pthread_atfork(3) — Linux manual page

pthread_atfork(3)       Library Functions Manual       pthread_atfork(3)

NAME

       pthread_atfork - register fork handlers

LIBRARY

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS

       #include <pthread.h>

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

DESCRIPTION

       The pthread_atfork() function registers fork handlers that are to
       be executed when fork(2) is called by any thread in a process.
       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 in the parent
          process 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

       On success, pthread_atfork() returns zero.  On error, it returns
       an error number.  pthread_atfork() may be called multiple times
       by a process to register additional handlers.  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

       ENOMEM Could not allocate memory to record the fork handler list
              entry.

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001.

NOTES

       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 child process 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 EINTR.

SEE ALSO

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

COLOPHON

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Linux man-pages 6.9.1          2024-05-02              pthread_atfork(3)

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

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