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pthread_atfork(3)
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 exe‐
cuted 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) process‐
ing 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 af‐
ter 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 er‐
ror 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.
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 un‐
locked, 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 pro‐
gram.
POSIX.1 specifies that pthread_atfork() shall not fail with the error
EINTR.
SEE ALSO
fork(2), atexit(3), pthreads(7)
COLOPHON
This page is part of release 5.02 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
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 PTHREAD_ATFORK(3)