模式6--ReadWriteLock

来至《java多线程设计模式》

自己提供一个逻辑锁代替JDK的物理锁synchronized

优点：1.对read操作不进行共享互斥，可以进行多个read操作，提高系统性能

2.适合read》write的情况

package Sample;public final class ReadWriteLock {private int readingReaders = 0; // (A)...实际正在读取的执行绪数量private int waitingWriters = 0; // (B)...正在等待写入的执行绪数量private int writingWriters = 0; // (C)...实际正在写入的执行绪数量private boolean preferWriter = true; // 写入优先的话，值为truepublic synchronized void readLock() throws InterruptedException {while (writingWriters > 0 || (preferWriter && waitingWriters > 0)) {wait();}readingReaders++;                       //  (A)实际正在读取的线程数量加1}public synchronized void readUnlock() {readingReaders--;                       //  (A)实际正在读取的线程数量减1preferWriter = true;  //read处理后优先处理writenotifyAll();}public synchronized void writeLock() throws InterruptedException {waitingWriters++;                       // (B)正在等待写入的线程数量加1try {while (readingReaders > 0 || writingWriters > 0) {wait();}} finally {waitingWriters--;                   // (B)正在等待写入的线程数量减1}writingWriters++;                       //  (C)实际正在写入的线程数量加1}public synchronized void writeUnlock() {writingWriters--;                       // (C)实际正在写入的线程数量减preferWriter = false;  //write处理后优先处理readnotifyAll();}
}