Herbie Murray
Loop statements are used to repeat a section of code a certain number of times. Sometimes, a loop will be infinite, meaning it will continue to repeat unless it is stopped. Sleep is a function that can be called to pause the loop for a certain amount of time. This can be important to prevent the loop from spinning the CPU core and turning on the CPU fan, which can slow down the execution of the code. However, some people argue that you should never call Sleep as it can lead to lost efficiency. The amount of sleep time will depend on what is happening in the loop and the desired performance of the program.
| Characteristics | Values |
|---|---|
| Purpose of sleep | To allow the thread to sleep for as long as possible without impacting the program's performance |
| Determining sleep time | Calculate the desired framerate for the game and the delay that can be afforded between each frame |
| Busy-waiting | Sleep call will yield the scheduler and might prevent the thread from spinning the CPU core and turning on the CPU fan |
| Benchmarking | Watch the CPU usage in task manager with and without the Sleep call to see if it takes longer |
| Efficiency | Sleeping for 1 second gives nothing but lost efficiency |
| Spinning in a tight loop | Without sleep, the OS will schedule the process, using the CPU to do basically nothing very fast, meaning no other processes can run on that CPU |
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What You'll Learn
The correct amount of sleep time
There isn't a 'correct' amount of sleep time as such. Generally, your thread should sleep for as long as possible without impacting your program's performance. A good way to do this is to determine the desired framerate for your game and calculate how much of a delay you can afford between each frame. Every time round your main loop, check if that amount of time has elapsed since the previous frame. If not, sleep for a short period and try again next time round the loop.
The Sleep call will depend on what's happening in your loop. If it is busy-waiting and usually does nothing, then the Sleep call will yield the scheduler and might prevent the thread from spinning the CPU core and turning on your CPU fan. If it always has something to do, then the sleeps will add up and slow down your execution. You can watch the CPU usage in the task manager with and without the Sleep call to see if it takes longer.
Sleep is one of those functions that you should probably never call. When you just have a loop, the OS sees that you want to run all the time, and so will schedule your process, during which you'll use that CPU and do basically nothing very very fast - spinning in a tight loop where you check the same condition over and over again, millions of times a second. By calling sleep, you make a call to the OS that basically says "I don't need to run for at least X seconds - don't bother waking me up till then".
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How to determine the desired framerate for your game
There isn't a 'correct' amount of sleep time for a game loop. However, your thread should sleep for as long as possible without impacting your program's performance. To determine the desired framerate for your game, you should first calculate how much of a delay you can afford between each frame. Every time your main loop runs, check if that amount of time has elapsed since the previous frame. If not, sleep for a short period, and try again next time the loop runs.
If your loop is busy-waiting and usually does nothing, then a Sleep call will yield the scheduler and might prevent the thread from spinning the CPU core and turning on your CPU fan. If your loop always has something to do, then the sleeps will add up and slow down your execution. You can benchmark your code with known input to see if it takes longer with or without the Sleep call.
By calling sleep, you're telling the OS that you don't need to run for a certain amount of time. This prevents your process from using up system resources and slowing down other processes that are trying to run on the same CPU.
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Busy-waiting and the Sleep call
To address this issue, the Sleep call can be used. The Sleep call is a function that tells the operating system (OS) that the program doesn't need to run for a specified period of time. By doing so, the program yields control to the OS, allowing other processes to utilise the CPU and preventing unnecessary resource consumption.
The Sleep call is particularly useful in infinite while loops, where the loop runs continuously without a defined endpoint. By introducing the Sleep call, the program can take a break and allow other processes to execute. This helps in preventing the loop from spinning the CPU core and unnecessarily turning on the CPU fan.
However, it's important to note that the Sleep call should be used judiciously. While it can provide benefits in certain scenarios, it can also slow down the execution of the program if used excessively. As suggested by David Heffernan, "Sleep is one of those functions that you should probably never call". Instead of using Sleep, it's often more efficient to optimise the code and reduce unnecessary busy-waiting.
There is no 'correct' amount of sleep time, and it depends on the specific requirements of the program. A good practice is to determine the desired framerate and calculate the maximum delay that can be afforded between each frame. By checking if this amount of time has elapsed in each loop iteration, the program can decide whether to sleep for a short period or continue executing.
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Preventing the thread from spinning the CPU core
If your loop is busy-waiting and usually does nothing, then calling Sleep will yield the scheduler and might prevent the thread from spinning the CPU core and turning on your CPU fan.
When you just have a loop, the OS sees that you want to run all the time, and so will schedule your process, during which you'll use that CPU and do basically nothing very very fast - spinning in a tight loop where you check the same condition over and over again, millions of times a second. And your process doing this means no other processes can run on that same CPU, so you're taking up system resources and slowing them down.
By calling Sleep, you make a call to the OS that basically says "I don't need to run for at least X seconds - don't bother waking me up till then".
There isn't really a 'correct' amount of sleep time as such. Generally speaking though, your thread should sleep for as long as possible without impacting your program's performance. A good way to do that is to determine the desired framerate for your game, and from there calculate how much of a delay you can afford between each frame. Every time round your main loop, check if that amount of time has elapsed since the previous frame. If not, sleep for a short period, and try again next time round the loop.
Sleep is one of those functions that you should probably never call. If it always has something to do, then the sleeps will indeed add up and slow down your execution.
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How to slow down execution
If you want to slow down the execution of a loop, you can use a sleep statement. This is a function that tells the operating system (OS) that you don't need to run the loop for a certain amount of time. This is important because, without a sleep statement, the OS will schedule your process to run all the time, using up CPU and slowing down other processes.
However, some people advise against using sleep statements, as they can lead to lost efficiency. It depends on what your loop is doing. If it is busy-waiting and usually does nothing, then a sleep call will yield the scheduler and might prevent the thread from spinning the CPU core. If it always has something to do, then the sleeps will add up and slow down your execution.
There is no 'correct' amount of sleep time. Your thread should sleep for as long as possible without impacting your program's performance. A good way to do this is to determine the desired framerate for your game, and from there calculate how much of a delay you can afford between each frame. Every time round your main loop, check if that amount of time has elapsed since the previous frame. If not, sleep for a short period, and try again next time round the loop.
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Frequently asked questions
Loop statements need sleep to prevent the thread from spinning the CPU core and turning on your CPU fan.
If you don't include sleep, your process will use the CPU to do basically nothing very fast, spinning in a tight loop where you check the same condition over and over again, millions of times a second.
There isn't a 'correct' amount of sleep time. Your thread should sleep for as long as possible without impacting your program's performance.
You should determine the desired framerate for your game, and from there calculate how much of a delay you can afford between each frame.
If you include too much sleep time, you will slow down your execution.
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