linux-output.txt

~/trio/notes-to-self$ python sleep-time.py
----------------------------------------------------------------
Starting: import select; select.select([], [], [], 6)
Expected duration: 6 seconds
Putting it to sleep for 2.0 seconds
Waking it up again
Actual duration: 8.05
----------------------------------------------------------------
Starting: import select; ep = select.epoll(); ep.poll(6)
Expected duration: 6 seconds
Putting it to sleep for 2.0 seconds
Waking it up again
Actual duration: 6.06
----------------------------------------------------------------
Starting: import threading; ev = threading.Event(); ev.wait(6)
Expected duration: 6 seconds
Putting it to sleep for 2.0 seconds
Waking it up again
Actual duration: 6.07
----------------------------------------------------------------
Starting: import time; time.sleep(6)
Expected duration: 6 seconds
Putting it to sleep for 2.0 seconds
Waking it up again
Actual duration: 8.05

sleep-time.py

# Suppose:
# - we're blocked until a timeout occurs
# - our process gets put to sleep for a while (SIGSTOP or whatever)
# - then it gets woken up again
# what happens to our timeout?

import os
import signal
import subprocess
import sys
import time

DUR = 6

test_progs = [
    f"import select; select.select([], [], [], {DUR})",
    f"import select; ep = select.epoll(); ep.poll({DUR})",
    f"import threading; ev = threading.Event(); ev.wait({DUR})",
    f"import time; time.sleep({DUR})",
]

for test_prog in test_progs:
    print("----------------------------------------------------------------")
    start = time.monotonic()
    print(f"Starting: {test_prog}")
    print(f"Expected duration: {DUR} seconds")
    p = subprocess.Popen([sys.executable, "-c", test_prog])
    time.sleep(DUR / 3)
    print(f"Putting it to sleep for {DUR / 3} seconds")
    os.kill(p.pid, signal.SIGSTOP)
    time.sleep(DUR / 3)
    print("Waking it up again")
    os.kill(p.pid, signal.SIGCONT)
    p.wait()
    end = time.monotonic()
    print(f"Actual duration: {end - start:.2f}")