Coverage after fork seems not to be generated

[MarkSymsCtx]

Describe the bug
If a python process uses os.fork it seems that even with concurreny=multiprocessing no coverage of the child process is generated. Example file below

To Reproduce
How can we reproduce the problem? Please be specific. Don't link to a failing CI job. Answer the questions below:

1. What version of Python are you using?
   3.11
2. What version of coverage.py shows the problem? The output of coverage debug sys is helpful.
   7.6.12
3. What code shows the problem?
   This (not the nicest as it's just a quick hack to replicate some of our code)

#!/usr/bin/python3

import os
import tempfile
import time
import traceback

COMPLETE=tempfile.mkstemp()

print(f"Parent pid is {os.getpid()}")

pid = os.fork()
if pid:
    print(f"In parent, child is {pid}")
    try:
        while True:
            with open(COMPLETE[1], mode='r') as f:
                data = f.readline()

            print(f"Data is {data}")
            if "Complete" in data:
                print(f"Child is complete")
                break

            time.sleep(5)
    finally:
        wait_pid = 0
        while wait_pid == 0:
            wait_pid, rc = os.waitpid(pid, os.WNOHANG)
            if wait_pid == 0:
                time.sleep(2)
else:
    print(f"In child")
    time.sleep(10)
    print("Leaving child")
    with open(COMPLETE[1], mode='w') as f:
        f.write("Complete")
    os._exit(0)

Then run with coverage run -p --concurrency=multiprocessing test-fork-cover.py

Expected behavior
Expect to see coverage of both sides of the fork

[nedbat]

Does #310 provide a way to make it work?

[MarkSymsCtx]

Yes, it does, thanks, swapping os._exit to sys.exit results in coverage being generated.