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If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] .TH PTHREAD_ATFORK 3C "Dec 12, 2003" .SH NAME pthread_atfork \- register fork handlers .SH SYNOPSIS .LP .nf #include #include \fBint\fR \fBpthread_atfork\fR(\fBvoid (*\fR\fIprepare\fR) (void), \fBvoid (*\fR\fIparent\fR) (void), \fBvoid (*\fR\fIchild\fR) (void)); .fi .SH DESCRIPTION .sp .LP The \fBpthread_atfork()\fR function declares fork handlers to be called prior to and following \fBfork\fR(2), within the thread that called \fBfork()\fR. The order of calls to \fBpthread_atfork()\fR is significant. .sp .LP Before \fBfork()\fR processing begins, the \fIprepare\fR fork handler is called. The \fIprepare\fR handler is not called if its address is \fINULL.\fR .sp .LP The \fIparent\fR fork handler is called after \fBfork()\fR processing finishes in the parent process, and the \fIchild\fR fork handler is called after \fBfork()\fR processing finishes in the child process. If the address of \fIparent\fR or \fIchild\fR is \fINULL\fR, then its handler is not called. .sp .LP The \fIprepare\fR fork handler is called in \fBLIFO\fR (last-in first-out) order, whereas the \fIparent\fR and \fIchild\fR fork handlers are called in \fBFIFO\fR (first-in first-out) order. This calling order allows applications to preserve locking order. .SH RETURN VALUES .sp .LP Upon successful completion, \fBpthread_atfork()\fR returns \fB0\fR. Otherwise, an error number is returned. .SH ERRORS .sp .LP The \fBpthread_atfork()\fR function will fail if: .sp .ne 2 .na \fB\fBENOMEM\fR \fR .ad .RS 11n Insufficient table space exists to record the fork handler addresses. .RE .SH USAGE .sp .LP Solaris threads do not offer \fBpthread_atfork()\fR functionality (there is no \fBthr_atfork()\fR interface). However, a Solaris threads application can call \fBpthread_atfork()\fR to ensure \fBfork()\fR-safety, since the two thread APIs are interoperable. See \fBfork\fR(2) for information relating to \fBfork()\fR in a Solaris threads environment in Solaris 10 relative to previous releases. .SH EXAMPLES .LP \fBExample 1 \fRMake a library safe with respect to \fBfork()\fR. .sp .LP All multithreaded applications that call \fBfork()\fR in a POSIX threads program and do more than simply call \fBexec\fR(2) in the child of the fork need to ensure that the child is protected from deadlock. .sp .LP Since the "fork-one" model results in duplicating only the thread that called \fBfork()\fR, it is possible that at the time of the call another thread in the parent owns a lock. This thread is not duplicated in the child, so no thread will unlock this lock in the child. Deadlock occurs if the single thread in the child needs this lock. .sp .LP The problem is more serious with locks in libraries. Since a library writer does not know if the application using the library calls \fBfork()\fR, the library must protect itself from such a deadlock scenario. If the application that links with this library calls \fBfork()\fR and does not call \fBexec()\fR in the child, and if it needs a library lock that may be held by some other thread in the parent that is inside the library at the time of the fork, the application deadlocks inside the library. .sp .LP The following describes how to make a library safe with respect to \fBfork()\fR by using \fBpthread_atfork()\fR. .RS +4 .TP 1. Identify all locks used by the library (for example \fB{L1,\|.\|.\|.Ln}\fR). Identify also the locking order for these locks (for example \fB{L1\|.\|.\|.Ln}, as well\fR.) .RE .RS +4 .TP 2. Add a call to \fBpthread_atfork(f1, f2, f3)\fR in the library's \fI\&.init\fR section. \fBf1\fR, \fBf2\fR, \fBf3\fR are defined as follows: .RE .sp .in +2 .nf \fB f1(\|) { /* ordered in lock order */ pthread_mutex_lock(L1); pthread_mutex_lock(\|.\|.\|.); pthread_mutex_lock(Ln); } f2(\|) { pthread_mutex_unlock(L1); pthread_mutex_unlock(\|.\|.\|.); pthread_mutex_unlock(Ln); } f3(\|) { pthread_mutex_unlock(L1); pthread_mutex_unlock(\|.\|.\|.); pthread_mutex_unlock(Ln); }\fR .fi .in -2 .SH ATTRIBUTES .sp .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Standard _ MT-Level MT-Safe .TE .SH SEE ALSO .sp .LP \fBexec\fR(2), \fBfork\fR(2), \fBatexit\fR(3C), \fBattributes\fR(5), \fBstandards\fR(5)