heartbeat example

README.md

heartbeat example

shows high-CPU C code hogging the GIL

if you remove the with nogil decorator in loop.pyx this behaves Badly

hb.py

#!/usr/bin/env python
import threading, asyncio, time, multiprocessing
import loop

def threadmain(count: int = 100, kind: str = 'thread'):
    for i in range(count):
        time.sleep(0.01)
        if i % 10 == 0:
            print(kind, i)

def cpu_sleep():
    print('starting cpu_sleep')
    t0 = time.time()
    print('iters', loop.cpu_sleep(2000))
    print('cpu_sleep', time.time() - t0)

async def asyncmain(count: int = 100):
    # await asyncio.create_task(cpu_sleep())
    for i in range(count):
        await asyncio.sleep(0.01)
        if i % 10 == 0:
            print('async', i)

def main():
    tasks = [
        threading.Thread(target=threadmain),
        multiprocessing.Process(target=threadmain, kwargs={'kind': 'proc'}),
        threading.Thread(target=cpu_sleep),
        threading.Thread(target=cpu_sleep),
    ]
    for t in tasks: t.start()
    asyncio.run(asyncmain())
    for t in tasks: t.join()
    print('ok joins')

if __name__ == '__main__':
    main()

loop.pyx

import cython
from posix.time cimport timespec, clock_gettime, CLOCK_REALTIME, time_t

cdef int to_millis(timespec* t) nogil:
    return (t.tv_sec * 1000) + (t.tv_nsec // 1000000)

cdef int diff(timespec* a, timespec* b) nogil:
    "return diff in milliseconds"
    return to_millis(b) - to_millis(a)

cdef int _cpu_sleep(int milliseconds) nogil:
    cdef timespec base, latest;
    clock_gettime(CLOCK_REALTIME, &base)
    clock_gettime(CLOCK_REALTIME, &latest)
    cdef unsigned int iter = 0
    cdef int elapsed = diff(&base, &latest)
    cdef int ratchet = 0
    while elapsed < milliseconds:
        iter += 1
        clock_gettime(CLOCK_REALTIME, &latest)
        elapsed = diff(&base, &latest)
        if elapsed > ratchet + 100:
            ratchet += 100
            # print('elapsed', ratchet)
    return iter

def cpu_sleep(int milliseconds):
    cdef int ret
    # without nogil, this blocks python
    with nogil:
        ret = _cpu_sleep(milliseconds)
    return ret

Makefile

loop.cpython-310-x86_64-linux-gnu.so: loop.pyx
	cythonize -i $^