Python: Wait on all of `concurrent.futures.ThreadPoolExecutor`'s futures
Solution 1
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.
Solution 2
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 shutil with 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')
Solution 3
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()
Comments
-
Ram Rachum almost 2 years
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 callwait
on them? (I want an action on the executor.) -
roippi over 10 yearsas the name implies, this yields results as they are completed, i.e. it does not wait for the whole pool of tasks to finish, as the OP requested.
-
laike9m over 10 years@roippi If you know how many tasks there are, why not count the number of finished tasks? But that being said, there is no guarantee the program knows the number of concurrent tasks.
-
Ram Rachum over 10 yearsSo you're saying that if I use the executor as a context manager, then after the suite finishes, it'll wait until all futures are done, even if there are 10,000 of them and only 10 workers?
-
Bakuriu over 10 years@RamRachum Yes. From the documentation: "You can avoid having to call this method explicitly if you use the with statement, which will shutdown the
Executor
(waiting as ifExecutor.shutdown()
were called with wait set toTrue
):". -
Tim Richardson over 7 yearsDoes shutdown(wait=True) wait for callbacks of the future too?
-
ospider over 6 yearsif you are using the with statement, then shutdown is called automatically.
-
Bakuriu over 6 years@ospider in my experience the executor isn't usually used as context manager because it is used from different parts of the code.
-
Dejell over 6 years@roippi what is the different between completed and finished?
-
nodakai over 5 yearsNote this can't be used when the "top-level" futures might add "children" futures to the same pool as they run.
RuntimeError('cannot schedule new futures after shutdown',)
Sigh.