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

       *  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 program.

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

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

       This page is part of release 5.10 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)