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

NAME
       pthread_atfork - register fork handlers

SYNOPSIS
       #include <pthread.h>

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

       Link with -pthread.

DESCRIPTION
       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
       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  multi‐
       ple  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
       ENOMEM Could not allocate memory to record the form handler entry.

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

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  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 EINTR.

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

Linux                                                                          2020-08-13                                                              PTHREAD_ATFORK(3)