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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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pthread_atfork(3) Library Functions Manual pthread_atfork(3)
pthread_atfork - register fork handlers
POSIX threads library (libpthread, -lpthread)
#include <pthread.h>
int pthread_atfork(typeof(void (void)) *prepare,
typeof(void (void)) *parent,
typeof(void (void)) *child);
The pthread_atfork() function registers fork handlers that are to
be executed when fork(2) is called by any thread in a process.
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 in the parent
process 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 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.
ENOMEM Could not allocate memory to record the fork handler list
entry.
POSIX.1-2008.
POSIX.1-2001.
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 child process 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.
fork(2), atexit(3), pthreads(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 pthread_atfork(3)
Pages that refer to this page: clone(2), fork(2), vfork(2), posix_spawn(3), system(3), pthreads(7), signal-safety(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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