Dequeue atomic

[AlbertoCasasOrtiz]

Fixes #267.

Most changes are due to indentation. Real changes are the addition of atomic to make everything a single transaction:

with transaction.atomic():

Select for update, which locks the trial so other workers cannot modify or lock them. If already locked by another worker, it skips it.

.select_for_update(skip_locked=True)

And a status check that, if for any reason a worker gets a trial already locked and in a non-available status, will skip it:

if trial.status not in ["stopped", "reprocess"]:
    raise Http404

[AlbertoCasasOrtiz]

@carmichaelong I just fixed conflicts on this branch

[csherry04]

@AlbertoCasasOrtiz It looks like maybe this second section got copied in with merge but it reassigning the things just assigned in the atomic transaction. The second version (not atomic) seems to maybe be the one with updated logic for the delayed uploads? Perhaps then can get rid of the first one and wrap the second one in an atomic transaction?

[AlbertoCasasOrtiz]

Thank you @csherry04. I just updated it accordingly (to avoid conflicts with dev and duplicated code, I modified from original code again to be atomic).

[AlbertoCasasOrtiz]

I just created a new test for this. Also, changed some database calls to be more efficient.