CODEWITHSUNDEEP
pythonloops
jligeza
jligeza

Reputation: 4693

What is the point of adding short sleep to while true loop?

Across the internet, I've saw several examples of handling a service, which awaits for messages from clients in an endless loop, including a short sleep. Example:

while True:
    check_messages_stack()
    sleep(0.1)

What's the point of the sleep there? Is it supposed to save resources? If it does save some resources, would it be a meaningful amount?

Upvotes: 1

Views: 1098

Answers (4)

Florent Descroix
Florent Descroix

Reputation: 611

When your computer is running, the CPU needs to execute a lot of processes (just for the computer to work). As a CPU is exceedingly fast it can mimic to do many tasks at the same time but it doesn't really (nowadays with multiple cores CPU and mutithreading it can, but let's forget about it for now).

To mimic multiprocessing a CPU executes a part of a process during a certain amount of time then a part of an other process then go back to the first and so on.

The CPU is allow to switch to one process to another when it is not used by the process the first process, typically when the process requires some I/O (waiting for user interaction, displaying, reading the RAM or the HDD, etc).

When you do a while true it'll loop ASAP it has finished to execute the instructions in the while loop. Here ASAP really means ASAP.
So no other processes would be able to do anything in between of two loops, because the CPU is continuously processing, thus the computer hangs.

When you add a sleep in your loop, you release the CPU, allowing it to execute other processes. It doesn't matter how long the sleep is as a casual CPU runs millions of operations in a microsecond.

So about your question, the sleep(0.1) allows your CPU to execute millions of operations between two check_messages_stack() call.

For more information, take a look at "CPU Scheduling".

Upvotes: 2

Seekheart
Seekheart

Reputation: 1173

sleep like the others have said relaxes the CPU usage, but in addition if it's something like accessing network/web data the sleep is needed to not crash the host server and ban you.

Upvotes: 1

noteness
noteness

Reputation: 2520

If the function doesn't wait for anything, it would consume 100% CPU, by adding that sleep, it gives the CPU some time to execute other processes

Upvotes: 0

Krzysztof Krasoń
Krzysztof Krasoń

Reputation: 27476

sleep doesn't use CPU resources, but constantly executing check_messages_stack() might (depending what you have there) so if you don't need to do it constantly it is a good practice to give CPU some time off.

Upvotes: 0

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