Tcl_WaitPid(pid, statusPtr, options)
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 childs state cannot be completely
reclaimed by the system. If a parent continually creates children
and doesnt wait on them, the systems 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 system.