Hướng dẫn asynchronous api python
Asynchronous programming is different from classic “sequential” programming. Show This page lists common mistakes and traps and explains how to avoid them. Debug Mode¶By default asyncio runs in production mode. In order to ease the development asyncio has a debug mode. There are several ways to enable asyncio debug mode:
In addition to enabling the debug mode, consider also:
When the debug mode is enabled:
Concurrency and Multithreading¶An event loop runs in a thread (typically the main thread) and executes all callbacks and Tasks in its thread. While a Task is running in the event loop, no other Tasks can run in the same
thread. When a Task executes an To schedule a callback from another OS thread, the loop.call_soon_threadsafe(callback, *args) Almost all asyncio objects are not thread safe, which is typically not a problem unless there is code that works with them from outside of a Task or a callback. If there’s a need for such code to call a low-level asyncio API, the loop.call_soon_threadsafe(fut.cancel) To schedule a coroutine object from
a different OS thread, the async def coro_func(): return await asyncio.sleep(1, 42) # Later in another OS thread: future = asyncio.run_coroutine_threadsafe(coro_func(), loop) # Wait for the result: result = future.result() To handle signals and to execute subprocesses, the event loop must be run in the main thread. The There is currently no way to schedule coroutines or callbacks directly from a different process (such as one started with Running Blocking Code¶Blocking (CPU-bound) code should not be called directly. For example, if a function performs a CPU-intensive calculation for 1 second, all concurrent asyncio Tasks and IO operations would be delayed by 1 second. An executor can be used to run a task in a different thread or even in a different process to avoid blocking the OS thread with the
event loop. See the Logging¶asyncio uses the
The default log level is logging.getLogger("asyncio").setLevel(logging.WARNING) Detect never-awaited coroutines¶When a coroutine function is called, but not awaited (e.g. import asyncio async def test(): print("never scheduled") async def main(): test() asyncio.run(main()) Output: test.py:7: RuntimeWarning: coroutine 'test' was never awaited test() Output in debug mode: test.py:7: RuntimeWarning: coroutine 'test' was never awaited Coroutine created at (most recent call last) File "../t.py", line 9, in <module> asyncio.run(main(), debug=True) < .. > File "../t.py", line 7, in main test() test() The usual fix is to either await the coroutine or call the async def main(): await test() Detect never-retrieved exceptions¶If a Example of an unhandled exception: import asyncio async def bug(): raise Exception("not consumed") async def main(): asyncio.create_task(bug()) asyncio.run(main()) Output: Task exception was never retrieved future: <Task finished coro=<bug() done, defined at test.py:3> exception=Exception('not consumed')> Traceback (most recent call last): File "test.py", line 4, in bug raise Exception("not consumed") Exception: not consumed Enable the debug mode to get the traceback where the task was created: asyncio.run(main(), debug=True) Output in debug mode: Task exception was never retrieved future: <Task finished coro=<bug() done, defined at test.py:3> exception=Exception('not consumed') created at asyncio/tasks.py:321> source_traceback: Object created at (most recent call last): File "../t.py", line 9, in <module> asyncio.run(main(), debug=True) < .. > Traceback (most recent call last): File "../t.py", line 4, in bug raise Exception("not consumed") Exception: not consumed |