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 <time.h>
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().

Answer 2

from time import sleep
sleep(seconds)

More info.

Answer 3

Three lines to call the "original" usleep:

import ctypes

libc = ctypes.CDLL('libc.so.6')
libc.usleep(300000)

tested on centos & alpine both python 3.8.1

Answer 4

import time
usleep = lambda x: time.sleep(x/1000000.0)

usleep(100) #sleep during 100μs

Answer 5

Since usleep generally means you want to delay execution for x microseconds, you must divide the seconds value by 1000000.

import time
time.sleep(seconds/1000000.0)

time.sleep() takes seconds as a parameter.

http://docs.python.org/library/time.html#time.sleep

Answer 6

Be very very careful with time.sleep. I got burned by python3 using time.sleep because it is non-monotonic. If the wall clock changes backwards, the time.sleep call won't finish until the wall clock catches up with where it would have been if the sleep had gone forward as planned. I have not yet found a monotonic blocked sleep for python.

Instead, I recommend Event.wait, like this:

def call_repeatedly(interval, func, *args, **kwargs):
    stopped = Event()
    def loop():
        while not stopped.wait(interval):  # the first call is in `interval` secs
            try:
                func(*args)
            except Exception as e:
                logger.error(e);
                if kwargs.get('exception'):
                    kwargs.get('exception')(e) # SEND exception to the specified function if there is one.
                else:
                    raise Exception(e)
    Thread(target=loop).start()
    return stopped.set

http://pastebin.com/0rZdY8gB