Tcl_DetachPids (3)
manage child processes in background
SYNOPSIS
#include <tcl.h>
Tcl_DetachPids(numPids, pidPtr)
Tcl_ReapDetachedProcs()
ARGUMENTS
int *statusPtr
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.
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 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 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.
KEYWORDS
background, child, detach, process, wait
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