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All Rights Reserved. .\" Copyright (c) 2007, Sun Microsystems, Inc. All Rights Reserved. .\" .TH WAITPID 3C "Dec 7, 2007" .SH NAME waitpid \- wait for child process to change state .SH SYNOPSIS .LP .nf #include #include \fBpid_t\fR \fBwaitpid\fR(\fBpid_t\fR \fIpid\fR, \fBint *\fR\fIstat_loc\fR, \fBint\fR \fIoptions\fR); .fi .SH DESCRIPTION .sp .LP The \fBwaitpid()\fR function will suspend execution of the calling thread until status information for one of its terminated child processes is available, or until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process. If more than one thread is suspended in \fBwaitpid()\fR, \fBwait\fR(3C), or \fBwaitid\fR(2) awaiting termination of the same process, exactly one thread will return the process status at the time of the target process termination. If status information is available prior to the call to \fBwaitpid()\fR, return will be immediate. .sp .LP The \fIpid\fR argument specifies a set of child processes for which status is requested, as follows: .RS +4 .TP .ie t \(bu .el o If \fIpid\fR is less than \fB(pid_t)\(mi1\fR, status is requested for any child process whose process group \fBID\fR is equal to the absolute value of \fIpid\fR. .RE .RS +4 .TP .ie t \(bu .el o If \fIpid\fR is equal to \fB(pid_t)\(mi1\fR, status is requested for any child process. .RE .RS +4 .TP .ie t \(bu .el o If \fIpid\fR is equal to \fB(pid_t)0\fR status is requested for any child process whose process group \fBID\fR is equal to that of the calling process. .RE .RS +4 .TP .ie t \(bu .el o If \fIpid\fR is greater than \fB(pid_t)0\fR, it specifies the process \fBID\fR of the child process for which status is requested. .RE .sp .LP One instance of a \fBSIGCHLD\fR signal is queued for each child process whose status has changed. If \fBwaitpid()\fR returns because the status of a child process is available, and \fBWNOWAIT\fR was not specified in \fIoptions\fR, any pending \fBSIGCHLD\fR signal associated with the process ID of that child process is discarded. Any other pending \fBSIGCHLD\fR signals remain pending. .sp .LP If the calling process has \fBSA_NOCLDWAIT\fR set or has \fBSIGCHLD\fR set to \fBSIG_IGN\fR and the process has no unwaited children that were transformed into zombie processes, it will block until all of its children terminate, and \fBwaitpid()\fR will fail and set \fBerrno\fR to \fBECHILD\fR. .sp .LP If \fBwaitpid()\fR returns because the status of a child process is available, then that status may be evaluated with the macros defined by \fBwait.h\fR(3HEAD) If the calling process had specified a non-zero value of \fIstat_loc\fR, the status of the child process will be stored in the location pointed to by \fIstat_loc\fR. .sp .LP The \fIoptions\fR argument is constructed from the bitwise-inclusive OR of zero or more of the following flags, defined in the header <\fBsys/wait.h\fR>: .sp .ne 2 .na \fB\fBWCONTINUED\fR\fR .ad .RS 14n The status of any continued child process specified by \fIpid\fR, whose status has not been reported since it continued, is also reported to the calling process. .RE .sp .ne 2 .na \fB\fBWNOHANG\fR\fR .ad .RS 14n The \fBwaitpid()\fR function will not suspend execution of the calling process if status is not immediately available for one of the child processes specified by \fIpid\fR. .RE .sp .ne 2 .na \fB\fBWNOWAIT\fR\fR .ad .RS 14n Keep the process whose status is returned in \fIstat_loc\fR in a waitable state. The process may be waited for again with identical results. .RE .sp .ne 2 .na \fB\fBWUNTRACED\fR\fR .ad .RS 14n The status of any child processes specified by \fIpid\fR that are stopped, and whose status has not yet been reported since they stopped, is also reported to the calling process. \fBWSTOPPED\fR is a synonym for \fBWUNTRACED\fR. .RE .SH RETURN VALUES .sp .LP If \fBwaitpid()\fR returns because the status of a child process is available, it returns a value equal to the process \fBID\fR of the child process for which status is reported. If \fBwaitpid()\fR returns due to the delivery of a signal to the calling process, \fB\(mi1\fR is returned and \fBerrno\fR is set to \fBEINTR\fR. If \fBwaitpid()\fR was invoked with \fBWNOHANG\fR set in \fIoptions\fR, it has at least one child process specified by \fIpid\fR for which status is not available, and status is not available for any process specified by \fIpid\fR, then \fB0\fR is returned. Otherwise, \fB\(mi1\fR is returned and \fBerrno\fR is set to indicate the error. .SH ERRORS .sp .LP The \fBwaitpid()\fR function will fail if: .sp .ne 2 .na \fB\fBECHILD\fR\fR .ad .RS 10n The process or process group specified by \fIpid\fR does not exist or is not a child of the calling process or can never be in the states specified by \fIoptions\fR. .RE .sp .ne 2 .na \fB\fBEINTR\fR\fR .ad .RS 10n The \fBwaitpid()\fR function was interrupted due to the receipt of a signal sent by the calling process. .RE .sp .ne 2 .na \fB\fBEINVAL\fR\fR .ad .RS 10n An invalid value was specified for \fIoptions.\fR .RE .SH USAGE .sp .LP With \fIoptions\fR equal to \fB0\fR and \fIpid\fR equal to \fB(pid_t)\(mi1\fR, \fBwaitpid()\fR is identical to \fBwait\fR(3C). The \fBwaitpid()\fR function is implemented as a call to the more general \fBwaitid\fR(2) function. .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 Committed _ MT-Level Async-Signal-Safe _ Standard See \fBstandards\fR(5). .TE .SH SEE ALSO .sp .LP \fBIntro\fR(2), \fBexec\fR(2), \fBexit\fR(2), \fBfork\fR(2), \fBpause\fR(2), \fBsigaction\fR(2), \fBptrace\fR(3C), \fBsignal\fR(3C), \fBsiginfo.h\fR(3HEAD), \fBwait\fR(3C), \fBwait.h\fR(3HEAD), \fBattributes\fR(5), \fBstandards\fR(5)