diff options
Diffstat (limited to 'Doc/library/concurrent.futures.rst')
| -rw-r--r-- | Doc/library/concurrent.futures.rst | 45 |
1 files changed, 35 insertions, 10 deletions
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst index eee2285c53..575b1ea56c 100644 --- a/Doc/library/concurrent.futures.rst +++ b/Doc/library/concurrent.futures.rst @@ -40,7 +40,7 @@ Executor Objects .. method:: map(func, *iterables, timeout=None) - Equivalent to ``map(func, *iterables)`` except *func* is executed + Equivalent to :func:`map(func, *iterables) <map>` except *func* is executed asynchronously and several calls to *func* may be made concurrently. The returned iterator raises a :exc:`TimeoutError` if :meth:`~iterator.__next__` is called and the result isn't available @@ -136,20 +136,23 @@ ThreadPoolExecutor Example 'http://www.bbc.co.uk/', 'http://some-made-up-domain.com/'] + # Retrieve a single page and report the url and contents def load_url(url, timeout): - return urllib.request.urlopen(url, timeout=timeout).read() + conn = urllib.request.urlopen(url, timeout=timeout) + return conn.readall() + # We can use a with statement to ensure threads are cleaned up promptly with concurrent.futures.ThreadPoolExecutor(max_workers=5) as executor: - future_to_url = dict((executor.submit(load_url, url, 60), url) - for url in URLS) - + # Start the load operations and mark each future with its URL + future_to_url = {executor.submit(load_url, url, 60): url for url in URLS} for future in concurrent.futures.as_completed(future_to_url): url = future_to_url[future] - if future.exception() is not None: - print('%r generated an exception: %s' % (url, - future.exception())) + try: + data = future.result() + except Exception as exc: + print('%r generated an exception: %s' % (url, exc)) else: - print('%r page is %d bytes' % (url, len(future.result()))) + print('%r page is %d bytes' % (url, len(data))) ProcessPoolExecutor @@ -170,6 +173,12 @@ to a :class:`ProcessPoolExecutor` will result in deadlock. 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. + .. versionchanged:: 3.3 + When one of the worker processes terminates abruptly, a + :exc:`BrokenProcessPool` error is now raised. Previously, behaviour + was undefined but operations on the executor or its futures would often + freeze or deadlock. + .. _processpoolexecutor-example: @@ -337,6 +346,8 @@ Module Functions *return_when* indicates when this function should return. It must be one of the following constants: + .. tabularcolumns:: |l|L| + +-----------------------------+----------------------------------------+ | Constant | Description | +=============================+========================================+ @@ -357,7 +368,8 @@ Module Functions Returns an iterator over the :class:`Future` instances (possibly created by different :class:`Executor` instances) given by *fs* that yields futures as - they complete (finished or were cancelled). Any futures that completed + they complete (finished or were cancelled). Any futures given by *fs* that + are duplicated will be returned once. Any futures that completed before :func:`as_completed` is called will be yielded first. The returned iterator raises a :exc:`TimeoutError` if :meth:`~iterator.__next__` is called and the result isn't available after *timeout* seconds from the @@ -371,3 +383,16 @@ Module Functions :pep:`3148` -- futures - execute computations asynchronously The proposal which described this feature for inclusion in the Python standard library. + + +Exception classes +----------------- + +.. exception:: BrokenProcessPool + + Derived from :exc:`RuntimeError`, this exception class is raised when + one of the workers of a :class:`ProcessPoolExecutor` has terminated + in a non-clean fashion (for example, if it was killed from the outside). + + .. versionadded:: 3.3 + |