ReadWriteLock 又稱為共享鎖，的讀寫分離鎖，內部分為讀鎖和寫鎖

關於 A 和 B 執行緒，讀和寫的關係

A 讀 — B 讀：不互斥、不阻塞 A 讀 — B 寫：互斥，互相阻塞 A 寫 — B 寫：互斥，互相阻塞

用法：非常簡單，和 ReentrantLock 一樣

public class TestReadWriteLock {
	
	// 例項化讀寫鎖
	private static final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();	
	private static final Lock readLock =
 
 readWriteLock.readLock();	
	private static final Lock writeLock = readWriteLock.writeLock();	
	private static int count = 0;
	
	static class ReadThread implements Runnable {
		@Override
		public void run() {
			readLock.lock();
			try {
				System.out.println(System.currentTimeMillis() + " : " + Thread.
 
currentThread().getName() + " 進來了: count = " + count);
				Thread.sleep(2000);
			} catch (Exception e) {
			} finally {
				readLock.unlock();
			}
		}
	}
	
	static class WriteThread implements Runnable {
		@Override
		public void run() {
			writeLock.lock();
			try {
				System.out.println(System.currentTimeMillis
 
() + " : " + Thread.currentThread().getName() + " 進來了: count = " + (++count));
				Thread.sleep(2000);
			} catch (Exception e) {
			} finally {
				writeLock.unlock();
			}
		}
	}
	
	public static void main(String[] args) throws InterruptedException {
		System.out.println("======開始測試寫鎖======");
		Thread[] threads = new Thread[10];
		ReadThread read = new ReadThread();
		for (int i = 0; i < threads.length; i++) threads[i] = new Thread(read, "執行緒 " + i);
		for (int i = 0; i < threads.length; i++) threads[i].start();
		for (int i = 0; i < threads.length; i++) threads[i].join();
		
		System.out.println("\n======開始測試讀鎖======");
		WriteThread write = new WriteThread();
		for (int i = 0; i < threads.length; i++) threads[i] = new Thread(write, "執行緒 " + i);
		for (int i = 0; i < threads.length; i++) threads[i].start();
		for (int i = 0; i < threads.length; i++) threads[i].join();
	}
}

輸出結果，讀鎖相當於沒有鎖 ======開始測試寫鎖====== 1537876265912 : 執行緒 0 進來了: count = 0 1537876265912 : 執行緒 1 進來了: count = 0 1537876265912 : 執行緒 2 進來了: count = 0 1537876265912 : 執行緒 3 進來了: count = 0 1537876265913 : 執行緒 5 進來了: count = 0 1537876265912 : 執行緒 4 進來了: count = 0 1537876265913 : 執行緒 7 進來了: count = 0 1537876265913 : 執行緒 8 進來了: count = 0 1537876265913 : 執行緒 6 進來了: count = 0 1537876265913 : 執行緒 9 進來了: count = 0 ======開始測試讀鎖====== 1537876267915 : 執行緒 0 進來了: count = 1 1537876269916 : 執行緒 2 進來了: count = 2 1537876271916 : 執行緒 1 進來了: count = 3 1537876273917 : 執行緒 4 進來了: count = 4 1537876275918 : 執行緒 3 進來了: count = 5 1537876277918 : 執行緒 5 進來了: count = 6 1537876279919 : 執行緒 6 進來了: count = 7 1537876281919 : 執行緒 7 進來了: count = 8 1537876283920 : 執行緒 8 進來了: count = 9 1537876285920 : 執行緒 9 進來了: count = 10