19.5.1. 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.

19.5.1.1. Run an event loop

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.

3.5.1 版更變.

AbstractEventLoop.run_until_complete(future)

Run until the Future is done.

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()

Returns running status of event loop.

AbstractEventLoop.stop()

Stop running the event loop.

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

3.5.1 版更變.

AbstractEventLoop.is_closed()

Returns True if the event loop was closed.

3.4.2 版新加入.

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()

3.6 版新加入.

19.5.1.2. Calls

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).

備註

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, context=None)

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 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 optional keyword-only context argument allows specifying a custom contextvars.Context for the callback to run in. The current context is used when no context is provided.

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

Use functools.partial to pass keywords to the callback.

3.7 版更變: The context keyword-only parameter was added. See PEP 567 for more details.

AbstractEventLoop.call_soon_threadsafe(callback, *args, context=None)

Like call_soon(), but thread safe.

See the concurrency and multithreading section of the documentation.

3.7 版更變: The context keyword-only parameter was added. See PEP 567 for more details.

19.5.1.3. 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 time.time().

備註

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

AbstractEventLoop.call_later(delay, callback, *args, context=None)

Arrange for the callback to be called after the given delay seconds (either an int or float).

An instance of asyncio.TimerHandle 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().

An optional keyword-only context argument allows specifying a custom contextvars.Context for the callback to run in. The current context is used when no context is provided.

Use functools.partial to pass keywords to the callback.

3.7 版更變: The context keyword-only parameter was added. See PEP 567 for more details.

AbstractEventLoop.call_at(when, callback, *args, context=None)

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.TimerHandle is returned, which can be used to cancel the callback.

Use functools.partial to pass keywords to the callback.

3.7 版更變: The context keyword-only parameter was added. See PEP 567 for more details.

AbstractEventLoop.time()

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

也參考

The asyncio.sleep() function.

19.5.1.4. Futures

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).

3.5.2 版新加入.

19.5.1.5. Tasks

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.

3.4.2 版新加入.

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.

3.4.4 版新加入.

AbstractEventLoop.get_task_factory()

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

3.4.4 版新加入.

19.5.1.6. Creating 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, ssl_handshake_timeout=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 will try to establish the connection in the background. When successful, it 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.

備註

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 that 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 ssl.SSLContext object, this context is used to create the transport; if ssl is True, a context with some unspecified default settings is used.

    也參考

    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.

  • ssl_handshake_timeout is (for an SSL connection) the time in seconds to wait for the SSL handshake to complete before aborting the connection. 60.0 seconds if None (default).

3.7 版新加入: The ssl_handshake_timeout parameter.

3.5 版更變: On Windows with ProactorEventLoop, SSL/TLS is now supported.

也參考

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)

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

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

Options changing how the connection is created:

  • 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_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 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.

3.4.4 版更變: The family, proto, flags, reuse_address, reuse_port, *allow_broadcast, and sock parameters were added.

coroutine AbstractEventLoop.create_unix_connection(protocol_factory, path=None, *, ssl=None, sock=None, server_hostname=None, ssl_handshake_timeout=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 will try to establish the connection in the background. When successful, it 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, bytes, and Path paths are supported.

See the AbstractEventLoop.create_connection() method for parameters.

Availability: UNIX.

3.7 版新加入: The ssl_handshake_timeout parameter.

3.7 版更變: The path parameter can now be a path-like object.

19.5.1.7. Creating listening 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, ssl_handshake_timeout=None, start_serving=True)

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.

Parameters:

  • 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 is a bitmask for 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.
  • ssl_handshake_timeout is (for an SSL server) the time in seconds to wait for the SSL handshake to complete before aborting the connection. 60.0 seconds if None (default).
  • start_serving set to True (the default) causes the created server to start accepting connections immediately. When set to False, the user should await on Server.start_serving() or Server.serve_forever() to make the server to start accepting connections.

3.7 版新加入: ssl_handshake_timeout and start_serving parameters.

3.5 版更變: On Windows with ProactorEventLoop, SSL/TLS is now supported.

也參考

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

3.5.1 版更變: 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, ssl_handshake_timeout=None, start_serving=True)

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

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

Availability: UNIX.

3.7 版新加入: The ssl_handshake_timeout and start_serving parameters.

3.7 版更變: The path parameter can now be a Path object.

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

Handle an accepted connection.

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

Parameters:

  • 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.
  • ssl_handshake_timeout is (for an SSL connection) the time in seconds to wait for the SSL handshake to complete before aborting the connection. 60.0 seconds if None (default).

When completed it returns a (transport, protocol) pair.

3.7 版新加入: The ssl_handshake_timeout parameter.

3.5.3 版新加入.

19.5.1.8. File Transferring

coroutine AbstractEventLoop.sendfile(transport, file, offset=0, count=None, *, fallback=True)

Send a file to transport, return the total number of bytes which were sent.

The method uses high-performance os.sendfile() if available.

file must be a regular file object opened in binary mode.

offset tells from where to start reading the file. If specified, count is the total number of bytes to transmit as opposed to sending the file until EOF is reached. File position is updated on return or also in case of error in which case file.tell() can be used to figure out the number of bytes which were sent.

fallback set to True makes asyncio to manually read and send the file when the platform does not support the sendfile syscall (e.g. Windows or SSL socket on Unix).

Raise SendfileNotAvailableError if the system does not support sendfile syscall and fallback is False.

3.7 版新加入.

19.5.1.9. TLS Upgrade

coroutine AbstractEventLoop.start_tls(transport, protocol, sslcontext, *, server_side=False, server_hostname=None, ssl_handshake_timeout=None)

Upgrades an existing connection to TLS.

Returns a new transport instance, that the protocol must start using immediately after the await. The transport instance passed to the start_tls method should never be used again.

Parameters:

  • transport and protocol instances that methods like create_server() and create_connection() return.
  • sslcontext: a configured instance of SSLContext.
  • server_side pass True when a server-side connection is being upgraded (like the one created by create_server()).
  • server_hostname: sets or overrides the host name that the target server’s certificate will be matched against.
  • ssl_handshake_timeout is (for an SSL connection) the time in seconds to wait for the SSL handshake to complete before aborting the connection. 60.0 seconds if None (default).

3.7 版新加入.

19.5.1.10. Watch file descriptors

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.

19.5.1.11. Low-level socket operations

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.

3.7 版更變: Even though the method was always documented as a coroutine method, before Python 3.7 it returned a Future. Since Python 3.7, this is an async def method.

coroutine AbstractEventLoop.sock_recv_into(sock, buf)

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

The received data is written into buf (a writable buffer). The return value is the number of bytes written.

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

3.7 版新加入.

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.

3.7 版更變: Even though the method was always documented as a coroutine method, before Python 3.7 it returned an Future. Since Python 3.7, this is an async def method.

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.

3.5.2 版更變: 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.

也參考

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.

The socket sock must be non-blocking.

3.7 版更變: Even though the method was always documented as a coroutine method, before Python 3.7 it returned a Future. Since Python 3.7, this is an async def method.

也參考

AbstractEventLoop.create_server() and start_server().

coroutine AbstractEventLoop.sock_sendfile(sock, file, offset=0, count=None, *, fallback=True)

Send a file using high-performance os.sendfile if possible and return the total number of bytes which were sent.

Asynchronous version of socket.socket.sendfile().

sock must be non-blocking socket of socket.SOCK_STREAM type.

file must be a regular file object opened in binary mode.

offset tells from where to start reading the file. If specified, count is the total number of bytes to transmit as opposed to sending the file until EOF is reached. File position is updated on return or also in case of error in which case file.tell() can be used to figure out the number of bytes which were sent.

fallback set to True makes asyncio to manually read and send the file when the platform does not support the sendfile syscall (e.g. Windows or SSL socket on Unix).

Raise SendfileNotAvailableError if the system does not support sendfile syscall and fallback is False.

3.7 版新加入.

19.5.1.12. Resolve host name

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.

3.7 版更變: Both getaddrinfo and getnameinfo methods were always documented to return a coroutine, but prior to Python 3.7 they were, in fact, returning asyncio.Future objects. Starting with Python 3.7 both methods are coroutines.

19.5.1.13. 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.

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.

也參考

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

19.5.1.14. UNIX signals

Availability: UNIX only.

AbstractEventLoop.add_signal_handler(signum, callback, *args)

Add a handler for a 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)

Remove a handler for a signal.

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

也參考

The signal module.

19.5.1.15. Executor

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

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*.

This method returns a asyncio.Future object.

3.5.3 版更變: 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().

19.5.1.16. Error Handling API

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.

3.5.2 版新加入.

AbstractEventLoop.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 call_exception_handler().

AbstractEventLoop.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): asyncio.Future instance;
  • 『handle』 (optional): asyncio.Handle instance;
  • 『protocol』 (optional): Protocol instance;
  • 『transport』 (optional): Transport instance;
  • 『socket』 (optional): socket.socket instance.

備註

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

19.5.1.17. Debug mode

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.

3.4.2 版新加入.

AbstractEventLoop.set_debug(enabled: bool)

Set the debug mode of the event loop.

3.4.2 版新加入.

也參考

The debug mode of asyncio.

19.5.1.18. Server

class asyncio.Server

Server listening on sockets.

Object created by AbstractEventLoop.create_server(), AbstractEventLoop.create_unix_server(), start_server(), and start_unix_server() functions. Don’t instantiate the class directly.

Server objects are asynchronous context managers. When used in an async with statement, it’s guaranteed that the Server object is closed and not accepting new connections when the async with statement is completed:

srv = await loop.create_server(...)

async with srv:
    # some code

# At this point, srv is closed and no longer accepts new connections.

3.7 版更變: Server object is an asynchronous context manager since Python 3.7.

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.

get_loop()

Gives the event loop associated with the server object.

3.7 版新加入.

coroutine start_serving()

Start accepting connections.

This method is idempotent, so it can be called when the server is already being serving.

The new start_serving keyword-only parameter to AbstractEventLoop.create_server() and asyncio.start_server() allows to create a Server object that is not accepting connections right away. In which case this method, or Server.serve_forever() can be used to make the Server object to start accepting connections.

3.7 版新加入.

coroutine serve_forever()

Start accepting connections until the coroutine is cancelled. Cancellation of serve_forever task causes the server to be closed.

This method can be called if the server is already accepting connections. Only one serve_forever task can exist per one Server object.

Example:

async def client_connected(reader, writer):
    # Communicate with the client with
    # reader/writer streams.  For example:
    await reader.readline()

async def main(host, port):
    srv = await asyncio.start_server(
        client_connected, host, port)
    await srv.serve_forever()

asyncio.run(main('127.0.0.1', 0))

3.7 版新加入.

is_serving()

Return True if the server is accepting new connections.

3.7 版新加入.

coroutine wait_closed()

Wait until the close() method completes.

sockets

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

3.7 版更變: Prior to Python 3.7 Server.sockets used to return the internal list of server’s sockets directly. In 3.7 a copy of that list is returned.

19.5.1.19. Handle

class asyncio.Handle

A callback wrapper object returned by AbstractEventLoop.call_soon(), AbstractEventLoop.call_soon_threadsafe().

cancel()

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

cancelled()

Return True if the call was cancelled.

3.7 版新加入.

class asyncio.TimerHandle

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

The class is inherited from Handle.

when()

Return a scheduled callback time as float seconds.

The time is an absolute timestamp, using the same time reference as AbstractEventLoop.time().

3.7 版新加入.

19.5.1.20. SendfileNotAvailableError

exception asyncio.SendfileNotAvailableError

Sendfile syscall is not available, subclass of RuntimeError.

Raised if the OS does not support sendfile syscall for given socket or file type.

19.5.1.21. Event loop examples

19.5.1.21.1. Hello World with 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()

也參考

The Hello World coroutine example uses a coroutine.

19.5.1.21.2. Display the current date with 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()

也參考

The coroutine displaying the current date example uses a coroutine.

19.5.1.21.3. 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
from socket 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()

也參考

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.

19.5.1.21.4. Set signal handlers for SIGINT and 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()

This example only works on UNIX.