PTHREAD_ATFORK
Section: Linux Programmer's Manual (3)
Updated: 2020-08-13
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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 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 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)
COLOPHON
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project.
A description of the project,
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https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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Time: 06:22:48 GMT, May 09, 2021