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+.Dd January 17, 1999
+.Dt PTHREAD_ATFORK 3
+.Os BSD 4
+.Sh NAME
+.Nm pthread_atfork
+.Nd specify handler functions to call when the process forks
+.Sh SYNOPSIS
+.Fd #include <pthread.h>
+.Ft int
+.Fn pthread_atfork "void (*prepare)(void)" "void (*parent)(void)" "void (*child)(void)"
+.Sh DESCRIPTION
+The
+.Fn pthread_atfork
+function declares fork handlers to be called before and after
+.Fn fork ,
+in the context of the thread that called
+.Fn fork .
+The
+.Fa prepare
+fork handler will be called before
+.Fn fork
+processing commences. The
+.Fa parent
+fork handler will be called after
+.Fn fork
+prcessing completes in the parent process. The
+.Fa child
+fork handler will be called after
+.Fn fork
+processing completes in the child process. If no handling is desired at
+one or more of these three points, the correspoding fork handler
+address(es) may be set to
+.Dv NULL .
+.Pp
+The order of calls to
+.Fn pthread_atfork
+is significant. The
+.Fa parent
+and
+.Fa child
+fork handlers will be called in the order in which they were established
+by calls to
+.Fn pthread_atfork .
+The
+.Fa prepare
+fork handlers will be called in the opposite order.
+.Sh RETURN VALUES
+Upon successful completion,
+.Fn pthread_atfork
+will return a value of zero. Otherwise, an error number will be
+returned to indicate the error.
+.Sh ERRORS
+.Fn pthread_atfork
+will fail if:
+.Bl -tag -width Er
+.It Bq Er ENOMEM
+Insufficient table space exists to record the fork handler addresses.
+None of the handler lists are modified.
+.El
+.Pp
+.Sh SEE ALSO
+.Xr fork 2 ,
+.Xr atexit 3
+.Sh STANDARDS
+.Fn pthread_atfork
+conforms to ISO/IEC 9945-1 ANSI/IEEE
+.Pq Dq Tn POSIX
+Std 1003.1 Second Edition 1996-07-12.