The problem was caused by a race condition of all things. ClangCompleter would
set possibly_completions_ready when starting the first parse pass for the file
and then would try to extract diagnostics for the file before the diagnostics
were done. Technically this was not a problem because only an empty diagnostics
vector would be returned, but this triggered Syntastic because hey, we have some
diagnostics to show (even though we don't).
And then Syntastic would try to close the location list window during startup
when this operation is not available. Technically it's Syntastic's fault, but a
more principled way to check for done diagnostics is to return and use a future
for file parsing operations and this solution also works around the Syntastic
issue.
This change should fix the random hangs and segfaults when using the clang
completer. Also, assertion errors printed to the console on vim exit should go
away too, same thing with segfaults on vim exit. These "on exit" errors were
caused by not cleanly shutting down the background threads; both the identifier
completer and the clang one now join the threads on destruction. This results in
a clean shutdown.
The new clang completer architecture now uses only one clang thread (again)
instead of a completion and parsing thread. Since the parsing task needs to wait
on the completion task if it was started first (and vice-versa) there's no point
to using two threads. The desired "simplicity" of using two threads for these
two tasks actually created needless complexity (and bugs). Sigh. Such is life.
A TranslationUnit abstraction was also created and this in turn also reduces the
complexity of the clang completer.
The clang completer now also has some (very) basic tests.
