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markom |
'\"
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'\" Copyright (c) 1989-1993 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" RCS: @(#) $Id: DetachPids.3,v 1.1.1.1 2002-01-16 10:25:23 markom Exp $
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'\"
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.so man.macros
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.TH Tcl_DetachPids 3 "" Tcl "Tcl Library Procedures"
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.BS
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.SH NAME
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Tcl_DetachPids, Tcl_ReapDetachedProcs \- manage child processes in background
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.SH SYNOPSIS
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.nf
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\fB#include \fR
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.sp
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\fBTcl_DetachPids\fR(\fInumPids, pidPtr\fR)
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.sp
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\fBTcl_ReapDetachedProcs\fR()
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.SH ARGUMENTS
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.AS int *statusPtr
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.AP int numPids in
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Number of process ids contained in the array pointed to by \fIpidPtr\fR.
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.AP int *pidPtr in
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Address of array containing \fInumPids\fR process ids.
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.BE
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.SH DESCRIPTION
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.PP
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\fBTcl_DetachPids\fR and \fBTcl_ReapDetachedProcs\fR provide a
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mechanism for managing subprocesses that are running in background.
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These procedures are needed because the parent of a process must
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eventually invoke the \fBwaitpid\fR kernel call (or one of a few other
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similar kernel calls) to wait for the child to exit. Until the
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parent waits for the child, the child's state cannot be completely
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reclaimed by the system. If a parent continually creates children
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and doesn't wait on them, the system's process table will eventually
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overflow, even if all the children have exited.
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.PP
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\fBTcl_DetachPids\fR may be called to ask Tcl to take responsibility
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for one or more processes whose process ids are contained in the
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\fIpidPtr\fR array passed as argument. The caller presumably
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has started these processes running in background and doesn't
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want to have to deal with them again.
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.PP
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\fBTcl_ReapDetachedProcs\fR invokes the \fBwaitpid\fR kernel call
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on each of the background processes so that its state can be cleaned
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up if it has exited. If the process hasn't exited yet,
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\fBTcl_ReapDetachedProcs\fR doesn't wait for it to exit; it will check again
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the next time it is invoked.
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Tcl automatically calls \fBTcl_ReapDetachedProcs\fR each time the
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\fBexec\fR command is executed, so in most cases it isn't necessary
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for any code outside of Tcl to invoke \fBTcl_ReapDetachedProcs\fR.
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However, if you call \fBTcl_DetachPids\fR in situations where the
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\fBexec\fR command may never get executed, you may wish to call
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\fBTcl_ReapDetachedProcs\fR from time to time so that background
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processes can be cleaned up.
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.SH KEYWORDS
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background, child, detach, process, wait
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