A user on comp.lang.python has twisted himself into knots writing multi-threaded
code that avoids locks and queues but fails when running code with non-atomic
access to a shared resource. While his specific design is somewhat flawed, it
does suggest that we could offer an easy way to make a block of code atomic
without the complexity of other synchronization tools:
gil.acquire()
try:
#do some transaction that needs to be atomic
finally:
gil.release()
The idea is to temporarily suspend thread switches (either using the GIL or a
global variable in the eval-loop). Think of it as "non-cooperative"
multi-threading. While this is a somewhat rough approach, it is dramatically
simpler than the alternatives (i.e. wrapping locks around every access to a
resource or feeding all resource requests to a separate thread via a Queue).
While I haven't tried it yet, I think the implementation is likely to be
trivial.
FWIW, the new with-statement makes the above fragment even more readable:
with atomic_transaction():
# do a series of steps without interruption
Raymond
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