suplib/src/Reaper.i3

 Copyright 1996-2003 John D. Polstra.
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 * $Id: Reaper.i3.html,v 1.3 2010-04-29 17:20:02 wagner Exp $ 


 The Reaper interface provides facilities for controlling and
   harvesting threads. 


INTERFACE Reaper;

IMPORT Thread;

TYPE
  T <: Public;

  Public = Private OBJECT METHODS
    init(): T;
  END;

  Private <: ROOT;

 A Reaper.T manages a set of threads.  It allows you to fork several
   threads, and then wait until any one of them has terminated.  You do not
   need to know a priori which thread will terminate first.


   After one of the threads has terminated (or, actually, at any time),
   you can alert all of the remaining threads, for example, to terminate
   all of them prematurely.


   We say that the threads managed by the reaper are registered with it.
   A thread is registered with the reaper at the time it is forked.  To
   achieve that, use the following procedure to fork the thread, instead
   of Thread.Fork. 


PROCEDURE Fork(reaper: T; cl: Thread.Closure): Thread.T;

 Fork a thread, and register it with the reaper. 
 When a registered thread is about to terminate, it should notify its
   reaper via the following procedure. 


PROCEDURE Dying(reaper: T);

 Called by a thread to inform the reaper that it is about to exit. 
 The following procedures block until the next registered thread has
   terminated.  Then they perform the equivalent of Thread.Join on the
   terminated thread, and pass back the results. 


PROCEDURE JoinNext(reaper: T;
                   VAR thr: Thread.T;
                   VAR ret: REFANY): BOOLEAN;

 If there are still registered threads that have not died, wait for
   the next one to die.  When that occurs, return TRUE, passing back
   the thread's handle and return value.  If there are no more registered
   threads alive, return FALSE. 

PROCEDURE AlertJoinNext(reaper: T;
                        VAR thr: Thread.T;
                        VAR ret: REFANY): BOOLEAN
  RAISES {Thread.Alerted};

 An alertable version of JoinNext. 
 To alert all registered threads that have not yet terminated, use
   the procedure below. 


PROCEDURE AlertAll(reaper: T);

 Alerts all the registered threads that are still alive. 

END Reaper.