Basic knowledge of Java concurrent programming

With the continuous development of the Internet, the Java language has become an important tool for developers. In Java development, there are more and more situations involving concurrent programming. For this reason, it is very necessary to master the basic knowledge of Java concurrent programming.

The following is a detailed introduction to the basic knowledge of Java concurrent programming.

1. Thread

Thread is the smallest unit that the operating system can perform operation scheduling, that is, the execution path. In Java, multi-threading is a common means to implement concurrent programming.

In Java, use the Thread class to create and start new threads. When starting a thread, you can specify the tasks to be performed by the thread by overriding the run() method of the Thread class. For example:

class RunnableThread implements Runnable {
    public void run() {
        // 线程执行任务
    }
}

public class Main {
    public static void main(String[] args) {
        RunnableThread runnable = new RunnableThread();
        Thread thread = new Thread(runnable);
        thread.start();
    }
}

In the above code, a RunnableThread class is created that implements the Runnable interface, and a new thread is created in the main function and started. The task of the new thread is defined by the overridden run() method.

2. Synchronization

In multi-threaded programming, situations involving shared resources require synchronization to ensure data consistency and correctness. Java provides the synchronized keyword to implement synchronization locks. The following are several common synchronization methods:

• synchronized method

The synchronized method refers to using the synchronized keyword on the method declaration to make the method a synchronized method. As shown below:

public synchronized void method(){
    // 同步内容
}

The method() method in the above code is a synchronous method, and other threads are allowed to execute only after the method is completed.

• synchronized code block

In addition to using the synchronized keyword on method declarations, you can also use synchronized code blocks to achieve synchronization between threads. The following is an example of using a synchronized code block:

public void method(){
    synchronized (this){
        // 同步代码块
    }
}

In the above code, a synchronized code block is used, and this in parentheses indicates locking the object to which the method belongs.

3. volatile

The volatile keyword in Java is a lightweight synchronization mechanism that can guarantee thread visibility and a certain degree of orderliness. When a variable is modified volatile, the latest value is read from memory each time the variable is read. For example:

public volatile boolean flag = false;

The flag variable in the above code is declared as volatile type, indicating that its value may be modified by multiple threads. In a multi-threaded environment, using the volatile keyword can ensure the consistency of thread access to the variable.

4. Thread Pool

Thread pool is a very practical multi-thread programming tool in Java, which can reduce the cost of thread creation and destruction, and can effectively control the number of threads. Control to prevent excessive number of threads from causing waste of system resources. In Java, thread pools are provided through the Executor framework.

The following is an example of using the Executor framework to create a thread pool:

ExecutorService executor = Executors.newFixedThreadPool(5);
for(int i = 0; i < 10; i++){
    executor.execute(new RunnableThread());
}
executor.shutdown();

In the above code, a thread pool with a fixed number of threads of 5 is created, and then 10 tasks are submitted to the thread pool. implement. Finally, use the shutdown() method to close the thread pool.

5. Concurrent collection

Java provides many thread-safe collection classes, such as ConcurrentHashMap, ConcurrentLinkedQueue, etc. These collection classes can provide efficient and safe data operations in multi-threaded environments.

The following is an example of using ConcurrentHashMap:

ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
map.put("key1", "value1");
map.put("key2", "value2");
for(Map.Entry<String, String> entry : map.entrySet()){
    System.out.println(entry.getKey() + ":" + entry.getValue());
}

In the above code, a thread-safe ConcurrentHashMap is created, then two key-value pairs are inserted and the map is traversed.

6. Lock

Java provides a variety of lock implementation methods, such as synchronized, ReentrantLock, etc. In a multi-threaded environment, locks are an important mechanism to ensure synchronous execution of threads.

The following is an example of using ReentrantLock to implement synchronization lock:

ReentrantLock lock = new ReentrantLock();
lock.lock();
try {
    // 同步代码块
} finally {
    lock.unlock();
}

In the above code, use ReentrantLock to create a lock, and obtain the lock through the lock() method before locking. After the execution is completed, Release the lock through the unlock() method.

Summary

Java concurrent programming is a complex and important technology. Mastering its basic knowledge is of great significance for writing efficient and safe multi-threaded programs. This article provides an overview of threads, synchronization, volatile, thread pools, concurrent collections, and locks in Java concurrent programming. I believe that readers have a deeper understanding of Java concurrent programming.

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