[Python-bugs-list] [ python-Bugs-456024 ] event synchronization

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Bugs item #456024, was opened at 2001-08-27 22:56
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=456024&group_id=5470

Category: Threads
Group: Feature Request
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: event synchronization

Initial Comment:
It would be nice if the set and clear operations
on Event objects atomically returned the old state of
the internal flag:

  old_state = event.set()
  if old_state: nevermind()
  else: do_stuff ()

sets the flag to true and returns true if the flag
was already set, otherwise returns false.

This avoids the obvious race condition in
  if event.isSet(): nevermind()
  else: 
     event.set()
     do_stuff()

Maybe there's a way to accomplish this with
Semaphore objects (I haven't figured this thread
stuff out yet) but the event interface is more
natural for some purposes (i.e. the event represents
a lock on a resource).


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