'\" '\" Copyright (c) 1989-1993 The Regents of the University of California. '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" RCS: @(#) DetachPids.3,v 1.5 2003/01/21 19:39:58 hunt Exp '\" .so man.macros .TH Tcl_DetachPids 3 "" Tcl "Tcl Library Procedures" .BS .SH NAME Tcl_DetachPids, Tcl_ReapDetachedProcs, Tcl_WaitPid \- manage child processes in background .SH SYNOPSIS .nf \fB#include <tcl.h>\fR .sp \fBTcl_DetachPids\fR(\fInumPids, pidPtr\fR) .sp \fBTcl_ReapDetachedProcs\fR() .sp Tcl_Pid \fBTcl_WaitPid\fR(\fIpid, statPtr, options\fR) .SH ARGUMENTS .AS int *statusPtr .AP int numPids in Number of process ids contained in the array pointed to by \fIpidPtr\fR. .AP int *pidPtr in Address of array containing \fInumPids\fR process ids. .AP Tcl_Pid pid in The id of the process (pipe) to wait for. .AP int* statPtr out The result of waiting on a process (pipe). Either 0 or ECHILD. .AP int options The options controlling the wait. WNOHANG specifies not to wait when checking the process. .BE .SH DESCRIPTION .PP \fBTcl_DetachPids\fR and \fBTcl_ReapDetachedProcs\fR provide a mechanism for managing subprocesses that are running in background. These procedures are needed because the parent of a process must eventually invoke the \fBwaitpid\fR kernel call (or one of a few other similar kernel calls) to wait for the child to exit. Until the parent waits for the child, the child's state cannot be completely reclaimed by the system. If a parent continually creates children and doesn't wait on them, the system's process table will eventually overflow, even if all the children have exited. .PP \fBTcl_DetachPids\fR may be called to ask Tcl to take responsibility for one or more processes whose process ids are contained in the \fIpidPtr\fR array passed as argument. The caller presumably has started these processes running in background and doesn't want to have to deal with them again. .PP \fBTcl_ReapDetachedProcs\fR invokes the \fBwaitpid\fR kernel call on each of the background processes so that its state can be cleaned up if it has exited. If the process hasn't exited yet, \fBTcl_ReapDetachedProcs\fR doesn't wait for it to exit; it will check again the next time it is invoked. Tcl automatically calls \fBTcl_ReapDetachedProcs\fR each time the \fBexec\fR command is executed, so in most cases it isn't necessary for any code outside of Tcl to invoke \fBTcl_ReapDetachedProcs\fR. However, if you call \fBTcl_DetachPids\fR in situations where the \fBexec\fR command may never get executed, you may wish to call \fBTcl_ReapDetachedProcs\fR from time to time so that background processes can be cleaned up. .PP \fBTcl_WaitPid\fR is a thin wrapper around the facilities provided by the operating system to wait on the end of a spawned process and to check a whether spawned process is still running. It is used by \fBTcl_ReapDetachedProcs\fR and the channel system to portably access the operating system. .SH KEYWORDS background, child, detach, process, wait