tcl_detachpids(3)
NAME
Tcl_DetachPids, Tcl_ReapDetachedProcs, Tcl_WaitPid - man
age child processes in background
SYNOPSIS
#include <tcl.h> Tcl_DetachPids(numPids, pidPtr) Tcl_ReapDetachedProcs() Tcl_Pid Tcl_WaitPid(pid, statPtr, options)
ARGUMENTS
- int numPids (in) Number of process ids con
- tained 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* statPtr (out) The result of waiting on a
- process (pipe). Either 0 or
ECHILD. - int options The options controlling the
- wait. WNOHANG specifies not
to wait when checking the
process.
DESCRIPTION
Tcl_DetachPids and Tcl_ReapDetachedProcs provide a mecha
nism for managing subprocesses that are running in back
ground. 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 responsi
bility 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 doesn't 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 hasn't exited
yet, Tcl_ReapDetachedProcs doesn't 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 isn't neces
sary for any code outside of Tcl to invoke Tcl_ReapDe
tachedProcs. However, if you call Tcl_DetachPids in situ
ations 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 pro
vided 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 system.
KEYWORDS
- background, child, detach, process, wait