DragonFly On-Line Manual Pages
Tcl_DetachPids(3) Tcl Library Procedures Tcl_DetachPids(3)
Tcl_DetachPids, Tcl_ReapDetachedProcs, Tcl_WaitPid - manage child
processes in background
Tcl_WaitPid(pid, statusPtr, options)
int numPids (in) Number of process ids contained in the
array pointed to by pidPtr.
int *pidPtr (in) Address of array containing numPids
Tcl_Pid pid (in) The id of the process (pipe) to wait
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.
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
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
background, child, detach, process, wait