cpython/Lib/test/mp_preload_flush.py

import multiprocessing
import sys

print(__name__, end='', file=sys.stderr)
print(__name__, end='', file=sys.stdout)
if __name__ == '__main__':
    multiprocessing.set_start_method('forkserver')
    for _ in range(2):
        p = multiprocessing.Process()
        p.start()
        p.join()
gh-135335: flush stdout/stderr in forkserver after preloading modules (#135338) If a preloaded module writes to stdout or stderr, and the stream is buffered, child processes will inherit the buffered data after forking. Attempt to prevent this by flushing the streams after preload. Co-authored-by: Mikhail Efimov <efimov.mikhail@gmail.com> Co-authored-by: Victor Stinner <vstinner@python.org> 2025-06-19 00:17:02 +12:00			`import multiprocessing`
			`import sys`

gh-135335: Simplify preload regression test using __main__ (GH-138686) Simplify preload regression test using `__main__` With the fix for gh-126631 `__main__` modules can be preloaded and the regression test for gh-135335 can be simplified to just use a self-contained script rather than requiring a module. Note this assumes and implicitly tests that `__main__` is preloaded by default. 2025-11-24 12:37:15 +13:00			`print(__name__, end='', file=sys.stderr)`
			`print(__name__, end='', file=sys.stdout)`
gh-135335: flush stdout/stderr in forkserver after preloading modules (#135338) If a preloaded module writes to stdout or stderr, and the stream is buffered, child processes will inherit the buffered data after forking. Attempt to prevent this by flushing the streams after preload. Co-authored-by: Mikhail Efimov <efimov.mikhail@gmail.com> Co-authored-by: Victor Stinner <vstinner@python.org> 2025-06-19 00:17:02 +12:00			`if __name__ == '__main__':`
			`multiprocessing.set_start_method('forkserver')`
			`for _ in range(2):`
			`p = multiprocessing.Process()`
			`p.start()`
			`p.join()`