ReentrantLock保證了只有一個線程可以執行臨界區代碼。

允許多個線程同時讀，但只有一個線程在寫，其他線程就必須等待。

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使用ReadWriteLock可以解決：

只允許一個線程寫入（其他線程既不能寫入也不能讀取）

沒有寫入時，多個線程允許同時讀（提高性能）

程序運行截圖如下：

源碼如下：

import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock;class Counter{private ReadWriteLock lock = new ReentrantReadWriteLock();private Lock rlock = lock.readLock();private Lock wlock = lock.writeLock();private int value = 0;public void add(int m){wlock.lock();try{this.value += m;}finally {wlock.unlock();}}public void dec(int m){wlock.lock();try{this.value -= m;}finally {wlock.unlock();}}public int get(){rlock.lock();try{return this.value;}finally {System.out.println("Count get Finally");rlock.unlock();}} }public class Main1 {final static int LOOP = 100;public static void main(String[] args) throws InterruptedException {final Counter counter = new Counter();Thread t1 = new Thread(){@Overridepublic void run() {for(int i = 0; i < LOOP; i++){counter.add(1);}}};Thread t2 = new Thread(){@Overridepublic void run() {for(int i = 0; i < LOOP; i++){counter.dec(1);}}};t1.start();t2.start();t1.join();t2.join();System.out.println("COUNTER: " + counter.get());} }

condition中的：

await/signal/signalAll和wait/notify/notifyAll一樣。

await()會釋放當前鎖，進入等待狀態。

signal()會喚醒某個等待線程

signalAll()會喚醒所有等待線程

喚醒線程從await()返回后需要重新獲得：

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程序運行截圖如下：

源碼如下：

import java.util.LinkedList; import java.util.Queue; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock;class TaskQueue{final Queue<String> queue = new LinkedList<String>();final Lock lock = new ReentrantLock();final Condition notEmpty = lock.newCondition();public String getTask() throws InterruptedException {lock.lock();try{while(this.queue.isEmpty()){notEmpty.await();}return queue.remove();}finally {lock.unlock();}}public void addTask(String name){lock.lock();try{this.queue.add(name);notEmpty.signalAll();}finally {lock.unlock();}} }class WorkerThread extends Thread{TaskQueue taskQueue;public WorkerThread(TaskQueue taskQueue){this.taskQueue = taskQueue;}@Overridepublic void run() {while (!isInterrupted()){String name = "";try{name = taskQueue.getTask();}catch (InterruptedException e) {break;}String result = "HELLO, " + name + " !";System.out.println(result);}} }public class Main2 {public static void main(String[] args) throws InterruptedException {TaskQueue taskQueue = new TaskQueue();WorkerThread workerThread = new WorkerThread(taskQueue);workerThread.start();taskQueue.addTask("小明");Thread.sleep(1000);taskQueue.addTask("小紅");Thread.sleep(1000);taskQueue.addTask("小剛");Thread.sleep(1000);workerThread.interrupt();workerThread.join();System.out.println("END");} }

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