Thread synchronization and mutual exclusion mechanism in Java

Thread synchronization and mutual exclusion mechanism in Java

In Java, multi-threading is an important technology. To efficiently execute multiple tasks concurrently, you need to master the synchronization and cooperation mechanisms between threads. This article will introduce the thread synchronization and mutual exclusion mechanism in Java.

1. Thread synchronization

Thread synchronization refers to the cooperation of multiple threads to complete specified tasks during execution. Code segments executed by multiple threads access shared resources mutually. After a piece of code is executed, only one thread can access the shared resources, and other threads need to wait. Thread synchronization follows the following basic principles:

(1) Atomicity: a certain piece of code can only be accessed by one thread at the same time.

(2) Reentrancy: When a thread executes a synchronized block multiple times, it will not be locked because it already holds the lock.

In Java, there are two ways to maintain synchronization, namely synchronized and Lock.

1.1 synchronized

synchronized is the most basic synchronization mechanism in Java. The format of synchronized synchronization block is as follows:

synchronized (object) {

//Code segment

}
Among them, the object is a shared resource that needs to be synchronized, such as an object method or object itself. Only one thread can access the code block modified by the synchronized keyword at the same time. For example:

public synchronized void method(){

//代码

}

In the above code example, the method() method is modified with the synchronized keyword, and there is only a single Threads can execute this method simultaneously. In multi-threading, it can be guaranteed that the threads accessing this method are synchronized.

1.2 Lock

The Lock mechanism provides more fine-grained locking control. Lock is an interface in Java, implemented through ReentrantLock, a subclass of the Lock interface. The use of Lock locks is somewhat similar to the synchronized keyword, but it is more flexible in use. When using the Lock mechanism, the code segments that need to acquire and release the lock are included in the try and finally code blocks. For example:

Lock lock = new ReentrantLock();
lock.lock();
try {

//代码段

} finally {

lock.unlock();

}

In the above code, the lock() method is used to lock the shared resource, and the unlock() method is used to release the lock. Because the Lock mechanism has finer-grained locking control, it is more suitable in certain high-performance situations.

2. Mutual exclusion mechanism

The mutual exclusion mechanism refers to ensuring that only one thread can access shared resources at the same time during multi-thread execution. In Java, there are two ways to implement the mutual exclusion mechanism, namely synchronized and Lock.

2.1 synchronized

The synchronized synchronized block can not only achieve thread synchronization, but also implement a mutual exclusion mechanism. The code example of using synchronized to implement the mutual exclusion mechanism is as follows:

public synchronized void method(){

//代码段

}

In the above code, synchronized synchronization is added before the method keyword, this ensures that only one thread can access this code at the same time, thereby implementing a mutual exclusion mechanism.

2.2 Lock

Using the mutual exclusion mechanism provided in the LockAPI library, the mutual exclusion mechanism can also be implemented. The code example of using the Lock mechanism to implement the mutual exclusion mechanism is as follows:

private final Lock lock = new ReentrantLock();
public void method() {

lock.lock();
try {
    //代码段
} finally {
    lock.unlock();
}

}

In the above code, the lock() method is used to lock the shared resource, and the unlock() method is used to release the lock, thus realizing the mutual exclusion mechanism.

3. Comparison of thread synchronization and mutual exclusion mechanisms

Both the synchronized synchronized block and the Lock mechanism can implement thread synchronization and mutual exclusion mechanisms, but there are some differences between the two. .

(1) Different granularity: synchronized synchronization block has a larger granularity, while the Lock mechanism provides smaller granularity through the Lock interface. You can use the Lock mechanism to define more personalized locks and also control the lock. freed.

(2) Different visibility: When using synchronized synchronization block, when one thread owns the lock, the other thread cannot see the lock, so it cannot control the release of the lock independently. Using the Lock mechanism, when a thread acquires the lock, the lock is visible to all threads and can control the release of the lock.

To sum up, the thread synchronization and mutual exclusion mechanism in Java are very important mechanisms in multi-threaded programming. Different application scenarios require the use of different synchronization and mutual exclusion mechanisms. Choosing the appropriate mechanism can greatly improve the execution efficiency of multi-threaded applications.

The above is the detailed content of Thread synchronization and mutual exclusion mechanism in Java. For more information, please follow other related articles on the PHP Chinese website!