Tcl_DetachPids(3)

Tcl_DetachPids(3)    Tcl Library Procedures     Tcl_DetachPids(3)

_________________________________________________________________

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  con-
                                      tained 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 responsibil-
     ity  for  one  or  more processes whose process ids are con-
     tained in the pidPtr array passed as argument.   The  caller

Tcl                       Last change:                          1

Tcl_DetachPids(3)    Tcl Library Procedures     Tcl_DetachPids(3)

     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 automati-
     cally 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.  How-
     ever, 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 pro-
     cess and to check a whether spawned process  is  still  run-
     ning.  It  is  used by Tcl_ReapDetachedProcs and the channel
     system to portably access the operating system.

KEYWORDS

     background, child, detach, process, wait

Tcl                       Last change:                          2