How to Achieve Non-Blocking Subprocess Execution in Python?

Non-Blocking Subprocess Execution

To achieve non-blocking subprocess execution, consider using subprocess.Popen instead of subprocess.call. subprocess.call waits for the command to complete before returning, while subprocess.Popen immediately starts the subprocess and returns a file-like object.

<code class="python">import subprocess

subprocess.Popen(["python", "slave.py"] + sys.argv[1:])</code>

By using subprocess.Popen, you can pass arguments to slave.py and allow it to run independently of main.py. slave.py can then execute its tasks without blocking main.py.

<code class="python">import subprocess
import time

p = subprocess.Popen(['sleep', '5'])

while p.poll() is None:
    print('Still sleeping')
    time.sleep(1)

print('Not sleeping any longer.  Exited with returncode %d' % p.returncode)</code>

In Python 3.5 and later, you can also use coroutines to achieve parallelism and non-blocking subprocess execution.

<code class="python">import asyncio

async def do_subprocess():
    print('Subprocess sleeping')
    proc = await asyncio.create_subprocess_exec('sleep', '5')
    returncode = await proc.wait()
    print('Subprocess done sleeping.  Return code = %d' % returncode)

async def sleep_report(number):
    for i in range(number + 1):
        print('Slept for %d seconds' % i)
        await asyncio.sleep(1)

loop = asyncio.get_event_loop()

tasks = [
    asyncio.ensure_future(do_subprocess()),
    asyncio.ensure_future(sleep_report(5)),
]

loop.run_until_complete(asyncio.gather(*tasks))
loop.close()</code>

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