How to solve concurrent programming problems in Java

How to solve concurrent programming problems in Java

In multi-threaded programming, Java provides a rich concurrent programming library, but concurrent programming problems are still a problem that makes developers a headache. This article will introduce some common Java concurrent programming problems and provide corresponding solutions and code examples.

1. Thread safety issues

Thread safety refers to the feature that shared resources can be correctly and stably accessed and operated concurrently by multiple threads in a multi-threaded environment. In Java, thread safety issues often occur in read and write operations on shared resources.

There are many ways to solve thread safety issues. The most common way is to use the synchronized keyword to lock shared resources.

Sample code:

public class Counter {
  private int count;

  public synchronized void increment() {
    count++;
  }

  public int getCount() {
    return count;
  }
}

public class Main {
  public static void main(String[] args) {
    Counter counter = new Counter();

    // 创建多个线程对count进行累加
    Thread thread1 = new Thread(() -> {
       for (int i = 0; i < 1000; i++) {
         counter.increment();
       }
    });

    Thread thread2 = new Thread(() -> {
       for (int i = 0; i < 1000; i++) {
         counter.increment();
       }
    });

    // 启动线程
    thread1.start();
    thread2.start();

    // 等待线程执行完成
    try {
       thread1.join();
       thread2.join();
    } catch (InterruptedException e) {
       e.printStackTrace();
    }

    System.out.println(counter.getCount()); // 2000
  }
}

2. Deadlock problem

Deadlock refers to two or more threads waiting indefinitely for resources to be released, resulting in A situation in which the program cannot continue to execute.

A common way to avoid deadlock problems is to use the order of synchronized blocks to acquire locks. Ensuring that all threads acquire shared resources in the same order can avoid deadlocks.

Sample code:

public class DeadLockDemo {
  private static Object lock1 = new Object();
  private static Object lock2 = new Object();

  public static void main(String[] args) {
    Thread thread1 = new Thread(() -> {
       synchronized (lock1) {
         System.out.println("Thread1 acquired lock1");
         try {
           Thread.sleep(1000);
         } catch (InterruptedException e) {
           e.printStackTrace();
         }
         synchronized (lock2) {
           System.out.println("Thread1 acquired lock2");
         }
       }
    });

    Thread thread2 = new Thread(() -> {
       synchronized (lock2) {
       System.out.println("Thread2 acquired lock2");
       try {
         Thread.sleep(1000);
       } catch (InterruptedException e) {
         e.printStackTrace();
       }
       synchronized (lock1) {
         System.out.println("Thread2 acquired lock1");
       }
     }
    });

    thread1.start();
    thread2.start();
  }
}

3. Memory visibility problem

Memory visibility refers to the ability of shared variables between multiple threads to be updated in a timely and correct manner Characteristics read by other threads. In Java, variables shared between threads are often stored in main memory, and each thread has its own working memory.

One way to solve the memory visibility problem is to use the volatile keyword to modify shared variables. The volatile keyword ensures the visibility of shared variables, that is, after modifying the value of a shared variable, other threads can immediately see the latest value.

Sample code:

public class VolatileDemo {
  private static volatile boolean flag = false;

  public static void main(String[] args) {
    Thread thread1 = new Thread(() -> {
       while (!flag) {
         // do something
       }
       System.out.println("Thread1: flag is true");
    });

    Thread thread2 = new Thread(() -> {
       flag = true;
    });

    thread1.start();
    thread2.start();
  }
}

The above are some common methods and code examples for solving concurrent programming problems in Java. It is important to note that concurrent programming problems are a complex area and solutions may vary depending on the specific situation. In actual development, it is necessary to select the most suitable solution based on specific business scenarios and needs.

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