Condition 显式条件

显式条件在不同上下文中也可以被称为条件变量、条件队列、或条件

锁用于解决竞态条件问题，条件是线程间的协作机制。显式锁与synchronized相对应，而显式条件与wait/notify相对应。wait/notify与synchronized配合使用，显式条件与显式锁配合使用。条件与锁相关联，创建条件变量需要通过显式锁，Lock接口定义了创建方法：

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1	Condition newCondition();

Condition表示条件变量，是一个接口，它的定义为：

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public interface Condition {   void await() throws InterruptedException;   void awaitUninterruptibly();   long awaitNanos(long nanosTimeout) throws InterruptedException;   boolean await(long time, TimeUnit unit) throws InterruptedException;   boolean awaitUntil(Date deadline) throws InterruptedException;   void signal();   void signalAll(); }

await对应于Object的wait, signal对应于notify, signalAll对应于notifyAll，语义也是一样的。

使用显式条件进行协作的示例:

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public class WaitThread extends Thread {     private volatile boolean fire = false;     private Lock lock = new ReentrantLock();     private Condition condition = lock.newCondition();     @Override     public void run() {         try {             lock.lock();             try {                 while (!fire) {                     condition.await();                 }             } finally {                 lock.unlock();             }             System.out.println("fired");         } catch (InterruptedException e) {             Thread.interrupted();         }     }     public void fire() {         lock.lock();         try {             this.fire = true;             condition.signal();         } finally {             lock.unlock();         }     }     public static void main(String[] args) throws InterruptedException {         WaitThread waitThread = new WaitThread();         waitThread.start();         Thread.sleep(1000);         System.out.println("fire");         waitThread.fire();     } }

　　

参考: Java编程的逻辑 16.3 显式条件