NAME
pthread_atfork
—
register handlers to be called when
process forks
LIBRARY
library “libc”
SYNOPSIS
#include
<pthread.h>
int
pthread_atfork
(void
(*prepare)(void), void
(*parent)(void), void
(*child)(void));
DESCRIPTION
Thepthread_atfork
()
function registers the provided handler functions to be called when the
fork(2) function is called. Each of the three handlers is called at a
different place in the
fork(2) sequence. The prepare handler is called
in the parent process before the fork happens, the
parent handler is called in the parent process after the
fork has happened, and the child handler is called in
the child process after the fork has happened. The
parent and child handlers are
called in the order in which they were registered, while the
prepare handlers are called in reverse of the order in
which they were registered.
Any of the handlers given may be NULL
.
The intended use of
pthread_atfork
()
is to provide a consistent state to a child process from a multithreaded
parent process where locks may be acquired and released asynchronously with
respect to the fork(2) call. Each subsystem with locks that are used in a
child process should register handlers with
pthread_atfork
() that acquires those locks in the
prepare handler and releases them in the
parent handler.
RETURN VALUES
The pthread_atfork
() function returns 0 on
success and an error number on failure.
ERRORS
The following error code may be returned:
- [
ENOMEM
] - Insufficient memory exists to register the fork handlers.
SEE ALSO
STANDARDS
The pthread_atfork
() function conforms to
IEEE Std 1003.1c-1995
(“POSIX.1c”).
HISTORY
The pthread_atfork
() function first
appeared in NetBSD 2.0.
CAVEATS
After calling
fork(2) from a multithreaded process, it is only safe to call
async-signal-safe functions until calling one of the
exec(3) functions. The pthread_*
() functions
are not async-signal-safe, so it is not safe to use such functions in the
child handler. POSIX does not mandate that
pthread_mutex_unlock
() be async-signal-safe, but it
is in NetBSD and thus safe to use within the
child handler.
BUGS
There is no way to unregister a handler registered with
pthread_atfork
().