
    return (char*) realloc(cp, nbytes);
}

#endif /* !USE_TCLALLOC */

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