[tor-bugs] #28866 [Core Tor/sbws]: ResultDump.queue.put() can hang if the queue is full

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#28866: ResultDump.queue.put() can hang if the queue is full
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 Reporter:  teor           |          Owner:  juga
     Type:  defect         |         Status:  needs_revision
 Priority:  Medium         |      Milestone:  sbws: 1.0.x-final
Component:  Core Tor/sbws  |        Version:  sbws: 1.0.2
 Severity:  Normal         |     Resolution:
 Keywords:                 |  Actual Points:
Parent ID:  #28663         |         Points:  1
 Reviewer:  mikeperry      |        Sponsor:
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Changes (by mikeperry):

 * status:  needs_review => needs_revision


Comment:

 Ok I now understand a bit more of what's going on here. I am still not in
 favor of this solution, for the following reasons:

 1. The only way that the closure callback could block in the old code was
 if the result getter thread died/stalled/deadlocked and did not manage to
 actually pull a result to make the queue non-full.
 2. The new code has a while loop which will still run forever if the queue
 is full and nothing pulls from it. It will just log in that case.

 It seems like #1 and #2 both block and fail to return in the exact same
 way. What about:

 {{{
 try:
   result_dump.queue.put(measurement_result, timeout=3)
 except Full as e:
   log.warn("The results queue is staying full. Is the getter thread
 dead?")
 }}}

 This way, the closure will only block for at most 3 seconds, which should
 only happen if the getter is dead/hung, since the getter should have
 pulled in just 1 second. Hence the warn in that case.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28866#comment:12>
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