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, 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.
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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

Tcl Tcl_DetachPids(3)