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Full Discussion: about child process
Top Forums UNIX for Dummies Questions & Answers about child process Post 302068603 by Perderabo on Sunday 19th of March 2006 12:33:21 PM
Old 03-19-2006
A child process is created by the fork() system call. So if prog.c correctly calls fork() it will generate a child process. It might indirectly call fork() by doing something like this:
system("date");
The system() function creates a child process which will exec() a shell. Then the shell will run the date command.

A correct call to fork() can fail if there are too many processes already running or something like that.
 

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PTHREAD_ATFORK(3)					     Library Functions Manual						 PTHREAD_ATFORK(3)

NAME
pthread_atfork - register handlers to be called at fork(2) time SYNOPSIS
#include <pthread.h> int pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void)); DESCRIPTION
pthread_atfork registers handler functions to be called just before and just after a new process is created with fork(2). The prepare han- dler will be called from the parent process, just before the new process is created. The parent handler will be called from the parent process, just before fork(2) returns. The child handler will be called from the child process, just before fork(2) returns. One or several of the three handlers prepare, parent and child can be given as NULL, meaning that no handler needs to be called at the cor- responding point. pthread_atfork can be called several times to install several sets of handlers. At fork(2) time, the prepare handlers are called in LIFO order (last added with pthread_atfork, first called before fork), while the parent and child handlers are called in FIFO order (first added, first called). To understand the purpose of pthread_atfork, recall that fork(2) duplicates the whole memory space, including mutexes in their current locking state, but only the calling thread: other threads are not running in the child process. The mutexes are not usable after the fork and must be initialized with pthread_mutex_init in the child process. This is a limitation of the current implementation and might or might not be present in future versions. RETURN VALUE
pthread_atfork returns 0 on success and a non-zero error code on error. ERRORS
ENOMEM insufficient memory available to register the handlers. AUTHOR
Xavier Leroy <Xavier.Leroy@inria.fr> SEE ALSO
fork(2), pthread_mutex_lock(3), pthread_mutex_unlock(3). LinuxThreads PTHREAD_ATFORK(3)
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