[tor-bugs] #29497 [Applications/Tor Browser]: After tor crash, firefox.exe (tor browser) shoots up to 50+% cpu usage and stays there til killed in task list

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#29497: After tor crash, firefox.exe (tor browser) shoots up to 50+% cpu usage and
stays there til killed in task list
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 Reporter:  cypherpunks               |          Owner:  tbb-team
     Type:  defect                    |         Status:  needs_information
 Priority:  High                      |      Milestone:
Component:  Applications/Tor Browser  |        Version:  Tor: unspecified
 Severity:  Normal                    |     Resolution:
 Keywords:                            |  Actual Points:
Parent ID:                            |         Points:
 Reviewer:                            |        Sponsor:
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Changes (by mcs):

 * status:  new => needs_information
 * cc: igt0, arthuredelstein (added)


Comment:

 Replying to [comment:3 cypherpunks]:
 > `extensions.torbutton.display_circuit`
 > Bug stopped when it is set to false.

 Ah ha! Thanks for tracking that down.

 What happens when tor exits is that the code inside src/modules/tor-
 control-port.js enters a tight loop in which the `awaitNextChunk()`
 function within `io.pumpInputStream()` is called repeatedly. One possible
 fix would be to check for a zero return from
 `scriptableInputStream.available()` and shut down the circuit display
 monitor when that occurs (but I am not 100% sure that is a safe fix).
 Comments in Mozilla's code imply that the available() call should throw
 after the stream has closed, but apparently that is not true in all
 situations.

 Igor and/or Arthur, do you remember why the following change was made?
  Bug 26100: Use inputStream.asyncWait instead of nsIInputStreamPump
 https://gitweb.torproject.org/torbutton.git/commit/?id=2764f9a0019b1eb8704e6748bfa46b9f58aaf74a

 Kathy and I were unable to get circuit display working after we switched
 back to nsIInputStreamPump, and we are wondering if we should try harder.
 We also are hoping that the reason for the above change may shed some
 light on this bug.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29497#comment:4>
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