策略 ¶

An event loop policy is a global object used to get and set the current 事件循环，及创建新的事件循环。默认策略可以被替换 with 内置替代以使用不同事件循环实现，或被代入通过自定义策略可以覆盖这些行为。

The 策略对象 gets and sets a separate event loop per context . This is per-thread by default, though custom policies could define context differently.

Custom event loop policies can control the behavior of get_event_loop() , set_event_loop() ，和 new_event_loop() .

Policy objects should implement the APIs defined in the AbstractEventLoopPolicy abstract base class.

获取和设置策略 ¶

The following functions can be used to get and set the policy for the current process:

asyncio. get_event_loop_policy ( ) ¶: 返回当前进程范围的策略。

asyncio. set_event_loop_policy ( policy ) ¶

Set the current process-wide policy to policy .

若 policy 被设为 None , the default policy is restored.

策略对象 ¶

The abstract event loop policy base class is defined as follows:

class asyncio. AbstractEventLoopPolicy ¶

An abstract base class for asyncio policies.

get_event_loop ( ) ¶

Get the event loop for the current context.

Return an event loop object implementing the AbstractEventLoop 接口。

This method should never return None .

3.6 版改变。

进程看守程序 ¶

A process watcher allows customization of how an event loop monitors child processes on Unix. Specifically, the event loop needs to know when a child process has exited.

asyncio defines the


AbstractChildWatcher

abstract base class, which child watchers should implement, and has four different implementations:


ThreadedChildWatcher

(configured to be used by default),


MultiLoopChildWatcher


SafeChildWatcher

，和


FastChildWatcher

The following two functions can be used to customize the child process watcher implementation used by the asyncio event loop:

asyncio. get_child_watcher ( ) ¶

Return the current child watcher for the current policy.

Deprecated since version 3.12.

asyncio. set_child_watcher ( watcher ) ¶

Set the current child watcher to watcher for the current policy. watcher must implement methods defined in the AbstractChildWatcher 基类。

Deprecated since version 3.12.

注意

Third-party event loops implementations might not support custom child watchers. For such event loops, using set_child_watcher() might be prohibited or have no effect.

class asyncio. AbstractChildWatcher ¶

add_child_handler ( pid , callback , * args ) ¶

Arrange for callback(pid, returncode, *args) to be called when a process with PID equal to pid terminates. Specifying another callback for the same process replaces the previous handler.

The callback callable must be thread-safe.

remove_child_handler ( pid ) ¶

Removes the handler for process with PID equal to pid .

函数返回 True if the handler was successfully removed, False if there was nothing to remove.

attach_loop ( loop ) ¶

Attach the watcher to an event loop.

If the watcher was previously attached to an event loop, then it is first detached before attaching to the new loop.

Note: loop may be None .

is_active ( ) ¶

返回 True if the watcher is ready to use.

Spawning a subprocess with inactive current child watcher raises RuntimeError .

Added in version 3.8.

自定义策略 ¶

To implement a new event loop policy, it is recommended to subclass


DefaultEventLoopPolicy

and override the methods for which custom behavior is wanted, e.g.:

class MyEventLoopPolicy(asyncio.DefaultEventLoopPolicy): def get_event_loop(self): """Get the event loop. This may be None or an instance of EventLoop. """ loop = super().get_event_loop() # Do something with loop ... return loop asyncio.set_event_loop_policy(MyEventLoopPolicy())

策略 ¶

获取和设置策略 ¶

策略对象 ¶

进程看守程序 ¶

自定义策略 ¶

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