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 system.
KEYWORDS¶
background, child, detach, process, wait