tclalloc.c

tcl是工具命令语言

/* 
 * 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 1.16 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"

#if USE_TCLALLOC

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

/*
 * We should really make use of AC_CHECK_TYPE(caddr_t)
 * here, but it can wait until Tcl uses config.h properly.
 */
#if defined(MAC_TCL) || defined(_MSC_VER) || defined(__MINGW32__) || defined(__BORLANDC__)
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 --