[tor-bugs] #8746 [Tor]: Tor tries to kill nonexistent proxy PID on second SIGINT

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#8746: Tor tries to kill nonexistent proxy PID on second SIGINT
--------------------+-------------------------------------------------------
 Reporter:  dcf     |          Owner:     
     Type:  defect  |         Status:  new
 Priority:  normal  |      Milestone:     
Component:  Tor     |        Version:     
 Keywords:          |         Parent:     
   Points:          |   Actualpoints:     
--------------------+-------------------------------------------------------
 This is what 180-pluggable-transport.txt says about proxies and SIGINT:

   Proxies should respond to a single INT signal by closing their listener
 ports and not accepting any new connections, but keeping all connections
 open, then terminating when connections are all closed.  Proxies should
 respond to a second INT signal by shutting down cleanly.

 I implemented the websocket-server transport to work as specified:
 https://gitweb.torproject.org/flashproxy.git/blob/c23caf1f71f8281319cadf55002723dbcd333905
 :/websocket-transport/websocket-server.go#l238
 I noticed unexpected behavior when the proxy receives a SIGINT, and
 doesn't have any open connection, and so exits immediately without waiting
 for a second SIGINT. The parent tor process tries to kill a nonexistent
 PID:
 {{{
 ^CApr 19 17:58:59.000 [notice] Interrupt: we have stopped accepting new
 connections, and will shut down in 30 seconds. Interrupt again to exit
 now.
 ^CApr 19 17:59:05.000 [notice] SIGINT received a second time; exiting now.
 Apr 19 17:59:05.000 [notice] Failed to terminate process with PID '18277'
 ('No such process').
 }}}

 The PID might have been reclaimed in the meantime, and tor could be
 killing an unrelated process.

 (Originally from https://lists.torproject.org/pipermail/tor-
 dev/2013-April/004679.html.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/8746>
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