[tor-bugs] #9659 [Firefox Patch Issues]: high cpu usage from tbb-firefox.exe on web requests

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#9659: high cpu usage from tbb-firefox.exe on web requests
-------------------------------------+-------------------------------------
 Reporter:  cypherpunks              |          Owner:  mikeperry
     Type:  defect                   |         Status:  new
 Priority:  normal                   |      Milestone:  TorBrowserBundle
Component:  Firefox Patch Issues     |  2.3.x-stable
 Keywords:  hang unresponsive        |        Version:  Tor: 0.2.3.25
  throttle                           |  Actual Points:
Parent ID:                           |         Points:
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 Some change to tbb-firefox.exe after TBB for windows 2.3.25-6 has
 introduced a bad loop which throttles the CPU on every request sent
 through the proxy.  This will go unnoticed if you are not using all of
 your CPU at the time.  Running something like prime95 (www.mersenne.org)
 in the background will make the problem evident, as TBB versions after
 2.3.25-6 start to hang the system as you click open links or have other
 traffic through the proxy while waiting for their connections to be made
 and complete.  Something changed in how requests were handled in later
 versions which introduced the problem.

 In the old versions, when you sent a request for a web page (lets say
 www.google.com), you could have the tor network map open with the view the
 network button and watch how it works.  The browser status bar will say
 connecting to www.google.com and it will say that until a circuit is open
 in the network map (www.google.com appears in the list), at which point
 the browser status bar will change to say connected to www.google.com.  It
 then sends the request, and the status bar changes to waiting for
 www.google.com, then the page loads.  I can watch this happen in task
 manager and it uses hardly any CPU.

 In the new versions, this behavior is different.  When you request a web
 page, the browser immediately says waiting for www.google.com, even though
 there is no circuit open in tor, and this is where the bad loop is, as
 watching tbb-firefox.exe in task manager the CPU usage becomes abnormally
 high.  This will cause the system to hang, becoming temporarily
 unresponsive until the loops finish, if the rest of the system is under
 heavy cpu load.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9659>
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