1Tcl_DetachPids(3)           Tcl Library Procedures           Tcl_DetachPids(3)
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NAME

8       Tcl_DetachPids,  Tcl_ReapDetachedProcs, Tcl_WaitPid - manage child pro‐
9       cesses in background
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SYNOPSIS

12       #include <tcl.h>
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14       Tcl_DetachPids(numPids, pidPtr)
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16       Tcl_ReapDetachedProcs()
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18       Tcl_Pid
19       Tcl_WaitPid(pid, statusPtr, options)
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ARGUMENTS

22       int numPids (in)                 Number of process ids contained in the
23                                        array pointed to by pidPtr.
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25       int *pidPtr (in)                 Address  of  array  containing numPids
26                                        process ids.
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28       Tcl_Pid pid (in)                 The id of the process (pipe)  to  wait
29                                        for.
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31       int *statusPtr (out)             The  result  of  waiting  on a process
32                                        (pipe). Either 0 or ECHILD.
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34       int options (in)                 The options controlling the wait. WNO‐
35                                        HANG specifies not to wait when check‐
36                                        ing the process.
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DESCRIPTION

40       Tcl_DetachPids and Tcl_ReapDetachedProcs provide a mechanism for manag‐
41       ing  subprocesses that are running in background.  These procedures are
42       needed because the parent of a process must eventually invoke the wait‐
43       pid  kernel  call  (or one of a few other similar kernel calls) to wait
44       for the child to exit.  Until the  parent  waits  for  the  child,  the
45       child's  state cannot be completely reclaimed by the system.  If a par‐
46       ent continually creates children and doesn't wait on them, the system's
47       process  table  will eventually overflow, even if all the children have
48       exited.
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50       Tcl_DetachPids may be called to ask Tcl to take responsibility for  one
51       or  more  processes whose process ids are contained in the pidPtr array
52       passed as argument.  The caller presumably has started these  processes
53       running  in  background  and  does  not  want to have to deal with them
54       again.
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56       Tcl_ReapDetachedProcs invokes the waitpid kernel call on  each  of  the
57       background  processes  so  that  its  state can be cleaned up if it has
58       exited.  If the process has not exited yet, Tcl_ReapDetachedProcs  does
59       not  wait  for  it  to  exit;   it will check again the next time it is
60       invoked.  Tcl automatically calls Tcl_ReapDetachedProcs each  time  the
61       exec  command is executed, so in most cases it is not necessary for any
62       code outside of Tcl to invoke Tcl_ReapDetachedProcs.  However,  if  you
63       call  Tcl_DetachPids in situations where the exec command may never get
64       executed, you may wish to call Tcl_ReapDetachedProcs from time to  time
65       so that background processes can be cleaned up.
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67       Tcl_WaitPid  is  a  thin  wrapper around the facilities provided by the
68       operating system to wait on the end of a spawned process and to check a
69       whether  spawned  process  is  still running. It is used by Tcl_ReapDe‐
70       tachedProcs and the channel system to  portably  access  the  operating
71       system.
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KEYWORDS

75       background, child, detach, process, wait
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79Tcl                                                          Tcl_DetachPids(3)
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