tclPreserve.c Go to the documentation of this file. /* * tclPreserve.c -- * * This file contains a collection of functions that are used to make * sure that widget records and other data structures aren't reallocated * when there are nested functions 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 1.10 2007/03/21 18:02:51 dgp 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; /* Function to call to free. */ } Reference; /* * Global data structures used to hold the list of preserved data references. * These variables are protected by "preserveMutex". */ static Reference *refArray = NULL; /* 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. */ TCL_DECLARE_MUTEX(preserveMutex)/* To protect the above statics */ #define INITIAL_SIZE 2 /* Initial number of reference slots to make */ /* * 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 above 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;  /* *---------------------------------------------------------------------- * * TclFinalizePreserve -- * * Called during exit processing to clean up the reference array. * * Results: * None. * * Side effects: * Frees the storage of the reference array. * *---------------------------------------------------------------------- */ /* ARGSUSED */ void TclFinalizePreserve(void) { Tcl_MutexLock(&preserveMutex); if (spaceAvl != 0) { ckfree((char *) refArray); refArray = NULL; inUse = 0; spaceAvl = 0; } Tcl_MutexUnlock(&preserveMutex); }  /* *---------------------------------------------------------------------- * * Tcl_Preserve -- * * This function is used by a function 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) /* 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) { spaceAvl = spaceAvl ? 2*spaceAvl : INITIAL_SIZE; refArray = (Reference *) ckrealloc((char *) refArray, spaceAvl * sizeof(Reference)); } /* * 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 function 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) /* Pointer to malloc'ed block of memory. */ { Reference *refPtr; int i; Tcl_MutexLock(&preserveMutex); for (i=0, refPtr=refArray ; i<inUse ; i++, refPtr++) { int mustFree; Tcl_FreeProc *freeProc; if (refPtr->clientData != clientData) { continue; } if (--refPtr->refCount != 0) { Tcl_MutexUnlock(&preserveMutex); return; } /* * 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]; } /* * Now committed to disposing the data. But first, we've patched up * all the global data structures so we should release the mutex now. * Only then should we dabble around with potentially-slow memory * managers... */ Tcl_MutexUnlock(&preserveMutex); if (mustFree) { if (freeProc == TCL_DYNAMIC) { ckfree((char *) clientData); } else { (*freeProc)((char *) clientData); } } return; } Tcl_MutexUnlock(&preserveMutex); /* * Reference not found. This is a bug in the caller. */ Tcl_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 clientData, /* Pointer to malloc'ed block of memory. */ Tcl_FreeProc *freeProc) /* Function 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) { Tcl_Panic("Tcl_EventuallyFree called twice for 0x%x", 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) { 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( 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( 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) { Tcl_Panic("using previously disposed TclHandle %x", handlePtr); } if (handlePtr->ptr2 != handlePtr->ptr) { Tcl_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( 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) { Tcl_Panic("using previously disposed TclHandle %x", handlePtr); } if ((handlePtr->ptr != NULL) && (handlePtr->ptr != handlePtr->ptr2)) { Tcl_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 function 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( 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) { Tcl_Panic("using previously disposed TclHandle %x", handlePtr); } if ((handlePtr->ptr != NULL) && (handlePtr->ptr != handlePtr->ptr2)) { Tcl_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); } }  /* * Local Variables: * mode: c * c-basic-offset: 4 * fill-column: 78 * End: */

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