参考: http://ifeve.com/java-synchronousqueue/
1、信号量
参考: http://blog.163.com/xiaopengyan_109/blog/static/1498321732010666331610/
信号量的值表示资源的可用数量.在使用资源时,要先从该信号量上获取一个使用许可.成功获取许可之后,资源可用数量减1.在持有许可期,使用者可以对获取资源进行操作.完成对资源的使用之后,需要在信号量上释放一个许可,资源可用数加1,允许其他使用者获取资源.当资源可用数为0的时候,需要获取资源的线程以阻塞的方式来等待资源变为可用,或者过段时间之后再检查资源是否变为可用.
说白了,Semaphore是一个计数器,在计数器不为0的时候对线程就放行,一旦达到0,那么所有请求资源的新线程都会被阻塞,包括增加请求到许可的线程,也就是说Semaphore不是可重入的。每一次请求一个许可都会导致计数器减少1,同样每次释放一个许可都会导致计数器增加1,一旦达到了0,新的许可请求线程将被挂起。
import java.util.concurrent.Semaphore; public class TestSemaphore2 { public static void main(String[] args) { final Kfc kfc = new Kfc(); new Thread(){ public void run() { while(true){ kfc.eat(); } } }.start(); new Thread(){ public void run() { while(true){ kfc.cook(); } } }.start(); } } class Kfc{ private Semaphore s1 = new Semaphore(0); private Semaphore s2 = new Semaphore(1); private Semaphore s3 = new Semaphore(0); private int i = 0; public void eat(){ try { s1.acquire(); System.out.println("eat: " + --i); Thread.sleep(1000); s2.release(); s3.release(); } catch (InterruptedException e) { e.printStackTrace(); } } public void cook(){ try { s2.acquire(); System.out.println("cook: " + ++i); Thread.sleep(1000); s1.release(); s3.acquire(); } catch (InterruptedException e) { e.printStackTrace(); } } }
这个例子说的而是任务A执行 执行任务B 一次循环
参考: http://blog.csdn.net/java2000_net/article/details/3997449
import java.util.concurrent.Semaphore; public class TestSemaphore2 { public static void main(String[] args) { final Kfc kfc = new Kfc(); for(int i=0;i<10;i++){ new Thread("eat" + i){ public void run() { while(true){ kfc.eat(); } } }.start(); } for(int i=0;i<10;i++){ new Thread("cook" + i){ public void run() { while(true){ kfc.cook(); } } }.start(); } } } class Kfc{ private Semaphore s1 = new Semaphore(1);//核心锁 只有一个线程执行具体的任务 private Semaphore s2 = new Semaphore(10);//非满锁 令牌没了 就说明满了 private Semaphore s3 = new Semaphore(0);//非空锁 不为0 就说明不为空 private int i = 0; public void eat(){ try { s3.acquire();//是否为空 s1.acquire();//核心锁 System.out.println(Thread.currentThread().getName() + ": " + --i); Thread.sleep(1000); s1.release();//退出核心锁 s2.release();//肯定不满了 } catch (InterruptedException e) { e.printStackTrace(); } } public void cook(){ try { s2.acquire();//是否满了 s1.acquire();//核心锁 一直到“退出核心锁”只允许一个线程执行下面的代码 System.out.println(Thread.currentThread().getName() + ": " + ++i); Thread.sleep(1000); s1.release();//退出核心锁 s3.release();//肯定不空 } catch (InterruptedException e) { e.printStackTrace(); } } }
这个是消费者生产者模式
2、ReentrantLock
参考: http://blog.csdn.net/vernonzheng/article/details/8288251
import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; public class TestLock { public static void main(String[] args) { final Kfc2 kfc = new Kfc2(); for(int i=0;i<10;i++){ new Thread("eat" + i){ public void run() { while(true){ kfc.eat(); } } }.start(); } for(int i=0;i<10;i++){ new Thread("cook" + i){ public void run() { while(true){ kfc.cook(); } } }.start(); } } } class Kfc2{ private final Lock lock = new ReentrantLock(); private Condition notFull = lock.newCondition(); private Condition notEmpty = lock.newCondition(); private int i = 0; public void eat(){ try { Thread.sleep(1000); lock.lock(); while(i<=0){ notEmpty.await();//空了 } System.out.println(Thread.currentThread().getName() + ": " + --i); Thread.sleep(1000); notFull.signalAll();//已经不满了 } catch (InterruptedException e) { e.printStackTrace(); }finally{ lock.unlock(); } } public void cook(){ try { Thread.sleep(1000); lock.lock(); while(i>=10){ notFull.await();//满了 } System.out.println(Thread.currentThread().getName() + ": " + ++i); Thread.sleep(1000); notEmpty.signalAll();//已经不空了 } catch (InterruptedException e) { e.printStackTrace(); }finally{ lock.unlock(); } } }