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Tcl_DetachPids(3)           Tcl Library Procedures           Tcl_DetachPids(3)




NAME

       Tcl_DetachPids,  Tcl_ReapDetachedProcs, Tcl_WaitPid - manage child pro-
       cesses in background


SYNOPSIS

       #include <tcl.h>

       Tcl_DetachPids(numPids, pidPtr)

       Tcl_ReapDetachedProcs()

       Tcl_Pid
       Tcl_WaitPid(pid, statusPtr, options)


ARGUMENTS

       Number of process ids contained in the  array  pointed  to  by  pidPtr.
       Address of array containing numPids process ids.  The id of the process
       (pipe) to wait for.  The result of waiting on a process (pipe).  Either
       0  or  ECHILD.  The options controlling the wait. WNOHANG specifies not
       to wait when checking the process.


DESCRIPTION

       Tcl_DetachPids and Tcl_ReapDetachedProcs provide a mechanism for manag-
       ing  subprocesses that are running in background.  These procedures are
       needed because the parent of a process must eventually invoke the wait-
       pid  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 par-
       ent 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_ReapDe-
       tachedProcs and the channel system to  portably  access  the  operating
       system.



KEYWORDS

       background, child, detach, process, wait



Tcl                                                          Tcl_DetachPids(3)

DetachPids 8.5.4 - Generated Mon Aug 18 05:26:48 CDT 2008
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