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'\" RCS: @(#) $Id: DetachPids.3,v 1.3 2001/04/03 14:53:45 andreas_kupries Exp $
'\" The definitions below are for supplemental macros used in Tcl/Tk
'\" .AP type name in/out ?indent?
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'\" Print arg1 underlined, then print arg2 normally.
'\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $
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Command-Line Name: \\fB\\$1\\fR
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.TH Tcl_DetachPids 3 "" Tcl "Tcl Library Procedures"
Tcl_DetachPids, Tcl_ReapDetachedProcs, Tcl_WaitPid \- manage child processes in background
\fBTcl_DetachPids\fR(\fInumPids, pidPtr\fR)
\fBTcl_ReapDetachedProcs\fR()
\fBTcl_WaitPid\fR(\fIpid, statPtr, options\fR)
Number of process ids contained in the array pointed to by \fIpidPtr\fR.
Address of array containing \fInumPids\fR process ids.
The id of the process (pipe) to wait for.
The result of waiting on a process (pipe). Either 0 or ECHILD.
The options controlling the wait. WNOHANG specifies not to wait when
\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.
\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.
\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.
\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
background, child, detach, process, wait