05-30-2001
fork() and IPC
Hey all. I recently ported a multithreaded program from WinNT to LINUX using pthreads. Everything works fine, except that it turns out the drivers for the hardware I'm working with aren't thread safe. So, now I have to find a way to make this multi-process instead of multi-threaded.
I just started working with fork(), and am having a little trouble following the interprocess communication models. Is there an "easy" way to allow a child process(es) to have access to the global variables in the parent process? This is the way the original programmer did it under NT multithreaded, and I'd rather not rewrite the entire app (it's big).
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LEARN ABOUT NETBSD
pthread_atfork
PTHREAD_ATFORK(3) BSD 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
handlers is called at a different place in the fork(2) sequence. The prepare handler is called in the parent process before the fork hap-
pens, 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
fork(2)
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)
functions. The pthread_*() functions are not async-signal-safe, so it is not safe to use such functions in the child handler.
BUGS
There is no way to unregister a handler registered with pthread_atfork().
BSD
February 12, 2003 BSD