tclpreserve.c

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/* 
 * tclPreserve.c --
 *
 *	This file contains a collection of procedures that are used
 *	to make sure that widget records and other data structures
 *	aren't reallocated when there are nested procedures that
 *	depend on their existence.
 *
 * Copyright (c) 1991-1994 The Regents of the University of California.
 * Copyright (c) 1994-1998 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclPreserve.c,v 1.3 1999/04/16 00:46:52 stanton Exp $
 */

#include "tclInt.h"

/*
 * The following data structure is used to keep track of all the
 * Tcl_Preserve calls that are still in effect.  It grows as needed
 * to accommodate any number of calls in effect.
 */

typedef struct {
    ClientData clientData;	/* Address of preserved block. */
    int refCount;		/* Number of Tcl_Preserve calls in effect
				 * for block. */
    int mustFree;		/* Non-zero means Tcl_EventuallyFree was
				 * called while a Tcl_Preserve call was in
				 * effect, so the structure must be freed
				 * when refCount becomes zero. */
    Tcl_FreeProc *freeProc;	/* Procedure to call to free. */
} Reference;

static Reference *refArray;	/* First in array of references. */
static int spaceAvl = 0;	/* Total number of structures available
				 * at *firstRefPtr. */
static int inUse = 0;		/* Count of structures currently in use
				 * in refArray. */
#define INITIAL_SIZE 2
TCL_DECLARE_MUTEX(preserveMutex)/* To protect the above statics */

/*
 * The following data structure is used to keep track of whether an
 * arbitrary block of memory has been deleted.  This is used by the
 * TclHandle code to avoid the more time-expensive algorithm of
 * Tcl_Preserve().  This mechanism is mainly used when we have lots of
 * references to a few big, expensive objects that we don't want to live
 * any longer than necessary.
 */

typedef struct HandleStruct {
    VOID *ptr;			/* Pointer to the memory block being
				 * tracked.  This field will become NULL when
				 * the memory block is deleted.  This field
				 * must be the first in the structure. */
#ifdef TCL_MEM_DEBUG
    VOID *ptr2;			/* Backup copy of the abpve pointer used to
				 * ensure that the contents of the handle are
				 * not changed by anyone else. */
#endif
    int refCount;		/* Number of TclHandlePreserve() calls in
				 * effect on this handle. */
} HandleStruct;


/*
 * Static routines in this file:
 */

static void	PreserveExitProc _ANSI_ARGS_((ClientData clientData));


/*
 *----------------------------------------------------------------------
 *
 * PreserveExitProc --
 *
 *	Called during exit processing to clean up the reference array.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Frees the storage of the reference array.
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
static void
PreserveExitProc(clientData)
    ClientData clientData;		/* NULL -Unused. */
{
    Tcl_MutexLock(&preserveMutex);
    if (spaceAvl != 0) {
        ckfree((char *) refArray);
        refArray = (Reference *) NULL;
        inUse = 0;
        spaceAvl = 0;
    }
    Tcl_MutexUnlock(&preserveMutex);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Preserve --
 *
 *	This procedure is used by a procedure to declare its interest
 *	in a particular block of memory, so that the block will not be
 *	reallocated until a matching call to Tcl_Release has been made.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Information is retained so that the block of memory will
 *	not be freed until at least the matching call to Tcl_Release.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_Preserve(clientData)
    ClientData clientData;	/* Pointer to malloc'ed block of memory. */
{
    Reference *refPtr;
    int i;

    /*
     * See if there is already a reference for this pointer.  If so,
     * just increment its reference count.
     */

    Tcl_MutexLock(&preserveMutex);
    for (i = 0, refPtr = refArray; i < inUse; i++, refPtr++) {
	if (refPtr->clientData == clientData) {
	    refPtr->refCount++;
	    Tcl_MutexUnlock(&preserveMutex);
	    return;
	}
    }

    /*
     * Make a reference array if it doesn't already exist, or make it
     * bigger if it is full.
     */

    if (inUse == spaceAvl) {
	if (spaceAvl == 0) {
            Tcl_CreateExitHandler((Tcl_ExitProc *) PreserveExitProc,
                    (ClientData) NULL);
	    refArray = (Reference *) ckalloc((unsigned)
		    (INITIAL_SIZE*sizeof(Reference)));
	    spaceAvl = INITIAL_SIZE;
	} else {
	    Reference *new;

	    new = (Reference *) ckalloc((unsigned)
		    (2*spaceAvl*sizeof(Reference)));
	    memcpy((VOID *) new, (VOID *) refArray,
                    spaceAvl*sizeof(Reference));
	    ckfree((char *) refArray);
	    refArray = new;
	    spaceAvl *= 2;
	}
    }

    /*
     * Make a new entry for the new reference.
     */

    refPtr = &refArray[inUse];
    refPtr->clientData = clientData;
    refPtr->refCount = 1;
    refPtr->mustFree = 0;
    refPtr->freeProc = TCL_STATIC;
    inUse += 1;
    Tcl_MutexUnlock(&preserveMutex);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_Release --
 *
 *	This procedure is called to cancel a previous call to
 *	Tcl_Preserve, thereby allowing a block of memory to be
 *	freed (if no one else cares about it).
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If Tcl_EventuallyFree has been called for clientData, and if
 *	no other call to Tcl_Preserve is still in effect, the block of
 *	memory is freed.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_Release(clientData)
    ClientData clientData;	/* Pointer to malloc'ed block of memory. */
{
    Reference *refPtr;
    int mustFree;
    Tcl_FreeProc *freeProc;
    int i;

    Tcl_MutexLock(&preserveMutex);
    for (i = 0, refPtr = refArray; i < inUse; i++, refPtr++) {
	if (refPtr->clientData != clientData) {
	    continue;
	}
	refPtr->refCount--;
	if (refPtr->refCount == 0) {

            /*
             * Must remove information from the slot before calling freeProc
             * to avoid reentrancy problems if the freeProc calls Tcl_Preserve
             * on the same clientData. Copy down the last reference in the
             * array to overwrite the current slot.
             */

            freeProc = refPtr->freeProc;
            mustFree = refPtr->mustFree;
	    inUse--;
	    if (i < inUse) {
		refArray[i] = refArray[inUse];
	    }
	    if (mustFree) {
		if ((freeProc == TCL_DYNAMIC) ||
                        (freeProc == (Tcl_FreeProc *) free)) {
		    ckfree((char *) clientData);
		} else {
		    Tcl_MutexUnlock(&preserveMutex);
		    (*freeProc)((char *) clientData);
		    return;
		}
	    }
	}
	Tcl_MutexUnlock(&preserveMutex);
	return;
    }
    Tcl_MutexUnlock(&preserveMutex);

    /*
     * Reference not found.  This is a bug in the caller.
     */

    panic("Tcl_Release couldn't find reference for 0x%x", clientData);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_EventuallyFree --
 *
 *	Free up a block of memory, unless a call to Tcl_Preserve is in
 *	effect for that block.  In this case, defer the free until all
 *	calls to Tcl_Preserve have been undone by matching calls to
 *	Tcl_Release.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Ptr may be released by calling free().
 *
 *----------------------------------------------------------------------
 */

void
Tcl_EventuallyFree(clientData, freeProc)
    ClientData clientData;	/* Pointer to malloc'ed block of memory. */
    Tcl_FreeProc *freeProc;	/* Procedure to actually do free. */
{
    Reference *refPtr;
    int i;

    /*
     * See if there is a reference for this pointer.  If so, set its
     * "mustFree" flag (the flag had better not be set already!).
     */

    Tcl_MutexLock(&preserveMutex);
    for (i = 0, refPtr = refArray; i < inUse; i++, refPtr++) {
	if (refPtr->clientData != clientData) {
	    continue;
	}
	if (refPtr->mustFree) {
	    panic("Tcl_EventuallyFree called twice for 0x%x\n", clientData);
        }
        refPtr->mustFree = 1;
	refPtr->freeProc = freeProc;
	Tcl_MutexUnlock(&preserveMutex);
        return;
    }
    Tcl_MutexUnlock(&preserveMutex);

    /*
     * No reference for this block.  Free it now.
     */

    if ((freeProc == TCL_DYNAMIC)
	    || (freeProc == (Tcl_FreeProc *) free)) {
	ckfree((char *) clientData);
    } else {
	(*freeProc)((char *)clientData);
    }
}

/*
 *---------------------------------------------------------------------------
 *
 * TclHandleCreate --
 *
 *	Allocate a handle that contains enough information to determine
 *	if an arbitrary malloc'd block has been deleted.  This is 
 *	used to avoid the more time-expensive algorithm of Tcl_Preserve().
 *
 * Results:
 *	The return value is a TclHandle that refers to the given malloc'd
 *	block.  Doubly dereferencing the returned handle will give
 *	back the pointer to the block, or will give NULL if the block has
 *	been deleted.
 *
 * Side effects:
 *	The caller must keep track of this handle (generally by storing
 *	it in a field in the malloc'd block) and call TclHandleFree()
 *	on this handle when the block is deleted.  Everything else that
 *	wishes to keep track of whether the malloc'd block has been deleted
 *	should use calls to TclHandlePreserve() and TclHandleRelease()
 *	on the associated handle.
 *
 *---------------------------------------------------------------------------
 */

TclHandle
TclHandleCreate(ptr)
    VOID *ptr;			/* Pointer to an arbitrary block of memory
				 * to be tracked for deletion.  Must not be
				 * NULL. */
{
    HandleStruct *handlePtr;

    handlePtr = (HandleStruct *) ckalloc(sizeof(HandleStruct));
    handlePtr->ptr = ptr;
#ifdef TCL_MEM_DEBUG
    handlePtr->ptr2 = ptr;
#endif
    handlePtr->refCount = 0;
    return (TclHandle) handlePtr;
}

/*
 *---------------------------------------------------------------------------
 *
 * TclHandleFree --
 *
 *	Called when the arbitrary malloc'd block associated with the
 *	handle is being deleted.  Modifies the handle so that doubly
 *	dereferencing it will give NULL.  This informs any user of the
 *	handle that the block of memory formerly referenced by the
 *	handle has been freed.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	If nothing is referring to the handle, the handle will be reclaimed.
 *
 *---------------------------------------------------------------------------
 */

void
TclHandleFree(handle)
    TclHandle handle;		/* Previously created handle associated
				 * with a malloc'd block that is being
				 * deleted.  The handle is modified so that
				 * doubly dereferencing it will give NULL. */
{
    HandleStruct *handlePtr;

    handlePtr = (HandleStruct *) handle;
#ifdef TCL_MEM_DEBUG
    if (handlePtr->refCount == 0x61616161) {
	panic("using previously disposed TclHandle %x", handlePtr);
    }
    if (handlePtr->ptr2 != handlePtr->ptr) {
	panic("someone has changed the block referenced by the handle %x\nfrom %x to %x",
		handlePtr, handlePtr->ptr2, handlePtr->ptr);
    }
#endif
    handlePtr->ptr = NULL;
    if (handlePtr->refCount == 0) {
	ckfree((char *) handlePtr);
    }
}

/*
 *---------------------------------------------------------------------------
 *
 * TclHandlePreserve --
 *
 *	Declare an interest in the arbitrary malloc'd block associated
 *	with the handle.  
 *
 * Results:
 *	The return value is the handle argument, with its ref count
 *	incremented.
 *
 * Side effects:
 *	For each call to TclHandlePreserve(), there should be a matching
 *	call to TclHandleRelease() when the caller is no longer interested
 *	in the malloc'd block associated with the handle.
 *
 *---------------------------------------------------------------------------
 */

TclHandle
TclHandlePreserve(handle)
    TclHandle handle;		/* Declare an interest in the block of
				 * memory referenced by this handle. */
{
    HandleStruct *handlePtr;

    handlePtr = (HandleStruct *) handle;
#ifdef TCL_MEM_DEBUG
    if (handlePtr->refCount == 0x61616161) {
	panic("using previously disposed TclHandle %x", handlePtr);
    }
    if ((handlePtr->ptr != NULL)
	    && (handlePtr->ptr != handlePtr->ptr2)) {
	panic("someone has changed the block referenced by the handle %x\nfrom %x to %x",
		handlePtr, handlePtr->ptr2, handlePtr->ptr);
    }
#endif
    handlePtr->refCount++;

    return handle;
}

/*
 *---------------------------------------------------------------------------
 *
 * TclHandleRelease --
 *
 *	This procedure is called to release an interest in the malloc'd
 *	block associated with the handle.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The ref count of the handle is decremented.  If the malloc'd block
 *	has been freed and if no one is using the handle any more, the
 *	handle will be reclaimed.
 *
 *---------------------------------------------------------------------------
 */
 
void
TclHandleRelease(handle)
    TclHandle handle;		/* Unregister interest in the block of
				 * memory referenced by this handle. */
{
    HandleStruct *handlePtr;

    handlePtr = (HandleStruct *) handle;
#ifdef TCL_MEM_DEBUG
    if (handlePtr->refCount == 0x61616161) {
	panic("using previously disposed TclHandle %x", handlePtr);
    }
    if ((handlePtr->ptr != NULL)
	    && (handlePtr->ptr != handlePtr->ptr2)) {
	panic("someone has changed the block referenced by the handle %x\nfrom %x to %x",
		handlePtr, handlePtr->ptr2, handlePtr->ptr);
    }
#endif
    handlePtr->refCount--;
    if ((handlePtr->refCount == 0) && (handlePtr->ptr == NULL)) {
	ckfree((char *) handlePtr);
    }
}