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java中多線程加鎖的四種方式

更新時間：2024年10月18日 08:35:27 作者：我叫汪楓

Java中實現(xiàn)多線程安全的關(guān)鍵是加鎖,主要方式有synchronized關(guān)鍵字、ReentrantLock類、ReadWriteLock接口和Semaphore類,本文就來介紹一下這四種方式,感興趣的可以了解一下

1. 使用synchronized關(guān)鍵字

synchronized可以用于方法或代碼塊，確保只有一個線程能訪問被鎖定的代碼。

方法鎖

class SynchronizedMethod {
    public synchronized void synchronizedMethod() {
        System.out.println("Synchronized method executed by " + Thread.currentThread().getName());
    }
}

代碼塊鎖

class SynchronizedBlock {
    private final Object lock = new Object();

    public void synchronizedBlock() {
        synchronized (lock) {
            System.out.println("Synchronized block executed by " + Thread.currentThread().getName());
        }
    }
}

2. 使用ReentrantLock類

ReentrantLock是java.util.concurrent.locks包中的一種鎖，具有比synchronized更靈活的鎖定機制。

import java.util.concurrent.locks.ReentrantLock;

class ReentrantLockExample {
    private final ReentrantLock lock = new ReentrantLock();

    public void lockMethod() {
        lock.lock();
        try {
            System.out.println("ReentrantLock method executed by " + Thread.currentThread().getName());
        } finally {
            lock.unlock();
        }
    }
}

3. 使用讀寫鎖（ReadWriteLock）

ReadWriteLock允許多個讀線程同時訪問共享資源，但在寫線程訪問時，阻止其他線程的讀和寫訪問。

import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

class ReadWriteLockExample {
    private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void readMethod() {
        readWriteLock.readLock().lock();
        try {
            System.out.println("Read lock method executed by " + Thread.currentThread().getName());
        } finally {
            readWriteLock.readLock().unlock();
        }
    }

    public void writeMethod() {
        readWriteLock.writeLock().lock();
        try {
            System.out.println("Write lock method executed by " + Thread.currentThread().getName());
        } finally {
            readWriteLock.writeLock().unlock();
        }
    }
}

4. 使用信號量（Semaphore）

Semaphore是一種計數(shù)信號量，可以限制同時訪問某個資源的線程數(shù)量。

import java.util.concurrent.Semaphore;

class SemaphoreExample {
    private final Semaphore semaphore = new Semaphore(2); // 允許最多兩個線程訪問

    public void accessResource() {
        try {
            semaphore.acquire();
            System.out.println("Accessing resource by " + Thread.currentThread().getName());
            Thread.sleep(1000); // 模擬工作
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            semaphore.release();
        }
    }
}