Section (3) pthread_atfork
pthread_atfork — register fork handlers
Three kinds of handler can be registered:
Any of the three arguments may be NULL if no handler is needed in the corresponding phase of fork(2) processing.
returns zero. On error, it returns an error number.
pthread_atfork() may be called
multiple times by a thread, to register multiple handlers for
each phase. The handlers for each phase are called in a
specified order: the
prepare handlers are called in
reverse order of registration; the
child handlers are called in
the order of registration.
When fork(2) is called in a
multithreaded process, only the calling thread is duplicated
in the child process. The original intention of
pthread_atfork() was to allow the calling
thread to be returned to a consistent state. For example, at
the time of the call to fork(2), other threads may
have locked mutexes that are visible in the user-space memory
duplicated in the child. Such mutexes would never be
unlocked, since the threads that placed the locks are not
duplicated in the child. The intent of
pthread_atfork() was to provide a mechanism
whereby the application (or a library) could ensure that
mutexes and other process and thread state would be restored
to a consistent state. In practice, this task is generally
too difficult to be practicable.
After a fork(2) in a multithreaded process returns in the child, the child should call only async-signal-safe functions (see signal-safety(7)) until such time as it calls execve(2) to execute a new program.
POSIX.1 specifies that
pthread_atfork() shall not fail with the
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