Platform Support#
The asyncio
module is designed to be portable,
but some platforms have subtle differences and limitations
due to the platforms’ underlying architecture and capabilities.
All Platforms#
loop.add_reader()
andloop.add_writer()
cannot be used to monitor file I/O.
Windows#
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_connection()
andloop.create_unix_server()
are not supported. Thesocket.AF_UNIX
socket family is specific to Unix.loop.add_signal_handler()
andloop.remove_signal_handler()
are not supported.
SelectorEventLoop
has the following limitations:
SelectSelector
is used to wait on socket events: it supports sockets and is limited to 512 sockets.loop.add_reader()
andloop.add_writer()
only accept socket handles (e.g. pipe file descriptors are not supported).Pipes are not supported, so the
loop.connect_read_pipe()
andloop.connect_write_pipe()
methods are not implemented.Subprocesses are not supported, i.e.
loop.subprocess_exec()
andloop.subprocess_shell()
methods are not implemented.
ProactorEventLoop
has the following limitations:
The
loop.add_reader()
andloop.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.
The policy.set_child_watcher()
function is also
not supported, as ProactorEventLoop
has a different mechanism
to watch child processes.
macOS#
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 SelectSelector
or 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)