/* * s e m _ t i m e d w a i t * * Function: * Implements a version of sem_timedwait(). * * Description: * Not all systems implement sem_timedwait(), which is a version of * sem_wait() with a timeout. Mac OS X is one example, at least up to * and including version 10.6 (Leopard). If such a function is needed, * this code provides a reasonable implementation, which I think is * compatible with the standard version, although possibly less * efficient. It works by creating a thread that interrupts a normal * sem_wait() call after the specified timeout. * * Call: * * The Linux man pages say: * * #include * * int sem_timedwait(sem_t *sem, const struct timespec *abs_timeout); * * sem_timedwait() is the same as sem_wait(), except that abs_timeout * specifies a limit on the amount of time that the call should block if * the decrement cannot be immediately performed. The abs_timeout argument * points to a structure that specifies an absolute timeout in seconds and * nanoseconds since the Epoch (00:00:00, 1 January 1970). This structure * is defined as follows: * * struct timespec { * time_t tv_sec; Seconds * long tv_nsec; Nanoseconds [0 .. 999999999] * }; * * If the timeout has already expired by the time of the call, and the * semaphore could not be locked immediately, then sem_timedwait() fails * with a timeout error (errno set to ETIMEDOUT). * If the operation can be performed immediately, then sem_timedwait() * never fails with a timeout error, regardless of the value of abs_timeout. * Furthermore, the validity of abs_timeout is not checked in this case. * * Limitations: * * The mechanism used involves sending a SIGUSR2 signal to the thread * calling sem_timedwait(). The handler for this signal is set to a null * routine which does nothing, and with any flags for the signal * (eg SA_RESTART) cleared. Note that this effective disabling of the * SIGUSR2 signal is a side-effect of using this routine, and means it * may not be a completely transparent plug-in replacement for a * 'normal' sig_timedwait() call. Since OS X does not declare the * sem_timedwait() call in its standard include files, the relevant * declaration (shown above in the man pages extract) will probably have * to be added to any code that uses this. * * Compiling: * This compiles and runs cleanly on OS X (10.6) with gcc with the * -Wall -ansi -pedantic flags. On Linux, using -ansi causes a sweep of * compiler complaints about the timespec structure, but it compiles * and works fine with just -Wall -pedantic. (Since Linux provides * sem_timedwait() anyway, this really isn't needed on Linux.) However, * since Linux provides sem_timedwait anyway, the sem_timedwait() * code in this file is only compiled on OS X, and is a null on other * systems. * * Testing: * This file contains a test program that exercises the sem_timedwait * code. It is compiled if the pre-processor variable TEST is defined. * For more details, see the comments for the test routine at the end * of the file. * * Author: Keith Shortridge, AAO. * * History: * 8th Sep 2009. Original version. KS. * 24th Sep 2009. Added test that the calling thread still exists before * trying to set the timed-out flag. KS. * 2nd Oct 2009. No longer restores the original SIGUSR2 signal handler. * See comments in the body of the code for more details. * Prototypes for now discontinued internal routines removed. * 12th Aug 2010. Added the cleanup handler, so that this code no longer * leaks resources if the calling thread is cancelled. KS. * 21st Sep 2011. Added copyright notice below. Modified header comments * to describe the use of SIGUSR2 more accurately in the * light of the 2/10/09 change above. Now undefs DEBUG * before defining it, to avoid any possible clash. KS. * 14th Feb 2012. Tidied out a number of TABs that had got into the * code. KS. * 6th May 2013. Copyright notice modified to one based on the MIT licence, * which is more permissive than the previous notice. KS. * * Copyright (c) Australian Astronomical Observatory (AAO), (2013). * Permission is hereby granted, free of charge, to any person obtaining a * copy of this software and associated documentation files (the "Software"), * to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, * and/or sell copies of the Software, and to permit persons to whom the * Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS * IN THE SOFTWARE. */ #ifdef __APPLE__ #include #include #include #include #include #include #include #include #include #include #include #include "sem_timedwait.h" /* Some useful definitions - TRUE, FALSE, and DEBUG */ #undef TRUE #define TRUE 1 #undef FALSE #define FALSE 0 #undef DEBUG #define DEBUG printf /* A structure of type timeoutDetails is passed to the thread used to * implement the timeout. */ typedef struct { struct timespec delay; /* Specifies the delay, relative to now */ pthread_t callingThread; /* The thread doing the sem_wait call */ volatile short *timedOutShort; /* Address of a flag set to indicate that * the timeout was triggered. */ } timeoutDetails; /* A structure of type cleanupDetails is passed to the thread cleanup * routine which is called at the end of the routine or if the thread calling * it is cancelled. */ typedef struct { pthread_t *threadIdAddr; /* Address of the variable that holds * the Id of the timeout thread. */ struct sigaction *sigHandlerAddr; /* Address of the old signal action * handler. */ volatile short *timedOutShort; /* Address of a flag set to indicate that * the timeout was triggered. */ } cleanupDetails; /* Forward declarations of internal routines */ static void* timeoutThreadMain (void* passedPtr); static int triggerSignal (int Signal, pthread_t Thread); static void ignoreSignal (int Signal); static void timeoutThreadCleanup (void* passedPtr); /* -------------------------------------------------------------------------- */ /* * s e m _ t i m e d w a i t * * This is the main code for the sem_timedwait() implementation. */ int sem_timedwait ( sem_t *sem, const struct timespec *abs_timeout) { int result = 0; /* Code returned by this routine 0 or -1 */ /* "Under no circumstances shall the function fail if the semaphore * can be locked immediately". So we try to get it quickly to see if we * can avoid all the timeout overheads. */ if (sem_trywait(sem) == 0) { /* Yes, got it immediately. */ result = 0; } else { /* No, we've got to do it with a sem_wait() call and a thread to run * the timeout. First, work out the time from now to the specified * timeout, which we will pass to the timeout thread in a way that can * be used to pass to nanosleep(). So we need this in seconds and * nanoseconds. Along the way, we check for an invalid passed time, * and for one that's already expired. */ if ((abs_timeout->tv_nsec < 0) || (abs_timeout->tv_nsec > 1000000000)) { /* Passed time is invalid */ result = -1; errno = EINVAL; } else { struct timeval currentTime; /* Time now */ long secsToWait,nsecsToWait; /* Seconds and nsec to delay */ gettimeofday (¤tTime,NULL); secsToWait = abs_timeout->tv_sec - currentTime.tv_sec; nsecsToWait = (abs_timeout->tv_nsec - (currentTime.tv_usec * 1000)); while (nsecsToWait < 0) { nsecsToWait += 1000000000; secsToWait--; } if ((secsToWait < 0) || ((secsToWait == 0) && (nsecsToWait < 0))) { /* Time has passed. Report an immediate timeout. */ result = -1; errno = ETIMEDOUT; } else { /* We're going to have to do a sem_wait() with a timeout thread. * The thread will wait the specified time, then will issue a * SIGUSR2 signal that will interrupt the sem_wait() call. * We pass the thread the id of the current thread, the delay, * and the address of a flag to set on a timeout, so we can * distinguish an interrupt caused by the timeout thread from * one caused by some other signal. */ volatile short timedOut; /* Flag to set on timeout */ timeoutDetails details; /* All the stuff the thread must know */ struct sigaction oldSignalAction; /* Current signal setting */ pthread_t timeoutThread; /* Id of timeout thread */ cleanupDetails cleaningDetails; /* What the cleanup routine needs */ int oldCancelState; /* Previous cancellation state */ int ignoreCancelState; /* Used in call, but ignored */ int createStatus; /* Status of pthread_create() call */ /* If the current thread is cancelled (and CML does do this) * we don't want to leave our timer thread running - if we've * started the thread we want to make sure we join it in order * to release its resources. So we set a cleanup handler to * do this. We pass it the address of the structure that will * hold all it needs to know. While we set all this up, * we prevent ourselves being cancelled, so all this data is * coherent. */ pthread_setcancelstate (PTHREAD_CANCEL_DISABLE,&oldCancelState); timeoutThread = (pthread_t) 0; cleaningDetails.timedOutShort = &timedOut; cleaningDetails.threadIdAddr = &timeoutThread; cleaningDetails.sigHandlerAddr = &oldSignalAction; pthread_cleanup_push (timeoutThreadCleanup,&cleaningDetails); /* Set up the details for the thread. Clear the timeout flag, * record the current SIGUSR2 action settings so we can restore * them later. */ details.delay.tv_sec = secsToWait; details.delay.tv_nsec = nsecsToWait; details.callingThread = pthread_self(); details.timedOutShort = &timedOut; timedOut = FALSE; sigaction (SIGUSR2,NULL,&oldSignalAction); /* Start up the timeout thread. Once we've done that, we can * restore the previous cancellation state. */ createStatus = pthread_create(&timeoutThread,NULL, timeoutThreadMain, (void*)&details); pthread_setcancelstate (oldCancelState,&ignoreCancelState); if (createStatus < 0) { /* Failed to create thread. errno will already be set properly */ result = -1; } else { /* Thread created OK. This is where we wait for the semaphore. */ if (sem_wait(sem) == 0) { /* Got the semaphore OK. We return zero, and all's well. */ result = 0; } else { /* If we got a -1 error from sem_wait(), it may be because * it was interrupted by a timeout, or failed for some * other reason. We check for the expected timeout * condition, which is an 'interrupted' status and the * timeout flag set by the timeout thread. We report that as * a timeout error. Anything else is some other error and * errno is already set properly. */ result = -1; if (errno == EINTR) { if (timedOut) errno = ETIMEDOUT; } } } /* The cleanup routine - timeoutThreadCleanup() - packages up * any tidying up that is needed, including joining with the * timer thread. This will be called if the current thread is * cancelled, but we need it to happen anyway, so we set the * execute flag true here as we remove it from the list of * cleanup routines to be called. So normally, this line amounts * to calling timeoutThreadCleanup(). */ pthread_cleanup_pop (TRUE); } } } return (result); } /* -------------------------------------------------------------------------- */ /* * t i m e o u t T h r e a d C l e a n u p * * This internal routine tidies up at the end of a sem_timedwait() call. * It is set as a cleanup routine for the current thread (not the timer * thread) so it is executed even if the thread is cancelled. This is * important, as we need to tidy up the timeout thread. If we took the * semaphore (in other words, if we didn't timeout) then the timer thread * will still be running, sitting in its nanosleep() call, and we need * to cancel it. If the timer thread did signal a timeout then it will * now be closing down. In either case, we need to join it (using a call * to pthread_join()) or its resources will never be released. * The single argument is a pointer to a cleanupDetails structure that has * all the routine needs to know. */ static void timeoutThreadCleanup (void* passedPtr) { /* Get what we need from the structure we've been passed. */ cleanupDetails *detailsPtr = (cleanupDetails*) passedPtr; short timedOut = *(detailsPtr->timedOutShort); pthread_t timeoutThread = *(detailsPtr->threadIdAddr); /* If we created the thread, stop it - doesn't matter if it's no longer * running, pthread_cancel can handle that. We make sure we wait for it * to complete, because it is this pthread_join() call that releases any * memory the thread may have allocated. Note that cancelling a thread is * generally not a good idea, because of the difficulty of cleaning up * after it, but this is a very simple thread that does nothing but call * nanosleep(), and that we can cancel quite happily. */ if (!timedOut) pthread_cancel(timeoutThread); pthread_join(timeoutThread,NULL); /* The code originally restored the old action handler, which generally * was the default handler that caused the task to exit. Just occasionally, * there seem to be cases where the signal is still queued and ready to * trigger even though the thread that presumably sent it off just before * it was cancelled has finished. I had thought that once we'd joined * that thread, we could be sure of not seeing the signal, but that seems * not to be the case, and so restoring a handler that will allow the task * to crash is not a good idea, and so the line below has been commented * out. * * sigaction (SIGUSR2,detailsPtr->sigHandlerAddr,NULL); */ } /* -------------------------------------------------------------------------- */ /* * t i m e o u t T h r e a d M a i n * * This internal routine is the main code for the timeout thread. * The single argument is a pointer to a timeoutDetails structure that has * all the thread needs to know - thread to signal, delay time, and the * address of a flag to set if it triggers a timeout. */ static void* timeoutThreadMain (void* passedPtr) { void* Return = (void*) 0; /* We grab all the data held in the calling thread right now. In some * cases, we find that the calling thread has vanished and released * its memory, including the details structure, by the time the timeout * expires, and then we get an access violation when we try to set the * 'timed out' flag. */ timeoutDetails details = *((timeoutDetails*) passedPtr); struct timespec requestedDelay = details.delay; /* We do a nanosleep() for the specified delay, and then trigger a * timeout. Note that we allow for the case where the nanosleep() is * interrupted, and restart it for the remaining time. If the * thread that is doing the sem_wait() call gets the semaphore, it * will cancel this thread, which is fine as we aren't doing anything * other than a sleep and a signal. */ for (;;) { struct timespec remainingDelay; if (nanosleep (&requestedDelay,&remainingDelay) == 0) { break; } else if (errno == EINTR) { requestedDelay = remainingDelay; } else { Return = (void*) errno; break; } } /* We've completed the delay without being cancelled, so we now trigger * the timeout by sending a signal to the calling thread. And that's it, * although we set the timeout flag first to indicate that it was us * that interrupted the sem_wait() call. One precaution: before we * try to set the timed-out flag, make sure the calling thread still * exists - this may not be the case if things are closing down a bit * messily. We check this quickly using a zero test signal. */ if (pthread_kill(details.callingThread,0) == 0) { *(details.timedOutShort) = TRUE; if (triggerSignal (SIGUSR2,details.callingThread) < 0) { Return = (void*) errno; } } return Return; } /* -------------------------------------------------------------------------- */ /* * t r i g g e r S i g n a l * * This is a general purpose routine that sends a specified signal to * a specified thread, setting up a signal handler that does nothing, * and then giving the signal. The only effect will be to interrupt any * operation that is currently blocking - in this case, we expect this to * be a sem_wait() call. */ static int triggerSignal (int Signal, pthread_t Thread) { int Result = 0; struct sigaction SignalDetails; SignalDetails.sa_handler = ignoreSignal; SignalDetails.sa_flags = 0; (void) sigemptyset(&SignalDetails.sa_mask); if ((Result = sigaction(Signal,&SignalDetails,NULL)) == 0) { Result = pthread_kill(Thread,Signal); } return Result; } /* -------------------------------------------------------------------------- */ /* * i g n o r e S i g n a l * * And this is the signal handler that does nothing. (It clears its argument, * but this has no effect and prevents a compiler warning about an unused * argument.) */ static void ignoreSignal (int Signal) { Signal = 0; } #endif