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This article mainly explains "how to use the java volatile keyword", interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn how to use the java volatile keyword.

Basic introduction to volatile

Volatile can be regarded as a lightweight implementation of synchronized, but volatile can not completely replace synchronized,volatile with the visibility of synchronized, but not the atomicity of synchronized. Visibility, that is, the member variable modified with the volatile keyword indicates that there is no copy of the worker thread, and the thread reads directly from the main memory every time, and each read is the latest value, which ensures the visibility of the variable to other threads. In addition, the use of volatile ensures that variables cannot be reordered, ensuring ordering.

Volatile only needs to modify one member variable, such as private volatile balance

Volatile is easier and less expensive to program than synchronized, but it has a little limitation and should be used very carefully and should not be used as a lock. Volatile does not block programs like synchronized, and volatile is recommended if there are far more reads than writes. It will have better performance.

Volatile usage scenario

If you use volatile correctly, you must rely on the following conditions:

1. Writing to a variable does not depend on the value of the current variable.

2. This variable is not included in the invariants of other variables.

The first condition shows that volatile is not an atomic operation, you can't use counters like nasty +, and it's not thread-safe.

1. Change of state

In some scenarios, there is bound to be a state change, completing the stop of a main thread, and so on. First of all, we start an infinite loop of the main thread to determine whether the variable isStop variable is true, if true, then exit the program, otherwise it will always loop, so the value of this isStop is changed by another thread.

If the above program does not add volatile, it will always be stuck in the loop, at this time the thread will always get the value of false, after adding volatile3 seconds, it will output stop, so this program well explains the characteristics of visibility.

2. Read more and write less

Suppose such a scenario, there are N threads reading the value of the variable, only one thread writes the value of the variable, which can ensure the visibility of the reading thread and the thread safety of the writing thread.

Like nasty + is not an atomic operation, in fact, you can lock the write method through synchronized, and then modify the variable with volatile, which ensures the visibility of the reader thread to the variable and the atomicity of the variable.

If n does not add volatile, the program will always loop and will not be able to output stop, that is, the thread at this time will always get a value of 0. Of course, without volatile, the synchronized modification of the method of getting n can get the latest value in time, but the performance will be much lower than that of volatile.

At this point, I believe you have a deeper understanding of "how to use the java volatile keyword". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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