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[Launchpad Bug Tracker <1340669@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package mir - 0.5.0+14.10.20140717-0ubuntu1

---------------
mir (0.5.0+14.10.20140717-0ubuntu1) utopic; urgency=medium

  [ Daniel van Vugt ]
  * New upstream release 0.5.0 (https://launchpad.net/mir/+milestone/0.5.0)
    - mirclient ABI unchanged at 8. Clients do not need rebuilding.
    - mirserver ABI bumped to 23. Servers need rebuilding, but probably don't
      need modification:
      . DefaultServerConfiguration/Cursor API: Cursor interfaces changed, most
        notably CursorImages moved from ::mir::graphics to ::mir::input.
      . DefaultServerConfiguration: New "prompt" API.
      . DefaultServerConfiguration: "clock" member is now static.
      . SessionAuthorizer: New functions.
      . ServerConfiguration: New function added: the_prompt_connector().
    - Enhancements:
      . Add AddressSanitizer cmake build type.
      . frontend, client API, tests: add support for prompt session
        permissions and for client detecting errors.
      . server: Ensure our emergency cleanup handling infrastructure is
        signal-safe.
      . Implement and enable an xcursor based image loader for cursors.
      . Fix warnings raised by the new g++-4.9.
      . shared, scene: Introduce a generic listener collection.
      . MirMotionEvent: Define a struct typedef to allow for
        pointer_coordinates to be used individually.
    - Bugs fixed:
      . Nexus 10 leaks during overlay operations (LP: #1331769)
      . MultiThreadedCompositor deadlocks (LP: #1335311)
      . Intermittent test failure in ClientSurfaceEvents can client query
        orientation (LP: #1335741)
      . Intermittent test failure in ClientSurfaceEvents/OrientationEvents
        (LP: #1335752)
      . Intermittent memory error in ClientSurfaceEvents on
        orientation query (LP: #1335819)
      . mir_unit_tests.EventDistributorTest.* SEGFAULT (LP: #1338902)
      . [regression] Device locks randomly on welcome screen (LP: #1339700)
      . Intermittent deadlock when switching to session with custom display
        config & closing other session (LP: #1340669)
      . Mir cursor has no hotspot setting, assumes (0, 0) (LP: #1189775)
      . clang built mir_unit_tests.ProtobufSocketCommunicatorFD crashes
        intermittently (LP: #1300653)
      . g++-4.9 binary incompatibilities with libraries built with g++-4.8
        (LP: #1329089)
      . [test regression] SurfaceLoop fails sporadically on deleting surfaces
        for a disconnecting client (LP: #1335747)
      . Intermittent test failure ServerShutdown when clients are blocked
        (LP: #1335873)
      . [regression] mir_demo_client_multiwin is displayed with obviously
        wrong colours (LP: #1339471)
      . Partially onscreen surfaces not occluded when covered by another
        surface (LP: #1340078)
      . SurfaceConfigurator::attribute_set always say "unfocused" for focus
        property changes (LP: #1336548)
 -- Ubuntu daily release <ps-jenkins@xxxxxxxxxxxxxxxxxxx>   Thu, 17 Jul 2014 07:58:53 +0000

** Changed in: mir (Ubuntu)
       Status: Triaged => Fix Released

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https://bugs.launchpad.net/bugs/1340669

Title:
  Intermittent deadlock when swithcing to session with custom display
  configuration while closing other session

Status in Mir:
  Fix Committed
Status in Mir 0.4 series:
  Won't Fix
Status in “mir” package in Ubuntu:
  Fix Released

Bug description:
  If when closing a session we change focus to another session that has
  a custom display configuration, we may hit a deadlock.

  This can been seen occasionally as a hang when logging out of an X
  session under XMir. It currently only affects XMir because it is the
  only production client that applies custom display configurations.

  Here is how it happens:

  [IPC thread]

  ~SessionMediator
  SessionManager::close_session()
  SessionManager::set_focus_to_locked(next session)
  BroadcastingSessionEventSink::handle_focus_change()
  MediatingDisplayChanger handles the focus change event and enqueues a display reconfiguration action into AsioMainLoop

  From this point we have two interesting execution threads:

  [IPC thread continues]

  ~ApplicationSession
  ...
  mir::scene::Observers::surface_removed() *** Acquires READ lock on surface observer [1]
  ...
  AsioMainLoop::unregister_fd_handler *** Enqueues an action into AsioMainLoop and waits for it to complete

  [MainLoop thread]

  Executes display reconfiguration action:
  MultiThreadedCompositor::stop()
  mir::scene::Observers::remove() ** Acquires WRITE lock on observer [2]

  If the IPC thread calls the surface_removed() observer before the
  display reconfiguration action is executed, then the MainLoop thread
  at [2] ends up waiting for a WRITE lock, but can't get it because a
  READ lock has been acquired at [1]. At the same time, the IPC thread
  is blocked waiting for unregister_fd_handler() to return, but it
  doesn't return because the unregistration action has been enqueued
  after the display reconfiguration handler which is now blocked at [2].

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