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互斥鎖和信號(hào)量都是操作系統(tǒng)中為并發(fā)編程設(shè)計(jì)基本概念,互斥鎖和信號(hào)量的概念上的不同在于,對(duì)于同一個(gè)資源,互斥鎖只有0和1 的概念,而信號(hào)量不止于此。也就是說,信號(hào)量可以使資源同時(shí)被多個(gè)線程訪問,而互斥鎖同時(shí)只能被一個(gè)線程訪問
互斥鎖在java中的實(shí)現(xiàn)就是 ReetranLock , 在訪問一個(gè)同步資源時(shí),它的對(duì)象需要通過方法 tryLock() 獲得這個(gè)鎖,如果失敗,返回 false,成功返回true。根據(jù)返回的信息來判斷是否要訪問這個(gè)被同步的資源??聪旅娴睦?/p>
public class ReentranLockExample { private static int count = 0; private static ReentrantLock reentrantLock = new ReentrantLock(); static class MyThread extends Thread{ @Override public void run() { super.run(); try { while (true){ boolean result = reentrantLock.tryLock(); if (result){ System.out.println(Thread.currentThread().getName() + "get the lock success and run the syn code " + count ++); reentrantLock.unlock(); }else{ System.out.println(Thread.currentThread().getName() + "get the lock failed and run the syn code " + count); } System.out.println(Thread.currentThread().getName() + "run the asyntronized code " + count); Thread.sleep(500); } } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args){ MyThread thread1 = new MyThread(); MyThread thread2 = new MyThread(); thread1.start(); thread2.start(); } }
信號(hào)量相當(dāng)于一個(gè)計(jì)數(shù)器,如果線程想要訪問某個(gè)資源,則先要獲得這個(gè)資源的信號(hào)量,并且信號(hào)量內(nèi)部的計(jì)數(shù)器減1 ,信號(hào)量內(nèi)部的計(jì)數(shù)器大于0則意味著有可以使用的資源,當(dāng)線程使用完某個(gè)資源時(shí),必須釋放這個(gè)資源的信號(hào)量。信號(hào)量的一個(gè)作用就是可以實(shí)現(xiàn)指定個(gè)線程去同事訪問某個(gè)資源。只需要在初始化 。
信號(hào)量在 Java中的實(shí)現(xiàn)是 Semaphore ,其在初始化時(shí)傳入一個(gè)整型數(shù), 用來指定同步資源最大的并發(fā)訪問量
public class SemaphoreExample { private static Semaphore semaphore = new Semaphore(2); private String lock = "lock"; private static int count = 0; static class MyThread extends Thread { @Override public void run() { super.run(); try { while (true) { semaphore.acquire(); Thread.sleep(500); System.out.println(Thread.currentThread().getName() + "get the lock success and run the syn code " + count++); semaphore.release(); Thread.sleep(500); } } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args){ MyThread thread1 = new MyThread(); MyThread thread2 = new MyThread(); MyThread thread3 = new MyThread(); thread1.start(); thread2.start(); thread3.start(); } }
CountDownLatch 實(shí)現(xiàn)一個(gè)等待機(jī)制,在諸如 等待與會(huì)者到達(dá)后,開始會(huì)議的使用中。ConutDownLatch 在初始化中一個(gè)計(jì)數(shù)器,用來指定需要等待的個(gè)數(shù)。在并發(fā)編程中,所解決的需求就是,等待所有的線程到達(dá)某個(gè)點(diǎn)后。才開始進(jìn)行下一步,有點(diǎn)類似于開會(huì),只有當(dāng)所有的與會(huì)人員都到齊后,會(huì)議才能開始
public class CountDownLatchExample { private static CountDownLatch mCountDownLatch = new CountDownLatch(3); static class MyThread extends Thread { int awaitTime; public MyThread(int i) { this.awaitTime = i; } @Override public void run() { super.run(); try { while (true) { Thread.sleep(awaitTime); System.out.println(Thread.currentThread().getName() + "arrived " ); mCountDownLatch.countDown(); mCountDownLatch.await(); //可以指定等待時(shí)間 System.out.println(Thread.currentThread().getName() + "start meeting " ); } } catch (InterruptedException e) { e.printStackTrace(); } } } public static void main(String[] args){ MyThread thread1 = new MyThread(500); MyThread thread2 = new MyThread(1000); MyThread thread3 = new MyThread(2000); thread1.start(); thread2.start(); thread3.start(); } }
總結(jié)
以上就是本文有關(guān)Java編程中的互斥鎖,信號(hào)量和多線程等待機(jī)制實(shí)例詳解的全部內(nèi)容,希望對(duì)大家有所幫助。
有興趣的朋友可以了解:Java多線程賣票實(shí)例、Java多線程并發(fā)編程(互斥鎖Reentrant Lock)等。
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