Python: Wait on all of `concurrent.futures.ThreadPoolExecutor`'s futures
concurrency, future, python
Solution
Just call `Executor.shutdown`:
`shutdown(wait=True)`
Signal the executor that it should free any resources that it is using when the currently pending futures are done executing. Calls to `Executor.submit()` and `Executor.map()` made after shutdown will raise `RuntimeError`.
If wait is `True` then this method will not return until all the pending futures are done executing and the resources associated with the executor have been freed.
However if you keep track of your futures in a list then you can avoid shutting the executor down for future use using the `futures.wait()` function:
`concurrent.futures.wait(fs, timeout=None, return_when=ALL_COMPLETED)`
Wait for the `Future` instances (possibly created by different `Executor` instances) given by `fs` to complete. Returns a named 2-tuple of sets. The first set, named done, contains the futures that completed (finished or were cancelled) before the wait completed. The second set, named not_done, contains uncompleted futures.
note that if you don't provide a `timeout` it waits until all futures have completed.
You can also use `futures.as_completed()` instead, however you'd have to iterate over it.
Problem
I've given `concurrent.futures.ThreadPoolExecutor` a bunch of tasks, and I want to wait until they're all completed before proceeding with the flow. How can I do that, without having to save all the futures and call `wait` on them? (I want an action on the executor.)