On Thursday 08 October 2009 13:45:08 Matt Hammond wrote:
> Yes, its
> purpose when I coded it was to ensure queues are flushed.
It does not guarantee in order delivery though, when you chain 2 threaded
components together
Specifically, given this sequence of messages being *logically* sent:
ProducerThread
( 1, "outbox")
( 2, "outbox")
( 3, "outbox")
( 4, "outbox")
( 5, "outbox")
( 6, "outbox")
( 7, "outbox")
( 8, "outbox")
( producerFinished, "signal")
Note that I've divided those into 3 chunks of messages.
These get appended to outqueues in that order. Due to the way this loop...
for box in self.outboxes:
... works this ensures that these will get sent to the actual outboxes as
follows:
( 1, "outbox")
( 2, "outbox")
( 3, "outbox")
( 4, "outbox")
( 5, "outbox")
( 6, "outbox")
( 7, "outbox")
( 8, "outbox")
( producerFinished, "signal")
This arrives in the inboxes of the recipient:
( 1, "inbox")
( 2, "inbox")
( 3, "inbox")
( 4, "inbox")
( 5, "inbox")
( 6, "inbox")
( 7, "inbox")
( 8, "inbox")
( producerFinished, "control")
Now we hit the problem point. We hit this loop:
for box in self.inboxes:
This causes this delivery order - control box, then inbox. This comes in fits
and starts - due to timeslice interleaving:
{ no control messages }
( 1, "inbox")
( 2, "inbox")
( 3, "inbox")
{ no control messages }
( 4, "inbox")
( 5, "inbox")
( 6, "inbox")
( producerFinished, "control")
( 7, "inbox")
( 8, "inbox")
The consumer then exits early. This is because order is not guaranteed in this
way by the implementation. It's a rather subtle bug, one only really visible
if you are connecting two threads together.
Michael.
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