pthread_atfork(3) - NetBSD Manual Pages

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PTHREAD_ATFORK(3)       NetBSD Library Functions Manual      PTHREAD_ATFORK(3)


NAME

     pthread_atfork -- register handlers to be called when process forks


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <pthread.h>

     int
     pthread_atfork(void (*prepare)(void), void (*parent)(void),
         void (*child)(void));


DESCRIPTION

     The pthread_atfork() function registers the provided handler functions to
     be called when the fork(2) function is called.  Each of the three han-
     dlers 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 regis-
     ter 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 han-
                        dlers.


SEE ALSO

     fork(2), pthread_mutex(3), signal(7)


STANDARDS

     The pthread_atfork() function conforms to IEEE Std 1003.1c-1995
     (``POSIX.1'').


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) func-
     tions.  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().

NetBSD 10.1                      July 18, 2014                     NetBSD 10.1