Tcl_DetachPids(3) Tcl Library Procedures Tcl_DetachPids(3)
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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, statPtr, 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* 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.
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DESCRIPTION
Tcl_DetachPids and Tcl_ReapDetachedProcs provide a mechanism for managing subprocesses that are run-ning running
ning 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 ta-ble table
ble 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 neces-sary necessary
sary for any code outside of Tcl to invoke Tcl_ReapDetachedProcs. However, if you call Tcl_Detach-Pids Tcl_DetachPids
Pids in situations where the exec command may never get executed, you may wish to call Tcl_ReapDe-tachedProcs Tcl_ReapDetachedProcs
tachedProcs 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
Tcl Tcl_DetachPids(3)
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