pthread_atfork(3)					     Library Functions Manual						 pthread_atfork(3)

NAME

       pthread_atfork - Declares fork handler routines to be called when the calling thread's process forks a child process.

LIBRARY

       Standard C Library (libc.so, libc.a)

SYNOPSIS

       #include <pthread.h>

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

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       IEEE Std 1003.1c-1995, POSIX System Application Program Interface

PARAMETERS

       Address	of  a routine that performs the fork preparation handling.  This routine is called in the parent process before creating the child
       process.  Address of a routine that performs the fork parent handling.  This routine is called in the parent  process  after  creating  the
       child  process  and before returning to the caller of fork(2).  Address of a routine that performs the fork child handling. This routine is
       called in the child process before returning to the caller of fork(2).

DESCRIPTION

       This routine allows a main program or library to control resources during a fork(2) operation by declaring fork handler routines,  as  fol-
       lows:  The fork handler routine specified in the prepare argument is called before fork(2) executes.  The fork handler routine specified in
       the parent argument is called after fork(2) executes within the parent process.	The fork handler routine specified in the  child  argument
       is  called in the new child process after fork(2) executes.  Your program (or library) can use fork handlers to ensure that program context
       in the child process is consistent and meaningful. After fork(2) executes, only the calling thread exists in the  child	process,  and  the
       state of all memory in the parent process is replicated in the child process, including the states of any mutexes, condition variables, and
       so on.

       For example, in the new child process there might exist locked mutexes that are copies of mutexes that were locked in the parent process by
       threads that do not exist in the child process. Therefore, any associated program state might be inconsistent in the child process.

       The  program  can  avoid this problem by calling pthread_atfork to provide routines that acquire and release resources that are critical to
       the child process. For example, the prepare handler should lock all mutexes that you want to be usable in the  child  process.  The  parent
       handler	just  unlocks those mutexes. The child handler will also unlock them all--and might also create threads or reset any program state
       for the child process.

       If no fork handling is desired, you can set any of this routine's arguments to NULL.

NOTES

       It is not legal to call pthread_atfork from within a fork handler routine.  Doing so could cause a deadlock.

EXAMPLES

       For example, if your library uses a mutex my_mutex, you might provide pthread_atfork handler routines coded as follows:
	void  my_prepare(void)
	      {
	      pthread_mutex_lock(&my_mutex);
	      }

	void  my_parent(void)
	      {
	      pthread_mutex_unlock(&my_mutex);
	      }

	void  my_child(void)
	      {
	      pthread_mutex_unlock(&my_mutex);
	      /* Reinitialize state that doesn't apply...like heap owned */
	      /* by other threads	  */
	      }

	   {
	      .
	      .
	      .

	    pthread_atfork(my_prepare, my_parent, my_child);
	      .
	      .
	    fork();
	   }

RETURN VALUES

       If an error condition occurs, this routine returns an integer value indicating the type of error.  Possible return values are  as  follows:
       Successful completion Insufficient table space exists to record the fork handler routines' addresses.

ERRORS

       None

RELATED INFORMATION

       Functions: pthread_create(3)

       Manuals: Guide to DECthreads, Programmer's Guide

       delim off

																 pthread_atfork(3)