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This article will explain in detail how to achieve multithreaded thread safety in python. The editor thinks it is very practical, so I share it with you for reference. I hope you can get something after reading this article.

1. Introduction

At present, with the rapid development of computer hardware, the CPU on personal computers is also multi-core. Now the common number of CUP cores is 4-core or 8-core. Therefore, when writing programs, we need to write parallel programs in order to improve efficiency and give full play to the ability of hardware. As the main language of Internet applications, Java is widely used in the development of enterprise applications. It also supports multithreading (Multithreading), but although multithreading is good, it has higher requirements for programming.

A program that can run correctly with a single thread does not mean that it can run correctly in a multi-threaded scenario. The correctness here is often not easy to find, and it may only occur when the number of concurrency reaches a certain amount. This is also the reason why it is not easy to reproduce in the testing process. Therefore, in multithreading (concurrent) scenarios, how to write thread-safe (Thread-Safety) programs is of great significance for the correct and stable operation of the program.

The following will be combined with examples to talk about how to implement thread-safe programs in the Java language.

In order to give a perceptual understanding, here is an example of thread unsafety, as follows:

Package com.example.learn;public class Counter {private static int counter = 0; public static int getCount () {return counter;} public static void add () {counter = counter + 1;}}

2. Synchronized method

Based on the above example, the most direct way to make it a thread-safe program is to add the synchronized keyword to the corresponding method to make it a synchronized method. It can decorate a class, a method, and a code block. Modify the above counting program, the code is as follows:

Package com.example.learn;public class Counter {private static int counter = 0; public static int getCount () {return counter;} public static synchronized void add () {counter = counter + 1;}}

3. Locking mechanism

Another common synchronization method is locking. For example, there is a reentrant lock ReentrantLock in Java, which is a recursive non-blocking synchronization mechanism. Compared with synchronized, it can provide a more powerful and flexible locking mechanism and reduce the probability of deadlock. The sample code is as follows:

Package com.example.learn;import java.util.concurrent.locks.ReentrantLock;public class Counter {private static int counter = 0; private static final ReentrantLock lock = new ReentrantLock (true); public static int getCount () {return counter;} public static void add () {lock.lock (); try {counter = counter + 1;} finally {lock.unlock ();}

4. Use the Atomic object

Because the locking mechanism will affect some performance, but in some scenarios, it can be implemented in a lock-free way. Java has built-in Atomic-related atomic manipulation classes, such as AtomicInteger,AtomicLong, AtomicBoolean, and AtomicReference, which can be selected according to different scenarios. Here is the example code:

Package com.example.learn;import java.util.concurrent.atomic.AtomicInteger;public class Counter {private static final AtomicInteger counter = new AtomicInteger (); public static int getCount () {return counter.get ();} public static void add () {counter.incrementAndGet ();}}

5. Stateless object

As mentioned earlier, one of the reasons for thread unsafety is that multiple threads access data in an object at the same time, and the data is shared, so if the data is made exclusive, that is, stateless, then it is naturally thread-safe. The so-called stateless method is to give the same input and return a consistent result. Here is the example code:

Package com.example.learn;public class Counter {public static int sum (int n) {int ret = 0; for (int I = 1; I)

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