pthread_atfork(3) — Linux manual page


PTHREAD_ATFORK(3)         Linux Programmer's Manual        PTHREAD_ATFORK(3)

NAME         top

       pthread_atfork - register fork handlers

SYNOPSIS         top

       #include <pthread.h>

       int pthread_atfork(void (*prepare)(void), void (*parent)(void),
                          void (*child)(void));

       Link with -pthread.

DESCRIPTION         top

       The pthread_atfork() function registers fork handlers that are to be
       executed when fork(2) is called by this thread.  The handlers are
       executed in the context of the thread that calls fork(2).

       Three kinds of handler can be registered:

       *  prepare specifies a handler that is executed before fork(2)
          processing starts.

       *  parent specifies a handler that is executed in the parent process
          after fork(2) processing completes.

       *  child specifies a handler that is executed in the child process
          after fork(2) processing completes.

       Any of the three arguments may be NULL if no handler is needed in the
       corresponding phase of fork(2) processing.

RETURN VALUE         top

       On success, pthread_atfork() returns zero.  On error, it returns an
       error number.  pthread_atfork() may be called multiple times by a
       thread, to register multiple handlers for each phase.  The handlers
       for each phase are called in a specified order: the prepare handlers
       are called in reverse order of registration; the parent and child
       handlers are called in the order of registration.

ERRORS         top

       ENOMEM Could not allocate memory to record the form handler entry.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

NOTES         top

       When fork(2) is called in a multithreaded process, only the calling
       thread is duplicated in the child process.  The original intention of
       pthread_atfork() was to allow the calling thread to be returned to a
       consistent state.  For example, at the time of the call to fork(2),
       other threads may have locked mutexes that are visible in the user-
       space memory duplicated in the child.  Such mutexes would never be
       unlocked, since the threads that placed the locks are not duplicated
       in the child.  The intent of pthread_atfork() was to provide a
       mechanism whereby the application (or a library) could ensure that
       mutexes and other process and thread state would be restored to a
       consistent state.  In practice, this task is generally too difficult
       to be practicable.

       After a fork(2) in a multithreaded process returns in the child, the
       child should call only async-signal-safe functions (see
       signal-safety(7)) until such time as it calls execve(2) to execute a
       new program.

       POSIX.1 specifies that pthread_atfork() shall not fail with the error

SEE ALSO         top

       fork(2), atexit(3), pthreads(7)

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2020-08-13                PTHREAD_ATFORK(3)

Pages that refer to this page: clone2(2)__clone2(2)clone(2)clone3(2)fork(2)vfork(2)posix_spawn(3)posix_spawnp(3)system(3)pthreads(7)signal-safety(7)