java并发
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luoxiang
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@ -17,9 +17,9 @@ public class AwaitAndSignal {
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try {
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lock.lock();
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String threadName = Thread.currentThread().getName();
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System.out.println(threadName + "等待通知...");
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System.out.println(threadName + "线程等待通知...");
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condition.await();
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System.out.println(threadName + "获得锁");
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System.out.println(threadName + "线程后续操作");
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} catch (InterruptedException e) {
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e.printStackTrace();
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} finally {
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@ -31,9 +31,10 @@ public class AwaitAndSignal {
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public static void main(String[] args) throws InterruptedException {
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Thread thread1 = new Thread(new IncreaseTask());
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thread1.start();
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Thread.sleep(2000);
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// 必须要再次获取该重入锁，否则会抛出IllegalMonitorStateException异常
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Thread.sleep(1000);
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System.out.println("主线程开始操作");
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lock.lock();
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System.out.println("主线程唤醒");
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condition.signal();
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lock.unlock();
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}
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@ -36,7 +36,6 @@ public class J5_NotifyAll {
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System.out.println("对象object唤醒");
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// 如果是object.notify()则是随机唤醒任意一个等待
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object.notifyAll();
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}
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}).start();
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}
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189
notes/Java_并发.md
189
notes/Java_并发.md
@ -453,48 +453,6 @@ ReentrantLock 即支持公平锁也支持非公平锁，公平锁在调度时候
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private static ReentrantLock fairLock = new ReentrantLock(true);
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```
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ReentrantLock 锁通常可以配合 `condition` 来使用，从而实现有条件的等待，示例如下：
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```java
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public class AwaitAndSignal {
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private static ReentrantLock lock = new ReentrantLock();
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private static Condition condition = lock.newCondition();
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static class IncreaseTask implements Runnable {
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@Override
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public void run() {
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try {
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lock.lock();
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String threadName = Thread.currentThread().getName();
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System.out.println(threadName + "等待通知...");
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condition.await();
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System.out.println(threadName + "获得锁");
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} catch (InterruptedException e) {
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e.printStackTrace();
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} finally {
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lock.unlock();
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}
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}
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}
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public static void main(String[] args) throws InterruptedException {
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Thread thread1 = new Thread(new IncreaseTask());
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thread1.start();
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Thread.sleep(2000);
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// 必须要再次获取该重入锁，否则会抛出IllegalMonitorStateException异常
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lock.lock();
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condition.signal();
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lock.unlock();
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}
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}
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// 输出
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Thread-0等待通知...
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// 睡眠2秒...
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Thread-0获得锁
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```
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### 6.3 读写锁
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由于锁的排它性，导致多个线程无法以安全的方式并发地读取共享变量，这不利于提高系统的并发能力，因此产生了读写锁：
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@ -599,8 +557,155 @@ public class ReadWriteLock {
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### 7.1 等待与通知
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为了支持多线程之间的协作，JDK 中提供了两个非常重要的方法：`wait()` 和 `notify()` ，这两个方法定义在 `Object` 类中，这意味着任何 Java 对象都可以调用者两个方法。如果一个线程调用了 `object.wait()` 方法，那么它就会进入该对象的等待队列中，这个队列中可能包含了多个线程，此时代表多个线程都在等待同一个对象；当 `object.notify()` 方法被调用时，它就会从这个等待队列中**随机**唤醒一个线程。
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需要特别注意的是在调用这两个方法时，它们都必须位于对应对象的 synchronzied 语句中，因为这两个对象在调用前都需要获得对应对象的监视器，过程如下：
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TODO
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使用示例如下：
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```java
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public class J3_WaitAndNotify {
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private static final Object object = new Object();
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public static void main(String[] args) {
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new Thread(() -> {
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synchronized (object) {
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try {
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System.out.println("对象object等待");
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object.wait();
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System.out.println("线程1后续操作");
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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}).start();
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new Thread(() -> {
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synchronized (object) {
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System.out.println("线程2开始操作");
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System.out.println("对象object唤醒");
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object.notify();
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}
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}).start();
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}
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}
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// 输出
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对象object等待
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线程2开始操作
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对象object唤醒
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线程1后续操作
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```
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`notify()` 表示随机唤醒任意一个等待线程，如果想要唤醒所有等待线程，则可以使用 `notifyAll()` 方法：
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```java
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public class J5_NotifyAll {
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private static final Object object = new Object();
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public static void main(String[] args) {
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new Thread(() -> {
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synchronized (object) {
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try {
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System.out.println("对象object在线程1等待");
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object.wait();
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System.out.println("线程1后续操作");
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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}).start();
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new Thread(() -> {
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synchronized (object) {
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try {
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System.out.println("对象object在线程2等待");
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object.wait();
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System.out.println("线程2后续操作");
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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}).start();
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new Thread(() -> {
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synchronized (object) {
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System.out.println("线程3开始操作");
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System.out.println("对象object唤醒");
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object.notifyAll();
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}
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}).start();
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}
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}
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// 输出
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对象object在线程1等待
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对象object在线程2等待
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线程3开始操作
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对象object唤醒
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线程2后续操作
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线程1后续操作
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```
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在上面的示例中，由于有两个线程处于等待状态，所以 `notifyAll()` 的效果等价于调用 `notify()` 两次：
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```java
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object.notify();
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object.notify();
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```
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### 7.2 条件变量
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综上所述可以使用 `wait()` 和 `notify()` 配合内部锁 synchronized 来实现线程间的等待与唤醒，如果你使用的是显示锁而不是内部锁，此时可以使用 Condition 来实现同样的等待唤醒效果。Condition 接口中定义了如下方法：
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+ await()：
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+ awaitUninterruptibly()：
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使用示例如下：
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```java
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public class AwaitAndSignal {
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private static ReentrantLock lock = new ReentrantLock();
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private static Condition condition = lock.newCondition();
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static class IncreaseTask implements Runnable {
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@Override
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public void run() {
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try {
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lock.lock();
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String threadName = Thread.currentThread().getName();
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System.out.println(threadName + "线程等待通知...");
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condition.await();
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System.out.println(threadName + "线程后续操作");
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} catch (InterruptedException e) {
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e.printStackTrace();
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} finally {
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lock.unlock();
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}
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}
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}
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public static void main(String[] args) throws InterruptedException {
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Thread thread1 = new Thread(new IncreaseTask());
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thread1.start();
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Thread.sleep(1000);
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System.out.println("主线程开始操作");
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lock.lock();
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System.out.println("主线程唤醒");
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condition.signal();
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lock.unlock();
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}
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}
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// 输出：
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Thread-0线程等待通知...
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主线程开始操作
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主线程唤醒
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Thread-0线程后续操作
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```
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### 7.3 CountDownLatch
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### 7.4 CyclicBarrier
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