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tclUnixNotfy.c

/*
 * tclUnixNotify.c --
 *
 *    This file contains the implementation of the select()-based
 *    Unix-specific notifier, which is the lowest-level part of the Tcl
 *    event loop. This file works together with generic/tclNotify.c.
 *
 * Copyright (c) 1995-1997 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: tclUnixNotfy.c,v 1.32 2006/08/21 01:08:03 das Exp $
 */

#include "tclInt.h"
#ifndef HAVE_COREFOUNDATION   /* Darwin/Mac OS X CoreFoundation notifier is
                         * in tclMacOSXNotify.c */
#include <signal.h>

/*
 * This code does deep stub magic to allow replacement of the notifier at
 * runtime.
 */

extern TclStubs tclStubs;
extern Tcl_NotifierProcs tclOriginalNotifier;

/*
 * This structure is used to keep track of the notifier info for a registered
 * file.
 */

typedef struct FileHandler {
    int fd;
    int mask;                 /* Mask of desired events: TCL_READABLE,
                         * etc. */
    int readyMask;            /* Mask of events that have been seen since
                         * the last time file handlers were invoked
                         * for this file. */
    Tcl_FileProc *proc;       /* Function to call, in the style of
                         * Tcl_CreateFileHandler. */
    ClientData clientData;    /* Argument to pass to proc. */
    struct FileHandler *nextPtr;/* Next in list of all files we care about. */
} FileHandler;

/*
 * The following structure is what is added to the Tcl event queue when file
 * handlers are ready to fire.
 */

typedef struct FileHandlerEvent {
    Tcl_Event header;         /* Information that is standard for all
                         * events. */
    int fd;             /* File descriptor that is ready. Used to find
                         * the FileHandler structure for the file
                         * (can't point directly to the FileHandler
                         * structure because it could go away while
                         * the event is queued). */
} FileHandlerEvent;

/*
 * The following structure contains a set of select() masks to track readable,
 * writable, and exceptional conditions.
 */

typedef struct SelectMasks {
    fd_set readable;
    fd_set writable;
    fd_set exceptional;
} SelectMasks;

/*
 * The following static structure contains the state information for the
 * select based implementation of the Tcl notifier. One of these structures is
 * created for each thread that is using the notifier.
 */

typedef struct ThreadSpecificData {
    FileHandler *firstFileHandlerPtr;
                        /* Pointer to head of file handler list. */
    SelectMasks checkMasks;   /* This structure is used to build up the
                         * masks to be used in the next call to
                         * select. Bits are set in response to calls
                         * to Tcl_CreateFileHandler. */
    SelectMasks readyMasks;   /* This array reflects the readable/writable
                         * conditions that were found to exist by the
                         * last call to select. */
    int numFdBits;            /* Number of valid bits in checkMasks (one
                         * more than highest fd for which
                         * Tcl_WatchFile has been called). */
#ifdef TCL_THREADS
    int onList;               /* True if it is in this list */
    unsigned int pollState;   /* pollState is used to implement a polling
                         * handshake between each thread and the
                         * notifier thread. Bits defined below. */
    struct ThreadSpecificData *nextPtr, *prevPtr;
                        /* All threads that are currently waiting on
                         * an event have their ThreadSpecificData
                         * structure on a doubly-linked listed formed
                         * from these pointers. You must hold the
                         * notifierMutex lock before accessing these
                         * fields. */
    Tcl_Condition waitCV;     /* Any other thread alerts a notifier that an
                         * event is ready to be processed by signaling
                         * this condition variable. */
    int eventReady;           /* True if an event is ready to be processed.
                         * Used as condition flag together with waitCV
                         * above. */
#endif
} ThreadSpecificData;

static Tcl_ThreadDataKey dataKey;

#ifdef TCL_THREADS
/*
 * The following static indicates the number of threads that have initialized
 * notifiers.
 *
 * You must hold the notifierMutex lock before accessing this variable.
 */

static int notifierCount = 0;

/*
 * The following variable points to the head of a doubly-linked list of
 * ThreadSpecificData structures for all threads that are currently waiting on
 * an event.
 *
 * You must hold the notifierMutex lock before accessing this list.
 */

static ThreadSpecificData *waitingListPtr = NULL;

/*
 * The notifier thread spends all its time in select() waiting for a file
 * descriptor associated with one of the threads on the waitingListPtr list to
 * do something interesting. But if the contents of the waitingListPtr list
 * ever changes, we need to wake up and restart the select() system call. You
 * can wake up the notifier thread by writing a single byte to the file
 * descriptor defined below. This file descriptor is the input-end of a pipe
 * and the notifier thread is listening for data on the output-end of the same
 * pipe. Hence writing to this file descriptor will cause the select() system
 * call to return and wake up the notifier thread.
 *
 * You must hold the notifierMutex lock before accessing this list.
 */

static int triggerPipe = -1;

/*
 * The notifierMutex locks access to all of the global notifier state.
 */

TCL_DECLARE_MUTEX(notifierMutex)

/*
 * The notifier thread signals the notifierCV when it has finished
 * initializing the triggerPipe and right before the notifier thread
 * terminates.
 */

static Tcl_Condition notifierCV;

/*
 * The pollState bits
 *    POLL_WANT is set by each thread before it waits on its condition
 *          variable. It is checked by the notifier before it does select.
 *    POLL_DONE is set by the notifier if it goes into select after seeing
 *          POLL_WANT. The idea is to ensure it tries a select with the
 *          same bits the initial thread had set.
 */

#define POLL_WANT 0x1
#define POLL_DONE 0x2

/*
 * This is the thread ID of the notifier thread that does select.
 */

static Tcl_ThreadId notifierThread;

#endif

/*
 * Static routines defined in this file.
 */

#ifdef TCL_THREADS
static void NotifierThreadProc(ClientData clientData);
#endif
static int  FileHandlerEventProc(Tcl_Event *evPtr, int flags);

/*
 *----------------------------------------------------------------------
 *
 * Tcl_InitNotifier --
 *
 *    Initializes the platform specific notifier state.
 *
 * Results:
 *    Returns a handle to the notifier state for this thread..
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

ClientData
Tcl_InitNotifier(void)
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

#ifdef TCL_THREADS
    tsdPtr->eventReady = 0;

    /*
     * Start the Notifier thread if necessary.
     */

    Tcl_MutexLock(&notifierMutex);
    if (notifierCount == 0) {
      if (TclpThreadCreate(&notifierThread, NotifierThreadProc, NULL,
            TCL_THREAD_STACK_DEFAULT, TCL_THREAD_JOINABLE) != TCL_OK) {
          Tcl_Panic("Tcl_InitNotifier: unable to start notifier thread");
      }
    }
    notifierCount++;

    /*
     * Wait for the notifier pipe to be created.
     */

    while (triggerPipe < 0) {
      Tcl_ConditionWait(&notifierCV, &notifierMutex, NULL);
    }

    Tcl_MutexUnlock(&notifierMutex);
#endif
    return (ClientData) tsdPtr;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_FinalizeNotifier --
 *
 *    This function is called to cleanup the notifier state before a thread
 *    is terminated.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    May terminate the background notifier thread if this is the last
 *    notifier instance.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_FinalizeNotifier(
    ClientData clientData)          /* Not used. */
{
#ifdef TCL_THREADS
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    Tcl_MutexLock(&notifierMutex);
    notifierCount--;

    /*
     * If this is the last thread to use the notifier, close the notifier pipe
     * and wait for the background thread to terminate.
     */

    if (notifierCount == 0) {
      int result;

      if (triggerPipe < 0) {
          Tcl_Panic("Tcl_FinalizeNotifier: notifier pipe not initialized");
      }

      /*
       * Send "q" message to the notifier thread so that it will terminate.
       * The notifier will return from its call to select() and notice that
       * a "q" message has arrived, it will then close its side of the pipe
       * and terminate its thread. Note the we can not just close the pipe
       * and check for EOF in the notifier thread because if a background
       * child process was created with exec, select() would not register
       * the EOF on the pipe until the child processes had terminated. [Bug:
       * 4139] [Bug: 1222872]
       */

      write(triggerPipe, "q", 1);
      close(triggerPipe);
      while(triggerPipe >= 0) {
          Tcl_ConditionWait(&notifierCV, &notifierMutex, NULL);
      }

      result = Tcl_JoinThread(notifierThread, NULL);
      if (result) {
          Tcl_Panic("Tcl_FinalizeNotifier: unable to join notifier thread");
      }
    }

    /*
     * Clean up any synchronization objects in the thread local storage.
     */

    Tcl_ConditionFinalize(&(tsdPtr->waitCV));

    Tcl_MutexUnlock(&notifierMutex);
#endif
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_AlertNotifier --
 *
 *    Wake up the specified notifier from any thread. This routine is called
 *    by the platform independent notifier code whenever the Tcl_ThreadAlert
 *    routine is called. This routine is guaranteed not to be called on a
 *    given notifier after Tcl_FinalizeNotifier is called for that notifier.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Signals the notifier condition variable for the specified notifier.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_AlertNotifier(
    ClientData clientData)
{
#ifdef TCL_THREADS
    ThreadSpecificData *tsdPtr = (ThreadSpecificData *) clientData;
    Tcl_MutexLock(&notifierMutex);
    tsdPtr->eventReady = 1;
    Tcl_ConditionNotify(&tsdPtr->waitCV);
    Tcl_MutexUnlock(&notifierMutex);
#endif
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_SetTimer --
 *
 *    This function sets the current notifier timer value. This interface is
 *    not implemented in this notifier because we are always running inside
 *    of Tcl_DoOneEvent.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_SetTimer(
    Tcl_Time *timePtr)        /* Timeout value, may be NULL. */
{
    /*
     * The interval timer doesn't do anything in this implementation, because
     * the only event loop is via Tcl_DoOneEvent, which passes timeout values
     * to Tcl_WaitForEvent.
     */

    if (tclStubs.tcl_SetTimer != tclOriginalNotifier.setTimerProc) {
      tclStubs.tcl_SetTimer(timePtr);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_ServiceModeHook --
 *
 *    This function is invoked whenever the service mode changes.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    None.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_ServiceModeHook(
    int mode)                 /* Either TCL_SERVICE_ALL, or
                         * TCL_SERVICE_NONE. */
{
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_CreateFileHandler --
 *
 *    This function registers a file handler with the select notifier.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Creates a new file handler structure.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_CreateFileHandler(
    int fd,             /* Handle of stream to watch. */
    int mask,                 /* OR'ed combination of TCL_READABLE,
                         * TCL_WRITABLE, and TCL_EXCEPTION: indicates
                         * conditions under which proc should be
                         * called. */
    Tcl_FileProc *proc,       /* Function to call for each selected
                         * event. */
    ClientData clientData)    /* Arbitrary data to pass to proc. */
{
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);
    FileHandler *filePtr;

    if (tclStubs.tcl_CreateFileHandler !=
          tclOriginalNotifier.createFileHandlerProc) {
      tclStubs.tcl_CreateFileHandler(fd, mask, proc, clientData);
      return;
    }

    for (filePtr = tsdPtr->firstFileHandlerPtr; filePtr != NULL;
          filePtr = filePtr->nextPtr) {
      if (filePtr->fd == fd) {
          break;
      }
    }
    if (filePtr == NULL) {
      filePtr = (FileHandler*) ckalloc(sizeof(FileHandler));
      filePtr->fd = fd;
      filePtr->readyMask = 0;
      filePtr->nextPtr = tsdPtr->firstFileHandlerPtr;
      tsdPtr->firstFileHandlerPtr = filePtr;
    }
    filePtr->proc = proc;
    filePtr->clientData = clientData;
    filePtr->mask = mask;

    /*
     * Update the check masks for this file.
     */

    if (mask & TCL_READABLE) {
      FD_SET(fd, &(tsdPtr->checkMasks.readable));
    } else {
      FD_CLR(fd, &(tsdPtr->checkMasks.readable));
    }
    if (mask & TCL_WRITABLE) {
      FD_SET(fd, &(tsdPtr->checkMasks.writable));
    } else {
      FD_CLR(fd, &(tsdPtr->checkMasks.writable));
    }
    if (mask & TCL_EXCEPTION) {
      FD_SET(fd, &(tsdPtr->checkMasks.exceptional));
    } else {
      FD_CLR(fd, &(tsdPtr->checkMasks.exceptional));
    }
    if (tsdPtr->numFdBits <= fd) {
      tsdPtr->numFdBits = fd+1;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_DeleteFileHandler --
 *
 *    Cancel a previously-arranged callback arrangement for a file.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    If a callback was previously registered on file, remove it.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_DeleteFileHandler(
    int fd)             /* Stream id for which to remove callback
                         * function. */
{
    FileHandler *filePtr, *prevPtr;
    int i;
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if (tclStubs.tcl_DeleteFileHandler !=
          tclOriginalNotifier.deleteFileHandlerProc) {
      tclStubs.tcl_DeleteFileHandler(fd);
      return;
    }

    /*
     * Find the entry for the given file (and return if there isn't one).
     */

    for (prevPtr = NULL, filePtr = tsdPtr->firstFileHandlerPtr; ;
       prevPtr = filePtr, filePtr = filePtr->nextPtr) {
      if (filePtr == NULL) {
          return;
      }
      if (filePtr->fd == fd) {
          break;
      }
    }

    /*
     * Update the check masks for this file.
     */

    if (filePtr->mask & TCL_READABLE) {
      FD_CLR(fd, &(tsdPtr->checkMasks.readable));
    }
    if (filePtr->mask & TCL_WRITABLE) {
      FD_CLR(fd, &(tsdPtr->checkMasks.writable));
    }
    if (filePtr->mask & TCL_EXCEPTION) {
      FD_CLR(fd, &(tsdPtr->checkMasks.exceptional));
    }

    /*
     * Find current max fd.
     */

    if (fd+1 == tsdPtr->numFdBits) {
      tsdPtr->numFdBits = 0;
      for (i = fd-1; i >= 0; i--) {
          if (FD_ISSET(i, &(tsdPtr->checkMasks.readable))
                || FD_ISSET(i, &(tsdPtr->checkMasks.writable))
                || FD_ISSET(i, &(tsdPtr->checkMasks.exceptional))) {
            tsdPtr->numFdBits = i+1;
            break;
          }
      }
    }

    /*
     * Clean up information in the callback record.
     */

    if (prevPtr == NULL) {
      tsdPtr->firstFileHandlerPtr = filePtr->nextPtr;
    } else {
      prevPtr->nextPtr = filePtr->nextPtr;
    }
    ckfree((char *) filePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * FileHandlerEventProc --
 *
 *    This function is called by Tcl_ServiceEvent when a file event reaches
 *    the front of the event queue. This function is responsible for
 *    actually handling the event by invoking the callback for the file
 *    handler.
 *
 * Results:
 *    Returns 1 if the event was handled, meaning it should be removed from
 *    the queue. Returns 0 if the event was not handled, meaning it should
 *    stay on the queue. The only time the event isn't handled is if the
 *    TCL_FILE_EVENTS flag bit isn't set.
 *
 * Side effects:
 *    Whatever the file handler's callback function does.
 *
 *----------------------------------------------------------------------
 */

static int
FileHandlerEventProc(
    Tcl_Event *evPtr,         /* Event to service. */
    int flags)                /* Flags that indicate what events to handle,
                         * such as TCL_FILE_EVENTS. */
{
    int mask;
    FileHandler *filePtr;
    FileHandlerEvent *fileEvPtr = (FileHandlerEvent *) evPtr;
    ThreadSpecificData *tsdPtr;

    if (!(flags & TCL_FILE_EVENTS)) {
      return 0;
    }

    /*
     * Search through the file handlers to find the one whose handle matches
     * the event. We do this rather than keeping a pointer to the file handler
     * directly in the event, so that the handler can be deleted while the
     * event is queued without leaving a dangling pointer.
     */

    tsdPtr = TCL_TSD_INIT(&dataKey);
    for (filePtr = tsdPtr->firstFileHandlerPtr; filePtr != NULL;
          filePtr = filePtr->nextPtr) {
      if (filePtr->fd != fileEvPtr->fd) {
          continue;
      }

      /*
       * The code is tricky for two reasons:
       * 1. The file handler's desired events could have changed since the
       *    time when the event was queued, so AND the ready mask with the
       *    desired mask.
       * 2. The file could have been closed and re-opened since the time
       *    when the event was queued. This is why the ready mask is stored
       *    in the file handler rather than the queued event: it will be
       *    zeroed when a new file handler is created for the newly opened
       *    file.
       */

      mask = filePtr->readyMask & filePtr->mask;
      filePtr->readyMask = 0;
      if (mask != 0) {
          (*filePtr->proc)(filePtr->clientData, mask);
      }
      break;
    }
    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_WaitForEvent --
 *
 *    This function is called by Tcl_DoOneEvent to wait for new events on
 *    the message queue. If the block time is 0, then Tcl_WaitForEvent just
 *    polls without blocking.
 *
 * Results:
 *    Returns -1 if the select would block forever, otherwise returns 0.
 *
 * Side effects:
 *    Queues file events that are detected by the select.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_WaitForEvent(
    Tcl_Time *timePtr)        /* Maximum block time, or NULL. */
{
    FileHandler *filePtr;
    FileHandlerEvent *fileEvPtr;
    int mask;
    Tcl_Time myTime;
#ifdef TCL_THREADS
    int waitForFiles;
    Tcl_Time *myTimePtr;
#else
    /*
     * Impl. notes: timeout & timeoutPtr are used if, and only if threads are
     * not enabled. They are the arguments for the regular select() used when
     * the core is not thread-enabled.
     */

    struct timeval timeout, *timeoutPtr;
    int numFound;
#endif /* TCL_THREADS */
    ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

    if (tclStubs.tcl_WaitForEvent != tclOriginalNotifier.waitForEventProc) {
      return tclStubs.tcl_WaitForEvent(timePtr);
    }

    /*
     * Set up the timeout structure. Note that if there are no events to check
     * for, we return with a negative result rather than blocking forever.
     */

    if (timePtr != NULL) {
      /*
       * TIP #233 (Virtualized Time). Is virtual time in effect? And do we
       * actually have something to scale? If yes to both then we call the
       * handler to do this scaling.
       */

      myTime.sec  = timePtr->sec;
      myTime.usec = timePtr->usec;

      if (myTime.sec != 0 || myTime.usec != 0) {
          (*tclScaleTimeProcPtr) (&myTime, tclTimeClientData);
      }

#ifdef TCL_THREADS
      myTimePtr = &myTime;
#else
      timeout.tv_sec = myTime.sec;
      timeout.tv_usec = myTime.usec;
      timeoutPtr = &timeout;
#endif /* TCL_THREADS */

#ifndef TCL_THREADS
    } else if (tsdPtr->numFdBits == 0) {
      /*
       * If there are no threads, no timeout, and no fds registered, then
       * there are no events possible and we must avoid deadlock. Note that
       * this is not entirely correct because there might be a signal that
       * could interrupt the select call, but we don't handle that case if
       * we aren't using threads.
       */

      return -1;
#endif /* !TCL_THREADS */
    } else {
#ifdef TCL_THREADS
      myTimePtr = NULL;
#else
      timeoutPtr = NULL;
#endif /* TCL_THREADS */
    }

#ifdef TCL_THREADS
    /*
     * Place this thread on the list of interested threads, signal the
     * notifier thread, and wait for a response or a timeout.
     */

    Tcl_MutexLock(&notifierMutex);

    waitForFiles = (tsdPtr->numFdBits > 0);
    if (myTimePtr != NULL && myTimePtr->sec == 0 && (myTimePtr->usec == 0
#if defined(__APPLE__) && defined(__LP64__)
          /*
           * On 64-bit Darwin, pthread_cond_timedwait() appears to have a bug
           * that causes it to wait forever when passed an absolute time which
           * has already been exceeded by the system time; as a workaround,
           * when given a very brief timeout, just do a poll. [Bug 1457797]
           */
          || myTimePtr->usec < 10
#endif
          )) {
      /*
       * Cannot emulate a polling select with a polling condition variable.
       * Instead, pretend to wait for files and tell the notifier thread
       * what we are doing. The notifier thread makes sure it goes through
       * select with its select mask in the same state as ours currently is.
       * We block until that happens.
       */

      waitForFiles = 1;
      tsdPtr->pollState = POLL_WANT;
      myTimePtr = NULL;
    } else {
      tsdPtr->pollState = 0;
    }

    if (waitForFiles) {
      /*
       * Add the ThreadSpecificData structure of this thread to the list of
       * ThreadSpecificData structures of all threads that are waiting on
       * file events.
       */

      tsdPtr->nextPtr = waitingListPtr;
      if (waitingListPtr) {
          waitingListPtr->prevPtr = tsdPtr;
      }
      tsdPtr->prevPtr = 0;
      waitingListPtr = tsdPtr;
      tsdPtr->onList = 1;

      write(triggerPipe, "", 1);
    }

    FD_ZERO(&(tsdPtr->readyMasks.readable));
    FD_ZERO(&(tsdPtr->readyMasks.writable));
    FD_ZERO(&(tsdPtr->readyMasks.exceptional));

    if (!tsdPtr->eventReady) {
      Tcl_ConditionWait(&tsdPtr->waitCV, &notifierMutex, myTimePtr);
    }
    tsdPtr->eventReady = 0;

    if (waitForFiles && tsdPtr->onList) {
      /*
       * Remove the ThreadSpecificData structure of this thread from the
       * waiting list. Alert the notifier thread to recompute its select
       * masks - skipping this caused a hang when trying to close a pipe
       * which the notifier thread was still doing a select on.
       */

      if (tsdPtr->prevPtr) {
          tsdPtr->prevPtr->nextPtr = tsdPtr->nextPtr;
      } else {
          waitingListPtr = tsdPtr->nextPtr;
      }
      if (tsdPtr->nextPtr) {
          tsdPtr->nextPtr->prevPtr = tsdPtr->prevPtr;
      }
      tsdPtr->nextPtr = tsdPtr->prevPtr = NULL;
      tsdPtr->onList = 0;
      write(triggerPipe, "", 1);
    }

#else
    tsdPtr->readyMasks = tsdPtr->checkMasks;
    numFound = select(tsdPtr->numFdBits, &(tsdPtr->readyMasks.readable),
          &(tsdPtr->readyMasks.writable), &(tsdPtr->readyMasks.exceptional),
          timeoutPtr);

    /*
     * Some systems don't clear the masks after an error, so we have to do it
     * here.
     */

    if (numFound == -1) {
      FD_ZERO(&(tsdPtr->readyMasks.readable));
      FD_ZERO(&(tsdPtr->readyMasks.writable));
      FD_ZERO(&(tsdPtr->readyMasks.exceptional));
    }
#endif /* TCL_THREADS */

    /*
     * Queue all detected file events before returning.
     */

    for (filePtr = tsdPtr->firstFileHandlerPtr; (filePtr != NULL);
          filePtr = filePtr->nextPtr) {

      mask = 0;
      if (FD_ISSET(filePtr->fd, &(tsdPtr->readyMasks.readable))) {
          mask |= TCL_READABLE;
      }
      if (FD_ISSET(filePtr->fd, &(tsdPtr->readyMasks.writable))) {
          mask |= TCL_WRITABLE;
      }
      if (FD_ISSET(filePtr->fd, &(tsdPtr->readyMasks.exceptional))) {
          mask |= TCL_EXCEPTION;
      }

      if (!mask) {
          continue;
      }

      /*
       * Don't bother to queue an event if the mask was previously non-zero
       * since an event must still be on the queue.
       */

      if (filePtr->readyMask == 0) {
          fileEvPtr = (FileHandlerEvent *) ckalloc(sizeof(FileHandlerEvent));
          fileEvPtr->header.proc = FileHandlerEventProc;
          fileEvPtr->fd = filePtr->fd;
          Tcl_QueueEvent((Tcl_Event *) fileEvPtr, TCL_QUEUE_TAIL);
      }
      filePtr->readyMask = mask;
    }
#ifdef TCL_THREADS
    Tcl_MutexUnlock(&notifierMutex);
#endif /* TCL_THREADS */
    return 0;
}

#ifdef TCL_THREADS
/*
 *----------------------------------------------------------------------
 *
 * NotifierThreadProc --
 *
 *    This routine is the initial (and only) function executed by the
 *    special notifier thread. Its job is to wait for file descriptors to
 *    become readable or writable or to have an exception condition and then
 *    to notify other threads who are interested in this information by
 *    signalling a condition variable. Other threads can signal this
 *    notifier thread of a change in their interests by writing a single
 *    byte to a special pipe that the notifier thread is monitoring.
 *
 * Result:
 *    None. Once started, this routine never exits. It dies with the overall
 *    process.
 *
 * Side effects:
 *    The trigger pipe used to signal the notifier thread is created when
 *    the notifier thread first starts.
 *
 *----------------------------------------------------------------------
 */

static void
NotifierThreadProc(
    ClientData clientData)    /* Not used. */
{
    ThreadSpecificData *tsdPtr;
    fd_set readableMask;
    fd_set writableMask;
    fd_set exceptionalMask;
    int fds[2];
    int i, status, numFdBits = 0, receivePipe;
    long found;
    struct timeval poll = {0., 0.}, *timePtr;
    char buf[2];

    if (pipe(fds) != 0) {
      Tcl_Panic("NotifierThreadProc: could not create trigger pipe");
    }

    receivePipe = fds[0];

#ifndef USE_FIONBIO
    status = fcntl(receivePipe, F_GETFL);
    status |= O_NONBLOCK;
    if (fcntl(receivePipe, F_SETFL, status) < 0) {
      Tcl_Panic("NotifierThreadProc: could not make receive pipe non blocking");
    }
    status = fcntl(fds[1], F_GETFL);
    status |= O_NONBLOCK;
    if (fcntl(fds[1], F_SETFL, status) < 0) {
      Tcl_Panic("NotifierThreadProc: could not make trigger pipe non blocking");
    }
#else
    if (ioctl(receivePipe, (int) FIONBIO, &status) < 0) {
      Tcl_Panic("NotifierThreadProc: could not make receive pipe non blocking");
    }
    if (ioctl(fds[1], (int) FIONBIO, &status) < 0) {
      Tcl_Panic("NotifierThreadProc: could not make trigger pipe non blocking");
    }
#endif /* FIONBIO */

    /*
     * Install the write end of the pipe into the global variable.
     */

    Tcl_MutexLock(&notifierMutex);
    triggerPipe = fds[1];

    /*
     * Signal any threads that are waiting.
     */

    Tcl_ConditionNotify(&notifierCV);
    Tcl_MutexUnlock(&notifierMutex);

    /*
     * Look for file events and report them to interested threads.
     */

    while (1) {
      FD_ZERO(&readableMask);
      FD_ZERO(&writableMask);
      FD_ZERO(&exceptionalMask);

      /*
       * Compute the logical OR of the select masks from all the waiting
       * notifiers.
       */

      Tcl_MutexLock(&notifierMutex);
      timePtr = NULL;
      for (tsdPtr = waitingListPtr; tsdPtr; tsdPtr = tsdPtr->nextPtr) {
          for (i = tsdPtr->numFdBits-1; i >= 0; --i) {
            if (FD_ISSET(i, &(tsdPtr->checkMasks.readable))) {
                FD_SET(i, &readableMask);
            }
            if (FD_ISSET(i, &(tsdPtr->checkMasks.writable))) {
                FD_SET(i, &writableMask);
            }
            if (FD_ISSET(i, &(tsdPtr->checkMasks.exceptional))) {
                FD_SET(i, &exceptionalMask);
            }
          }
          if (tsdPtr->numFdBits > numFdBits) {
            numFdBits = tsdPtr->numFdBits;
          }
          if (tsdPtr->pollState & POLL_WANT) {
            /*
             * Here we make sure we go through select() with the same mask
             * bits that were present when the thread tried to poll.
             */

            tsdPtr->pollState |= POLL_DONE;
            timePtr = &poll;
          }
      }
      Tcl_MutexUnlock(&notifierMutex);

      /*
       * Set up the select mask to include the receive pipe.
       */

      if (receivePipe >= numFdBits) {
          numFdBits = receivePipe + 1;
      }
      FD_SET(receivePipe, &readableMask);

      if (select(numFdBits, &readableMask, &writableMask, &exceptionalMask,
            timePtr) == -1) {
          /*
           * Try again immediately on an error.
           */

          continue;
      }

      /*
       * Alert any threads that are waiting on a ready file descriptor.
       */

      Tcl_MutexLock(&notifierMutex);
      for (tsdPtr = waitingListPtr; tsdPtr; tsdPtr = tsdPtr->nextPtr) {
          found = 0;

          for (i = tsdPtr->numFdBits-1; i >= 0; --i) {
            if (FD_ISSET(i, &(tsdPtr->checkMasks.readable))
                  && FD_ISSET(i, &readableMask)) {
                FD_SET(i, &(tsdPtr->readyMasks.readable));
                found = 1;
            }
            if (FD_ISSET(i, &(tsdPtr->checkMasks.writable))
                  && FD_ISSET(i, &writableMask)) {
                FD_SET(i, &(tsdPtr->readyMasks.writable));
                found = 1;
            }
            if (FD_ISSET(i, &(tsdPtr->checkMasks.exceptional))
                  && FD_ISSET(i, &exceptionalMask)) {
                FD_SET(i, &(tsdPtr->readyMasks.exceptional));
                found = 1;
            }
          }

          if (found || (tsdPtr->pollState & POLL_DONE)) {
            tsdPtr->eventReady = 1;
            if (tsdPtr->onList) {
                /*
                 * Remove the ThreadSpecificData structure of this thread
                 * from the waiting list. This prevents us from
                 * continuously spining on select until the other threads
                 * runs and services the file event.
                 */

                if (tsdPtr->prevPtr) {
                  tsdPtr->prevPtr->nextPtr = tsdPtr->nextPtr;
                } else {
                  waitingListPtr = tsdPtr->nextPtr;
                }
                if (tsdPtr->nextPtr) {
                  tsdPtr->nextPtr->prevPtr = tsdPtr->prevPtr;
                }
                tsdPtr->nextPtr = tsdPtr->prevPtr = NULL;
                tsdPtr->onList = 0;
                tsdPtr->pollState = 0;
            }
            Tcl_ConditionNotify(&tsdPtr->waitCV);
          }
      }
      Tcl_MutexUnlock(&notifierMutex);

      /*
       * Consume the next byte from the notifier pipe if the pipe was
       * readable. Note that there may be multiple bytes pending, but to
       * avoid a race condition we only read one at a time.
       */

      if (FD_ISSET(receivePipe, &readableMask)) {
          i = read(receivePipe, buf, 1);

          if ((i == 0) || ((i == 1) && (buf[0] == 'q'))) {
            /*
             * Someone closed the write end of the pipe or sent us a Quit
             * message [Bug: 4139] and then closed the write end of the
             * pipe so we need to shut down the notifier thread.
             */

            break;
          }
      }
    }

    /*
     * Clean up the read end of the pipe and signal any threads waiting on
     * termination of the notifier thread.
     */

    close(receivePipe);
    Tcl_MutexLock(&notifierMutex);
    triggerPipe = -1;
    Tcl_ConditionNotify(&notifierCV);
    Tcl_MutexUnlock(&notifierMutex);

    TclpThreadExit (0);
}
#endif /* TCL_THREADS */

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

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