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tcl_detachpids

Tcl_DetachPids(3)					      Tcl Library Procedures						 Tcl_DetachPids(3)

__________________________________________________________________________________________________________________________________________________

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

       int 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. WNOHANG specifies not to wait when checking the process.
_________________________________________________________________

DESCRIPTION

       Tcl_DetachPids  and  Tcl_ReapDetachedProcs  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 waitpid 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.

       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
       exited.	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
       invoked.   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 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 Tcl_ReapDetachedProcs and the channel system to portably access the operating  sys-
       tem.

KEYWORDS

       background, child, detach, process, wait

Tcl																 Tcl_DetachPids(3)

Programming