[docs] [issue21680] asyncio: document event loops

[STINNER Victor]

STINNER Victor added the comment:

On Windows, the default event loop is _WindowsSelectorEventLoop which calls select.select(). On Windows, select() only accepts socket handles:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms740141%28v=vs.85%29.aspx

Only file descriptors of sockets are accepted for add_reader() and add_writer()? This event loop doesn't support subprocesses. 


On Windows, the proactor event loop can be used instead to support subprocesses. But this event loop doesn't support add_reader() nor add_writer() :-( This event loop doesn't support SSL.


On Windows, the granularity of the monotonic time is usually 15.6 msec. I don't know if it's interesting to mention it. The resolution is different if HPET is enabled on Windows.


On Mac OS X older than 10.9 (Mavericks), selectors.KqueueSelector is the default selector but it doesn't character devices like PTY. The SelectorEventLoop can be used with SelectSelector or PollSelector to handle character devices on Mac OS X 10.6 (Snow Leopard) and later.

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