| .. currentmodule:: asyncio |
| |
| .. _asyncio-event-loop: |
| |
| Base Event Loop |
| =============== |
| |
| The event loop is the central execution device provided by :mod:`asyncio`. |
| It provides multiple facilities, amongst which: |
| |
| * Registering, executing and cancelling delayed calls (timeouts). |
| |
| * Creating client and server :ref:`transports <asyncio-transport>` for various |
| kinds of communication. |
| |
| * Launching subprocesses and the associated :ref:`transports |
| <asyncio-transport>` for communication with an external program. |
| |
| * Delegating costly function calls to a pool of threads. |
| |
| .. class:: BaseEventLoop |
| |
| Base class of event loops. |
| |
| Run an event loop |
| ----------------- |
| |
| .. method:: BaseEventLoop.run_forever() |
| |
| Run until :meth:`stop` is called. |
| |
| .. method:: BaseEventLoop.run_until_complete(future) |
| |
| Run until the :class:`Future` is done. |
| |
| If the argument is a :ref:`coroutine object <coroutine>`, it is wrapped by |
| :func:`async`. |
| |
| Return the Future's result, or raise its exception. |
| |
| .. method:: BaseEventLoop.is_running() |
| |
| Returns running status of event loop. |
| |
| .. method:: BaseEventLoop.stop() |
| |
| Stop running the event loop. |
| |
| Every callback scheduled before :meth:`stop` is called will run. |
| Callbacks scheduled after :meth:`stop` is called will not run. |
| However, those callbacks will run if :meth:`run_forever` is called |
| again later. |
| |
| .. method:: BaseEventLoop.is_closed() |
| |
| Returns ``True`` if the event loop was closed. |
| |
| .. versionadded:: 3.4.2 |
| |
| .. method:: BaseEventLoop.close() |
| |
| Close the event loop. The loop must not be running. |
| |
| This clears the queues and shuts down the executor, but does not wait for |
| the executor to finish. |
| |
| This is idempotent and irreversible. No other methods should be called after |
| this one. |
| |
| |
| Calls |
| ----- |
| |
| .. method:: BaseEventLoop.call_soon(callback, \*args) |
| |
| Arrange for a callback to be called as soon as possible. |
| |
| This operates as a FIFO queue, callbacks are called in the order in |
| which they are registered. Each callback will be called exactly once. |
| |
| Any positional arguments after the callback will be passed to the |
| callback when it is called. |
| |
| An instance of :class:`asyncio.Handle` is returned. |
| |
| .. method:: BaseEventLoop.call_soon_threadsafe(callback, \*args) |
| |
| Like :meth:`call_soon`, but thread safe. |
| |
| |
| .. _asyncio-delayed-calls: |
| |
| Delayed calls |
| ------------- |
| |
| The event loop has its own internal clock for computing timeouts. |
| Which clock is used depends on the (platform-specific) event loop |
| implementation; ideally it is a monotonic clock. This will generally be |
| a different clock than :func:`time.time`. |
| |
| .. note:: |
| |
| Timeouts (relative *delay* or absolute *when*) should not exceed one day. |
| |
| |
| .. method:: BaseEventLoop.call_later(delay, callback, *args) |
| |
| Arrange for the *callback* to be called after the given *delay* |
| seconds (either an int or float). |
| |
| An instance of :class:`asyncio.Handle` is returned. |
| |
| *callback* will be called exactly once per call to :meth:`call_later`. |
| If two callbacks are scheduled for exactly the same time, it is |
| undefined which will be called first. |
| |
| The optional positional *args* will be passed to the callback when it |
| is called. If you want the callback to be called with some named |
| arguments, use a closure or :func:`functools.partial`. |
| |
| .. method:: BaseEventLoop.call_at(when, callback, *args) |
| |
| Arrange for the *callback* to be called at the given absolute timestamp |
| *when* (an int or float), using the same time reference as :meth:`time`. |
| |
| This method's behavior is the same as :meth:`call_later`. |
| |
| .. method:: BaseEventLoop.time() |
| |
| Return the current time, as a :class:`float` value, according to the |
| event loop's internal clock. |
| |
| .. seealso:: |
| |
| The :func:`asyncio.sleep` function. |
| |
| |
| Coroutines |
| ---------- |
| |
| .. method:: BaseEventLoop.create_task(coro) |
| |
| Schedule the execution of a :ref:`coroutine object <coroutine>`: wrap it in |
| a future. Return a :class:`Task` object. |
| |
| Third-party event loops can use their own subclass of :class:`Task` for |
| interoperability. In this case, the result type is a subclass of |
| :class:`Task`. |
| |
| This method was added in Python 3.4.2. Use the :func:`async` function to |
| support also older Python versions. |
| |
| .. versionadded:: 3.4.2 |
| |
| |
| Creating connections |
| -------------------- |
| |
| .. method:: BaseEventLoop.create_connection(protocol_factory, host=None, port=None, \*, ssl=None, family=0, proto=0, flags=0, sock=None, local_addr=None, server_hostname=None) |
| |
| Create a streaming transport connection to a given Internet *host* and |
| *port*: socket family :py:data:`~socket.AF_INET` or |
| :py:data:`~socket.AF_INET6` depending on *host* (or *family* if specified), |
| socket type :py:data:`~socket.SOCK_STREAM`. *protocol_factory* must be a |
| callable returning a :ref:`protocol <asyncio-protocol>` instance. |
| |
| This method is a :ref:`coroutine <coroutine>` which will try to |
| establish the connection in the background. When successful, the |
| coroutine returns a ``(transport, protocol)`` pair. |
| |
| The chronological synopsis of the underlying operation is as follows: |
| |
| #. The connection is established, and a :ref:`transport <asyncio-transport>` |
| is created to represent it. |
| |
| #. *protocol_factory* is called without arguments and must return a |
| :ref:`protocol <asyncio-protocol>` instance. |
| |
| #. The protocol instance is tied to the transport, and its |
| :meth:`connection_made` method is called. |
| |
| #. The coroutine returns successfully with the ``(transport, protocol)`` |
| pair. |
| |
| The created transport is an implementation-dependent bidirectional stream. |
| |
| .. note:: |
| *protocol_factory* can be any kind of callable, not necessarily |
| a class. For example, if you want to use a pre-created |
| protocol instance, you can pass ``lambda: my_protocol``. |
| |
| Options allowing to change how the connection is created: |
| |
| * *ssl*: if given and not false, a SSL/TLS transport is created |
| (by default a plain TCP transport is created). If *ssl* is |
| a :class:`ssl.SSLContext` object, this context is used to create |
| the transport; if *ssl* is :const:`True`, a context with some |
| unspecified default settings is used. |
| |
| .. seealso:: :ref:`SSL/TLS security considerations <ssl-security>` |
| |
| * *server_hostname*, is only for use together with *ssl*, |
| and sets or overrides the hostname that the target server's certificate |
| will be matched against. By default the value of the *host* argument |
| is used. If *host* is empty, there is no default and you must pass a |
| value for *server_hostname*. If *server_hostname* is an empty |
| string, hostname matching is disabled (which is a serious security |
| risk, allowing for man-in-the-middle-attacks). |
| |
| * *family*, *proto*, *flags* are the optional address family, protocol |
| and flags to be passed through to getaddrinfo() for *host* resolution. |
| If given, these should all be integers from the corresponding |
| :mod:`socket` module constants. |
| |
| * *sock*, if given, should be an existing, already connected |
| :class:`socket.socket` object to be used by the transport. |
| If *sock* is given, none of *host*, *port*, *family*, *proto*, *flags* |
| and *local_addr* should be specified. |
| |
| * *local_addr*, if given, is a ``(local_host, local_port)`` tuple used |
| to bind the socket to locally. The *local_host* and *local_port* |
| are looked up using getaddrinfo(), similarly to *host* and *port*. |
| |
| On Windows with :class:`ProactorEventLoop`, SSL/TLS is not supported. |
| |
| .. seealso:: |
| |
| The :func:`open_connection` function can be used to get a pair of |
| (:class:`StreamReader`, :class:`StreamWriter`) instead of a protocol. |
| |
| |
| .. method:: BaseEventLoop.create_datagram_endpoint(protocol_factory, local_addr=None, remote_addr=None, \*, family=0, proto=0, flags=0) |
| |
| Create datagram connection: socket family :py:data:`~socket.AF_INET` or |
| :py:data:`~socket.AF_INET6` depending on *host* (or *family* if specified), |
| socket type :py:data:`~socket.SOCK_DGRAM`. |
| |
| This method is a :ref:`coroutine <coroutine>` which will try to |
| establish the connection in the background. When successful, the |
| coroutine returns a ``(transport, protocol)`` pair. |
| |
| See the :meth:`BaseEventLoop.create_connection` method for parameters. |
| |
| On Windows with :class:`ProactorEventLoop`, this method is not supported. |
| |
| |
| .. method:: BaseEventLoop.create_unix_connection(protocol_factory, path, \*, ssl=None, sock=None, server_hostname=None) |
| |
| Create UNIX connection: socket family :py:data:`~socket.AF_UNIX`, socket |
| type :py:data:`~socket.SOCK_STREAM`. The :py:data:`~socket.AF_UNIX` socket |
| family is used to communicate between processes on the same machine |
| efficiently. |
| |
| This method is a :ref:`coroutine <coroutine>` which will try to |
| establish the connection in the background. When successful, the |
| coroutine returns a ``(transport, protocol)`` pair. |
| |
| On Windows with :class:`ProactorEventLoop`, SSL/TLS is not supported. |
| |
| See the :meth:`BaseEventLoop.create_connection` method for parameters. |
| |
| Availability: UNIX. |
| |
| |
| Creating listening connections |
| ------------------------------ |
| |
| .. method:: BaseEventLoop.create_server(protocol_factory, host=None, port=None, \*, family=socket.AF_UNSPEC, flags=socket.AI_PASSIVE, sock=None, backlog=100, ssl=None, reuse_address=None) |
| |
| Create a TCP server bound to *host* and *port*. Return a :class:`Server` object, |
| its :attr:`~Server.sockets` attribute contains created sockets. Use the |
| :meth:`Server.close` method to stop the server: close listening sockets. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| If *host* is an empty string or ``None``, all interfaces are assumed |
| and a list of multiple sockets will be returned (most likely |
| one for IPv4 and another one for IPv6). |
| |
| *family* can be set to either :data:`socket.AF_INET` or |
| :data:`~socket.AF_INET6` to force the socket to use IPv4 or IPv6. If not set |
| it will be determined from host (defaults to :data:`socket.AF_UNSPEC`). |
| |
| *flags* is a bitmask for :meth:`getaddrinfo`. |
| |
| *sock* can optionally be specified in order to use a preexisting |
| socket object. |
| |
| *backlog* is the maximum number of queued connections passed to |
| :meth:`~socket.socket.listen` (defaults to 100). |
| |
| *ssl* can be set to an :class:`~ssl.SSLContext` to enable SSL over the |
| accepted connections. |
| |
| *reuse_address* tells the kernel to reuse a local socket in |
| TIME_WAIT state, without waiting for its natural timeout to |
| expire. If not specified will automatically be set to True on |
| UNIX. |
| |
| On Windows with :class:`ProactorEventLoop`, SSL/TLS is not supported. |
| |
| .. seealso:: |
| |
| The function :func:`start_server` creates a (:class:`StreamReader`, |
| :class:`StreamWriter`) pair and calls back a function with this pair. |
| |
| |
| .. method:: BaseEventLoop.create_unix_server(protocol_factory, path=None, \*, sock=None, backlog=100, ssl=None) |
| |
| Similar to :meth:`BaseEventLoop.create_server`, but specific to the |
| socket family :py:data:`~socket.AF_UNIX`. |
| |
| Availability: UNIX. |
| |
| |
| Watch file descriptors |
| ---------------------- |
| |
| On Windows with :class:`SelectorEventLoop`, only socket handles are supported |
| (ex: pipe file descriptors are not supported). |
| |
| On Windows with :class:`ProactorEventLoop`, these methods are not supported. |
| |
| .. method:: BaseEventLoop.add_reader(fd, callback, \*args) |
| |
| Start watching the file descriptor for read availability and then call the |
| *callback* with specified arguments. |
| |
| .. method:: BaseEventLoop.remove_reader(fd) |
| |
| Stop watching the file descriptor for read availability. |
| |
| .. method:: BaseEventLoop.add_writer(fd, callback, \*args) |
| |
| Start watching the file descriptor for write availability and then call the |
| *callback* with specified arguments. |
| |
| .. method:: BaseEventLoop.remove_writer(fd) |
| |
| Stop watching the file descriptor for write availability. |
| |
| |
| Low-level socket operations |
| --------------------------- |
| |
| .. method:: BaseEventLoop.sock_recv(sock, nbytes) |
| |
| Receive data from the socket. The return value is a bytes object |
| representing the data received. The maximum amount of data to be received |
| at once is specified by *nbytes*. |
| |
| With :class:`SelectorEventLoop` event loop, the socket *sock* must be |
| non-blocking. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. seealso:: |
| |
| The :meth:`socket.socket.recv` method. |
| |
| .. method:: BaseEventLoop.sock_sendall(sock, data) |
| |
| Send data to the socket. The socket must be connected to a remote socket. |
| This method continues to send data from *data* until either all data has |
| been sent or an error occurs. ``None`` is returned on success. On error, |
| an exception is raised, and there is no way to determine how much data, if |
| any, was successfully processed by the receiving end of the connection. |
| |
| With :class:`SelectorEventLoop` event loop, the socket *sock* must be |
| non-blocking. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. seealso:: |
| |
| The :meth:`socket.socket.sendall` method. |
| |
| .. method:: BaseEventLoop.sock_connect(sock, address) |
| |
| Connect to a remote socket at *address*. |
| |
| The *address* must be already resolved to avoid the trap of hanging the |
| entire event loop when the address requires doing a DNS lookup. For |
| example, it must be an IP address, not an hostname, for |
| :py:data:`~socket.AF_INET` and :py:data:`~socket.AF_INET6` address families. |
| Use :meth:`getaddrinfo` to resolve the hostname asynchronously. |
| |
| With :class:`SelectorEventLoop` event loop, the socket *sock* must be |
| non-blocking. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. seealso:: |
| |
| The :meth:`BaseEventLoop.create_connection` method, the |
| :func:`open_connection` function and the :meth:`socket.socket.connect` |
| method. |
| |
| |
| .. method:: BaseEventLoop.sock_accept(sock) |
| |
| Accept a connection. The socket must be bound to an address and listening |
| for connections. The return value is a pair ``(conn, address)`` where *conn* |
| is a *new* socket object usable to send and receive data on the connection, |
| and *address* is the address bound to the socket on the other end of the |
| connection. |
| |
| The socket *sock* must be non-blocking. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. seealso:: |
| |
| The :meth:`BaseEventLoop.create_server` method, the :func:`start_server` |
| function and the :meth:`socket.socket.accept` method. |
| |
| |
| Resolve host name |
| ----------------- |
| |
| .. method:: BaseEventLoop.getaddrinfo(host, port, \*, family=0, type=0, proto=0, flags=0) |
| |
| This method is a :ref:`coroutine <coroutine>`, similar to |
| :meth:`socket.getaddrinfo` function but non-blocking. |
| |
| .. method:: BaseEventLoop.getnameinfo(sockaddr, flags=0) |
| |
| This method is a :ref:`coroutine <coroutine>`, similar to |
| :meth:`socket.getnameinfo` function but non-blocking. |
| |
| |
| Connect pipes |
| ------------- |
| |
| On Windows with :class:`SelectorEventLoop`, these methods are not supported. |
| Use :class:`ProactorEventLoop` to support pipes on Windows. |
| |
| .. method:: BaseEventLoop.connect_read_pipe(protocol_factory, pipe) |
| |
| Register read pipe in eventloop. |
| |
| *protocol_factory* should instantiate object with :class:`Protocol` |
| interface. *pipe* is a :term:`file-like object <file object>`. |
| Return pair ``(transport, protocol)``, where *transport* supports the |
| :class:`ReadTransport` interface. |
| |
| With :class:`SelectorEventLoop` event loop, the *pipe* is set to |
| non-blocking mode. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. method:: BaseEventLoop.connect_write_pipe(protocol_factory, pipe) |
| |
| Register write pipe in eventloop. |
| |
| *protocol_factory* should instantiate object with :class:`BaseProtocol` |
| interface. *pipe* is file-like object. |
| Return pair (transport, protocol), where transport support |
| :class:`WriteTransport` interface. |
| |
| With :class:`SelectorEventLoop` event loop, the *pipe* is set to |
| non-blocking mode. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. seealso:: |
| |
| The :meth:`BaseEventLoop.subprocess_exec` and |
| :meth:`BaseEventLoop.subprocess_shell` methods. |
| |
| |
| UNIX signals |
| ------------ |
| |
| Availability: UNIX only. |
| |
| .. method:: BaseEventLoop.add_signal_handler(signum, callback, \*args) |
| |
| Add a handler for a signal. |
| |
| Raise :exc:`ValueError` if the signal number is invalid or uncatchable. |
| Raise :exc:`RuntimeError` if there is a problem setting up the handler. |
| |
| .. method:: BaseEventLoop.remove_signal_handler(sig) |
| |
| Remove a handler for a signal. |
| |
| Return ``True`` if a signal handler was removed, ``False`` if not. |
| |
| .. seealso:: |
| |
| The :mod:`signal` module. |
| |
| |
| Executor |
| -------- |
| |
| Call a function in an :class:`~concurrent.futures.Executor` (pool of threads or |
| pool of processes). By default, an event loop uses a thread pool executor |
| (:class:`~concurrent.futures.ThreadPoolExecutor`). |
| |
| .. method:: BaseEventLoop.run_in_executor(executor, callback, \*args) |
| |
| Arrange for a callback to be called in the specified executor. |
| |
| The *executor* argument should be an :class:`~concurrent.futures.Executor` |
| instance. The default executor is used if *executor* is ``None``. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. method:: BaseEventLoop.set_default_executor(executor) |
| |
| Set the default executor used by :meth:`run_in_executor`. |
| |
| |
| Error Handling API |
| ------------------ |
| |
| Allows to customize how exceptions are handled in the event loop. |
| |
| .. method:: BaseEventLoop.set_exception_handler(handler) |
| |
| Set *handler* as the new event loop exception handler. |
| |
| If *handler* is ``None``, the default exception handler will |
| be set. |
| |
| If *handler* is a callable object, it should have a |
| matching signature to ``(loop, context)``, where ``loop`` |
| will be a reference to the active event loop, ``context`` |
| will be a ``dict`` object (see :meth:`call_exception_handler` |
| documentation for details about context). |
| |
| .. method:: BaseEventLoop.default_exception_handler(context) |
| |
| Default exception handler. |
| |
| This is called when an exception occurs and no exception |
| handler is set, and can be called by a custom exception |
| handler that wants to defer to the default behavior. |
| |
| *context* parameter has the same meaning as in |
| :meth:`call_exception_handler`. |
| |
| .. method:: BaseEventLoop.call_exception_handler(context) |
| |
| Call the current event loop exception handler. |
| |
| *context* is a ``dict`` object containing the following keys |
| (new keys may be introduced later): |
| |
| * 'message': Error message; |
| * 'exception' (optional): Exception object; |
| * 'future' (optional): :class:`asyncio.Future` instance; |
| * 'handle' (optional): :class:`asyncio.Handle` instance; |
| * 'protocol' (optional): :ref:`Protocol <asyncio-protocol>` instance; |
| * 'transport' (optional): :ref:`Transport <asyncio-transport>` instance; |
| * 'socket' (optional): :class:`socket.socket` instance. |
| |
| .. note:: |
| |
| Note: this method should not be overloaded in subclassed |
| event loops. For any custom exception handling, use |
| :meth:`set_exception_handler()` method. |
| |
| Debug mode |
| ---------- |
| |
| .. method:: BaseEventLoop.get_debug() |
| |
| Get the debug mode (:class:`bool`) of the event loop. |
| |
| The default value is ``True`` if the environment variable |
| :envvar:`PYTHONASYNCIODEBUG` is set to a non-empty string, ``False`` |
| otherwise. |
| |
| .. versionadded:: 3.4.2 |
| |
| .. method:: BaseEventLoop.set_debug(enabled: bool) |
| |
| Set the debug mode of the event loop. |
| |
| .. versionadded:: 3.4.2 |
| |
| .. seealso:: |
| |
| The :ref:`debug mode of asyncio <asyncio-debug-mode>`. |
| |
| Server |
| ------ |
| |
| .. class:: Server |
| |
| Server listening on sockets. |
| |
| Object created by the :meth:`BaseEventLoop.create_server` method and the |
| :func:`start_server` function. Don't instanciate the class directly. |
| |
| .. method:: close() |
| |
| Stop serving: close listening sockets and set the :attr:`sockets` |
| attribute to ``None``. |
| |
| The sockets that represent existing incoming client connections are |
| leaved open. |
| |
| The server is closed asynchonously, use the :meth:`wait_closed` coroutine |
| to wait until the server is closed. |
| |
| .. method:: wait_closed() |
| |
| Wait until the :meth:`close` method completes. |
| |
| This method is a :ref:`coroutine <coroutine>`. |
| |
| .. attribute:: sockets |
| |
| List of :class:`socket.socket` objects the server is listening to, or |
| ``None`` if the server is closed. |
| |
| |
| Handle |
| ------ |
| |
| .. class:: Handle |
| |
| A callback wrapper object returned by :func:`BaseEventLoop.call_soon`, |
| :func:`BaseEventLoop.call_soon_threadsafe`, :func:`BaseEventLoop.call_later`, |
| and :func:`BaseEventLoop.call_at`. |
| |
| .. method:: cancel() |
| |
| Cancel the call. |
| |
| |
| Event loop examples |
| =================== |
| |
| .. _asyncio-hello-world-callback: |
| |
| Hello World with a callback |
| --------------------------- |
| |
| Print ``"Hello World"`` every two seconds using a callback scheduled by the |
| :meth:`BaseEventLoop.call_soon` method:: |
| |
| import asyncio |
| |
| def print_and_repeat(loop): |
| print('Hello World') |
| loop.call_later(2, print_and_repeat, loop) |
| |
| loop = asyncio.get_event_loop() |
| loop.call_soon(print_and_repeat, loop) |
| try: |
| loop.run_forever() |
| finally: |
| loop.close() |
| |
| .. seealso:: |
| |
| The :ref:`Hello World coroutine <asyncio-hello-world-coroutine>` example |
| uses a :ref:`coroutine <coroutine>`. |
| |
| |
| Example: Set signal handlers for SIGINT and SIGTERM |
| --------------------------------------------------- |
| |
| Register handlers for signals :py:data:`SIGINT` and :py:data:`SIGTERM`:: |
| |
| import asyncio |
| import functools |
| import os |
| import signal |
| |
| def ask_exit(signame): |
| print("got signal %s: exit" % signame) |
| loop.stop() |
| |
| loop = asyncio.get_event_loop() |
| for signame in ('SIGINT', 'SIGTERM'): |
| loop.add_signal_handler(getattr(signal, signame), |
| functools.partial(ask_exit, signame)) |
| |
| print("Event loop running forever, press CTRL+c to interrupt.") |
| print("pid %s: send SIGINT or SIGTERM to exit." % os.getpid()) |
| try: |
| loop.run_forever() |
| finally: |
| loop.close() |
| |