python_doc_md/Intermediate/library/asyncio-platforms.md

::: currentmodule asyncio :::

Platform Support {#asyncio-platform-support}

The asyncio{.interpreted-text role="mod"} 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{.interpreted-text role="meth"} and loop.add_writer{.interpreted-text role="meth"} cannot be used to monitor file I/O.

Windows

Source code: Lib/asyncio/proactor_events.py{.interpreted-text role="source"}, Lib/asyncio/windows_events.py{.interpreted-text role="source"}, Lib/asyncio/windows_utils.py{.interpreted-text role="source"}

---

::: versionchanged 3.8

On Windows, ProactorEventLoop{.interpreted-text role="class"} is now the default event loop. :::

All event loops on Windows do not support the following methods:

• loop.create_unix_connection{.interpreted-text role="meth"} and loop.create_unix_server{.interpreted-text role="meth"} are not supported. The socket.AF_UNIX{.interpreted-text role="const"} socket family is specific to Unix.
• loop.add_signal_handler{.interpreted-text role="meth"} and loop.remove_signal_handler{.interpreted-text role="meth"} are not supported.

SelectorEventLoop{.interpreted-text role="class"} has the following limitations:

• ~selectors.SelectSelector{.interpreted-text role="class"} is used to wait on socket events: it supports sockets and is limited to 512 sockets.
• loop.add_reader{.interpreted-text role="meth"} and loop.add_writer{.interpreted-text role="meth"} only accept socket handles (e.g. pipe file descriptors are not supported).
• Pipes are not supported, so the loop.connect_read_pipe{.interpreted-text role="meth"} and loop.connect_write_pipe{.interpreted-text role="meth"} methods are not implemented.
• Subprocesses <asyncio-subprocess>{.interpreted-text role="ref"} are not supported, i.e. loop.subprocess_exec{.interpreted-text role="meth"} and loop.subprocess_shell{.interpreted-text role="meth"} methods are not implemented.

ProactorEventLoop{.interpreted-text role="class"} has the following limitations:

• The loop.add_reader{.interpreted-text role="meth"} and loop.add_writer{.interpreted-text role="meth"} methods are not supported.

The resolution of the monotonic clock on Windows is usually around 15.6 milliseconds. The best resolution is 0.5 milliseconds. The resolution depends on the hardware (availability of HPET) and on the Windows configuration.

Subprocess Support on Windows {#asyncio-windows-subprocess}

On Windows, the default event loop ProactorEventLoop{.interpreted-text role="class"} supports subprocesses, whereas SelectorEventLoop{.interpreted-text role="class"} does not.

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{.interpreted-text role="class"}, which does not support character devices on these versions. The SelectorEventLoop{.interpreted-text role="class"} can be manually configured to use ~selectors.SelectSelector{.interpreted-text role="class"} or ~selectors.PollSelector{.interpreted-text role="class"} 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)