I figured out how to run a subprocess with a time limit for datasette-ripgrep, using the
asyncio.create_subprocess_exec() method. The pattern looks like this:
import asyncio proc = await asyncio.create_subprocess_exec( "rg", "-e", ".*", stdout=asyncio.subprocess.PIPE, stdin=asyncio.subprocess.PIPE, ) try: stdout, stderr = await asyncio.wait_for(proc.communicate(), timeout=0.1) print(stdout) except asyncio.exceptions.TimeoutError: print("Command timed out") # If it timed out we should terminate the process try: proc.kill() except OSError: # Ignore 'no such process' error pass
For datasette-seaborn I wanted to render a chart using the Python seaborn library with a time limit of five seconds for the render.
I realized I could do this by launching Python itself as the subprocess executable (using
sys.executable) and sending Python code to
stdin to be executed in a process, using the same time limit mechanism.
It seems to work! Here's the pattern wrapped up in a function:
import asyncio, sys async def execute_python_with_time_limit(code, time_limit): proc = await asyncio.create_subprocess_exec( sys.executable, "-", stdout=asyncio.subprocess.PIPE, stdin=asyncio.subprocess.PIPE, ) try: stdout, stderr = await asyncio.wait_for( proc.communicate(code.encode("utf-8")), timeout=time_limit ) except asyncio.exceptions.TimeoutError: try: proc.kill() except OSError: # Ignore 'no such process' error pass raise return stdout, stderr
Example of using it (pasting into the shell you get from
python3 -m asyncio in Python 3.8+):
>>> await execute_python_with_time_limit('print("hello")', 1) (b'hello\n', None) >>> await execute_python_with_time_limit('import time\ntime.sleep(1)', 0.7) Traceback (most recent call last): File "/email@example.com/Frameworks/Python.framework/Versions/3.8/lib/python3.8/concurrent/futures/_base.py", line 439, in result return self.__get_result() File "/firstname.lastname@example.org/Frameworks/Python.framework/Versions/3.8/lib/python3.8/concurrent/futures/_base.py", line 388, in __get_result raise self._exception File "<console>", line 1, in <module> File "<console>", line 9, in execute_python_with_time_limit File "/email@example.com/Frameworks/Python.framework/Versions/3.8/lib/python3.8/asyncio/tasks.py", line 498, in wait_for raise exceptions.TimeoutError() asyncio.exceptions.TimeoutError
It returns the stdout output of the code, so to use this you'll need to figure out some kind of serialization format for the data that is returned from the subprocess. JSON or pickle should work fine.
sys.executable is the path to the current Python interpreter. This ensures that any imports will take place in the correct Python virtual environment. Passing
- as the first argument causes Python to execute code from standard input, which is then provided using the
Is this a good idea? I think so, but I'd love to hear from you if there's a simpler, cleaner way to do this.
Created 2020-12-06T17:03:30-08:00, updated 2020-12-06T23:35:41-08:00 · History · Edit