Async: support (re-)executing single Job multiple times

Storing Future and current Job progress directly in Executors means
that we cannot re-execute finished job, or even execute the same Job
multiple times in parallel. To do so, we need to make Executors stateless
and track the state elsewhere.

This change does that by moving the execution state from Executor to Execution
class. Executors now only describe the tasks to execute, while Execution holds
the current state of execution. New Execution is created every time Job::exec()
is called.

Execution holds reference to it's result (Future) and Executor which created
the Execution. This ensures that Executor is not deleted when Job (which owns
Executors) goes out of scope while the execution is still running. At the same
time Future holds reference to relevant Execution, so that the Execution is
deleted when all copies of Future referring result from the respective Execution
are deleted.

0 files changed, 0 insertions, 0 deletions