18.5.1. Base Event Loop
***********************

**Source code:** Lib/asyncio/events.py

The event loop is the central execution device provided by "asyncio".
It provides multiple facilities, including:

* Registering, executing and cancelling delayed calls (timeouts).

* Creating client and server transports for various kinds of
  communication.

* Launching subprocesses and the associated transports for
  communication with an external program.

* Delegating costly function calls to a pool of threads.

class asyncio.BaseEventLoop

   This class is an implementation detail.  It is a subclass of
   "AbstractEventLoop" and may be a base class of concrete event loop
   implementations found in "asyncio".  It should not be used
   directly; use "AbstractEventLoop" instead. "BaseEventLoop" should
   not be subclassed by third-party code; the internal interface is
   not stable.

class asyncio.AbstractEventLoop

   Abstract base class of event loops.

   This class is not thread safe.


18.5.1.1. Exécuter une boucle d'évènements
==========================================

AbstractEventLoop.run_forever()

   Run until "stop()" is called.  If "stop()" is called before
   "run_forever()" is called, this polls the I/O selector once with a
   timeout of zero, runs all callbacks scheduled in response to I/O
   events (and those that were already scheduled), and then exits. If
   "stop()" is called while "run_forever()" is running, this will run
   the current batch of callbacks and then exit.  Note that callbacks
   scheduled by callbacks will not run in that case; they will run the
   next time "run_forever()" is called.

   Modifié dans la version 3.5.1.

AbstractEventLoop.run_until_complete(future)

   Exécuter jusqu'à ce que "Future" soit terminé.

   If the argument is a coroutine object, it is wrapped by
   "ensure_future()".

   Return the Future's result, or raise its exception.

AbstractEventLoop.is_running()

   Donne le status d'exécution de la boucle d'évènements.

AbstractEventLoop.stop()

   Arrête l'exécution de la boucle d'évènements.

   This causes "run_forever()" to exit at the next suitable
   opportunity (see there for more details).

   Modifié dans la version 3.5.1.

AbstractEventLoop.is_closed()

   Donne "True" si la boucle d'évènements est fermée.

   Nouveau dans la version 3.4.2.

AbstractEventLoop.close()

   Close the event loop. The loop must not be running.  Pending
   callbacks will be lost.

   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.

coroutine AbstractEventLoop.shutdown_asyncgens()

   Schedule all currently open *asynchronous generator* objects to
   close with an "aclose()" call.  After calling this method, the
   event loop will issue a warning whenever a new asynchronous
   generator is iterated.  Should be used to finalize all scheduled
   asynchronous generators reliably.  Example:

      try:
          loop.run_forever()
      finally:
          loop.run_until_complete(loop.shutdown_asyncgens())
          loop.close()

   Nouveau dans la version 3.6.


18.5.1.2. Appels
================

Most "asyncio" functions don't accept keywords. If you want to pass
keywords to your callback, use "functools.partial()". For example,
"loop.call_soon(functools.partial(print, "Hello", flush=True))" will
call "print("Hello", flush=True)".

Note:

  "functools.partial()" is better than "lambda" functions, because
  "asyncio" can inspect "functools.partial()" object to display
  parameters in debug mode, whereas "lambda" functions have a poor
  representation.

AbstractEventLoop.call_soon(callback, *args)

   Arrange for a callback to be called as soon as possible.  The
   callback is called after "call_soon()" returns, when control
   returns to the event loop.

   This operates as a FIFO (first-in, first-out) 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 "asyncio.Handle" is returned, which can be used to
   cancel the callback.

   Use functools.partial to pass keywords to the callback.

AbstractEventLoop.call_soon_threadsafe(callback, *args)

   Comme "call_soon()" mais *thread safe*.

   Voir la section exécution concurrente et multi-fils d'exécution de
   la documentation.


18.5.1.3. Appels différés
=========================

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 "time.time()".

Note:

  Timeouts (relative *delay* or absolute *when*) should not exceed one
  day.

AbstractEventLoop.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 "asyncio.Handle" is returned, which can be used to
   cancel the callback.

   *callback* will be called exactly once per call to "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 "functools.partial()".

   Use functools.partial to pass keywords to the callback.

AbstractEventLoop.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 "AbstractEventLoop.time()".

   This method's behavior is the same as "call_later()".

   An instance of "asyncio.Handle" is returned, which can be used to
   cancel the callback.

   Use functools.partial to pass keywords to the callback.

AbstractEventLoop.time()

   Return the current time, as a "float" value, according to the event
   loop's internal clock.

Voir aussi: La fonction "asyncio.sleep()".


18.5.1.4. Futurs
================

AbstractEventLoop.create_future()

   Create an "asyncio.Future" object attached to the loop.

   This is a preferred way to create futures in asyncio, as event loop
   implementations can provide alternative implementations of the
   Future class (with better performance or instrumentation).

   Nouveau dans la version 3.5.2.


18.5.1.5. Tâches
================

AbstractEventLoop.create_task(coro)

   Schedule the execution of a coroutine object: wrap it in a future.
   Return a "Task" object.

   Third-party event loops can use their own subclass of "Task" for
   interoperability. In this case, the result type is a subclass of
   "Task".

   This method was added in Python 3.4.2. Use the "async()" function
   to support also older Python versions.

   Nouveau dans la version 3.4.2.

AbstractEventLoop.set_task_factory(factory)

   Set a task factory that will be used by
   "AbstractEventLoop.create_task()".

   If *factory* is "None" the default task factory will be set.

   If *factory* is a *callable*, it should have a signature matching
   "(loop, coro)", where *loop* will be a reference to the active
   event loop, *coro* will be a coroutine object.  The callable must
   return an "asyncio.Future" compatible object.

   Nouveau dans la version 3.4.4.

AbstractEventLoop.get_task_factory()

   Return a task factory, or "None" if the default one is in use.

   Nouveau dans la version 3.4.4.


18.5.1.6. Créer des connections
===============================

coroutine AbstractEventLoop.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 "AF_INET" or "AF_INET6" depending on
   *host* (or *family* if specified), socket type "SOCK_STREAM".
   *protocol_factory* must be a callable returning a protocol
   instance.

   This method is a 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:

   1. The connection is established, and a transport is created to
      represent it.

   2. *protocol_factory* is called without arguments and must return a
      protocol instance.

   3. The protocol instance is tied to the transport, and its
      "connection_made()" method is called.

   4. 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 modifiant la création de la connexion :

   * *ssl*: if given and not false, a SSL/TLS transport is created (by
     default a plain TCP transport is created).  If *ssl* is a
     "ssl.SSLContext" object, this context is used to create the
     transport; if *ssl* is "True", a context with some unspecified
     default settings is used.

     Voir aussi: SSL/TLS security considerations

   * *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 "socket" module constants.

   * *sock*, if given, should be an existing, already connected
     "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*.

   Modifié dans la version 3.5: On Windows with "ProactorEventLoop",
   SSL/TLS is now supported.

   Voir aussi:

     The "open_connection()" function can be used to get a pair of
     ("StreamReader", "StreamWriter") instead of a protocol.

coroutine AbstractEventLoop.create_datagram_endpoint(protocol_factory, local_addr=None, remote_addr=None, *, family=0, proto=0, flags=0, reuse_address=None, reuse_port=None, allow_broadcast=None, sock=None)

   Note:

     The parameter *reuse_address* is no longer supported, as using
     "SO_REUSEADDR" poses a significant security concern for UDP.
     Explicitly passing "reuse_address=True" will raise an
     exception.When multiple processes with differing UIDs assign
     sockets to an indentical UDP socket address with "SO_REUSEADDR",
     incoming packets can become randomly distributed among the
     sockets.For supported platforms, *reuse_port* can be used as a
     replacement for similar functionality. With *reuse_port*,
     "SO_REUSEPORT" is used instead, which specifically prevents
     processes with differing UIDs from assigning sockets to the same
     socket address.

   Create a datagram connection.

   Create datagram connection: socket family "AF_INET" or "AF_INET6"
   depending on *host* (or *family* if specified), socket type
   "SOCK_DGRAM". *protocol_factory* must be a callable returning a
   protocol instance.

   This method is a coroutine which will try to establish the
   connection in the background.  When successful, the coroutine
   returns a "(transport, protocol)" pair.

   Options modifiant la création de la connexion :

   * *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()".

   * *remote_addr*, if given, is a "(remote_host, remote_port)" tuple
     used to connect the socket to a remote address.  The
     *remote_host* and *remote_port* are looked up using
     "getaddrinfo()".

   * *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 "socket" module constants.

   * *reuse_port* tells the kernel to allow this endpoint to be bound
     to the same port as other existing endpoints are bound to, so
     long as they all set this flag when being created. This option is
     not supported on Windows and some UNIX's. If the "SO_REUSEPORT"
     constant is not defined then this capability is unsupported.

   * *allow_broadcast* tells the kernel to allow this endpoint to send
     messages to the broadcast address.

   * *sock* can optionally be specified in order to use a preexisting,
     already connected, "socket.socket" object to be used by the
     transport. If specified, *local_addr* and *remote_addr* should be
     omitted (must be "None").

   On Windows with "ProactorEventLoop", this method is not supported.

   See UDP echo client protocol and UDP echo server protocol examples.

   Modifié dans la version 3.4.4: The *family*, *proto*, *flags*,
   *reuse_address*, *reuse_port, *allow_broadcast*, and *sock*
   parameters were added.

   Modifié dans la version 3.6.10: The *reuse_address* parameter is no
   longer supporter due to security concerns

coroutine AbstractEventLoop.create_unix_connection(protocol_factory, path, *, ssl=None, sock=None, server_hostname=None)

   Create UNIX connection: socket family "AF_UNIX", socket type
   "SOCK_STREAM". The "AF_UNIX" socket family is used to communicate
   between processes on the same machine efficiently.

   This method is a coroutine which will try to establish the
   connection in the background.  When successful, the coroutine
   returns a "(transport, protocol)" pair.

   *path* is the name of a UNIX domain socket, and is required unless
   a *sock* parameter is specified.  Abstract UNIX sockets, "str", and
   "bytes" paths are supported.

   See the "AbstractEventLoop.create_connection()" method for
   parameters.

   Disponible sur : UNIX.


18.5.1.7. Attendre des connections
==================================

coroutine AbstractEventLoop.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, reuse_port=None)

   Create a TCP server (socket type "SOCK_STREAM") bound to *host* and
   *port*.

   Return a "Server" object, its "sockets" attribute contains created
   sockets. Use the "Server.close()" method to stop the server: close
   listening sockets.

   Paramètres :

   * The *host* parameter can be a string, in that case the TCP server
     is bound to *host* and *port*. The *host* parameter can also be a
     sequence of strings and in that case the TCP server is bound to
     all hosts of the sequence. 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 "socket.AF_INET" or "AF_INET6" to
     force the socket to use IPv4 or IPv6. If not set it will be
     determined from host (defaults to "socket.AF_UNSPEC").

   * *flags* est un masque de bits pour "getaddrinfo()".

   * *sock* can optionally be specified in order to use a preexisting
     socket object. If specified, *host* and *port* should be omitted
     (must be "None").

   * *backlog* is the maximum number of queued connections passed to
     "listen()" (defaults to 100).

   * *ssl* can be set to an "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.

   * *reuse_port* tells the kernel to allow this endpoint to be bound
     to the same port as other existing endpoints are bound to, so
     long as they all set this flag when being created. This option is
     not supported on Windows.

   Cette méthode est une coroutine.

   Modifié dans la version 3.5: On Windows with "ProactorEventLoop",
   SSL/TLS is now supported.

   Voir aussi:

     The function "start_server()" creates a ("StreamReader",
     "StreamWriter") pair and calls back a function with this pair.

   Modifié dans la version 3.5.1: The *host* parameter can now be a
   sequence of strings.

coroutine AbstractEventLoop.create_unix_server(protocol_factory, path=None, *, sock=None, backlog=100, ssl=None)

   Similar to "AbstractEventLoop.create_server()", but specific to the
   socket family "AF_UNIX".

   Cette méthode est une coroutine.

   Disponible sur : UNIX.

coroutine BaseEventLoop.connect_accepted_socket(protocol_factory, sock, *, ssl=None)

   Handle an accepted connection.

   This is used by servers that accept connections outside of asyncio
   but that use asyncio to handle them.

   Paramètres :

   * *sock* is a preexisting socket object returned from an "accept"
     call.

   * *ssl* can be set to an "SSLContext" to enable SSL over the
     accepted connections.

   This method is a coroutine.  When completed, the coroutine returns
   a "(transport, protocol)" pair.

   Nouveau dans la version 3.5.3.


18.5.1.8. Surveiller des descripteurs de fichiers
=================================================

On Windows with "SelectorEventLoop", only socket handles are supported
(ex: pipe file descriptors are not supported).

On Windows with "ProactorEventLoop", these methods are not supported.

AbstractEventLoop.add_reader(fd, callback, *args)

   Start watching the file descriptor for read availability and then
   call the *callback* with specified arguments.

   Use functools.partial to pass keywords to the callback.

AbstractEventLoop.remove_reader(fd)

   Stop watching the file descriptor for read availability.

AbstractEventLoop.add_writer(fd, callback, *args)

   Start watching the file descriptor for write availability and then
   call the *callback* with specified arguments.

   Use functools.partial to pass keywords to the callback.

AbstractEventLoop.remove_writer(fd)

   Stop watching the file descriptor for write availability.

The watch a file descriptor for read events example uses the low-level
"AbstractEventLoop.add_reader()" method to register the file
descriptor of a socket.


18.5.1.9. Opérations bas niveau sur les *socket*
================================================

coroutine AbstractEventLoop.sock_recv(sock, nbytes)

   Receive data from the socket.  Modeled after blocking
   "socket.socket.recv()" method.

   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 "SelectorEventLoop" event loop, the socket *sock* must be non-
   blocking.

   Cette méthode est une coroutine.

coroutine AbstractEventLoop.sock_sendall(sock, data)

   Send data to the socket.  Modeled after blocking
   "socket.socket.sendall()" method.

   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 "SelectorEventLoop" event loop, the socket *sock* must be non-
   blocking.

   Cette méthode est une coroutine.

coroutine AbstractEventLoop.sock_connect(sock, address)

   Connect to a remote socket at *address*.  Modeled after blocking
   "socket.socket.connect()" method.

   With "SelectorEventLoop" event loop, the socket *sock* must be non-
   blocking.

   Cette méthode est une coroutine.

   Modifié dans la version 3.5.2: "address" no longer needs to be
   resolved.  "sock_connect" will try to check if the *address* is
   already resolved by calling "socket.inet_pton()".  If not,
   "AbstractEventLoop.getaddrinfo()" will be used to resolve the
   *address*.

   Voir aussi:

     "AbstractEventLoop.create_connection()" and
     "asyncio.open_connection()".

coroutine AbstractEventLoop.sock_accept(sock)

   Accept a connection.  Modeled after blocking
   "socket.socket.accept()".

   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.

   La *socket* *sock* ne soit pas être bloquante.

   Cette méthode est une coroutine.

   Voir aussi:

     "AbstractEventLoop.create_server()" and "start_server()".


18.5.1.10. Résout le nom d'hôte
===============================

coroutine AbstractEventLoop.getaddrinfo(host, port, *, family=0, type=0, proto=0, flags=0)

   This method is a coroutine, similar to "socket.getaddrinfo()"
   function but non-blocking.

coroutine AbstractEventLoop.getnameinfo(sockaddr, flags=0)

   This method is a coroutine, similar to "socket.getnameinfo()"
   function but non-blocking.


18.5.1.11. Connect pipes
========================

On Windows with "SelectorEventLoop", these methods are not supported.
Use "ProactorEventLoop" to support pipes on Windows.

coroutine AbstractEventLoop.connect_read_pipe(protocol_factory, pipe)

   Register read pipe in eventloop.

   *protocol_factory* should instantiate object with "Protocol"
   interface.  *pipe* is a *file-like object*. Return pair
   "(transport, protocol)", where *transport* supports the
   "ReadTransport" interface.

   With "SelectorEventLoop" event loop, the *pipe* is set to non-
   blocking mode.

   Cette méthode est une coroutine.

coroutine AbstractEventLoop.connect_write_pipe(protocol_factory, pipe)

   Register write pipe in eventloop.

   *protocol_factory* should instantiate object with "BaseProtocol"
   interface. *pipe* is *file-like object*. Return pair "(transport,
   protocol)", where *transport* supports "WriteTransport" interface.

   With "SelectorEventLoop" event loop, the *pipe* is set to non-
   blocking mode.

   Cette méthode est une coroutine.

Voir aussi:

  The "AbstractEventLoop.subprocess_exec()" and
  "AbstractEventLoop.subprocess_shell()" methods.


18.5.1.12. Signaux UNIX
=======================

Disponibilité : UNIX seulement.

AbstractEventLoop.add_signal_handler(signum, callback, *args)

   Ajouter un gestionnaire (*handler*) pour un signal.

   Raise "ValueError" if the signal number is invalid or uncatchable.
   Raise "RuntimeError" if there is a problem setting up the handler.

   Use functools.partial to pass keywords to the callback.

AbstractEventLoop.remove_signal_handler(sig)

   Supprimer un *handler* pour un signal.

   Return "True" if a signal handler was removed, "False" if not.

Voir aussi: Le module "signal".


18.5.1.13. Exécuteur
====================

Call a function in an "Executor" (pool of threads or pool of
processes). By default, an event loop uses a thread pool executor
("ThreadPoolExecutor").

coroutine AbstractEventLoop.run_in_executor(executor, func, *args)

   Arrange for a *func* to be called in the specified executor.

   The *executor* argument should be an "Executor" instance. The
   default executor is used if *executor* is "None".

   Use functools.partial to pass keywords to the *func*.

   Cette méthode est une coroutine.

   Modifié dans la version 3.5.3: "BaseEventLoop.run_in_executor()" no
   longer configures the "max_workers" of the thread pool executor it
   creates, instead leaving it up to the thread pool executor
   ("ThreadPoolExecutor") to set the default.

AbstractEventLoop.set_default_executor(executor)

   Set the default executor used by "run_in_executor()".


18.5.1.14. API de gestion d'erreur
==================================

Allows customizing how exceptions are handled in the event loop.

AbstractEventLoop.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
   "call_exception_handler()" documentation for details about
   context).

AbstractEventLoop.get_exception_handler()

   Return the exception handler, or "None" if the default one is in
   use.

   Nouveau dans la version 3.5.2.

AbstractEventLoop.default_exception_handler(context)

   Gestionnaire d'exception par défaut.

   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
   "call_exception_handler()".

AbstractEventLoop.call_exception_handler(context)

   Appelle le gestionnaire d'exception de la boucle d'évènements
   actuelle.

   *context* is a "dict" object containing the following keys (new
   keys may be introduced later):

   * "message" : Message d'erreur ;

   * "exception" (optionnel): Un objet exception ;

   * 'future' (optional): "asyncio.Future" instance;

   * 'handle' (optional): "asyncio.Handle" instance;

   * 'protocol' (optional): Protocol instance;

   * 'transport' (optional): Transport instance;

   * 'socket' (optional): "socket.socket" instance.

   Note:

     Note: this method should not be overloaded in subclassed event
     loops.  For any custom exception handling, use
     "set_exception_handler()" method.


18.5.1.15. Mode débogage
========================

AbstractEventLoop.get_debug()

   Get the debug mode ("bool") of the event loop.

   The default value is "True" if the environment variable
   "PYTHONASYNCIODEBUG" is set to a non-empty string, "False"
   otherwise.

   Nouveau dans la version 3.4.2.

AbstractEventLoop.set_debug(enabled: bool)

   Active le mode débogage pour la boucle d'évènements.

   Nouveau dans la version 3.4.2.

Voir aussi: The debug mode of asyncio.


18.5.1.16. Serveur
==================

class asyncio.Server

   Serveur écoutant sur des *sockets*.

   Object created by the "AbstractEventLoop.create_server()" method
   and the "start_server()" function. Don't instantiate the class
   directly.

   close()

      Stop serving: close listening sockets and set the "sockets"
      attribute to "None".

      The sockets that represent existing incoming client connections
      are left open.

      The server is closed asynchronously, use the "wait_closed()"
      coroutine to wait until the server is closed.

   coroutine wait_closed()

      Attends que la méthode "close()" se termine.

      Cette méthode est une coroutine.

   sockets

      List of "socket.socket" objects the server is listening to, or
      "None" if the server is closed.


18.5.1.17. Handle
=================

class asyncio.Handle

   A callback wrapper object returned by
   "AbstractEventLoop.call_soon()",
   "AbstractEventLoop.call_soon_threadsafe()",
   "AbstractEventLoop.call_later()", and
   "AbstractEventLoop.call_at()".

   cancel()

      Cancel the call.  If the callback is already canceled or
      executed, this method has no effect.


18.5.1.18. Exemples de boucles d'évènements
===========================================


18.5.1.18.1. "Hello World" avec "call_soon()"
---------------------------------------------

Example using the "AbstractEventLoop.call_soon()" method to schedule a
callback. The callback displays ""Hello World"" and then stops the
event loop:

   import asyncio

   def hello_world(loop):
       print('Hello World')
       loop.stop()

   loop = asyncio.get_event_loop()

   # Schedule a call to hello_world()
   loop.call_soon(hello_world, loop)

   # Blocking call interrupted by loop.stop()
   loop.run_forever()
   loop.close()

Voir aussi: The Hello World coroutine example uses a coroutine.


18.5.1.18.2. Afficher la date actuelle avec "call_later()"
----------------------------------------------------------

Example of callback displaying the current date every second. The
callback uses the "AbstractEventLoop.call_later()" method to
reschedule itself during 5 seconds, and then stops the event loop:

   import asyncio
   import datetime

   def display_date(end_time, loop):
       print(datetime.datetime.now())
       if (loop.time() + 1.0) < end_time:
           loop.call_later(1, display_date, end_time, loop)
       else:
           loop.stop()

   loop = asyncio.get_event_loop()

   # Schedule the first call to display_date()
   end_time = loop.time() + 5.0
   loop.call_soon(display_date, end_time, loop)

   # Blocking call interrupted by loop.stop()
   loop.run_forever()
   loop.close()

Voir aussi:

  The coroutine displaying the current date example uses a coroutine.


18.5.1.18.3. Watch a file descriptor for read events
----------------------------------------------------

Wait until a file descriptor received some data using the
"AbstractEventLoop.add_reader()" method and then close the event loop:

   import asyncio
   try:
       from socket import socketpair
   except ImportError:
       from asyncio.windows_utils import socketpair

   # Create a pair of connected file descriptors
   rsock, wsock = socketpair()
   loop = asyncio.get_event_loop()

   def reader():
       data = rsock.recv(100)
       print("Received:", data.decode())
       # We are done: unregister the file descriptor
       loop.remove_reader(rsock)
       # Stop the event loop
       loop.stop()

   # Register the file descriptor for read event
   loop.add_reader(rsock, reader)

   # Simulate the reception of data from the network
   loop.call_soon(wsock.send, 'abc'.encode())

   # Run the event loop
   loop.run_forever()

   # We are done, close sockets and the event loop
   rsock.close()
   wsock.close()
   loop.close()

Voir aussi:

  The register an open socket to wait for data using a protocol
  example uses a low-level protocol created by the
  "AbstractEventLoop.create_connection()" method.

  The register an open socket to wait for data using streams example
  uses high-level streams created by the "open_connection()" function
  in a coroutine.


18.5.1.18.4. Définit les gestionnaires de signaux pour *SIGINT* et *SIGTERM*
----------------------------------------------------------------------------

Register handlers for signals "SIGINT" and "SIGTERM" using the
"AbstractEventLoop.add_signal_handler()" method:

   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()

Cet exemple fonctionne seulement sur Unix.
