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Diffstat (limited to 'Doc/library/concurrent.futures.rst')
| -rw-r--r-- | Doc/library/concurrent.futures.rst | 25 |
1 files changed, 22 insertions, 3 deletions
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst index cc8b335b8f..9ac617117f 100644 --- a/Doc/library/concurrent.futures.rst +++ b/Doc/library/concurrent.futures.rst @@ -38,7 +38,7 @@ Executor Objects future = executor.submit(pow, 323, 1235) print(future.result()) - .. method:: map(func, *iterables, timeout=None) + .. method:: map(func, *iterables, timeout=None, chunksize=1) Equivalent to :func:`map(func, *iterables) <map>` except *func* is executed asynchronously and several calls to *func* may be made concurrently. The @@ -48,7 +48,16 @@ Executor Objects *timeout* can be an int or a float. If *timeout* is not specified or ``None``, there is no limit to the wait time. If a call raises an exception, then that exception will be raised when its value is - retrieved from the iterator. + retrieved from the iterator. When using :class:`ProcessPoolExecutor`, this + method chops *iterables* into a number of chunks which it submits to the + pool as separate tasks. The (approximate) size of these chunks can be + specified by setting *chunksize* to a positive integer. For very long + iterables, using a large value for *chunksize* can significantly improve + performance compared to the default size of 1. With :class:`ThreadPoolExecutor`, + *chunksize* has no effect. + + .. versionchanged:: 3.5 + Added the *chunksize* argument. .. method:: shutdown(wait=True) @@ -115,11 +124,19 @@ And:: executor.submit(wait_on_future) -.. class:: ThreadPoolExecutor(max_workers) +.. class:: ThreadPoolExecutor(max_workers=None) An :class:`Executor` subclass that uses a pool of at most *max_workers* threads to execute calls asynchronously. + .. versionchanged:: 3.5 + If *max_workers* is ``None`` or + not given, it will default to the number of processors on the machine, + multiplied by ``5``, assuming that :class:`ThreadPoolExecutor` is often + used to overlap I/O instead of CPU work and the number of workers + should be higher than the number of workers + for :class:`ProcessPoolExecutor`. + .. _threadpoolexecutor-example: @@ -175,6 +192,8 @@ to a :class:`ProcessPoolExecutor` will result in deadlock. An :class:`Executor` subclass that executes calls asynchronously using a pool of at most *max_workers* processes. If *max_workers* is ``None`` or not given, it will default to the number of processors on the machine. + If *max_workers* is lower or equal to ``0``, then a :exc:`ValueError` + will be raised. .. versionchanged:: 3.3 When one of the worker processes terminates abruptly, a |