The problem was:
- MessageFileViewFragment.clearContent (A) is called in onDestroy
- MessageFileViewFragment.openMessageSync (B) is called in a bg thread
to load an eml file
- And both try to hold the same lock. (mLock)
- If EML is large enough, B takes _seconds_. If you press back during this,
onDestroy gets blocked trying to lock mLock.
- This could also cause a crash, because the task that runs openMessageSync
won't get cancelled in this case, because that's done in clearContent.
Because of this, the task's onPostExecute tries to touch a UI element
when the fragment is actually being destroyed.
The lock was introduced to protect mFileEmailUri, only to keep the same
semantics for openMessage() as MessageViewFragment. i.e. openMessage can be
called multiple times for the same instance of the fragment.
However, in practice, this won't happen. Unlike the regular message view,
we never reuse MessageFileViewFragment. MessageFileViewFragment instances
are created per message. This lock was just reminiscence from the early
developmen stage.
So, fix is simple -- just remove the lock.
Bug 3500487
Change-Id: If2b22a683666de535454bb1293563796fa7acfd7
ee82e34a28