Sync with asyncio repo

Lib/asyncio/coroutines.py

@@ -27,8 +27,8 @@ _YIELD_FROM = opcode.opmap['YIELD_FROM']
 # before you define your coroutines.  A downside of using this feature
 # is that tracebacks show entries for the CoroWrapper.__next__ method
 # when _DEBUG is true.
-_DEBUG = (not sys.flags.ignore_environment
-          and bool(os.environ.get('PYTHONASYNCIODEBUG')))
+_DEBUG = (not sys.flags.ignore_environment and
+          bool(os.environ.get('PYTHONASYNCIODEBUG')))
 
 
 try:
@@ -86,7 +86,7 @@ class CoroWrapper:
     def __init__(self, gen, func=None):
         assert inspect.isgenerator(gen) or inspect.iscoroutine(gen), gen
         self.gen = gen
-        self.func = func # Used to unwrap @coroutine decorator
+        self.func = func  # Used to unwrap @coroutine decorator
         self._source_traceback = traceback.extract_stack(sys._getframe(1))
         self.__name__ = getattr(gen, '__name__', None)
         self.__qualname__ = getattr(gen, '__qualname__', None)
@@ -283,10 +283,13 @@ def _format_coroutine(coro):
         coro_frame = coro.cr_frame
 
     filename = coro_code.co_filename
-    if (isinstance(coro, CoroWrapper)
-    and not inspect.isgeneratorfunction(coro.func)
-    and coro.func is not None):
-        filename, lineno = events._get_function_source(coro.func)
+    lineno = 0
+    if (isinstance(coro, CoroWrapper) and
+            not inspect.isgeneratorfunction(coro.func) and
+            coro.func is not None):
+        source = events._get_function_source(coro.func)
+        if source is not None:
+            filename, lineno = source
         if coro_frame is None:
             coro_repr = ('%s done, defined at %s:%s'
                          % (coro_name, filename, lineno))

Lib/asyncio/tasks.py

@@ -4,6 +4,7 @@ __all__ = ['Task',
            'FIRST_COMPLETED', 'FIRST_EXCEPTION', 'ALL_COMPLETED',
            'wait', 'wait_for', 'as_completed', 'sleep', 'async',
            'gather', 'shield', 'ensure_future', 'run_coroutine_threadsafe',
+           'timeout',
            ]
 
 import concurrent.futures
@@ -732,3 +733,53 @@ def run_coroutine_threadsafe(coro, loop):
 
     loop.call_soon_threadsafe(callback)
     return future
+
+
+def timeout(timeout, *, loop=None):
+    """A factory which produce a context manager with timeout.
+
+    Useful in cases when you want to apply timeout logic around block
+    of code or in cases when asyncio.wait_for is not suitable.
+
+    For example:
+
+    >>> with asyncio.timeout(0.001):
+    >>>     yield from coro()
+
+
+    timeout: timeout value in seconds
+    loop: asyncio compatible event loop
+    """
+    if loop is None:
+        loop = events.get_event_loop()
+    return _Timeout(timeout, loop=loop)
+
+
+class _Timeout:
+    def __init__(self, timeout, *, loop):
+        self._timeout = timeout
+        self._loop = loop
+        self._task = None
+        self._cancelled = False
+        self._cancel_handler = None
+
+    def __enter__(self):
+        self._task = Task.current_task(loop=self._loop)
+        if self._task is None:
+            raise RuntimeError('Timeout context manager should be used '
+                               'inside a task')
+        self._cancel_handler = self._loop.call_later(
+            self._timeout, self._cancel_task)
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        if exc_type is futures.CancelledError and self._cancelled:
+            self._cancel_handler = None
+            self._task = None
+            raise futures.TimeoutError
+        self._cancel_handler.cancel()
+        self._cancel_handler = None
+        self._task = None
+
+    def _cancel_task(self):
+        self._cancelled = self._task.cancel()