事件循环 ¶

源代码： Lib/asyncio/events.py , Lib/asyncio/base_events.py

前言

事件循环是每个 asyncio 应用程序的核心。事件循环运行异步任务和回调、履行网络 IO 操作，及运行子进程。

应用程序开发者通常应该使用高级 asyncio 函数，譬如 asyncio.run() ，且应该很少需要引用循环对象 (或调用其方法)。此节主要针对低级代码、库及框架的作者，他们需要对事件循环行为进行更好的控制。

获得事件循环

下列低级函数可以用于获取、设置或创建事件循环：

asyncio. get_running_loop ( ) ¶

返回当前 OS 线程中正运行的事件循环。

引发 RuntimeError if there is no running event loop.

This function can only be called from a coroutine or a callback.

3.7 版添加。

asyncio. get_event_loop ( ) ¶

获取当前事件循环。

When called from a coroutine or a callback (e.g. scheduled with call_soon or similar API), this function will always return the running event loop.

If there is no running event loop set, the function will return the result of the get_event_loop_policy().get_event_loop() 调用。

Because this function has rather complex behavior (especially when custom event loop policies are in use), using the get_running_loop() function is preferred to get_event_loop() in coroutines and callbacks.

As noted above, consider using the higher-level asyncio.run() function, instead of using these lower level functions to manually create and close an event loop.

Deprecated since version 3.12: Deprecation warning is emitted if there is no current event loop. In some future Python release this will become an error.

asyncio. set_event_loop ( loop ) ¶: Set loop as the current event loop for the current OS thread.

asyncio. new_event_loop ( ) ¶: Create and return a new event loop object.

Note that the behaviour of get_event_loop() , set_event_loop() ，和 new_event_loop() functions can be altered by 设置自定义事件循环策略 .

内容

此文档页面包含下列章节：

The 事件循环方法 section is the reference documentation of the event loop APIs;
The 回调处理 section documents the Handle and TimerHandle instances which are returned from scheduling methods such as loop.call_soon() and loop.call_later() ;
The 服务器对象 section documents types returned from event loop methods like loop.create_server() ;
The 事件循环实现 section documents the SelectorEventLoop and ProactorEventLoop 类；
The 范例 section showcases how to work with some event loop APIs.

事件循环方法 ¶

事件循环拥有低级 API 为下列：

运行和停止循环  ¶

循环。 run_until_complete ( future ) ¶

运行直到 future (实例化的 Future ) 已完成。

若自变量是协程对象 it is implicitly scheduled to run as a asyncio.Task .

返回 Future 结果 (或引发其异常)。

循环。 run_forever ( ) ¶

运行事件循环直到 stop() 被调用。

若 stop() is called before run_forever() is called, the loop will poll the I/O selector once with a timeout of zero, run all callbacks scheduled in response to I/O events (and those that were already scheduled), and then exit.

若 stop() is called while run_forever() is running, the loop will run the current batch of callbacks and then exit. Note that new callbacks scheduled by callbacks will not run in this case; instead, they will run the next time run_forever() or run_until_complete() 被调用。

循环。 stop ( ) ¶: 停止事件循环。

循环。 is_running ( ) ¶: 返回 True if the event loop is currently running.

循环。 is_closed ( ) ¶: 返回 True 若事件循环被关闭。

循环。 close ( ) ¶

关闭事件循环。

The loop must not be running when this function is called. Any pending callbacks will be discarded.

This method clears all queues and shuts down the executor, but does not wait for the executor to finish.

This method is idempotent and irreversible. No other methods should be called after the event loop is closed.

协程循环。 shutdown_asyncgens ( ) ¶

Schedule all currently open 异步生成器 objects to close with an aclose() call. After calling this method, the event loop will issue a warning if a new asynchronous generator is iterated. This should be used to reliably finalize all scheduled asynchronous generators.

Note that there is no need to call this function when asyncio.run() 被使用。

范例：

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

Added in version 3.6.

协程循环。 shutdown_default_executor ( timeout = None ) ¶

Schedule the closure of the default executor and wait for it to join all of the threads in the ThreadPoolExecutor . Once this method has been called, using the default executor with loop.run_in_executor() 将引发 RuntimeError .

The timeout parameter specifies the amount of time (in float seconds) the executor will be given to finish joining. With the default, None , the executor is allowed an unlimited amount of time.

若 timeout is reached, a RuntimeWarning is emitted and the default executor is terminated without waiting for its threads to finish joining.

注意

Do not call this method when using asyncio.run() , as the latter handles default executor shutdown automatically.

Added in version 3.9.

3.12 版改变：添加 timeout 参数。

调度回调  ¶

循环。 call_soon ( callback , * args , context = None ) ¶

Schedule the callback callback to be called with args arguments at the next iteration of the event loop.

Return an instance of asyncio.Handle , which can be used later to cancel the callback.

Callbacks are called in the order in which they are registered. Each callback will be called exactly once.

可选仅关键词 context argument specifies a custom contextvars.Context 为 callback to run in. Callbacks use the current context when no context 被提供。

不像 call_soon_threadsafe() , this method is not thread-safe.

循环。 call_soon_threadsafe ( callback , * args , context = None ) ¶

A thread-safe variant of call_soon() . When scheduling callbacks from another thread, this function must be used, since call_soon() is not thread-safe.

引发 RuntimeError if called on a loop that’s been closed. This can happen on a secondary thread when the main application is shutting down.

见并发和多线程章节的文档编制。

3.7 版改变： The context keyword-only parameter was added. See PEP 567 了解更多细节。

注意

Most asyncio scheduling functions don’t allow passing keyword arguments. To do that, use functools.partial() :

# will schedule "print("Hello", flush=True)"
loop.call_soon(
    functools.partial(print, "Hello", flush=True))

Using partial objects is usually more convenient than using lambdas, as asyncio can render partial objects better in debug and error messages.

调度延迟回调  ¶

Event loop provides mechanisms to schedule callback functions to be called at some point in the future. Event loop uses monotonic clocks to track time.

循环。 call_later ( delay , callback , * args , context = None ) ¶

Schedule callback to be called after the given delay number of seconds (can be either an int or a float).

实例化的 asyncio.TimerHandle is returned which can be used to cancel the callback.

callback will be called exactly once. If two callbacks are scheduled for exactly the same time, the order in which they are called is undefined.

The optional positional args will be passed to the callback when it is called. If you want the callback to be called with keyword arguments use functools.partial() .

可选仅关键词 context 自变量允许指定自定义 contextvars.Context 为 callback to run in. The current context is used when no context 被提供。

3.7 版改变： The context keyword-only parameter was added. See PEP 567 了解更多细节。

3.8 版改变： In Python 3.7 and earlier with the default event loop implementation, the delay could not exceed one day. This has been fixed in Python 3.8.

循环。 call_at ( 当 , callback , * args , context = None ) ¶

Schedule callback to be called at the given absolute timestamp 当 (an int or a float), using the same time reference as loop.time() .

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

实例化的 asyncio.TimerHandle is returned which can be used to cancel the callback.

3.7 版改变： The context keyword-only parameter was added. See PEP 567 了解更多细节。

3.8 版改变： In Python 3.7 and earlier with the default event loop implementation, the difference between 当 and the current time could not exceed one day. This has been fixed in Python 3.8.

循环。 time ( ) ¶: Return the current time, as a float value, according to the event loop’s internal monotonic clock.

注意

3.8 版改变： In Python 3.7 and earlier timeouts (relative delay or absolute 当 ) should not exceed one day. This has been fixed in Python 3.8.

另请参阅

The asyncio.sleep() 函数。

创建未来和任务  ¶

循环。 create_future ( ) ¶

创建 asyncio.Future 对象附加到事件循环。

This is the preferred way to create Futures in asyncio. This lets third-party event loops provide alternative implementations of the Future object (with better performance or instrumentation).

Added in version 3.5.2.

循环。 create_task ( coro , * , 名称 = None , context = None ) ¶

Schedule the execution of 协程 coro 。返回 Task 对象。

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

若 name argument is provided and not None ，将它设为任务名称使用 Task.set_name() .

可选仅关键词 context 自变量允许指定自定义 contextvars.Context 为 coro 以在其中运行。创建当前上下文副本当没有 context 被提供。

3.8 版改变：添加 name 参数。

3.11 版改变：添加 context 参数。

循环。 set_task_factory ( factory ) ¶

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

若 factory is None the default task factory will be set. Otherwise, factory 必须为 callable with the signature matching (loop, coro, context=None) ，其中 loop is a reference to the active event loop, and coro is a coroutine object. The callable must return a asyncio.Future -compatible object.

循环。 get_task_factory ( ) ¶: 返回任务工厂或 None if the default one is in use.

打开网络连接  ¶

协程循环。 create_connection ( protocol_factory , host = None , port = None , * , ssl = None , 系列 = 0 , proto = 0 , flags = 0 , sock = None , local_addr = None , server_hostname = None , ssl_handshake_timeout = None , ssl_shutdown_timeout = None , happy_eyeballs_delay = None , interleave = None , all_errors = False ) ¶

Open a streaming transport connection to a given address specified by host and port .

套接字族可以是 AF_INET or AF_INET6 从属 host (或系列自变量，若有提供)。

套接字类型将是 SOCK_STREAM .

protocol_factory must be a callable returning an asyncio protocol 实现。

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

The chronological synopsis of the underlying operation is as follows:

The connection is established and a transport is created for it.
protocol_factory is called without arguments and is expected to return a protocol 实例。
The protocol instance is coupled with the transport by calling its connection_made() 方法。
A (transport, protocol) tuple is returned on success.

The created transport is an implementation-dependent bidirectional stream.

其它自变量：

ssl : if given and not false, a SSL/TLS transport is created (by default a plain TCP transport is created). If ssl 是 ssl.SSLContext object, this context is used to create the transport; if ssl is True , a default context returned from ssl.create_default_context() 被使用。

另请参阅

SSL/TLS 安全注意事项
server_hostname sets or overrides the hostname that the target server’s certificate will be matched against. Should only be passed if ssl 不是 None . 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 。若 server_hostname is an empty string, hostname matching is disabled (which is a serious security risk, allowing for potential man-in-the-middle attacks).
系列 , 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.
happy_eyeballs_delay , if given, enables Happy Eyeballs for this connection. It should be a floating-point number representing the amount of time in seconds to wait for a connection attempt to complete, before starting the next attempt in parallel. This is the “Connection Attempt Delay” as defined in RFC 8305 . A sensible default value recommended by the RFC is 0.25 (250 milliseconds).
interleave controls address reordering when a host name resolves to multiple IP addresses. If 0 or unspecified, no reordering is done, and addresses are tried in the order returned by getaddrinfo() . If a positive integer is specified, the addresses are interleaved by address family, and the given integer is interpreted as “First Address Family Count” as defined in RFC 8305 。默认为 0 if happy_eyeballs_delay is not specified, and 1 if it is.
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 , 系列 , proto , flags , happy_eyeballs_delay , interleave and local_addr should be specified.

注意

The sock argument transfers ownership of the socket to the transport created. To close the socket, call the transport’s close() 方法。
local_addr ，若给定，是 (local_host, local_port) tuple used to bind the socket locally. The local_host and local_port are looked up using getaddrinfo() , similarly to host and port .
ssl_handshake_timeout is (for a TLS connection) the time in seconds to wait for the TLS handshake to complete before aborting the connection. 60.0 seconds if None (default).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 30.0 seconds if None (default).
all_errors determines what exceptions are raised when a connection cannot be created. By default, only a single Exception is raised: the first exception if there is only one or all errors have same message, or a single OSError with the error messages combined. When all_errors is True ， ExceptionGroup will be raised containing all exceptions (even if there is only one).

3.5 版改变： Added support for SSL/TLS in ProactorEventLoop .

3.6 版改变：套接字选项 socket.TCP_NODELAY is set by default for all TCP connections.

3.7 版改变：添加 ssl_handshake_timeout 参数。

3.8 版改变：添加 happy_eyeballs_delay and interleave 参数。

Happy Eyeballs Algorithm: Success with Dual-Stack Hosts. When a server’s IPv4 path and protocol are working, but the server’s IPv6 path and protocol are not working, a dual-stack client application experiences significant connection delay compared to an IPv4-only client. This is undesirable because it causes the dual-stack client to have a worse user experience. This document specifies requirements for algorithms that reduce this user-visible delay and provides an algorithm.

3.11 版改变：添加 ssl_shutdown_timeout 参数。

3.12 版改变： all_errors 被添加。

另请参阅

The open_connection() function is a high-level alternative API. It returns a pair of ( StreamReader , StreamWriter ) that can be used directly in async/await code.

协程循环。 create_datagram_endpoint ( protocol_factory , local_addr = None , remote_addr = None , * , 系列 = 0 , proto = 0 , flags = 0 , reuse_port = None , allow_broadcast = None , sock = None ) ¶

创建数据报连接。

套接字族可以是 AF_INET , AF_INET6 ，或 AF_UNIX ，从属 host (或系列自变量，若有提供)。

套接字类型将是 SOCK_DGRAM .

protocol_factory must be a callable returning a protocol 实现。

元组 (transport, protocol) 被返回当成功时。

其它自变量：

local_addr ，若给定，是 (local_host, local_port) tuple used to bind the socket locally. The local_host and local_port are looked up using getaddrinfo() .
remote_addr ，若给定，是 (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() .
系列 , 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 Unixes. If the socket.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 ).

注意

The sock argument transfers ownership of the socket to the transport created. To close the socket, call the transport’s close() 方法。

见 UDP echo client protocol and UDP echo server protocol 范例。

3.4.4 版改变： The 系列 , proto , flags , reuse_address , reuse_port , allow_broadcast ，和 sock 参数被添加。

3.8 版改变：添加支持 Windows。

3.8.1 版改变： The reuse_address parameter is no longer supported, as using socket.SO_REUSEADDR poses a significant security concern for UDP. Explicitly passing reuse_address=True 会引发异常。

When multiple processes with differing UIDs assign sockets to an identical 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 , socket.SO_REUSEPORT is used instead, which specifically prevents processes with differing UIDs from assigning sockets to the same socket address.

3.11 版改变： The reuse_address parameter, disabled since Python 3.8.1, 3.7.6 and 3.6.10, has been entirely removed.

协程循环。 create_unix_connection ( protocol_factory , path = None , * , ssl = None , sock = None , server_hostname = None , ssl_handshake_timeout = None , ssl_shutdown_timeout = None ) ¶

Create a Unix connection.

The socket family will be AF_UNIX ; socket type will be SOCK_STREAM .

元组 (transport, protocol) 被返回当成功时。

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

See the documentation of the loop.create_connection() method for information about arguments to this method.

可用性：Unix。

3.7 版改变：添加 ssl_handshake_timeout parameter. The path parameter can now be a 像路径对象 .

3.11 版改变：添加 ssl_shutdown_timeout 参数。

创建网络服务器  ¶

协程循环。 create_server ( protocol_factory , host = None , port = None , * , 系列 = socket.AF_UNSPEC , flags = socket.AI_PASSIVE , sock = None , backlog = 100 , ssl = None , reuse_address = None , reuse_port = None , keep_alive = None , ssl_handshake_timeout = None , ssl_shutdown_timeout = None , start_serving = True ) ¶

Create a TCP server (socket type SOCK_STREAM ) listening on port 的 host 地址。

返回 Server 对象。

Arguments:

protocol_factory must be a callable returning a protocol 实现。
The host parameter can be set to several types which determine where the server would be listening:
- 若 host is a string, the TCP server is bound to a single network interface specified by host .
- 若 host is a sequence of strings, the TCP server is bound to all network interfaces specified by the sequence.
- 若 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).
The port parameter can be set to specify which port the server should listen on. If 0 or None (the default), a random unused port will be selected (note that if host resolves to multiple network interfaces, a different random port will be selected for each interface).
系列 can be set to either socket.AF_INET or AF_INET6 to force the socket to use IPv4 or IPv6. If not set, the 系列 will be determined from host name (defaults to 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 must not be specified.

注意

The sock argument transfers ownership of the socket to the server created. To close the socket, call the server’s close() 方法。
backlog is the maximum number of queued connections passed to listen() (defaults to 100).
ssl can be set to an SSLContext instance to enable TLS 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 在 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.
keep_alive 设为 True keeps connections active by enabling the periodic transmission of messages.

Changed in version 3.13: 添加 keep_alive 参数。

ssl_handshake_timeout is (for a TLS server) the time in seconds to wait for the TLS handshake to complete before aborting the connection. 60.0 seconds if None (default).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 30.0 seconds if None (default).
start_serving 设为 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.

3.5 版改变： Added support for SSL/TLS in ProactorEventLoop .

3.5.1 版改变： The host parameter can be a sequence of strings.

3.6 版改变：添加 ssl_handshake_timeout and start_serving parameters. The socket option socket.TCP_NODELAY is set by default for all TCP connections.

3.11 版改变：添加 ssl_shutdown_timeout 参数。

另请参阅

The start_server() function is a higher-level alternative API that returns a pair of StreamReader and StreamWriter that can be used in an async/await code.

协程循环。 create_unix_server ( protocol_factory , path = None , * , sock = None , backlog = 100 , ssl = None , ssl_handshake_timeout = None , ssl_shutdown_timeout = None , start_serving = True , cleanup_socket = True ) ¶

类似于 loop.create_server() but works with the AF_UNIX socket family.

path is the name of a Unix domain socket, and is required, unless a sock argument is provided. Abstract Unix sockets, str , bytes ，和 Path paths are supported.

若 cleanup_socket is true then the Unix socket will automatically be removed from the filesystem when the server is closed, unless the socket has been replaced after the server has been created.

See the documentation of the loop.create_server() method for information about arguments to this method.

可用性：Unix。

3.7 版改变：添加 ssl_handshake_timeout and start_serving parameters. The path parameter can now be a Path 对象。

3.11 版改变：添加 ssl_shutdown_timeout 参数。

Changed in version 3.13: 添加 cleanup_socket 参数。

协程循环。 connect_accepted_socket ( protocol_factory , sock , * , ssl = None , ssl_handshake_timeout = None , ssl_shutdown_timeout = None ) ¶

Wrap an already accepted connection into a transport/protocol pair.

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

参数：

protocol_factory must be a callable returning a protocol 实现。
sock is a preexisting socket object returned from socket.accept .

注意

The sock argument transfers ownership of the socket to the transport created. To close the socket, call the transport’s close() 方法。
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).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 30.0 seconds if None (default).

返回 (transport, protocol) 对。

Added in version 3.5.3.

3.7 版改变：添加 ssl_handshake_timeout 参数。

3.11 版改变：添加 ssl_shutdown_timeout 参数。

传输文件  ¶

协程循环。 sendfile ( transport , file , offset = 0 , count = None , * , fallback = True ) ¶

发送 file over a transport . Return the total number of bytes 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 always updated, even when this method raises an error, and file.tell() can be used to obtain the actual number of bytes sent.

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

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

3.7 版添加。

TLS 升级  ¶

协程循环。 start_tls ( transport , protocol , sslcontext , * , server_side = False , server_hostname = None , ssl_handshake_timeout = None , ssl_shutdown_timeout = None ) ¶

Upgrade an existing transport-based connection to TLS.

Create a TLS coder/decoder instance and insert it between the transport 和 protocol . The coder/decoder implements both transport -facing protocol and protocol -facing transport.

Return the created two-interface instance. After await ， protocol must stop using the original transport and communicate with the returned object only because the coder caches protocol -side data and sporadically exchanges extra TLS session packets with transport .

In some situations (e.g. when the passed transport is already closing) this may return None .

参数：

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 a TLS connection) the time in seconds to wait for the TLS handshake to complete before aborting the connection. 60.0 seconds if None (default).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 30.0 seconds if None (default).

3.7 版添加。

3.11 版改变：添加 ssl_shutdown_timeout 参数。

看守文件描述符  ¶

循环。 add_reader ( fd , callback , * args ) ¶: Start monitoring the fd file descriptor for read availability and invoke callback with the specified arguments once fd is available for reading.

循环。 remove_reader ( fd ) ¶: Stop monitoring the fd file descriptor for read availability. Returns True if fd was previously being monitored for reads.

循环。 add_writer ( fd , callback , * args ) ¶

Start monitoring the fd file descriptor for write availability and invoke callback with the specified arguments once fd is available for writing.

使用 functools.partial() to pass keyword arguments to callback .

循环。 remove_writer ( fd ) ¶: Stop monitoring the fd file descriptor for write availability. Returns True if fd was previously being monitored for writes.

另请参阅平台支持 section for some limitations of these methods.

直接操控套接字对象  ¶

In general, protocol implementations that use transport-based APIs such as loop.create_connection() and loop.create_server() are faster than implementations that work with sockets directly. However, there are some use cases when performance is not critical, and working with socket objects directly is more convenient.

协程循环。 sock_recv ( sock , nbytes ) ¶

接收直到 nbytes from sock . Asynchronous version of socket.recv() .

Return the received data as a bytes object.

sock 必须是非阻塞套接字。

3.7 版改变： Even though this method was always documented as a coroutine method, releases before Python 3.7 returned a Future . Since Python 3.7 this is an async def 方法。

协程循环。 sock_recv_into ( sock , buf ) ¶

Receive data from sock 到 buf buffer. Modeled after the blocking socket.recv_into() 方法。

Return the number of bytes written to the buffer.

sock 必须是非阻塞套接字。

3.7 版添加。

协程循环。 sock_recvfrom ( sock , bufsize ) ¶

Receive a datagram of up to bufsize from sock . Asynchronous version of socket.recvfrom() .

Return a tuple of (received data, remote address).

sock 必须是非阻塞套接字。

Added in version 3.11.

协程循环。 sock_recvfrom_into ( sock , buf , nbytes = 0 ) ¶

Receive a datagram of up to nbytes from sock into buf . Asynchronous version of socket.recvfrom_into() .

Return a tuple of (number of bytes received, remote address).

sock 必须是非阻塞套接字。

Added in version 3.11.

协程循环。 sock_sendall ( sock , data ) ¶

发送 data 到 sock 套接字。异步版本的 socket.sendall() .

This method continues to send to the socket until either all data in data has been sent or an error occurs. None is returned on success. On error, an exception is raised. Additionally, there is no way to determine how much data, if any, was successfully processed by the receiving end of the connection.

sock 必须是非阻塞套接字。

3.7 版改变： 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 方法。

协程循环。 sock_sendto ( sock , data , address ) ¶

Send a datagram from sock to address . Asynchronous version of socket.sendto() .

Return the number of bytes sent.

sock 必须是非阻塞套接字。

Added in version 3.11.

协程循环。 sock_connect ( sock , address ) ¶

连接 sock to a remote socket at address .

Asynchronous version of socket.connect() .

sock 必须是非阻塞套接字。

3.5.2 版改变： 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, loop.getaddrinfo() will be used to resolve the address .

另请参阅

loop.create_connection() and asyncio.open_connection() .

协程循环。 sock_accept ( sock ) ¶

Accept a connection. Modeled after the blocking socket.accept() 方法。

The socket must be bound to an address and listening for connections. The return value is a pair (conn, address) where conn 是 new 套接字对象用于发送和接收数据当连接上时，和 address 是绑定到连接另一端的套接字地址。

sock 必须是非阻塞套接字。

3.7 版改变： 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 方法。

另请参阅

loop.create_server() and start_server() .

协程循环。 sock_sendfile ( sock , file , offset = 0 , count = None , * , fallback = True ) ¶

Send a file using high-performance os.sendfile if possible. Return the total number of bytes sent.

Asynchronous version of socket.sendfile() .

sock must be a non-blocking socket.SOCK_STREAM socket .

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

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

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

sock 必须是非阻塞套接字。

3.7 版添加。

DNS ¶

协程循环。 getaddrinfo ( host , port , * , 系列 = 0 , type = 0 , proto = 0 , flags = 0 ) ¶: Asynchronous version of socket.getaddrinfo() .

协程循环。 getnameinfo ( sockaddr , flags = 0 ) ¶: Asynchronous version of socket.getnameinfo() .

注意

Both getaddrinfo and getnameinfo internally utilize their synchronous versions through the loop’s default thread pool executor. When this executor is saturated, these methods may experience delays, which higher-level networking libraries may report as increased timeouts. To mitigate this, consider using a custom executor for other user tasks, or setting a default executor with a larger number of workers.

3.7 版改变： 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.

操控管道  ¶

协程循环。 connect_read_pipe ( protocol_factory , pipe ) ¶

protocol_factory must be a callable returning an asyncio protocol 实现。

pipe 是像文件对象 .

Return pair (transport, protocol) ，其中 transport 支持 ReadTransport interface and protocol is an object instantiated by the protocol_factory .

采用 SelectorEventLoop event loop, the pipe is set to non-blocking mode.

协程循环。 connect_write_pipe ( protocol_factory , pipe ) ¶

protocol_factory must be a callable returning an asyncio protocol 实现。

pipe is 像文件对象 .

Return pair (transport, protocol) ，其中 transport supports WriteTransport interface and protocol is an object instantiated by the protocol_factory .

采用 SelectorEventLoop event loop, the pipe is set to non-blocking mode.

注意

SelectorEventLoop does not support the above methods on Windows. Use ProactorEventLoop instead for Windows.

另请参阅

The loop.subprocess_exec() and loop.subprocess_shell() 方法。

Unix 信号  ¶

循环。 add_signal_handler ( signum , callback , * args ) ¶

Set callback as the handler for the signum 信号。

The callback will be invoked by loop , along with other queued callbacks and runnable coroutines of that event loop. Unlike signal handlers registered using signal.signal() , a callback registered with this function is allowed to interact with the event loop.

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

使用 functools.partial() to pass keyword arguments to callback .

像 signal.signal() , this function must be invoked in the main thread.

循环。 remove_signal_handler ( sig ) ¶

Remove the handler for the sig 信号。

返回 True if the signal handler was removed, or False if no handler was set for the given signal.

可用性：Unix。

另请参阅

The signal 模块。

在线程 (或进程池) 中执行代码  ¶

awaitable 循环。 run_in_executor ( executor , func , * args ) ¶

Arrange for func to be called in the specified executor.

The executor argument should be an concurrent.futures.Executor instance. The default executor is used if executor is None . The default executor can be set by loop.set_default_executor() , otherwise, a concurrent.futures.ThreadPoolExecutor will be lazy-initialized and used by run_in_executor() 若需要。

范例：

import asyncio
import concurrent.futures
def blocking_io():
    # File operations (such as logging) can block the
    # event loop: run them in a thread pool.
    with open('/dev/urandom', 'rb') as f:
        return f.read(100)
def cpu_bound():
    # CPU-bound operations will block the event loop:
    # in general it is preferable to run them in a
    # process pool.
    return sum(i * i for i in range(10 ** 7))
async def main():
    loop = asyncio.get_running_loop()
    ## Options:
    # 1. Run in the default loop's executor:
    result = await loop.run_in_executor(
        None, blocking_io)
    print('default thread pool', result)
    # 2. Run in a custom thread pool:
    with concurrent.futures.ThreadPoolExecutor() as pool:
        result = await loop.run_in_executor(
            pool, blocking_io)
        print('custom thread pool', result)
    # 3. Run in a custom process pool:
    with concurrent.futures.ProcessPoolExecutor() as pool:
        result = await loop.run_in_executor(
            pool, cpu_bound)
        print('custom process pool', result)
if __name__ == '__main__':
    asyncio.run(main())

Note that the entry point guard ( if __name__ == '__main__' ) is required for option 3 due to the peculiarities of multiprocessing , which is used by ProcessPoolExecutor 。见 Safe importing of main module .

此方法返回 asyncio.Future 对象。

使用 functools.partial() to pass keyword arguments to func .

3.5.3 版改变： loop.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.

循环。 set_default_executor ( executor ) ¶

Set executor as the default executor used by run_in_executor() . executor 必须是实例化的 ThreadPoolExecutor .

3.11 版改变： executor 必须是实例化的 ThreadPoolExecutor .

错误处理 API ¶

Allows customizing how exceptions are handled in the event loop.

循环。 set_exception_handler ( handler ) ¶

Set handler as the new event loop exception handler.

若 handler is None , the default exception handler will be set. Otherwise, handler must be a callable with the signature matching (loop, context) ，其中 loop is a reference to the active event loop, and context 是 dict object containing the details of the exception (see call_exception_handler() documentation for details about context).

If the handler is called on behalf of a Task or Handle , it is run in the contextvars.Context of that task or callback handle.

3.12 版改变： The handler may be called in the Context of the task or handle where the exception originated.

循环。 get_exception_handler ( ) ¶

返回当前异常处理程序，或 None if no custom exception handler was set.

Added in version 3.5.2.

循环。 default_exception_handler ( context ) ¶

默认异常处理程序。

This is called when an exception occurs and no exception handler is set. This can be called by a custom exception handler that wants to defer to the default handler behavior.

context parameter has the same meaning as in call_exception_handler() .

循环。 call_exception_handler ( context ) ¶

Call the current event loop exception handler.

context 是 dict object containing the following keys (new keys may be introduced in future Python versions):

‘message’: Error message;
‘exception’ (optional): Exception object;
‘future’ (optional): asyncio.Future 实例；
‘task’ (optional): asyncio.Task 实例；
‘handle’ (optional): asyncio.Handle 实例；
‘protocol’ (optional): Protocol 实例；
‘transport’ (optional): Transport 实例；
‘socket’ (optional): socket.socket 实例；
‘asyncgen’ (optional): Asynchronous generator that caused

the exception.

注意

This method should not be overloaded in subclassed event loops. For custom exception handling, use the set_exception_handler() 方法。

启用调试模式  ¶

循环。 get_debug ( ) ¶

获取调试模式 ( bool ) of the event loop.

默认值为 True if the environment variable PYTHONASYNCIODEBUG is set to a non-empty string, False 否则。

循环。 set_debug ( 被启用 : bool ) ¶

Set the debug mode of the event loop.

3.7 版改变：新的 Python 开发模式 can now also be used to enable the debug mode.

循环。 slow_callback_duration ¶

This attribute can be used to set the minimum execution duration in seconds that is considered “slow”. When debug mode is enabled, “slow” callbacks are logged.

Default value is 100 milliseconds.

另请参阅

The asyncio 的调试模式 .

运行子进程  ¶

Methods described in this subsections are low-level. In regular async/await code consider using the high-level asyncio.create_subprocess_shell() and asyncio.create_subprocess_exec() convenience functions instead.

注意

On Windows, the default event loop ProactorEventLoop supports subprocesses, whereas SelectorEventLoop does not. See Windows 中的子进程支持了解细节。

协程循环。 subprocess_exec ( protocol_factory , * args , stdin = subprocess.PIPE , stdout = subprocess.PIPE , stderr = subprocess.PIPE , ** kwargs ) ¶

Create a subprocess from one or more string arguments specified by args .

args must be a list of strings represented by:

str ;
or bytes , encoded to the 文件系统编码 .

The first string specifies the program executable, and the remaining strings specify the arguments. Together, string arguments form the argv of the program.

This is similar to the standard library subprocess.Popen class called with shell=False and the list of strings passed as the first argument; however, where Popen takes a single argument which is list of strings, subprocess_exec takes multiple string arguments.

The protocol_factory must be a callable returning a subclass of the asyncio.SubprocessProtocol 类。

其它参数：

stdin can be any of these:
- a file-like object
- an existing file descriptor (a positive integer), for example those created with os.pipe()
- the subprocess.PIPE constant (default) which will create a new pipe and connect it,
- 值 None which will make the subprocess inherit the file descriptor from this process
- the subprocess.DEVNULL constant which indicates that the special os.devnull file will be used
stdout can be any of these:
- a file-like object
- the subprocess.PIPE constant (default) which will create a new pipe and connect it,
- 值 None which will make the subprocess inherit the file descriptor from this process
- the subprocess.DEVNULL constant which indicates that the special os.devnull file will be used
stderr can be any of these:
- a file-like object
- the subprocess.PIPE constant (default) which will create a new pipe and connect it,
- 值 None which will make the subprocess inherit the file descriptor from this process
- the subprocess.DEVNULL constant which indicates that the special os.devnull file will be used
- the subprocess.STDOUT constant which will connect the standard error stream to the process’ standard output stream
All other keyword arguments are passed to subprocess.Popen without interpretation, except for bufsize , universal_newlines , shell , text , encoding and errors , which should not be specified at all.

The asyncio subprocess API does not support decoding the streams as text. bytes.decode() can be used to convert the bytes returned from the stream to text.

If a file-like object passed as stdin , stdout or stderr represents a pipe, then the other side of this pipe should be registered with connect_write_pipe() or connect_read_pipe() for use with the event loop.

See the constructor of the subprocess.Popen class for documentation on other arguments.

Returns a pair of (transport, protocol) ，其中 transport conforms to the asyncio.SubprocessTransport 基类和 protocol is an object instantiated by the protocol_factory .

协程循环。 subprocess_shell ( protocol_factory , cmd , * , stdin = subprocess.PIPE , stdout = subprocess.PIPE , stderr = subprocess.PIPE , ** kwargs ) ¶

创建子进程从 cmd , which can be a str 或 bytes string encoded to the 文件系统编码 , using the platform’s “shell” syntax.

This is similar to the standard library subprocess.Popen class called with shell=True .

The protocol_factory must be a callable returning a subclass of the SubprocessProtocol 类。

见 subprocess_exec() for more details about the remaining arguments.

Returns a pair of (transport, protocol) ，其中 transport conforms to the SubprocessTransport 基类和 protocol is an object instantiated by the protocol_factory .

注意

It is the application’s responsibility to ensure that all whitespace and special characters are quoted appropriately to avoid shell injection vulnerabilities. The shlex.quote() function can be used to properly escape whitespace and special characters in strings that are going to be used to construct shell commands.

回调处理 ¶

class asyncio. Handle ¶

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

get_context ( ) ¶

返回 contextvars.Context object associated with the handle.

3.12 版添加。

cancel ( ) ¶: Cancel the callback. If the callback has already been canceled or executed, this method has no effect.

cancelled ( ) ¶

返回 True if the callback was cancelled.

3.7 版添加。

class asyncio. TimerHandle ¶

A callback wrapper object returned by loop.call_later() ，和 loop.call_at() .

This class is a subclass of Handle .

当 ( ) ¶

Return a scheduled callback time as float 秒。

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

3.7 版添加。

服务器对象 ¶

Server objects are created by loop.create_server() , loop.create_unix_server() , start_server() ，和 start_unix_server() 函数。

Do not instantiate the Server class directly.

class asyncio. Server ¶

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 版改变： Server object is an asynchronous context manager since Python 3.7.

3.11 版改变： This class was exposed publicly as asyncio.Server in Python 3.9.11, 3.10.3 and 3.11.

close ( ) ¶

Stop serving: close listening sockets and set the sockets 属性为 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 (and no more connections are active).

close_clients ( ) ¶

Close all existing incoming client connections.

调用 close() on all associated transports.

close() should be called before close_clients() when closing the server to avoid races with new clients connecting.

3.13 版添加。

abort_clients ( ) ¶

Close all existing incoming client connections immediately, without waiting for pending operations to complete.

调用 abort() on all associated transports.

close() should be called before abort_clients() when closing the server to avoid races with new clients connecting.

3.13 版添加。

get_loop ( ) ¶

Return the event loop associated with the server object.

3.7 版添加。

协程 start_serving ( ) ¶

开始接受连接。

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

The start_serving keyword-only parameter to loop.create_server() and asyncio.start_server() allows creating a Server object that is not accepting connections initially. In this case Server.start_serving() ，或 Server.serve_forever() can be used to make the Server start accepting connections.

3.7 版添加。

协程 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 对象。

范例：

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 版添加。

is_serving ( ) ¶

返回 True if the server is accepting new connections.

3.7 版添加。

协程 wait_closed ( ) ¶: 等待直到 close() method completes and all active connections have finished.

sockets ¶

List of socket-like objects, asyncio.trsock.TransportSocket , which the server is listening on.

3.7 版改变： Prior to Python 3.7 Server.sockets used to return an internal list of server sockets directly. In 3.7 a copy of that list is returned.

事件循环实现 ¶

asyncio ships with two different event loop implementations: SelectorEventLoop and ProactorEventLoop .

By default asyncio is configured to use EventLoop .

class asyncio. SelectorEventLoop ¶

子类化的 AbstractEventLoop 基于 selectors 模块。

Uses the most efficient 选择器 available for the given platform. It is also possible to manually configure the exact selector implementation to be used:

import asyncio
import selectors
class MyPolicy(asyncio.DefaultEventLoopPolicy):
   def new_event_loop(self):
      selector = selectors.SelectSelector()
      return asyncio.SelectorEventLoop(selector)
asyncio.set_event_loop_policy(MyPolicy())

可用性：Unix、Windows。

class asyncio. ProactorEventLoop ¶: 子类化的 AbstractEventLoop for Windows that uses “I/O Completion Ports” (IOCP).

可用性：Windows。

另请参阅

MSDN documentation on I/O Completion Ports .

class asyncio. EventLoop ¶: An alias to the most efficient available subclass of AbstractEventLoop for the given platform.

It is an alias to SelectorEventLoop on Unix and ProactorEventLoop 在 Windows。

3.13 版添加。

class asyncio. AbstractEventLoop ¶

Abstract base class for asyncio-compliant event loops.

The 事件循环方法 section lists all methods that an alternative implementation of AbstractEventLoop should have defined.

范例 ¶

Note that all examples in this section purposefully show how to use the low-level event loop APIs, such as loop.run_forever() and loop.call_soon() . Modern asyncio applications rarely need to be written this way; consider using the high-level functions like asyncio.run() .

Hello World 采用 call_soon() ¶

范例使用 loop.call_soon() method to schedule a callback. The callback displays "Hello World" and then stops the event loop:

import asyncio
def hello_world(loop):
    """A callback to print 'Hello World' and stop the event loop"""
    print('Hello World')
    loop.stop()
loop = asyncio.new_event_loop()
# Schedule a call to hello_world()
loop.call_soon(hello_world, loop)
# Blocking call interrupted by loop.stop()
try:
    loop.run_forever()
finally:
    loop.close()

另请参阅

类似 Hello World example created with a coroutine and the run() 函数。

显示当前日期采用 call_later() ¶

An example of a callback displaying the current date every second. The callback uses the loop.call_later() method to reschedule itself after 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.new_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()
try:
    loop.run_forever()
finally:
    loop.close()

另请参阅

类似 current date example created with a coroutine and the run() 函数。

为读取事件看守文件描述符 ¶

Wait until a file descriptor received some data using the loop.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.new_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())
try:
    # Run the event loop
    loop.run_forever()
finally:
    # We are done. Close sockets and the event loop.
    rsock.close()
    wsock.close()
    loop.close()

另请参阅

类似范例使用传输、协议及 loop.create_connection() 方法。
另一类似范例使用高级 asyncio.open_connection() function and streams.

为 SIGINT 和 SIGTERM 设置信号处理程序 ¶

(此 signals 范例仅工作于 Unix)。

import asyncio
import functools
import os
import signal
def ask_exit(signame, loop):
    print("got signal %s: exit" % signame)
    loop.stop()
async def main():
    loop = asyncio.get_running_loop()
    for signame in {'SIGINT', 'SIGTERM'}:
        loop.add_signal_handler(
            getattr(signal, signame),
            functools.partial(ask_exit, signame, loop))
    await asyncio.sleep(3600)
print("Event loop running for 1 hour, press Ctrl+C to interrupt.")
print(f"pid {os.getpid()}: send SIGINT or SIGTERM to exit.")
asyncio.run(main())

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事件循环 ¶

事件循环方法 ¶

回调处理 ¶

服务器对象 ¶

事件循环实现 ¶

范例 ¶

Hello World 采用 call_soon() ¶

显示当前日期采用 call_later() ¶

为读取事件看守文件描述符 ¶

为 SIGINT 和 SIGTERM 设置信号处理程序 ¶

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