Python: Wait on all of `concurrent.futures.ThreadPoolExecutor`'s futures
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()
andExecutor.map()
made after shutdown will raiseRuntimeError
.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 differentExecutor
instances) given byfs
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.
Bakuriu's answer is correct. Just to extend a little bit. As we all know a context manager has __enter__
and __exit__
method. Here is how class Executor
(ThreadPoolExecutor's base class) is defined
class Executor(object): # other methods def shutdown(self, wait=True): """Clean-up the resources associated with the Executor. It is safe to call this method several times. Otherwise, no other methods can be called after this one. Args: wait: If True then shutdown will not return until all running futures have finished executing and the resources used by the executor have been reclaimed. """ pass def __enter__(self): return self def __exit__(self, exc_type, exc_val, exc_tb): self.shutdown(wait=True) return False
And it is ThreadPoolExecutor
that actually defines the shutdown
method
class ThreadPoolExecutor(_base.Executor): def shutdown(self, wait=True): with self._shutdown_lock: self._shutdown = True self._work_queue.put(None) if wait: for t in self._threads: t.join()
As stated before, one can use Executor.shutdown(wait=True)
, but also pay attention to the following note in the documentation:
You can avoid having to call this method explicitly if you use the
with
statement, which will shutdown theExecutor
(waiting as ifExecutor.shutdown()
were called withwait
set toTrue
):
import shutilwith ThreadPoolExecutor(max_workers=4) as e: e.submit(shutil.copy, 'src1.txt', 'dest1.txt') e.submit(shutil.copy, 'src2.txt', 'dest2.txt') e.submit(shutil.copy, 'src3.txt', 'dest3.txt') e.submit(shutil.copy, 'src4.txt', 'dest4.txt')