/*

  * tclMacOSXNotify.c --

  *

  *	This file contains the implementation of a merged CFRunLoop/select()

  *	based 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.

  * Copyright 2001, Apple Computer, Inc.

  * Copyright (c) 2005-2007 Daniel A. Steffen <das@users.sourceforge.net>

  *

  * See the file "license.terms" for information on usage and redistribution of

  * this file, and for a DISCLAIMER OF ALL WARRANTIES.

  *

  * RCS: @(#) $Id: tclMacOSXNotify.c,v 1.1.2.12 2007/04/29 02:21:33 das Exp $

  */

 #include "tclInt.h"

 #include "tclPort.h"

 #ifdef HAVE_COREFOUNDATION	/* Traditional unix select-based notifier is

 				 * in tclUnixNotfy.c */

 #include <CoreFoundation/CoreFoundation.h>

 #include <pthread.h>

 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). */

     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

 				 * notifierLock before accessing these

 				 * fields. */

     CFRunLoopSourceRef runLoopSource;

 				/* Any other thread alerts a notifier that an

 				 * event is ready to be processed by signaling

 				 * this CFRunLoopSource. */

     CFRunLoopRef runLoop;	/* This thread's CFRunLoop, needs to be woken

 				 * up whenever the runLoopSource is

 				 * signaled. */

     int eventReady;		/* True if an event is ready to be

 				 * processed. */

 } ThreadSpecificData;

 static Tcl_ThreadDataKey dataKey;

 /*

  * The following static indicates the number of threads that have initialized

  * notifiers.

  *

  * You must hold the notifierInitLock 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 notifierLock 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 notifierLock lock before writing to the pipe.

  */

 static int triggerPipe = -1;

 static int receivePipe = -1; /* Output end of triggerPipe */

 /*

  * We use the Darwin-native spinlock API rather than pthread mutexes for

  * notifier locking: this radically simplifies the implementation and lowers

  * overhead. Note that these are not pure spinlocks, they employ various

  * strategies to back off and relinquish the processor, making them immune to

  * most priority-inversion livelocks (c.f. 'man 3 OSSpinLockLock' and Darwin

  * sources: xnu/osfmk/{ppc,i386}/commpage/spinlocks.s).

  */

 #if defined(HAVE_LIBKERN_OSATOMIC_H) && defined(HAVE_OSSPINLOCKLOCK)

 /*

  * Use OSSpinLock API where available (Tiger or later).

  */

 #include <libkern/OSAtomic.h>

 #if defined(HAVE_WEAK_IMPORT) && MAC_OS_X_VERSION_MIN_REQUIRED < 1040

 /*

  * Support for weakly importing spinlock API.

  */

 #define WEAK_IMPORT_SPINLOCKLOCK

 #if MAC_OS_X_VERSION_MAX_ALLOWED >= 1050

 #define VOLATILE volatile

 #else

 #define VOLATILE

 #endif

 #ifndef bool

 #define bool int

 #endif

 extern void OSSpinLockLock(VOLATILE OSSpinLock *lock) WEAK_IMPORT_ATTRIBUTE;

 extern void OSSpinLockUnlock(VOLATILE OSSpinLock *lock) WEAK_IMPORT_ATTRIBUTE;

 extern bool OSSpinLockTry(VOLATILE OSSpinLock *lock) WEAK_IMPORT_ATTRIBUTE;

 extern void _spin_lock(VOLATILE OSSpinLock *lock) WEAK_IMPORT_ATTRIBUTE;

 extern void _spin_unlock(VOLATILE OSSpinLock *lock) WEAK_IMPORT_ATTRIBUTE;

 extern bool _spin_lock_try(VOLATILE OSSpinLock *lock) WEAK_IMPORT_ATTRIBUTE;

 static void (* lockLock)(VOLATILE OSSpinLock *lock) = NULL;

 static void (* lockUnlock)(VOLATILE OSSpinLock *lock) = NULL;

 static bool (* lockTry)(VOLATILE OSSpinLock *lock) = NULL;

 #undef VOLATILE

 static pthread_once_t spinLockLockInitControl = PTHREAD_ONCE_INIT;

 static void SpinLockLockInit(void) {

     lockLock   = OSSpinLockLock   != NULL ? OSSpinLockLock   : _spin_lock;

     lockUnlock = OSSpinLockUnlock != NULL ? OSSpinLockUnlock : _spin_unlock;

     lockTry    = OSSpinLockTry    != NULL ? OSSpinLockTry    : _spin_lock_try;

     if (lockLock == NULL || lockUnlock == NULL) {

 	Tcl_Panic("SpinLockLockInit: no spinlock API available");

     }

 }

 #define SpinLockLock(p) 	lockLock(p)

 #define SpinLockUnlock(p)	lockUnlock(p)

 #define SpinLockTry(p)  	lockTry(p)

 #else

 #define SpinLockLock(p) 	OSSpinLockLock(p)

 #define SpinLockUnlock(p)	OSSpinLockUnlock(p)

 #define SpinLockTry(p)  	OSSpinLockTry(p)

 #endif /* HAVE_WEAK_IMPORT */

 #define SPINLOCK_INIT   	OS_SPINLOCK_INIT

 #else

 /*

  * Otherwise, use commpage spinlock SPI directly.

  */

 typedef uint32_t OSSpinLock;

 extern void _spin_lock(OSSpinLock *lock);

 extern void _spin_unlock(OSSpinLock *lock);

 extern int  _spin_lock_try(OSSpinLock *lock);

 #define SpinLockLock(p) 	_spin_lock(p)

 #define SpinLockUnlock(p)	_spin_unlock(p)

 #define SpinLockTry(p)  	_spin_lock_try(p)

 #define SPINLOCK_INIT   	0

 #endif /* HAVE_LIBKERN_OSATOMIC_H && HAVE_OSSPINLOCKLOCK */

 /*

  * These spinlocks lock access to the global notifier state.

  */

 static OSSpinLock notifierInitLock = SPINLOCK_INIT;

 static OSSpinLock notifierLock     = SPINLOCK_INIT;

 /*

  * Macros abstracting notifier locking/unlocking

  */

 #define LOCK_NOTIFIER_INIT	SpinLockLock(&notifierInitLock)

 #define UNLOCK_NOTIFIER_INIT	SpinLockUnlock(&notifierInitLock)

 #define LOCK_NOTIFIER		SpinLockLock(&notifierLock)

 #define UNLOCK_NOTIFIER		SpinLockUnlock(&notifierLock)

 /*

  * 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 pthread_t notifierThread;

 /*

  * Custom run loop mode containing only the run loop source for the

  * notifier thread.

  */

 #ifndef TCL_EVENTS_ONLY_RUN_LOOP_MODE

 #define TCL_EVENTS_ONLY_RUN_LOOP_MODE "com.tcltk.tclEventsOnlyRunLoopMode"

 #endif

 #ifdef __CONSTANT_CFSTRINGS__

 #define tclEventsOnlyRunLoopMode CFSTR(TCL_EVENTS_ONLY_RUN_LOOP_MODE)

 #else

 static CFStringRef tclEventsOnlyRunLoopMode = NULL;

 #endif

 /*

  * Static routines defined in this file.

  */

 static void	NotifierThreadProc(ClientData clientData)

 	__attribute__ ((__noreturn__));

 static int	FileHandlerEventProc(Tcl_Event *evPtr, int flags);

 #ifdef HAVE_PTHREAD_ATFORK

 static int	atForkInit = 0;

 static void	AtForkPrepare(void);

 static void	AtForkParent(void);

 static void	AtForkChild(void);

 #if defined(HAVE_WEAK_IMPORT) && MAC_OS_X_VERSION_MIN_REQUIRED < 1040

 /* Support for weakly importing pthread_atfork. */

 #define WEAK_IMPORT_PTHREAD_ATFORK

 extern int pthread_atfork(void (*prepare)(void), void (*parent)(void),

                           void (*child)(void)) WEAK_IMPORT_ATTRIBUTE;

 #endif /* HAVE_WEAK_IMPORT */

 #endif /* HAVE_PTHREAD_ATFORK */

 /*

  *----------------------------------------------------------------------

  *

  * 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);

     tsdPtr->eventReady = 0;

 #ifdef WEAK_IMPORT_SPINLOCKLOCK

     /*

      * Initialize support for weakly imported spinlock API.

      */

     if (pthread_once(&spinLockLockInitControl, SpinLockLockInit)) {

 	Tcl_Panic("Tcl_InitNotifier: pthread_once failed");

     }

 #endif

 #ifndef __CONSTANT_CFSTRINGS__

     if (!tclEventsOnlyRunLoopMode) {

 	tclEventsOnlyRunLoopMode = CFSTR(TCL_EVENTS_ONLY_RUN_LOOP_MODE);

     }

 #endif

     /*

      * Initialize CFRunLoopSource and add it to CFRunLoop of this thread.

      */

     if (!tsdPtr->runLoop) {

 	CFRunLoopRef runLoop = CFRunLoopGetCurrent();

 	CFRunLoopSourceRef runLoopSource;

 	CFRunLoopSourceContext runLoopSourceContext;

 	bzero(&runLoopSourceContext, sizeof(CFRunLoopSourceContext));

 	runLoopSourceContext.info = tsdPtr;

 	runLoopSource = CFRunLoopSourceCreate(NULL, 0, &runLoopSourceContext);

 	if (!runLoopSource) {

 	    Tcl_Panic("Tcl_InitNotifier: could not create CFRunLoopSource");

 	}

 	CFRunLoopAddSource(runLoop, runLoopSource, kCFRunLoopCommonModes);

 	CFRunLoopAddSource(runLoop, runLoopSource, tclEventsOnlyRunLoopMode);

 	tsdPtr->runLoopSource = runLoopSource;

 	tsdPtr->runLoop = runLoop;

     }

     LOCK_NOTIFIER_INIT;

 #ifdef HAVE_PTHREAD_ATFORK

     /*

      * Install pthread_atfork handlers to reinitialize the notifier in the

      * child of a fork.

      */

     if (

 #ifdef WEAK_IMPORT_PTHREAD_ATFORK

 	    pthread_atfork != NULL &&

 #endif

 	    !atForkInit) {

 	int result = pthread_atfork(AtForkPrepare, AtForkParent, AtForkChild);

 	if (result) {

 	    Tcl_Panic("Tcl_InitNotifier: pthread_atfork failed");

 	}

 	atForkInit = 1;

     }

 #endif

     if (notifierCount == 0) {

 	int fds[2], status;

 	/*

 	 * Initialize trigger pipe.

 	 */

 	if (pipe(fds) != 0) {

 	    Tcl_Panic("Tcl_InitNotifier: could not create trigger pipe");

 	}

 	status = fcntl(fds[0], F_GETFL);

 	status |= O_NONBLOCK;

 	if (fcntl(fds[0], F_SETFL, status) < 0) {

 	    Tcl_Panic("Tcl_InitNotifier: 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("Tcl_InitNotifier: could not make trigger pipe non blocking");

 	}

 	receivePipe = fds[0];

 	triggerPipe = fds[1];

 	/*

 	 * Create notifier thread lazily in Tcl_WaitForEvent() to avoid

 	 * interfering with fork() followed immediately by execve()

 	 * (cannot execve() when more than one thread is present).

 	 */

 	notifierThread = 0;

     }

     notifierCount++;

     UNLOCK_NOTIFIER_INIT;

     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. */

 {

     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

     LOCK_NOTIFIER_INIT;

     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);

 	if (notifierThread) {

 	    result = pthread_join(notifierThread, NULL);

 	    if (result) {

 		Tcl_Panic("Tcl_FinalizeNotifier: unable to join notifier thread");

 	    }

 	    notifierThread = 0;

 	}

 	close(receivePipe);

 	triggerPipe = -1;

     }

     UNLOCK_NOTIFIER_INIT;

     LOCK_NOTIFIER;		/* for concurrency with Tcl_AlertNotifier */

     if (tsdPtr->runLoop) {

 	tsdPtr->runLoop = NULL;

 	/*

 	 * Remove runLoopSource from all CFRunLoops and release it.

 	 */

 	CFRunLoopSourceInvalidate(tsdPtr->runLoopSource);

 	CFRelease(tsdPtr->runLoopSource);

 	tsdPtr->runLoopSource = NULL;

     }

     UNLOCK_NOTIFIER;

 }

 /*

  *----------------------------------------------------------------------

  *

  * 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)

 {

     ThreadSpecificData *tsdPtr = (ThreadSpecificData *) clientData;

     LOCK_NOTIFIER;

     if (tsdPtr->runLoop) {

 	tsdPtr->eventReady = 1;

 	CFRunLoopSourceSignal(tsdPtr->runLoopSource);

 	CFRunLoopWakeUp(tsdPtr->runLoop);

     }

     UNLOCK_NOTIFIER;

 }

 /*

  *----------------------------------------------------------------------

  *

  * 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;

     int waitForFiles;

     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

     if (tclStubs.tcl_WaitForEvent != tclOriginalNotifier.waitForEventProc) {

 	return tclStubs.tcl_WaitForEvent(timePtr);

     }

     /*

      * Start notifier thread if necessary.

      */

     LOCK_NOTIFIER_INIT;

     if (!notifierCount) {

         Tcl_Panic("Tcl_WaitForEvent: notifier not initialized");

     }

     if (!notifierThread) {

 	int result;

 	pthread_attr_t attr;

 	pthread_attr_init(&attr);

 	pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);

 	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

 	pthread_attr_setstacksize(&attr, 60 * 1024);

 	result = pthread_create(&notifierThread, &attr,

 		(void * (*)(void *))NotifierThreadProc, NULL);

 	pthread_attr_destroy(&attr);

 	if (result || !notifierThread) {

 	    Tcl_Panic("Tcl_WaitForEvent: unable to start notifier thread");

 	}

     }

     UNLOCK_NOTIFIER_INIT;

     /*

      * Place this thread on the list of interested threads, signal the

      * notifier thread, and wait for a response or a timeout.

      */

     LOCK_NOTIFIER;

     if (!tsdPtr->runLoop) {

         Tcl_Panic("Tcl_WaitForEvent: CFRunLoop not initialized");

     }

     waitForFiles = (tsdPtr->numFdBits > 0);

     if (timePtr != NULL && timePtr->sec == 0 && timePtr->usec == 0) {

 	/*

 	 * 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;

 	timePtr = 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) {

 	CFTimeInterval waitTime;

 	CFStringRef runLoopMode;

 	if (timePtr == NULL) {

 	    waitTime = 1.0e10; /* Wait forever, as per CFRunLoop.c */

 	} else {

 	    waitTime = timePtr->sec + 1.0e-6 * timePtr->usec;

 	}

 	/*

 	 * If the run loop is already running (e.g. if Tcl_WaitForEvent was

 	 * called recursively), re-run it in a custom run loop mode containing

 	 * only the source for the notifier thread, otherwise wakeups from other

 	 * sources added to the common run loop modes might get lost.

 	 */

 	if ((runLoopMode = CFRunLoopCopyCurrentMode(tsdPtr->runLoop))) {

 	    CFRelease(runLoopMode);

 	    runLoopMode = tclEventsOnlyRunLoopMode;

 	} else {

 	    runLoopMode = kCFRunLoopDefaultMode;

 	}

 	UNLOCK_NOTIFIER;

 	CFRunLoopRunInMode(runLoopMode, waitTime, TRUE);

 	LOCK_NOTIFIER;

     }

     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);

     }

     /*

      * 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;

     }

     UNLOCK_NOTIFIER;

     return 0;

 }

 /*

  *----------------------------------------------------------------------

  *

  * 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 i, numFdBits = 0;

     long found;

     struct timeval poll = {0., 0.}, *timePtr;

     char buf[2];

     /*

      * 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.

 	 */

 	LOCK_NOTIFIER;

 	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;

 	    }

 	}

 	UNLOCK_NOTIFIER;

 	/*

 	 * 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.

 	 */

 	LOCK_NOTIFIER;

 	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;

 		}

 		if (tsdPtr->runLoop) {

 		    CFRunLoopSourceSignal(tsdPtr->runLoopSource);

 		    CFRunLoopWakeUp(tsdPtr->runLoop);

 		}

 	    }

 	}

 	UNLOCK_NOTIFIER;

 	/*

 	 * 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;

 	    }

 	}

     }

     pthread_exit(0);

 }

 #ifdef HAVE_PTHREAD_ATFORK

 /*

  *----------------------------------------------------------------------

  *

  * AtForkPrepare --

  *

  *	Lock the notifier in preparation for a fork.

  *

  * Results:

  *	None.

  *

  * Side effects:

  *	None.

  *

  *----------------------------------------------------------------------

  */

 static void

 AtForkPrepare(void)

 {

     LOCK_NOTIFIER_INIT;

     LOCK_NOTIFIER;

 }

 /*

  *----------------------------------------------------------------------

  *

  * AtForkParent --

  *

  *	Unlock the notifier in the parent after a fork.

  *

  * Results:

  *	None.

  *

  * Side effects:

  *	None.

  *

  *----------------------------------------------------------------------

  */

 static void

 AtForkParent(void)

 {

     UNLOCK_NOTIFIER;

     UNLOCK_NOTIFIER_INIT;

 }

 /*

  *----------------------------------------------------------------------

  *

  * AtForkChild --

  *

  *	Unlock and reinstall the notifier in the child after a fork.

  *

  * Results:

  *	None.

  *

  * Side effects:

  *	None.

  *

  *----------------------------------------------------------------------

  */

 static void

 AtForkChild(void)

 {

     ThreadSpecificData *tsdPtr = TCL_TSD_INIT(&dataKey);

     UNLOCK_NOTIFIER;

     UNLOCK_NOTIFIER_INIT;

     if (tsdPtr->runLoop) {

 	tsdPtr->runLoop = NULL;

 	CFRunLoopSourceInvalidate(tsdPtr->runLoopSource);

 	CFRelease(tsdPtr->runLoopSource);

 	tsdPtr->runLoopSource = NULL;

     }

     if (notifierCount > 0) {

 	notifierCount = 0;

 	/*

 	 * Assume that the return value of Tcl_InitNotifier in the child will

 	 * be identical to the one stored as clientData in tclNotify.c's

 	 * ThreadSpecificData by the parent's TclInitNotifier, so discard the

 	 * return value here. This assumption may require the fork() to be

 	 * executed in the main thread of the parent, otherwise

 	 * Tcl_AlertNotifier may break in the child.

 	 */

 	Tcl_InitNotifier();

     }

 }

 #endif /* HAVE_PTHREAD_ATFORK */

 #endif /* HAVE_COREFOUNDATION */