Tcl_WaitPid

Tcl_DetachPids(3)           Tcl Library Procedures           Tcl_DetachPids(3)



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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, 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 pro-
                                    cess 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 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 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 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)