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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.
 *
 * 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 1.3 1999/01/06 21:08:51 stanton Exp $
 */

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

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

typedef unsigned long caddr_t;

/*
 * The overhead on a block is at least 4 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 */
    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 */
#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];

#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));

/*
 *----------------------------------------------------------------------
 *
 * TclpAlloc --
 *
 *    Allocate more memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

char *
TclpAlloc(
    unsigned int nbytes)      /* Number of bytes to allocate. */
{
#ifdef USE_NATIVEMALLOC
    return (char*) malloc(nbytes);
#else
    register union overhead *op;
    register long bucket;
    register unsigned amt;

    /*
     * First the simple case: we simple allocate big blocks directly
     */
    if (nbytes + OVERHEAD >= MAXMALLOC) {
      op = (union overhead *)TclpSysAlloc(nbytes+OVERHEAD, 0);
      if (op == NULL) {
          return NULL;
      }
      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
      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) {
          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) {
          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
    return ((char *)(op + 1));
#endif /* USE_NATIVEMALLOC */
}

/*
 *----------------------------------------------------------------------
 *
 * MoreCore --
 *
 *    Allocate more memory to the indicated bucket.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Attempts to get more memory from the system.
 *
 *----------------------------------------------------------------------
 */

static void
MoreCore(
    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 */

    /*
     * 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);

    op = (union overhead *)TclpSysAlloc(amt, 1);
    /* no more room! */
    if (op == NULL) {
      return;
    }
    
    /*
     * 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(
    char *cp)           /* Pointer to memory to free. */
{   
#ifdef USE_NATIVEMALLOC
    free(cp);
    return;
#else
    register long size;
    register union overhead *op;

    if (cp == NULL) {
      return;
    }

    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) {
      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
      TclpSysFree(op);
      return;
    }
    ASSERT(size < NBUCKETS);
    op->ov_next = nextf[size];      /* also clobbers ov_magic */
    nextf[size] = op;
#ifdef MSTATS
    nmalloc[size]--;
#endif
#endif /* USE_NATIVEMALLOC */
}

/*
 *----------------------------------------------------------------------
 *
 * TclpRealloc --
 *
 *    Reallocate memory.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

char *
TclpRealloc(
    char *cp,                 /* Pointer to alloced block. */
    unsigned int nbytes)      /* New size of memory. */
{   
#ifdef USE_NATIVEMALLOC
    return (char*) realloc(cp, nbytes);
#else
    int i;
    union overhead *op;
    int expensive;
    unsigned long maxsize;

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

    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) {
      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) {
      op = (union overhead *) TclpSysRealloc(op, nbytes+OVERHEAD);
      if (op == NULL) {
          return NULL;
      }
#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
      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;
            
      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
    return(cp);
#endif /* USE_NATIVEMALLOC */
}

/*
 *----------------------------------------------------------------------
 *
 * 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(
    char *s)      /* Where to write info. */
{
    register int i, j;
    register union overhead *p;
    int totfree = 0,
      totused = 0;

    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]);
}
#endif


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