gistfile1.txt

1. Tasks are recieved on the "tasks"-queue.

2. A worker dequeues a task.

3. The worker locks the entity related to the task.

4. The worker executes the task with the given entity.

5. The worker releases the locked entity.

In step 2, if the entity is already locked, the worker should put the task
back on the queue and take another task. The problem is, I can't simply
enqueue the task, since that will fuck up the ordering.

Example, all tasks needs entity Entity A.

Task A, Task B, Task C, Task D

Worker 1 dequeues Task A, locks Entity A

Worker 2 dequeues Task B, sees that Entity A is locked, enqueues Task B
again.

Now the order is Task C, Task D, Task B.

What I want to do, is to put Task B back in it's original place.

In short, the workers should dequeue a task where the entity isn't locked.
The workers are placed in different physical hosts.