pthread_atfork(3) - Linux manual page (original) (raw)

pthreadatfork(3) Library Functions Manual pthreadatfork(3)

NAME top

   pthread_atfork - register fork handlers

LIBRARY top

   POSIX threads library (_libpthread_, _-lpthread_)

SYNOPSIS top

   **#include <pthread.h>**

   **int pthread_atfork(typeof(void (void)) ***_prepare_**,**
                      **typeof(void (void)) ***_parent_**,**
                      **typeof(void (void)) ***_child_**);**

DESCRIPTION top

   The **pthread_atfork**() function registers fork handlers that are to
   be executed when [fork(2)](../man2/fork.2.html) is called by any thread in a process.
   The handlers are executed in the context of the thread that calls
   [fork(2)](../man2/fork.2.html).

   Three kinds of handler can be registered:

   •  _prepare_ specifies a handler that is executed in the parent
      process before [fork(2)](../man2/fork.2.html) processing starts.

   •  _parent_ specifies a handler that is executed in the parent
      process after [fork(2)](../man2/fork.2.html) processing completes.

   •  _child_ specifies a handler that is executed in the child process
      after [fork(2)](../man2/fork.2.html) processing completes.

   Any of the three arguments may be NULL if no handler is needed in
   the corresponding phase of [fork(2)](../man2/fork.2.html) 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 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 top

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

STANDARDS top

   POSIX.1-2008.

HISTORY top

   POSIX.1-2001.

NOTES top

   When [fork(2)](../man2/fork.2.html) 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)](../man2/fork.2.html), 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)](../man2/fork.2.html) in a multithreaded process returns in the child,
   the child should call only async-signal-safe functions (see
   [signal-safety(7)](../man7/signal-safety.7.html)) until such time as it calls [execve(2)](../man2/execve.2.html) to execute
   a new program.

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

SEE ALSO top

   [fork(2)](../man2/fork.2.html), [atexit(3)](../man3/atexit.3.html), [pthreads(7)](../man7/pthreads.7.html)

COLOPHON top

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Linux man-pages 6.10 2024-12-13 pthreadatfork(3)

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