Simple script to run a shell command multiple times very quickly and concurrently, and report on the failure rate.

check_output_concurrent.py

#!/usr/bin/env python
"""

  Simple script to run a shell command repeatedly using concurrent
  subprocesses. Shows a pretty progress bar, and prints a percentage of
  times the command failed.

  Took a ~20 minute sequence of `npm run test` to under 2 minutes.

"""

from multiprocessing import Pool
import subprocess as sp

# pip install progressbar2
from progressbar import ProgressBar


NUM_RUNS  = 500
NUM_PROCS = 8
COMMAND   = 'npm run test'


def command(i):
    """
    Runs COMMAND in a subprocess, returning 0 if it was successful, 1 if
    it failed. The value of 1 is used to simplify the counting logic.
    """
    return min(1, sp.call(COMMAND.split(), stdout=sp.PIPE, stderr=sp.PIPE))


def main():
    """
    Entry point of the program, dispatches the calls to subprocesses,
    and manages the progress bar.
    """
    bar = ProgressBar()
    pool = Pool(processes=8)
    bad_runs = 0
    
    for res in bar(pool.imap_unordered(test, range(NUM_RUNS))):
        bad_runs += res
    
    print(f'Done. {bad_runs/NUM_RUNS:.2%} fail rate ({bad_runs} of {NUM_RUNS} runs)')


main()