python process takes 100% CPU

Question

I am trying to run python application and execute actions based on specified interval. Below code is consuming constantly 100% of CPU.

def action_print():

    print "hello there"

interval = 5
next_run = 0

while True:

    while next_run > time.time():
        pass

    next_run = time.time() + interval

    action_print()

I would like to avoid putting process to sleep as there will be more actions to execute at various intervals.

please advise

Answer 1

If you know when the next run will be, you can simply use time.sleep:

import time
interval = 5
next_run = 0
while True:
   time.sleep(max(0, next_run - time.time()))

   next_run = time.time() + interval
   action_print()

If you want other threads to be able to interrupt you, use an event like this:

import time,threading
interval = 5
next_run = 0
interruptEvent = threading.Event()
while True:
   interruptEvent.wait(max(0, next_run - time.time()))
   interruptEvent.clear()

   next_run = time.time() + interval
   action_print()

Another thread can now call interruptEvent.set() to wake up yours.

In many cases, you will also want to use a Lock to avoid race conditions on shared data. Make sure to clear the event while you hold the lock.

You should also be aware that under cpython, only one thread can execute Python code. Therefore, if your program is CPU-bound over multiple threads and you're using cpython or pypy, you should substitute threading with multiprocessing.

Answer 2

Presumably you do not want to write time.sleep(interval) , but replacing 'pass' with time.sleep(0.1) will almost completely free up your CPU, and still allow you flexibility in the WHILE predicate.

Alternatively you could use a thread for each event you are scheduling and use time.sleep(interval) but this will still tie up your CPU.

Bottom line : your loop WHILE : PASS is going round and round very fast consuming all your CPU.