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Tcl_DetachPids(3)	    Tcl	Library	Procedures	     Tcl_DetachPids(3)

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NAME
       Tcl_DetachPids,	 Tcl_ReapDetachedProcs,	 Tcl_WaitPid  -	 manage	 child
       processes in background

SYNOPSIS
       #include	<tcl.h>

       Tcl_DetachPids(numPids, pidPtr)

       Tcl_ReapDetachedProcs()

       Tcl_Pid
       Tcl_WaitPid(pid,	statusPtr, options)

ARGUMENTS
       Tcl_Size	numPids	(in)		Number of process ids contained	in the
					array pointed to by pidPtr.

       int *pidPtr (in)			Address	of  array  containing  numPids
					process	ids.

       Tcl_Pid pid (in)			The  id	 of the	process	(pipe) to wait
					for.

       int *statusPtr (out)		The result of  waiting	on  a  process
					(pipe).	Either 0 or ECHILD.

       int options (in)			The options controlling	the wait. WNO-
					HANG specifies not to wait when	check-
					ing the	process.
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DESCRIPTION
       Tcl_DetachPids and Tcl_ReapDetachedProcs	provide	a mechanism for	manag-
       ing  subprocesses that are running in background.  These	procedures are
       needed because the parent of a process must eventually invoke the wait-
       pid 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  par-
       ent continually creates children	and doesn't wait on them, the system's
       process	table  will eventually overflow, even if all the children have
       exited.

       Tcl_DetachPids may be called to ask Tcl to take responsibility for  one
       or  more	 processes whose process ids are contained in the pidPtr array
       passed as argument.  The	caller presumably has started these  processes
       running	in  background	and  does  not	want to	have to	deal with them
       again.

       Tcl_ReapDetachedProcs invokes the waitpid kernel	call on	 each  of  the
       background  processes so	that its state can be cleaned up if it has ex-
       ited.  If the process has not exited  yet,  Tcl_ReapDetachedProcs  does
       not  wait  for it to exit;  it will check again the next	time it	is in-
       voked.  Tcl automatically calls	Tcl_ReapDetachedProcs  each  time  the
       exec  command is	executed, so in	most cases it is not necessary for any
       code outside of Tcl to invoke Tcl_ReapDetachedProcs.  However,  if  you
       call  Tcl_DetachPids in situations where	the exec command may never get
       executed, you may wish to call Tcl_ReapDetachedProcs from time to  time
       so that background processes can	be cleaned up.

       Tcl_WaitPid is a	thin wrapper around the	facilities provided by the op-
       erating	system	to wait	on the end of a	spawned	process	and to check a
       whether spawned process is still	running. It  is	 used  by  Tcl_ReapDe-
       tachedProcs  and	 the  channel  system to portably access the operating
       system.

KEYWORDS
       background, child, detach, process, wait

Tcl							     Tcl_DetachPids(3)

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