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[Garth Wells <709149@xxxxxxxxxxxxxxxxxx>]

** Changed in: dolfin
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/709149

Title:
  Potential deadlock in parallel vector resize

Status in DOLFIN:
  Fix Released

Bug description:
  This may not be a problem in practice, but I'm reporting it because
  these things may fail very randomly (only with a specific number of
  processors and specific mesh).

  In PETScVector::resize (and probably other backends), there is a
  slight risk that this test triggers on only a subset of the processors
  (say if a vector with distribution 4-3-3 is resized to distribution
  3-4-3):

    // Check if resizing is required
    if (x && (this->local_range().first == range.first && this->local_range().second == range.second))
      return;

  Then, not all processors participate in the collective resizing, and a
  deadlock results. Similar problems may exist elsewhere, wherever the
  code path depend on local data.

  The easiest is to just skip the test (for distributed vectors at
  least). But this may be a performance issue? An alternative would be
  to let the vector "know" which distribution it has (i.e., give it a
  "mapping id" at creation/resize time), but to get that without
  parallel overhead might require changes in the interface.