How to solve thread synchronization and mutually exclusive resource problems in Java

How to solve the problem of thread synchronization and mutually exclusive resources in Java

Introduction:
In multi-threaded programming, the problem of thread synchronization and mutually exclusive resources is one Very important topic. When multiple threads access shared resources, problems such as data inconsistency, race conditions, and deadlocks may occur if effective synchronization is not performed. In order to solve these problems, Java provides a variety of mechanisms. This article will introduce in detail how to solve thread synchronization and mutually exclusive resource problems in Java, and give specific code examples.

1. The synchronized keyword
The synchronized keyword is the most basic mechanism in Java to solve thread synchronization problems. It can modify methods and code blocks to ensure that only one thread can enter the modified method or code block at the same time.

Sample code:

public class SynchronizedExample {
    private int count = 0;
    
    public synchronized void increment() {
        count++;
    }
    
    public synchronized int getCount() {
        return count;
    }
}

The above code defines a SynchronizedExample class that contains a counter. The synchronized keyword is added to both the increment method and the getCount method, which ensures that only one thread can enter these two methods at the same time.

2. Lock interface
In addition to the synchronized keyword, Java also provides the Lock interface as another mechanism to solve thread synchronization problems. The lock() method in the Lock interface acquires the lock, and the unlock() method releases the lock. Compared with the synchronized keyword, the Lock interface has more flexible control capabilities and can implement more complex synchronization operations.

Sample code:

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class LockExample {
    private int count = 0;
    private Lock lock = new ReentrantLock();
    
    public void increment() {
        lock.lock();
        try {
            count++;
        } finally {
            lock.unlock();
        }
    }
    
    public int getCount() {
        return count;
    }
}

In the above code, the Lock interface is used to implement a LockExample class containing a counter. In the increment method, first call the lock() method to acquire the lock, then perform the counter increment operation, and finally call the unlock() method to release the lock. This ensures that only one thread can perform the counter increment operation at the same time.

3. Volatile keyword
The volatile keyword is a keyword used to modify shared variables in Java. It can guarantee visibility and orderliness, but cannot guarantee atomicity. When a thread modifies a volatile variable, other threads can immediately see the modification.

Sample code:

public class VolatileExample {
    private volatile int count = 0;
    
    public void increment() {
        count++;
    }
    
    public int getCount() {
        return count;
    }
}

In the above code, the count variable is modified with the volatile keyword. This ensures that after one thread modifies count, other threads can immediately see the modification.

Conclusion:
There are many mechanisms to solve the problem of thread synchronization and mutually exclusive resources in Java. This article introduces three common mechanisms: synchronized keyword, Lock interface and volatile keyword. In actual development, an appropriate mechanism should be selected based on specific circumstances to ensure correct synchronization and mutually exclusive access of threads.

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