pthread_atfork

Declares handlers to be called when the process forks a child.

This routine is for Digital UNIX systems only.

Syntax

pthread_atfork( prepare, parent, child );

Argument Data Type Access

prepare Handler read parent Handler read child Handler read

C Binding

#include 


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

Arguments

prepare: Address of a procedure that performs the fork preparation handling. This routine is called in the parent process before creating the child.
parent: Address of a procedure that performs the fork parent handling. This routine is called in the parent process after creating the child and before returning to the caller of fork(2).
child: Address of a procedure 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 UNIX fork(2) operation by declaring fork handlers that are called before and after the fork(2) execution. The prepare fork handler is called before the fork(2) execution. The parent handler is called after the fork(2) execution within the parent process, and the child handler is called after fork(2) in the new child process. If no handling is desired, you can set any of the arguments to a NULL.

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

Mutex locks might be held by threads that no longer exist in a child process and any associated state might be inconsistent. The program can avoid this problem by calling pthread_atfork() to provide code that acquires and releases locks critical to the child process. For example, if your library uses a mutex named "my_mutex", you might provide pthread_atfork handlers like:

 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 occurs, this routine returns an integer indicating the type of error. Possible return values are as follows:

Return        Description
0             Successful completion.

[ENOMEM]      Insufficient table space exists to record the fork
              handler addresses.

Associated Routines

pthread_create