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

       pthread_atfork - register fork handlers

       #include <pthread.h>

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

       Link with -pthread.

       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.

       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.

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

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

       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

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

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

       This page is part of release 5.06 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                             2017-09-15                 PTHREAD_ATFORK(3)