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This article mainly explains "what is the meaning of Thread.sleep(0) in javascript". The explanation content in this article is simple and clear, easy to learn and understand. Please follow the ideas of Xiaobian slowly and deeply to study and learn "what is the meaning of Thread.sleep(0) in javascript" together!

Suppose it is 2008-4-7 12:00:00.000. If I call Thread.Sleep(1000), will this thread wake up on 2008-4-7 12:00:01.000?

Someone uses a seemingly inexplicable phrase in their code: Thread.Sleep(0). Since it is Sleep 0 milliseconds, what is the difference between it and removing this code?

Let's review the operating system principle first.

There are many strategies for CPU contention in operating systems. Unix systems use a time slice algorithm, while Windows is preemptive.

In the time slice algorithm, all processes are arranged in a queue. The operating system assigns each process, in their order, a certain amount of time that the process is allowed to run. If the process is still running at the end of the time slice, the CPU will be stripped and allocated to another process. If the process blocks or ends before the end of the time slice, the CPU switches immediately. All the scheduler has to do is maintain a list of ready processes, and when a process runs out of its time slice, it is moved to the end of the queue.

Preemptive operating systems mean that if a process gets CPU time, it will hoard the CPU completely unless it gives up using the CPU itself. Therefore, it can be seen that in a preemptive operating system, the operating system assumes that all processes are "good character" and will actively quit the CPU.

In a preemptive operating system, if there are several processes, the operating system calculates an overall priority for them based on their priority and hunger time (how long they have not used the CPU). The operating system hands the CPU to the process with the highest overall priority. When a process finishes executing or suspends itself, the operating system recalculates the total priority of all processes, and then selects the highest priority to give CPU control to him.

We describe both algorithms in terms of cake splitting scenarios. Suppose there is an endless stream of cake (endless time), a fork and knife (one CPU), and ten people waiting to eat cake (ten processes).

If Unix were to divide the cake, it would be as follows: everyone comes up for one minute, and when the time is up, the next one. When the last person finishes eating, we'll start again. So, regardless of whether these 10 people have different priorities, different hunger levels, and different meals, each person can eat for 1 minute when they come up. Of course, if someone is not hungry, or eats a small amount, and is full after 30 seconds, he can say to the operating system: I am full (hang up). So the operating system will let the next person come.

If Windows is responsible for dividing the cake, then the scene is very interesting. He would make rules like this: I would calculate a priority for each of you based on your priorities and hunger. The person with the highest priority can come up and eat the cake-until you don't want to. When the person finished eating, I re-calculated each person's priority according to priority and hunger, and then assigned it to the person with the highest priority.

So this is interesting-maybe some of them are PPMMs and therefore have high priority, so she can come and eat cake often. Maybe the other person is ugly and goes to ws, so the priority is especially low, so it takes him a long time to get his turn (because as time goes on, he will get hungry, so the total priority will get higher and higher, so one day it will be his turn). Moreover, if a fat man accidentally gets a knife and fork, because he eats a lot, he may occupy the cake for a long time, causing the people next to him to swallow there.

Moreover, there may be cases where the operating system now calculates that PPMM number 5 has the highest overall priority and is much higher than others. So I called number five to eat cake. Number 5 ate for a while and felt less hungry, so he said,"I'm not eating anymore." Pay attention to the public number Java interview those things, reply keyword interview, get the latest interview information! So the operating system recalculates everyone's priorities. Because Number 5 had just eaten, she was less hungry, and so her overall priority was lower; because everyone else waited longer, they were more hungry, and so their overall priority was higher. But it is still possible that number 5 has a higher priority than all the others, only now it is only slightly higher than the others-but she is still the highest priority overall. Therefore, the operating system will say: No. 5 mm up to eat cake…(No. 5 mm depressed, this is not just eaten…people want to lose weight…who told you to grow so beautiful, so high priority).

What does Thread.Sleep do? He also used the scene of dividing the cake just now to describe it. In the above scenario, MM No. 5 feels 8 minutes full after eating a cake. She feels that she doesn't want to eat cake again in the next half hour, so she will tell the operating system: Don't ask me to eat cake again in the next half hour. Thus, mm 5 is ignored when the OS recalculates the total priority of everyone for the next half hour. The Sleep function does this by telling the operating system "I'm not competing for CPU for a few milliseconds."

Now that we've seen what Thread.Sleep does, let's consider the two questions at the beginning of this article.

The answer to the first question is: Not necessarily. Because you're just telling the operating system: I don't want to compete for CPU for the next 1000 milliseconds. Then 1000 milliseconds later, another thread may be using CPU, then the operating system will not reallocate CPU until that thread hangs or ends; moreover, even if it happens to be the operating system's turn to allocate CPU at this time, then the current thread is not necessarily the one with the highest total priority, and the CPU may still be preempted by other threads.

Similarly, Thread has a Resume function that wakes up suspended threads. As mentioned above, this function simply "tells the operating system that I am now competing for CPU," and calls to this function do not immediately give the thread CPU control.

To the second question, the answer is yes, and the difference is obvious. Suppose we had another PPMM 7 in the cake scene, and she had a very, very high priority (because she was very, very pretty), so the OS would always call her to eat the cake. Also, No. 7 likes cake very much and eats a lot. However, number 7 is a good person. She is very kind. She will think after eating a few bites: If there is someone else who needs cake more than me, then I will give it to him. So she could say to the operating system every few bites: Let's recalculate everyone's overall priority. However, the operating system does not accept this advice-because the operating system does not provide this interface. So mm 7 changed his statement: "don't call me up for cake for the next 0 milliseconds." This command is accepted by the operating system, so the operating system will recalculate everyone's total priority-notice that this time it is calculated together with number 7, because "0 milliseconds have passed." So if no one else shows up who needs cake more than 7, 7 will be called up for cake the next time.

Thread.Sleep(0) therefore "triggers the operating system to immediately resume a CPU race." The result of the race may be that the current thread still gains CPU control, or another thread gains CPU control. This is also why we often write Thread.Sleep(0) in large loops, because this gives other threads such as the Paint thread the right to gain CPU control, so that the interface does not fake death there.

In addition, although it is mentioned above that "unless it gives up using the CPU itself, it will completely occupy the CPU," this behavior is still restricted-the operating system will monitor your CPU hogging situation, and if it finds that a thread has occupied the CPU for a long time, it will force this thread to suspend, so in fact, there will be no "one thread has been hogging the CPU." As for our large loop causing the program to fake death, it is not because this thread has been hogging the CPU. In fact, during this time the operating system has been competing for CPU many times, but other threads immediately quit after gaining control of the CPU, so it is the turn of this thread to continue executing the loop, so it takes a long time to be forcibly suspended by the operating system. So reflected in the interface, it looks as if this thread has been hogging the CPU.

Thank you for reading, the above is "javascript Thread.sleep(0) what is the meaning of the content, after the study of this article, I believe that we have a deeper understanding of the meaning of javascript Thread.sleep(0), the specific use of the situation also needs to be verified. Here is, Xiaobian will push more articles related to knowledge points for everyone, welcome to pay attention!

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