asyncio module is designed to be portable, but some platforms have subtle differences and limitations due to the platforms’ underlying architecture and capabilities.
loop.add_writer()cannot be used to monitor file I/O.
Source code: Lib/asyncio/proactor_events.py, Lib/asyncio/windows_events.py, Lib/asyncio/windows_utils.py
Changed in version 3.8: On Windows,
ProactorEventLoop is now the default event loop.
All event loops on Windows do not support the following methods:
loop.create_unix_server()are not supported. The
socket.AF_UNIXsocket family is specific to Unix.
loop.remove_signal_handler()are not supported.
SelectorEventLoop has the following limitations:
SelectSelectoris used to wait on socket events: it supports sockets and is limited to 512 sockets.
loop.add_writer()only accept socket handles (e.g. pipe file descriptors are not supported).
- Pipes are not supported, so the
loop.connect_write_pipe()methods are not implemented.
Subprocesses are not supported, i.e.
loop.subprocess_shell()methods are not implemented.
ProactorEventLoop has the following limitations:
loop.add_writer()methods 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.
Subprocess Support on Windows
On Windows, the default event loop
ProactorEventLoop supports subprocesses, whereas
SelectorEventLoop does not.
policy.set_child_watcher() function is also not supported, as
ProactorEventLoop has a different mechanism to watch child processes.
Modern macOS versions are fully supported.
macOS <= 10.8
On macOS 10.6, 10.7 and 10.8, the default event loop uses
selectors.KqueueSelector, which does not support character devices on these versions. The
SelectorEventLoop can be manually configured to use
PollSelector to support character devices on these older versions of macOS. Example:
import asyncio import selectors selector = selectors.SelectSelector() loop = asyncio.SelectorEventLoop(selector) asyncio.set_event_loop(loop)
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