Using synchronous subprocess calls like subprocess.Popen or similar functions in asynchronous code blocks the entire event loop. This
undermines the primary advantage of asynchronous programming - the ability to perform concurrent operations without blocking execution.
When an async function makes a synchronous call to create a subprocess:
- The event loop is completely blocked until the subprocess operation completes
- No other coroutines can run during this time, even if they’re ready to execute
- The responsiveness of the application is degraded
- In server applications, this can cause timeouts or failures for other concurrent requests
Instead, async libraries provide dedicated APIs for running subprocesses in a non-blocking way:
-
asyncio.create_subprocess_exec() and asyncio.create_subprocess_shell() for asyncio
-
trio.run_process() for Trio
-
anyio.run_process() for AnyIO
Using these APIs allows other tasks to continue executing while waiting for the subprocess to complete.
