[Python-Dev] Proposed addition to threading module - released

[Nick Coghlan]

Do we want to add a "released" context manager to the threading module for 
2.5? It was mentioned using the name "unlocked" in PEP 343, but never spelt out:

class released(object):
     def __init__(self, lock):
         self.lock = lock
     def __enter__(self):
         self.lock.release()
     def __exit__(self, *exc_info):
         self.lock.acquire()

(This context manager is the equivalent of PEP 319's asynchronize keyword)

Usage would be:

   from threading import RLock, released

   sync_lock = RLock()

   def thread_safe():
      with sync_lock:
          # This is thread-safe
          with released(sync_lock):
              # Perform long-running or blocking operation
              # that doesn't need to hold the lock
          # We have the lock back here

(This particular example could be handled by two separate "with sync_lock" 
statements with the asynchronous operation between them, but other cases put 
the asynchronous operation inside a loop or a conditional statement which 
means that particular trick won't work).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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