18.5.2. 事件循环 ¶

18.5.2.1. 事件循环函数 ¶

The following functions are convenient shortcuts to accessing the methods of the global policy. Note that this provides access to the default policy, unless an alternative policy was set by calling set_event_loop_policy() earlier in the execution of the process.

asyncio. get_event_loop ( ) ¶

asyncio. set_event_loop ( loop ) ¶

asyncio. new_event_loop ( ) ¶

18.5.2.2. 可用事件循环 ¶

asyncio currently provides two implementations of event loops: SelectorEventLoop and ProactorEventLoop .

class asyncio. SelectorEventLoop ¶

class asyncio. ProactorEventLoop ¶

Example to use a ProactorEventLoop on Windows:

import asyncio, sys
if sys.platform == 'win32':
    loop = asyncio.ProactorEventLoop()
    asyncio.set_event_loop(loop)

18.5.2.3. 平台支持 ¶

The asyncio module has been designed to be portable, but each platform still has subtle differences and may not support all asyncio features.

18.5.2.3.1. Windows ¶

Common limits of Windows event loops:

create_unix_connection() and create_unix_server() are not supported: the socket 系列 socket.AF_UNIX is specific to UNIX
add_signal_handler() and remove_signal_handler() are not supported
EventLoopPolicy.set_child_watcher() 不支持。 ProactorEventLoop supports subprocesses. It has only one implementation to watch child processes, there is no need to configure it.

SelectorEventLoop specific limits:

SelectSelector is used which only supports sockets and is limited to 512 sockets.
add_reader() and add_writer() only accept file descriptors of sockets
Pipes are not supported (ex: connect_read_pipe() , connect_write_pipe() )
子进程 are not supported (ex: subprocess_exec() , subprocess_shell() )

ProactorEventLoop specific limits:

create_datagram_endpoint() (UDP) is not supported
add_reader() and add_writer() are not supported

The resolution of the monotonic clock on Windows is usually around 15.6 msec. The best resolution is 0.5 msec. The resolution depends on the hardware (availability of HPET ) and on the Windows configuration. See asyncio delayed calls .

3.5 版改变： ProactorEventLoop now supports SSL.

18.5.2.3.2. Mac OS X ¶

Character devices like PTY are only well supported since Mavericks (Mac OS 10.9). They are not supported at all on Mac OS 10.5 and older.

On Mac OS 10.6, 10.7 and 10.8, the default event loop is SelectorEventLoop which uses selectors.KqueueSelector . selectors.KqueueSelector does not support character devices on these versions. The SelectorEventLoop 可以使用 SelectSelector or PollSelector to support character devices on these versions of Mac OS X. Example:

import asyncio
import selectors
selector = selectors.SelectSelector()
loop = asyncio.SelectorEventLoop(selector)
asyncio.set_event_loop(loop)

18.5.2.4. 事件循环策略和默认策略 ¶

Event loop management is abstracted with a policy pattern, to provide maximal flexibility for custom platforms and frameworks. Throughout the execution of a process, a single global policy object manages the event loops available to the process based on the calling context. A policy is an object implementing the AbstractEventLoopPolicy 接口。

For most users of asyncio , policies never have to be dealt with explicitly, since the default global policy is sufficient.

The default policy defines context as the current thread, and manages an event loop per thread that interacts with asyncio . The module-level functions get_event_loop() and set_event_loop() provide convenient access to event loops managed by the default policy.

18.5.2.5. 事件循环策略接口 ¶

An event loop policy must implement the following interface:

class asyncio. AbstractEventLoopPolicy ¶

get_event_loop ( ) ¶

set_event_loop ( loop ) ¶

new_event_loop ( ) ¶

18.5.2.6. 访问全局循环策略 ¶

asyncio. get_event_loop_policy ( ) ¶

asyncio. set_event_loop_policy ( policy ) ¶