usleep in Python

Question

I was searching for a usleep() function in Python 2.7.

Does anybody know if it does exist, maybe with another function name?

Answer 1

An alternate sleep function for python.

Note: Should not be used for multiple threads due to GIL lock, but for multiple subprocesses its fine. Same with time.sleep()

I'm wrapping a C function to Python. I'm using nanosleep() of C library, which halts that thread running for that much amount of time. It is not a busy-wait type of delay which uses much CPU to evaluate some math. The codes are as follows. Put all in a folder, say CWrapper.

C_functions.h

#include 
int c_sleep_msec(long milliseconds);
int c_sleep_nsec(long nanoseconds);

C_functions.c

#include "C_functions.h"
int c_sleep_msec(long milliseconds) {
    struct timespec req;
    //struct timespec rem;
    if(milliseconds > 999) {
      req.tv_sec = (int)(milliseconds / 1000);  /* Must be Non-Negative */
      req.tv_nsec = (milliseconds - ((long)req.tv_sec * 1000)) * 1000000; /* Must be in range of 0 to 999999999 */
    }
    else {
      req.tv_sec = 0;                         /* Must be Non-Negative */
      req.tv_nsec = milliseconds * 1000000;    /* Must be in range of 0 to 999999999 */
    }
    //rem = NULL;
    return nanosleep(&req , NULL);
}
//------------------------------------------------------
int c_sleep_nsec(long nanoseconds) {
    struct timespec req;
    //struct timespec rem;
    if (nanoseconds > 999999999) {
      req.tv_sec = (int)(nanoseconds / 1000000000);
      req.tv_nsec = (nanoseconds - ((long)req.tv_sec * 1000000000));
    }
    else {
      req.tv_sec = 0;
      req.tv_nsec = nanoseconds;
    }
    //rem = NULL;
    return nanosleep(&req , NULL);
}

You can also create a function for micro seconds using the same nanosleep()

CWrapper.pyx

cdef extern from "C_functions.h":
    int c_sleep_msec(long milliseconds)
    int c_sleep_nsec(long nanoseconds)

def sleep_msec(milliseconds):
    return c_sleep_msec(milliseconds)

def sleep_nsec(nanoseconds):
    return c_sleep_nsec(nanoseconds)

setup.py

from distutils.core import setup
from distutils.extension import Extension
from Pyrex.Distutils import build_ext

setup(
  name = "CWrapper",
  ext_modules=[ Extension("CWrapper", ["CWrapper.pyx", "C_functions.c"]) ],
  cmdclass = {'build_ext': build_ext}
)

Install python-pyrex. Then run in linux terminal

python setup.py build_ext -i

It will create CWrapper.c, build, and CWrapper.so files. Use CWrapper.so where ever you want, and just import in python.

Note: Compile separately for Raspberry Pi.

Now, test the function

Test_sleep.py

import serial
from multiprocessing import Process
import time
import CWrapper


class TestSleep:
    def __init__(self):
        self.delay_sec = 0.00000100
        self.delay_msec = 30
        self.delay_nsec = 1000 #200000000
        self.start_time = time.time()

        self.process_1 = Process(name="process_1", target=self.process_1_task, args=("process_1",))
        self.process_1.daemon = True
        self.process_1.start()

        self.process_2 = Process(name="process_2", target=self.process_1_task, args=("process_2",))
        self.process_2.daemon = True
        self.process_2.start()

        self.process_3 = Process(name="process_3", target=self.process_1_task, args=("process_3",))
        self.process_3.daemon = True
        self.process_3.start()

    def process_1_task(self, process_name):
        start = self.start_time
        delay_msec = self.delay_msec
        delay_sec = self.delay_sec
        delay_nsec = self.delay_nsec

        t1 = start
        for i in range(1, 81):
            status = CWrapper.sleep_msec(delay_msec)
            # status = CWrapper.sleep_nsec(delay_nsec)
            #status = time.sleep(delay_sec)
            t2 = time.time()
            elapsed_time = t2 - t1
            t1 = t2
            print process_name, i, "status:", status, "Elapsed-time:", elapsed_time


if __name__ == '__main__':
    test = TestSleep()
    # for i in range(1,10000):
    #     print "main thread", i
        # time.sleep(0.1)
    while True:    # Since daemon=True, main thread should check join() or stay in loop
        pass

Vary the parameters delay_sec for time.sleep(), delay_msec for CWrapper.sleep_msec(), delay_nsec for CWrapper.sleep_nsec(). Uncomment the function which you want to test in thread_1_task().