7月8日
以下文章來(lái)源于編程新說(shuō)?，作者編程新說(shuō)李新杰
多線程的問(wèn)題都曾經(jīng)困擾過(guò)每個(gè)開發(fā)人員，今天將從全新視角來(lái)解說(shuō)，希望讀者都能明白。
強(qiáng)烈建議去運(yùn)行下文章中的示例代碼，自己體會(huì)下。
問(wèn)題究竟出在哪里？ 事情起因 ：線程可以獨(dú)立自主的運(yùn)行，可以認(rèn)為它具有主觀能動(dòng)性。造成結(jié)果 ：對(duì)它的掌控能力變?nèi)趿?#xff0c;而且又不能直接把它“干掉”。解決方案 ：凡事商量著來(lái)，互相配合著把事情完成。作者觀點(diǎn) ：其實(shí)就是把線程當(dāng)作人來(lái)對(duì)待。
小試牛刀一下 停止
static void stopByFlag() {ARunnable ar = new ARunnable();new Thread(ar).start();ar.tellToStop();}static class ARunnable implements Runnable {volatile boolean stop;void tellToStop() {stop = true;}@Overridepublic void run() {println("進(jìn)入不可停止區(qū)域 1。。。");doingLongTime(5);println("退出不可停止區(qū)域 1。。。");println("檢測(cè)標(biāo)志stop = %s", String.valueOf(stop));if (stop) {println("停止執(zhí)行");return;}println("進(jìn)入不可停止區(qū)域 2。。。");doingLongTime(5);println("退出不可停止區(qū)域 2。。。");}}
解說(shuō)：線程在預(yù)設(shè)的地點(diǎn)檢測(cè)flag，來(lái)決定是否停止。
場(chǎng)景二，暫停/恢復(fù)
static void pauseByFlag() {BRunnable br = new BRunnable();new Thread(br).start();br.tellToPause();sleep(8);br.tellToResume();}static class BRunnable implements Runnable {volatile boolean pause;void tellToPause() {pause = true;}void tellToResume() {synchronized (this) {this.notify();}}@Overridepublic void run() {println("進(jìn)入不可暫停區(qū)域 1。。。");doingLongTime(5);println("退出不可暫停區(qū)域 1。。。");println("檢測(cè)標(biāo)志pause = %s", String.valueOf(pause));if (pause) {println("暫停執(zhí)行");try {synchronized (this) {this.wait();}} catch (InterruptedException e) {e.printStackTrace();}println("恢復(fù)執(zhí)行");}println("進(jìn)入不可暫停區(qū)域 2。。。");doingLongTime(5);println("退出不可暫停區(qū)域 2。。。");}}
解說(shuō)：還是在預(yù)設(shè)的地點(diǎn)檢測(cè)flag。然后就是wait/notify配合使用。
場(chǎng)景三，插隊(duì)
static void jqByJoin() {CRunnable cr = new CRunnable();Thread t = new Thread(cr);t.start();sleep(1);try {t.join();} catch (InterruptedException e) {e.printStackTrace();}println("終于輪到我了");}static class CRunnable implements Runnable {@Overridepublic void run() {println("進(jìn)入不可暫停區(qū)域 1。。。");doingLongTime(5);println("退出不可暫停區(qū)域 1。。。");}}
解說(shuō)：join方法可以讓某個(gè)線程插到自己前面，等它執(zhí)行完，自己才會(huì)繼續(xù)執(zhí)行。
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場(chǎng)景四，叫醒
static void stopByInterrupt() {DRunnable dr = new DRunnable();Thread t = new Thread(dr);t.start();sleep(2);t.interrupt();}static class DRunnable implements Runnable {@Overridepublic void run() {println("進(jìn)入暫停。。。");try {sleep2(5);} catch (InterruptedException e) {println("收到中斷異常。。。");println("做一些相關(guān)處理。。。");}println("繼續(xù)執(zhí)行或選擇退出。。。");}}
解說(shuō)：線程在sleep或wait時(shí)，是處于無(wú)法交互的狀態(tài)的，此時(shí)只能使用interrupt方法中斷它，線程會(huì)被激活并收到中斷異常。
常見(jiàn)的協(xié)作配合 考試
static final int COUNT = 20;public static void main(String[] args) throws Exception {new Thread(new Teacher(cdl)).start();sleep(1);for (int i = 0; i < COUNT; i++) {new Thread(new Student(i, cdl)).start();}synchronized (ThreadCo1.class) {ThreadCo1.class.wait();}}static CountDownLatch cdl = new CountDownLatch(COUNT);static class Teacher implements Runnable {CountDownLatch cdl;Teacher(CountDownLatch cdl) {this.cdl = cdl;}@Overridepublic void run() {println("老師發(fā)卷子。。。");try {cdl.await();} catch (InterruptedException e) {e.printStackTrace();}println("老師收卷子。。。");}}static class Student implements Runnable {CountDownLatch cdl;int num;Student(int num, CountDownLatch cdl) {this.num = num;this.cdl = cdl;}@Overridepublic void run() {println("學(xué)生(%d)寫卷子。。。", num);doingLongTime();println("學(xué)生(%d)交卷子。。。", num);cdl.countDown();}}
解說(shuō)：每完成一個(gè)線程，計(jì)數(shù)器減1，當(dāng)減到0時(shí)，被阻塞的線程自動(dòng)執(zhí)行。
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事件二，旅游
static final int COUNT = 5;public static void main(String[] args) throws Exception {for (int i = 0; i < COUNT; i++) {new Thread(new Staff(i, cb)).start();}synchronized (ThreadCo2.class) {ThreadCo2.class.wait();}}static CyclicBarrier cb = new CyclicBarrier(COUNT, new Singer());static class Singer implements Runnable {@Overridepublic void run() {println("為大家唱歌。。。");}}static class Staff implements Runnable {CyclicBarrier cb;int num;Staff(int num, CyclicBarrier cb) {this.num = num;this.cb = cb;}@Overridepublic void run() {println("員工(%d)出發(fā)。。。", num);doingLongTime();println("員工(%d)到達(dá)地點(diǎn)一。。。", num);try {cb.await();} catch (Exception e) {e.printStackTrace();}println("員工(%d)再出發(fā)。。。", num);doingLongTime();println("員工(%d)到達(dá)地點(diǎn)二。。。", num);try {cb.await();} catch (Exception e) {e.printStackTrace();}println("員工(%d)再出發(fā)。。。", num);doingLongTime();println("員工(%d)到達(dá)地點(diǎn)三。。。", num);try {cb.await();} catch (Exception e) {e.printStackTrace();}println("員工(%d)結(jié)束。。。", num);}}
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解說(shuō)：某個(gè)線程到達(dá)預(yù)設(shè)點(diǎn)時(shí)就在此等待，等所有的線程都到達(dá)時(shí)，大家再一起向下個(gè)預(yù)設(shè)點(diǎn)出發(fā)。如此循環(huán)反復(fù)下去。
事件三，勞動(dòng)
public static void main(String[] args) throws Exception {new Thread(new Staff("大胖", new Tool("笤帚", "掃地"), ex)).start();new Thread(new Staff("小白", new Tool("抹布", "擦桌"), ex)).start();synchronized (ThreadCo3.class) {ThreadCo3.class.wait();}}static Exchanger<Tool> ex = new Exchanger<>();static class Staff implements Runnable {String name;Tool tool;Exchanger<Tool> ex;Staff(String name, Tool tool, Exchanger<Tool> ex) {this.name = name;this.tool = tool;this.ex = ex;}@Overridepublic void run() {println("%s拿的工具是[%s]，他開始[%s]。。。", name, tool.name, tool.work);doingLongTime();println("%s開始交換工具。。。", name);try {tool = ex.exchange(tool);} catch (Exception e) {e.printStackTrace();}println("%s的工具變?yōu)閇%s]，他開始[%s]。。。", name, tool.name, tool.work);}}static class Tool {String name;String work;Tool(String name, String work) {this.name = name;this.work = work;}}
解說(shuō)：兩個(gè)線程在預(yù)設(shè)點(diǎn)交換變量，先到達(dá)的等待對(duì)方。
事件四，魔性游戲
static final int COUNT = 6;public static void main(String[] args) throws Exception {new Thread(new Challenger("張三")).start();new Thread(new Challenger("李四")).start();new Thread(new Challenger("王五")).start();new Thread(new Challenger("趙六")).start();new Thread(new Challenger("大胖")).start();new Thread(new Challenger("小白")).start();synchronized (ThreadCo4.class) {ThreadCo4.class.wait();}}static Phaser ph = new Phaser() {protected boolean onAdvance(int phase, int registeredParties) {println2("第(%d)局，剩余[%d]人", phase, registeredParties);return registeredParties == 0 ||(phase != 0 && registeredParties == COUNT);};};static class Challenger implements Runnable {String name;int state;Challenger(String name) {this.name = name;this.state = 0;}@Overridepublic void run() {println("[%s]開始挑戰(zhàn)。。。", name);ph.register();int phase = 0;int h;while (!ph.isTerminated() && phase < 100) {doingLongTime(5);if (state == 0) {if (Decide.goon()) {h = ph.arriveAndAwaitAdvance();if (h < 0)println("No%d.[%s]繼續(xù)，但已勝利。。。", phase, name);elseprintln("No%d.[%s]繼續(xù)at(%d)。。。", phase, name, h);} else {state = -1;h = ph.arriveAndDeregister();println("No%d.[%s]退出at(%d)。。。", phase, name, h);}} else {if (Decide.revive()) {state = 0;h = ph.register();if (h < 0)println("No%d.[%s]復(fù)活，但已失敗。。。", phase, name);elseprintln("No%d.[%s]復(fù)活at(%d)。。。", phase, name, h);} else {println("No%d.[%s]沒(méi)有復(fù)活。。。", phase, name);}}phase++;}if (state == 0) {ph.arriveAndDeregister();}println("[%s]結(jié)束。。。", name);}}static class Decide {static boolean goon() {return random(9) > 4;}static boolean revive() {return random(9) < 5;}}
生產(chǎn)與銷售的問(wèn)題 經(jīng)典的生產(chǎn)者和消費(fèi)者
public static void main(String[] args) {Queue queue = new Queue();new Thread(new Producer(queue)).start();new Thread(new Producer(queue)).start();new Thread(new Consumer(queue)).start();}static class Producer implements Runnable {Queue queue;Producer(Queue queue) {this.queue = queue;}@Overridepublic void run() {try {for (int i = 0; i < 10000; i++) {doingLongTime();queue.putEle(random(10000));}} catch (Exception e) {e.printStackTrace();}}}static class Consumer implements Runnable {Queue queue;Consumer(Queue queue) {this.queue = queue;}@Overridepublic void run() {try {for (int i = 0; i < 10000; i++) {doingLongTime();queue.takeEle();}} catch (Exception e) {e.printStackTrace();}}}static class Queue {Lock lock = new ReentrantLock();Condition prodCond = lock.newCondition();Condition consCond = lock.newCondition();final int CAPACITY = 10;Object[] container = new Object[CAPACITY];int count = 0;int putIndex = 0;int takeIndex = 0;public void putEle(Object ele) throws InterruptedException {try {lock.lock();while (count == CAPACITY) {println("隊(duì)列已滿：%d，生產(chǎn)者開始睡大覺(jué)。。。", count);prodCond.await();}container[putIndex] = ele;println("生產(chǎn)元素：%d", ele);putIndex++;if (putIndex >= CAPACITY) {putIndex = 0;}count++;println("通知消費(fèi)者去消費(fèi)。。。");consCond.signalAll();} finally {lock.unlock();}}
public Object takeEle() throws InterruptedException { try {lock.lock();while (count == 0) {println("隊(duì)列已空：%d，消費(fèi)者開始睡大覺(jué)。。。", count);consCond.await();}Object ele = container[takeIndex];println("消費(fèi)元素：%d", ele);takeIndex++;if (takeIndex >= CAPACITY) {takeIndex = 0;}count--;println("通知生產(chǎn)者去生產(chǎn)。。。");prodCond.signalAll();return ele;} finally {lock.unlock();}}}
解說(shuō)：其實(shí)就是對(duì)await/signalAll的應(yīng)用，幾乎面試必問(wèn)。
閱讀目錄（置頂)(長(zhǎng)期更新計(jì)算機(jī)領(lǐng)域知識(shí)）https://blog.csdn.net/weixin_43392489/article/details/102380691
閱讀目錄（置頂)(長(zhǎng)期更新計(jì)算機(jī)領(lǐng)域知識(shí)）https://blog.csdn.net/weixin_43392489/article/details/102380882
閱讀目錄（置頂)(長(zhǎng)期科技領(lǐng)域知識(shí)）https://blog.csdn.net/weixin_43392489/article/details/102600114
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