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PROLOG |NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLES |APPLICATION USAGE |RATIONALE |FUTURE DIRECTIONS |SEE ALSO |COPYRIGHT | |
PTHREAD_CLEANUP_POP(3P) POSIX Programmer's ManualPTHREAD_CLEANUP_POP(3P)This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
pthread_cleanup_pop, pthread_cleanup_push — establish cancellation handlers
#include <pthread.h> void pthread_cleanup_pop(intexecute); void pthread_cleanup_push(void (*routine)(void*), void *arg);
Thepthread_cleanup_pop() function shall remove the routine at the top of the calling thread's cancellation cleanup stack and optionally invoke it (ifexecute is non-zero). Thepthread_cleanup_push() function shall push the specified cancellation cleanup handlerroutine onto the calling thread's cancellation cleanup stack. The cancellation cleanup handler shall be popped from the cancellation cleanup stack and invoked with the argumentarg when: * The thread exits (that is, callspthread_exit()). * The thread acts upon a cancellation request. * The thread callspthread_cleanup_pop() with a non-zeroexecute argument. It is unspecified whetherpthread_cleanup_push() andpthread_cleanup_pop() are macros or functions. If a macro definition is suppressed in order to access an actual function, or a program defines an external identifier with any of these names, the behavior is undefined. The application shall ensure that they appear as statements, and in pairs within the same lexical scope (that is, thepthread_cleanup_push() macro may be thought to expand to a token list whose first token is'{'withpthread_cleanup_pop() expanding to a token list whose last token is the corresponding'}'). The effect of callinglongjmp() orsiglongjmp() is undefined if there have been any calls topthread_cleanup_push() orpthread_cleanup_pop() made without the matching call since the jump buffer was filled. The effect of callinglongjmp() orsiglongjmp() from inside a cancellation cleanup handler is also undefined unless the jump buffer was also filled in the cancellation cleanup handler. The effect of the use ofreturn,break,continue, andgototo prematurely leave a code block described by a pair ofpthread_cleanup_push() andpthread_cleanup_pop() functions calls is undefined.Thepthread_cleanup_push() andpthread_cleanup_pop() functions shall not return a value.
No errors are defined. These functions shall not return an error code of[EINTR].The following sections are informative.
The following is an example using thread primitives to implement a cancelable, writers-priority read-write lock: typedef struct { pthread_mutex_t lock; pthread_cond_t rcond, wcond; int lock_count; /* < 0 .. Held by writer. */ /* > 0 .. Held by lock_count readers. */ /* = 0 .. Held by nobody. */ int waiting_writers; /* Count of waiting writers. */ } rwlock; void waiting_reader_cleanup(void *arg) { rwlock *l; l = (rwlock *) arg; pthread_mutex_unlock(&l->lock); } void lock_for_read(rwlock *l) { pthread_mutex_lock(&l->lock); pthread_cleanup_push(waiting_reader_cleanup, l); while ((l->lock_count < 0) || (l->waiting_writers != 0)) pthread_cond_wait(&l->rcond, &l->lock); l->lock_count++; /* * Note the pthread_cleanup_pop executes * waiting_reader_cleanup. */ pthread_cleanup_pop(1); } void release_read_lock(rwlock *l) { pthread_mutex_lock(&l->lock); if (--l->lock_count == 0) pthread_cond_signal(&l->wcond); pthread_mutex_unlock(&l->lock); } void waiting_writer_cleanup(void *arg) { rwlock *l; l = (rwlock *) arg; if ((--l->waiting_writers == 0) && (l->lock_count >= 0)) { /* * This only happens if we have been canceled. If the * lock is not held by a writer, there may be readers who * were blocked because waiting_writers was positive; they * can now be unblocked. */ pthread_cond_broadcast(&l->rcond); } pthread_mutex_unlock(&l->lock); } void lock_for_write(rwlock *l) { pthread_mutex_lock(&l->lock); l->waiting_writers++; pthread_cleanup_push(waiting_writer_cleanup, l); while (l->lock_count != 0) pthread_cond_wait(&l->wcond, &l->lock); l->lock_count = -1; /* * Note the pthread_cleanup_pop executes * waiting_writer_cleanup. */ pthread_cleanup_pop(1); } void release_write_lock(rwlock *l) { pthread_mutex_lock(&l->lock); l->lock_count = 0; if (l->waiting_writers == 0) pthread_cond_broadcast(&l->rcond); else pthread_cond_signal(&l->wcond); pthread_mutex_unlock(&l->lock); } /* * This function is called to initialize the read/write lock. */ void initialize_rwlock(rwlock *l) { pthread_mutex_init(&l->lock, pthread_mutexattr_default); pthread_cond_init(&l->wcond, pthread_condattr_default); pthread_cond_init(&l->rcond, pthread_condattr_default); l->lock_count = 0; l->waiting_writers = 0; } reader_thread() { lock_for_read(&lock); pthread_cleanup_push(release_read_lock, &lock); /* * Thread has read lock. */ pthread_cleanup_pop(1); } writer_thread() { lock_for_write(&lock); pthread_cleanup_push(release_write_lock, &lock); /* * Thread has write lock. */ pthread_cleanup_pop(1); }The two routines that push and pop cancellation cleanup handlers,pthread_cleanup_push() andpthread_cleanup_pop(), can be thought of as left and right-parentheses. They always need to be matched.
The restriction that the two routines that push and pop cancellation cleanup handlers,pthread_cleanup_push() andpthread_cleanup_pop(), have to appear in the same lexical scope allows for efficient macro or compiler implementations and efficient storage management. A sample implementation of these routines as macros might look like this: #define pthread_cleanup_push(rtn,arg) { \ struct _pthread_handler_rec __cleanup_handler, **__head; \ __cleanup_handler.rtn = rtn; \ __cleanup_handler.arg = arg; \ (void) pthread_getspecific(_pthread_handler_key, &__head); \ __cleanup_handler.next = *__head; \ *__head = &__cleanup_handler; #define pthread_cleanup_pop(ex) \ *__head = __cleanup_handler.next; \ if (ex) (*__cleanup_handler.rtn)(__cleanup_handler.arg); \ } A more ambitious implementation of these routines might do even better by allowing the compiler to note that the cancellation cleanup handler is a constant and can be expanded inline. This volume of POSIX.1‐2017 currently leaves unspecified the effect of callinglongjmp() from a signal handler executing in a POSIX System Interfaces function. If an implementation wants to allow this and give the programmer reasonable behavior, thelongjmp() function has to call all cancellation cleanup handlers that have been pushed but not popped since the timesetjmp() was called. Consider a multi-threaded function called by a thread that uses signals. If a signal were delivered to a signal handler during the operation ofqsort() and that handler were to calllongjmp() (which, in turn, didnot call the cancellation cleanup handlers) the helper threads created by theqsort() function would not be canceled. Instead, they would continue to execute and write into the argument array even though the array might have been popped off the stack. Note that the specified cleanup handling mechanism is especially tied to the C language and, while the requirement for a uniform mechanism for expressing cleanup is language-independent, the mechanism used in other languages may be quite different. In addition, this mechanism is really only necessary due to the lack of a real exception mechanism in the C language, which would be the ideal solution. There is no notion of a cancellation cleanup-safe function. If an application has no cancellation points in its signal handlers, blocks any signal whose handler may have cancellation points while calling async-unsafe functions, or disables cancellation while calling async-unsafe functions, all functions may be safely called from cancellation cleanup routines.None.
pthread_cancel(3p),pthread_setcancelstate(3p) The Base Definitions volume of POSIX.1‐2017,pthread.h(0p)
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online athttp://www.opengroup.org/unix/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017PTHREAD_CLEANUP_POP(3P)Pages that refer to this page:pthread.h(0p)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |