source: downloads/tcl8.5.2/win/tclWinThrd.c @ 68

/*
 * tclWinThread.c --
 *
 *      This file implements the Windows-specific thread operations.
 *
 * Copyright (c) 1998 by Sun Microsystems, Inc.
 * Copyright (c) 1999 by Scriptics Corporation
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclWinThrd.c,v 1.43 2007/03/24 09:33:02 vasiljevic Exp $
 */

#include "tclWinInt.h"

#include <fcntl.h>
#include <io.h>
#include <sys/stat.h>

/*
 * This is the master lock used to serialize access to other serialization
 * data structures.
 */

static CRITICAL_SECTION masterLock;
static int init = 0;
#define MASTER_LOCK TclpMasterLock()
#define MASTER_UNLOCK TclpMasterUnlock()


/*
 * This is the master lock used to serialize initialization and finalization
 * of Tcl as a whole.
 */

static CRITICAL_SECTION initLock;

/*
 * allocLock is used by Tcl's version of malloc for synchronization. For
 * obvious reasons, cannot use any dyamically allocated storage.
 */

#ifdef TCL_THREADS

static CRITICAL_SECTION allocLock;
static Tcl_Mutex allocLockPtr = (Tcl_Mutex) &allocLock;
static int allocOnce = 0;

#endif /* TCL_THREADS */

/*
 * The joinLock serializes Create- and ExitThread. This is necessary to
 * prevent a race where a new joinable thread exits before the creating thread
 * had the time to create the necessary data structures in the emulation
 * layer.
 */

static CRITICAL_SECTION joinLock;

/*
 * Condition variables are implemented with a combination of a per-thread
 * Windows Event and a per-condition waiting queue. The idea is that each
 * thread has its own Event that it waits on when it is doing a ConditionWait;
 * it uses the same event for all condition variables because it only waits on
 * one at a time. Each condition variable has a queue of waiting threads, and
 * a mutex used to serialize access to this queue.
 *
 * Special thanks to David Nichols and Jim Davidson for advice on the
 * Condition Variable implementation.
 */

/*
 * The per-thread event and queue pointers.
 */

#ifdef TCL_THREADS

typedef struct ThreadSpecificData {
    HANDLE condEvent;                   /* Per-thread condition event */
    struct ThreadSpecificData *nextPtr; /* Queue pointers */
    struct ThreadSpecificData *prevPtr;
    int flags;                          /* See flags below */
} ThreadSpecificData;
static Tcl_ThreadDataKey dataKey;

#endif /* TCL_THREADS */

/*
 * State bits for the thread.
 * WIN_THREAD_UNINIT            Uninitialized. Must be zero because of the way
 *                              ThreadSpecificData is created.
 * WIN_THREAD_RUNNING           Running, not waiting.
 * WIN_THREAD_BLOCKED           Waiting, or trying to wait.
 */

#define WIN_THREAD_UNINIT       0x0
#define WIN_THREAD_RUNNING      0x1
#define WIN_THREAD_BLOCKED      0x2

/*
 * The per condition queue pointers and the Mutex used to serialize access to
 * the queue.
 */

typedef struct WinCondition {
    CRITICAL_SECTION condLock;  /* Lock to serialize queuing on the
                                 * condition. */
    struct ThreadSpecificData *firstPtr;        /* Queue pointers */
    struct ThreadSpecificData *lastPtr;
} WinCondition;

/*
 * Additions by AOL for specialized thread memory allocator.
 */

#ifdef USE_THREAD_ALLOC
static int once;
static DWORD tlsKey;

typedef struct allocMutex {
    Tcl_Mutex        tlock;
    CRITICAL_SECTION wlock;
} allocMutex;
#endif /* USE_THREAD_ALLOC */

/*
 *----------------------------------------------------------------------
 *
 * TclpThreadCreate --
 *
 *      This procedure creates a new thread.
 *
 * Results:
 *      TCL_OK if the thread could be created. The thread ID is returned in a
 *      parameter.
 *
 * Side effects:
 *      A new thread is created.
 *
 *----------------------------------------------------------------------
 */

int
TclpThreadCreate(
    Tcl_ThreadId *idPtr,        /* Return, the ID of the thread. */
    Tcl_ThreadCreateProc proc,  /* Main() function of the thread. */
    ClientData clientData,      /* The one argument to Main(). */
    int stackSize,              /* Size of stack for the new thread. */
    int flags)                  /* Flags controlling behaviour of the new
                                 * thread. */
{
    HANDLE tHandle;

    EnterCriticalSection(&joinLock);

#if defined(_MSC_VER) || defined(__MSVCRT__) || defined(__BORLANDC__)
    tHandle = (HANDLE) _beginthreadex(NULL, (unsigned) stackSize, proc,
            clientData, 0, (unsigned *)idPtr);
#else
    tHandle = CreateThread(NULL, (DWORD) stackSize,
            (LPTHREAD_START_ROUTINE) proc, (LPVOID) clientData,
            (DWORD) 0, (LPDWORD)idPtr);
#endif

    if (tHandle == NULL) {
        LeaveCriticalSection(&joinLock);
        return TCL_ERROR;
    } else {
        if (flags & TCL_THREAD_JOINABLE) {
            TclRememberJoinableThread(*idPtr);
        }

        /*
         * The only purpose of this is to decrement the reference count so the
         * OS resources will be reaquired when the thread closes.
         */

        CloseHandle(tHandle);
        LeaveCriticalSection(&joinLock);
        return TCL_OK;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_JoinThread --
 *
 *      This procedure waits upon the exit of the specified thread.
 *
 * Results:
 *      TCL_OK if the wait was successful, TCL_ERROR else.
 *
 * Side effects:
 *      The result area is set to the exit code of the thread we
 *      waited upon.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_JoinThread(
    Tcl_ThreadId threadId,      /* Id of the thread to wait upon */
    int *result)                /* Reference to the storage the result of the
                                 * thread we wait upon will be written into. */
{
    return TclJoinThread(threadId, result);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpThreadExit --
 *
 *      This procedure terminates the current thread.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      This procedure terminates the current thread.
 *
 *----------------------------------------------------------------------
 */

void
TclpThreadExit(
    int status)
{
    EnterCriticalSection(&joinLock);
    TclSignalExitThread(Tcl_GetCurrentThread(), status);
    LeaveCriticalSection(&joinLock);

#if defined(_MSC_VER) || defined(__MSVCRT__) || defined(__BORLANDC__)
    _endthreadex((unsigned) status);
#else
    ExitThread((DWORD) status);
#endif
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetCurrentThread --
 *
 *      This procedure returns the ID of the currently running thread.
 *
 * Results:
 *      A thread ID.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

Tcl_ThreadId
Tcl_GetCurrentThread(void)
{
    return (Tcl_ThreadId) GetCurrentThreadId();
}

/*
 *----------------------------------------------------------------------
 *
 * TclpInitLock
 *
 *      This procedure is used to grab a lock that serializes initialization
 *      and finalization of Tcl. On some platforms this may also initialize
 *      the mutex used to serialize creation of more mutexes and thread local
 *      storage keys.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Acquire the initialization mutex.
 *
 *----------------------------------------------------------------------
 */

void
TclpInitLock(void)
{
    if (!init) {
        /*
         * There is a fundamental race here that is solved by creating the
         * first Tcl interpreter in a single threaded environment. Once the
         * interpreter has been created, it is safe to create more threads
         * that create interpreters in parallel.
         */

        init = 1;
        InitializeCriticalSection(&joinLock);
        InitializeCriticalSection(&initLock);
        InitializeCriticalSection(&masterLock);
    }
    EnterCriticalSection(&initLock);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpInitUnlock
 *
 *      This procedure is used to release a lock that serializes
 *      initialization and finalization of Tcl.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Release the initialization mutex.
 *
 *----------------------------------------------------------------------
 */

void
TclpInitUnlock(void)
{
    LeaveCriticalSection(&initLock);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpMasterLock
 *
 *      This procedure is used to grab a lock that serializes creation of
 *      mutexes, condition variables, and thread local storage keys.
 *
 *      This lock must be different than the initLock because the initLock is
 *      held during creation of syncronization objects.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Acquire the master mutex.
 *
 *----------------------------------------------------------------------
 */

void
TclpMasterLock(void)
{
    if (!init) {
        /*
         * There is a fundamental race here that is solved by creating the
         * first Tcl interpreter in a single threaded environment. Once the
         * interpreter has been created, it is safe to create more threads
         * that create interpreters in parallel.
         */

        init = 1;
        InitializeCriticalSection(&joinLock);
        InitializeCriticalSection(&initLock);
        InitializeCriticalSection(&masterLock);
    }
    EnterCriticalSection(&masterLock);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpMasterUnlock
 *
 *      This procedure is used to release a lock that serializes creation and
 *      deletion of synchronization objects.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Release the master mutex.
 *
 *----------------------------------------------------------------------
 */

void
TclpMasterUnlock(void)
{
    LeaveCriticalSection(&masterLock);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_GetAllocMutex
 *
 *      This procedure returns a pointer to a statically initialized mutex for
 *      use by the memory allocator. The alloctor must use this lock, because
 *      all other locks are allocated...
 *
 * Results:
 *      A pointer to a mutex that is suitable for passing to Tcl_MutexLock and
 *      Tcl_MutexUnlock.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

Tcl_Mutex *
Tcl_GetAllocMutex(void)
{
#ifdef TCL_THREADS
    if (!allocOnce) {
        InitializeCriticalSection(&allocLock);
        allocOnce = 1;
    }
    return &allocLockPtr;
#else
    return NULL;
#endif
}

/*
 *----------------------------------------------------------------------
 *
 * TclpFinalizeLock
 *
 *      This procedure is used to destroy all private resources used in this
 *      file.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      Destroys everything private. TclpInitLock must be held entering this
 *      function.
 *
 *----------------------------------------------------------------------
 */

void
TclFinalizeLock(void)
{
    MASTER_LOCK;
    DeleteCriticalSection(&joinLock);

    /*
     * Destroy the critical section that we are holding!
     */

    DeleteCriticalSection(&masterLock);
    init = 0;

#ifdef TCL_THREADS
    if (allocOnce) {
        DeleteCriticalSection(&allocLock);
        allocOnce = 0;
    }
#endif

    LeaveCriticalSection(&initLock);

    /*
     * Destroy the critical section that we were holding.
     */

    DeleteCriticalSection(&initLock);
}

#ifdef TCL_THREADS

/* locally used prototype */
static void             FinalizeConditionEvent(ClientData data);

/*
 *----------------------------------------------------------------------
 *
 * Tcl_MutexLock --
 *
 *      This procedure is invoked to lock a mutex. This is a self initializing
 *      mutex that is automatically finalized during Tcl_Finalize.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      May block the current thread. The mutex is aquired when this returns.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_MutexLock(
    Tcl_Mutex *mutexPtr)        /* The lock */
{
    CRITICAL_SECTION *csPtr;
    if (*mutexPtr == NULL) {
        MASTER_LOCK;

        /*
         * Double inside master lock check to avoid a race.
         */

        if (*mutexPtr == NULL) {
            csPtr = (CRITICAL_SECTION *) ckalloc(sizeof(CRITICAL_SECTION));
            InitializeCriticalSection(csPtr);
            *mutexPtr = (Tcl_Mutex)csPtr;
            TclRememberMutex(mutexPtr);
        }
        MASTER_UNLOCK;
    }
    csPtr = *((CRITICAL_SECTION **)mutexPtr);
    EnterCriticalSection(csPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_MutexUnlock --
 *
 *      This procedure is invoked to unlock a mutex.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      The mutex is released when this returns.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_MutexUnlock(
    Tcl_Mutex *mutexPtr)        /* The lock */
{
    CRITICAL_SECTION *csPtr = *((CRITICAL_SECTION **)mutexPtr);
    LeaveCriticalSection(csPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpFinalizeMutex --
 *
 *      This procedure is invoked to clean up one mutex. This is only safe to
 *      call at the end of time.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      The mutex list is deallocated.
 *
 *----------------------------------------------------------------------
 */

void
TclpFinalizeMutex(
    Tcl_Mutex *mutexPtr)
{
    CRITICAL_SECTION *csPtr = *(CRITICAL_SECTION **)mutexPtr;
    if (csPtr != NULL) {
        DeleteCriticalSection(csPtr);
        ckfree((char *) csPtr);
        *mutexPtr = NULL;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ConditionWait --
 *
 *      This procedure is invoked to wait on a condition variable. The mutex
 *      is atomically released as part of the wait, and automatically grabbed
 *      when the condition is signaled.
 *
 *      The mutex must be held when this procedure is called.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      May block the current thread. The mutex is aquired when this returns.
 *      Will allocate memory for a HANDLE and initialize this the first time
 *      this Tcl_Condition is used.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_ConditionWait(
    Tcl_Condition *condPtr,     /* Really (WinCondition **) */
    Tcl_Mutex *mutexPtr,        /* Really (CRITICAL_SECTION **) */
    Tcl_Time *timePtr)          /* Timeout on waiting period */
{
    WinCondition *winCondPtr;   /* Per-condition queue head */
    CRITICAL_SECTION *csPtr;    /* Caller's Mutex, after casting */
    DWORD wtime;                /* Windows time value */
    int timeout;                /* True if we got a timeout */
    int doExit = 0;             /* True if we need to do exit setup */
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    /*
     * Self initialize the two parts of the condition. The per-condition and
     * per-thread parts need to be handled independently.
     */

    if (tsdPtr->flags == WIN_THREAD_UNINIT) {
        MASTER_LOCK;

        /*
         * Create the per-thread event and queue pointers.
         */

        if (tsdPtr->flags == WIN_THREAD_UNINIT) {
            tsdPtr->condEvent = CreateEvent(NULL, TRUE /* manual reset */,
                    FALSE /* non signaled */, NULL);
            tsdPtr->nextPtr = NULL;
            tsdPtr->prevPtr = NULL;
            tsdPtr->flags = WIN_THREAD_RUNNING;
            doExit = 1;
        }
        MASTER_UNLOCK;

        if (doExit) {
            /*
             * Create a per-thread exit handler to clean up the condEvent. We
             * must be careful to do this outside the Master Lock because
             * Tcl_CreateThreadExitHandler uses its own ThreadSpecificData,
             * and initializing that may drop back into the Master Lock.
             */

            Tcl_CreateThreadExitHandler(FinalizeConditionEvent,
                    (ClientData) tsdPtr);
        }
    }

    if (*condPtr == NULL) {
        MASTER_LOCK;

        /*
         * Initialize the per-condition queue pointers and Mutex.
         */

        if (*condPtr == NULL) {
            winCondPtr = (WinCondition *)ckalloc(sizeof(WinCondition));
            InitializeCriticalSection(&winCondPtr->condLock);
            winCondPtr->firstPtr = NULL;
            winCondPtr->lastPtr = NULL;
            *condPtr = (Tcl_Condition)winCondPtr;
            TclRememberCondition(condPtr);
        }
        MASTER_UNLOCK;
    }
    csPtr = *((CRITICAL_SECTION **)mutexPtr);
    winCondPtr = *((WinCondition **)condPtr);
    if (timePtr == NULL) {
        wtime = INFINITE;
    } else {
        wtime = timePtr->sec * 1000 + timePtr->usec / 1000;
    }

    /*
     * Queue the thread on the condition, using the per-condition lock for
     * serialization.
     */

    tsdPtr->flags = WIN_THREAD_BLOCKED;
    tsdPtr->nextPtr = NULL;
    EnterCriticalSection(&winCondPtr->condLock);
    tsdPtr->prevPtr = winCondPtr->lastPtr;              /* A: */
    winCondPtr->lastPtr = tsdPtr;
    if (tsdPtr->prevPtr != NULL) {
        tsdPtr->prevPtr->nextPtr = tsdPtr;
    }
    if (winCondPtr->firstPtr == NULL) {
        winCondPtr->firstPtr = tsdPtr;
    }

    /*
     * Unlock the caller's mutex and wait for the condition, or a timeout.
     * There is a minor issue here in that we don't count down the timeout if
     * we get notified, but another thread grabs the condition before we do.
     * In that race condition we'll wait again for the full timeout. Timed
     * waits are dubious anyway. Either you have the locking protocol wrong
     * and are masking a deadlock, or you are using conditions to pause your
     * thread.
     */

    LeaveCriticalSection(csPtr);
    timeout = 0;
    while (!timeout && (tsdPtr->flags & WIN_THREAD_BLOCKED)) {
        ResetEvent(tsdPtr->condEvent);
        LeaveCriticalSection(&winCondPtr->condLock);
        if (WaitForSingleObject(tsdPtr->condEvent, wtime) == WAIT_TIMEOUT) {
            timeout = 1;
        }
        EnterCriticalSection(&winCondPtr->condLock);
    }

    /*
     * Be careful on timeouts because the signal might arrive right around the
     * time limit and someone else could have taken us off the queue.
     */

    if (timeout) {
        if (tsdPtr->flags & WIN_THREAD_RUNNING) {
            timeout = 0;
        } else {
            /*
             * When dequeuing, we can leave the tsdPtr->nextPtr and
             * tsdPtr->prevPtr with dangling pointers because they are
             * reinitialilzed w/out reading them when the thread is enqueued
             * later.
             */

            if (winCondPtr->firstPtr == tsdPtr) {
                winCondPtr->firstPtr = tsdPtr->nextPtr;
            } else {
                tsdPtr->prevPtr->nextPtr = tsdPtr->nextPtr;
            }
            if (winCondPtr->lastPtr == tsdPtr) {
                winCondPtr->lastPtr = tsdPtr->prevPtr;
            } else {
                tsdPtr->nextPtr->prevPtr = tsdPtr->prevPtr;
            }
            tsdPtr->flags = WIN_THREAD_RUNNING;
        }
    }

    LeaveCriticalSection(&winCondPtr->condLock);
    EnterCriticalSection(csPtr);
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ConditionNotify --
 *
 *      This procedure is invoked to signal a condition variable.
 *
 *      The mutex must be held during this call to avoid races, but this
 *      interface does not enforce that.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      May unblock another thread.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_ConditionNotify(
    Tcl_Condition *condPtr)
{
    WinCondition *winCondPtr;
    ThreadSpecificData *tsdPtr;
    if (*condPtr != NULL) {
        winCondPtr = *((WinCondition **)condPtr);

        if (winCondPtr == NULL) {
            return;
        }

        /*
         * Loop through all the threads waiting on the condition and notify
         * them (i.e., broadcast semantics). The queue manipulation is guarded
         * by the per-condition coordinating mutex.
         */

        EnterCriticalSection(&winCondPtr->condLock);
        while (winCondPtr->firstPtr != NULL) {
            tsdPtr = winCondPtr->firstPtr;
            winCondPtr->firstPtr = tsdPtr->nextPtr;
            if (winCondPtr->lastPtr == tsdPtr) {
                winCondPtr->lastPtr = NULL;
            }
            tsdPtr->flags = WIN_THREAD_RUNNING;
            tsdPtr->nextPtr = NULL;
            tsdPtr->prevPtr = NULL;     /* Not strictly necessary, see A: */
            SetEvent(tsdPtr->condEvent);
        }
        LeaveCriticalSection(&winCondPtr->condLock);
    } else {
        /*
         * No-one has used the condition variable, so there are no waiters.
         */
    }
}

/*
 *----------------------------------------------------------------------
 *
 * FinalizeConditionEvent --
 *
 *      This procedure is invoked to clean up the per-thread event used to
 *      implement condition waiting. This is only safe to call at the end of
 *      time.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      The per-thread event is closed.
 *
 *----------------------------------------------------------------------
 */

static void
FinalizeConditionEvent(
    ClientData data)
{
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *) data;
    tsdPtr->flags = WIN_THREAD_UNINIT;
    CloseHandle(tsdPtr->condEvent);
}

/*
 *----------------------------------------------------------------------
 *
 * TclpFinalizeCondition --
 *
 *      This procedure is invoked to clean up a condition variable. This is
 *      only safe to call at the end of time.
 *
 *      This assumes the Master Lock is held.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      The condition variable is deallocated.
 *
 *----------------------------------------------------------------------
 */

void
TclpFinalizeCondition(
    Tcl_Condition *condPtr)
{
    WinCondition *winCondPtr = *(WinCondition **)condPtr;

    /*
     * Note - this is called long after the thread-local storage is reclaimed.
     * The per-thread condition waiting event is reclaimed earlier in a
     * per-thread exit handler, which is called before thread local storage is
     * reclaimed.
     */

    if (winCondPtr != NULL) {
        DeleteCriticalSection(&winCondPtr->condLock);
        ckfree((char *) winCondPtr);
        *condPtr = NULL;
    }
}

/*
 * Additions by AOL for specialized thread memory allocator.
 */
#ifdef USE_THREAD_ALLOC

Tcl_Mutex *
TclpNewAllocMutex(void)
{
    struct allocMutex *lockPtr;

    lockPtr = malloc(sizeof(struct allocMutex));
    if (lockPtr == NULL) {
        Tcl_Panic("could not allocate lock");
    }
    lockPtr->tlock = (Tcl_Mutex) &lockPtr->wlock;
    InitializeCriticalSection(&lockPtr->wlock);
    return &lockPtr->tlock;
}

void
TclpFreeAllocMutex(
    Tcl_Mutex *mutex)           /* The alloc mutex to free. */
{
    allocMutex *lockPtr = (allocMutex *) mutex;

    if (!lockPtr) {
        return;
    }
    DeleteCriticalSection(&lockPtr->wlock);
    free(lockPtr);
}

void *
TclpGetAllocCache(void)
{
    VOID *result;

    if (!once) {
        /*
         * We need to make sure that TclpFreeAllocCache is called on each
         * thread that calls this, but only on threads that call this.
         */

        tlsKey = TlsAlloc();
        once = 1;
        if (tlsKey == TLS_OUT_OF_INDEXES) {
            Tcl_Panic("could not allocate thread local storage");
        }
    }

    result = TlsGetValue(tlsKey);
    if ((result == NULL) && (GetLastError() != NO_ERROR)) {
        Tcl_Panic("TlsGetValue failed from TclpGetAllocCache");
    }
    return result;
}

void
TclpSetAllocCache(
    void *ptr)
{
    BOOL success;
    success = TlsSetValue(tlsKey, ptr);
    if (!success) {
        Tcl_Panic("TlsSetValue failed from TclpSetAllocCache");
    }
}

void
TclpFreeAllocCache(
    void *ptr)
{
    BOOL success;

    if (ptr != NULL) {
        /*
         * Called by us in TclpFinalizeThreadData when a thread exits and
         * destroys the tsd key which stores allocator caches.
         */

        TclFreeAllocCache(ptr);
        success = TlsSetValue(tlsKey, NULL);
        if (!success) {
            Tcl_Panic("TlsSetValue failed from TclpFreeAllocCache");
        }
    } else if (once) {
        /*
         * Called by us in TclFinalizeThreadAlloc() during the library
         * finalization initiated from Tcl_Finalize()
         */

        success = TlsFree(tlsKey);
        if (!success) {
            Tcl_Panic("TlsFree failed from TclpFreeAllocCache");
        }
        once = 0; /* reset for next time. */
    }

}
#endif /* USE_THREAD_ALLOC */
#endif /* TCL_THREADS */

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */