Fixed #2294 - Classes sometimes cannot be found

This patch should fix the race condition causing ticket 2294; it extends the loading logic so that:

    * initial load attempts are processed (as before),
    * recursive load attempts return immediately (as before),
    * but subsequent concurrent load attempts from different threads
      wait on a semaphore (condition variable) and then retry (e.g.
      use the now-valid results of the first thread).

This is a slight modification of the solution I'd originally proposed, to prevent a deadlock
that could have arisen if three or more threads simultaneously attempted to load the same item.
Though it solves the bug as reported, it has room for improvement:

    * Failures aren't cached, so repeated attempts will be made to
      import invalid items each time they are encountered
    * It doesn't address any of the underlying referential ambiguity
      (module vs. filename)
    * The threading logic should probably be refactored into a separate
      class (as a start I encapsulated it in an ad hoc singleton class,
      so at least it isn't cluttering up the load method)

Signed-off-by: Markus Roberts <Markus@reality.com>

0 files changed, 0 insertions, 0 deletions