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江苏工程建设信息网站,深圳中瑞建设集团官方网站,手机ps网页版在线制作,商城站人工售票时间表1.死锁是什么 死锁是这样一种情形#xff1a;多个线程同时被阻塞#xff0c;它们中的一个或者全部都在等待某个资源被释放。由于线程被无限期地阻塞#xff0c;因此程序不可能正常终止。 2.哲学家就餐问题 有五个哲学家#xff0c;他们的生活方式是交替地进行思考和进餐…1.死锁是什么 死锁是这样一种情形多个线程同时被阻塞它们中的一个或者全部都在等待某个资源被释放。由于线程被无限期地阻塞因此程序不可能正常终止。 2.哲学家就餐问题 有五个哲学家他们的生活方式是交替地进行思考和进餐。他们共用一张圆桌分别坐在五张椅子上。在圆桌上有五个碗和五支筷子平时一个哲学家进行思考饥饿时便试图取用其左、右最靠近他的筷子只有在他拿到两支筷子时才能进餐。进餐完毕放下筷子又继续思考。 为了进一步阐述死锁的形成, 很多资料上也会谈论到 哲学家就餐问题. 解决办法一哲学家要进餐时要么同时拿起两支筷子要么一支筷子都不拿 package thread4;import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;//解决办法一哲学家要进餐时要么同时拿起两支筷子要么一支筷子都不拿 class Philosopher {//哲学家编号public int id;public Philosopher(int id) {this.id id;}//思考public void thinking() throws InterruptedException {System.out.println(我是哲学家 this.id 号我正在思考);Thread.sleep(1000);}//吃饭public void eating() throws InterruptedException {System.out.println(我是哲学家 this.id 号我正在吃饭);Thread.sleep(1000);}//拿筷子public void takeUp(Chopsticks chopsticksLeft, Chopsticks chopsticksRight) throws InterruptedException {synchronized (Test3.locker) {if (chopsticksLeft.used || chopsticksRight.used) {Test3.locker.wait();}}chopsticksLeft.used true;chopsticksRight.used true;System.out.println(我是哲学家 this.id 号我拿到俩只筷子);}//放筷子public void putDown(Chopsticks chopsticksLeft, Chopsticks chopsticksRight) {synchronized (Test3.locker) {chopsticksLeft.used false;chopsticksRight.used false;System.out.println(我是哲学家 this.id 号我吃完了);Test3.locker.notify();}} }//筷子 class Chopsticks {//筷子编号public int id;//筷子状态public boolean used;public Chopsticks(int id, boolean used) {this.id id;this.used used;} }public class Test3 {public static Object locker new Object();public static void main(String[] args) {Philosopher philosopher1 new Philosopher(1);Philosopher philosopher2 new Philosopher(2);Philosopher philosopher3 new Philosopher(3);Philosopher philosopher4 new Philosopher(4);Philosopher philosopher5 new Philosopher(5);Chopsticks chopsticks1 new Chopsticks(1, false);Chopsticks chopsticks2 new Chopsticks(2, false);Chopsticks chopsticks3 new Chopsticks(3, false);Chopsticks chopsticks4 new Chopsticks(4, false);Chopsticks chopsticks5 new Chopsticks(5, false);ExecutorService pool Executors.newFixedThreadPool(5);pool.submit(new Runnable() {Overridepublic void run() {try {philosopher1.thinking();philosopher1.takeUp(chopsticks1, chopsticks2);philosopher1.eating();philosopher1.putDown(chopsticks1, chopsticks2);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher2.thinking();philosopher2.takeUp(chopsticks2, chopsticks3);philosopher2.eating();philosopher2.putDown(chopsticks2, chopsticks3);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher3.thinking();philosopher3.takeUp(chopsticks3, chopsticks4);philosopher3.eating();philosopher3.putDown(chopsticks3, chopsticks4);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher4.thinking();philosopher4.takeUp(chopsticks4, chopsticks5);philosopher4.eating();philosopher4.putDown(chopsticks4, chopsticks5);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher5.thinking();philosopher5.takeUp(chopsticks5, chopsticks1);philosopher5.eating();philosopher5.putDown(chopsticks5, chopsticks1);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.shutdown();} }解决办法二给筷子编号哲学家将要进餐时要先从小号左边的开始拿 package thread4;import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;class Philosopher {//哲学家编号public int id;public Philosopher(int id) {this.id id;}//思考public void thinking() throws InterruptedException {System.out.println(我是哲学家 this.id 号我正在思考);Thread.sleep(1000);}//吃饭public void eating() throws InterruptedException {System.out.println(我是哲学家 this.id 号我正在吃饭);Thread.sleep(1000);}//拿筷子public void takeUp(Chopsticks chopsticksMin, Chopsticks chopsticksMax) throws InterruptedException {synchronized (Test4.locker) {//先尝试拿小号筷子失败则进入等待状态并释放锁if (!chopsticksMin.used) {//false能拿true不能拿别人占用的了所以 是!chopsticksMin.usedchopsticksMin.used true;if (!chopsticksMax.used) {chopsticksMax.used true;} else {Test4.locker.wait();}} else {Test4.locker.wait();}}}//放筷子public void putDown(Chopsticks chopsticksMin, Chopsticks chopsticksMax) {synchronized (Test4.locker) {chopsticksMin.used false;chopsticksMax.used false;System.out.println(我是哲学家 this.id 号我吃完了);Test4.locker.notify();}} }//筷子 class Chopsticks {//筷子编号public int id;//筷子状态public boolean used;public Chopsticks(int id, boolean used) {this.id id;this.used used;} }public class Test4 {public static Object locker new Object();public static void main(String[] args) {Philosopher philosopher1 new Philosopher(1);Philosopher philosopher2 new Philosopher(2);Philosopher philosopher3 new Philosopher(3);Philosopher philosopher4 new Philosopher(4);Philosopher philosopher5 new Philosopher(5);Chopsticks chopsticks1 new Chopsticks(1, false);Chopsticks chopsticks2 new Chopsticks(2, false);Chopsticks chopsticks3 new Chopsticks(3, false);Chopsticks chopsticks4 new Chopsticks(4, false);Chopsticks chopsticks5 new Chopsticks(5, false);ExecutorService pool Executors.newFixedThreadPool(5);pool.submit(new Runnable() {Overridepublic void run() {try {philosopher1.thinking();philosopher1.takeUp(chopsticks1, chopsticks2);philosopher1.eating();philosopher1.putDown(chopsticks1, chopsticks2);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher2.thinking();philosopher2.takeUp(chopsticks2, chopsticks3);philosopher2.eating();philosopher2.putDown(chopsticks2, chopsticks3);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher3.thinking();philosopher3.takeUp(chopsticks3, chopsticks4);philosopher3.eating();philosopher3.putDown(chopsticks3, chopsticks4);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher4.thinking();philosopher4.takeUp(chopsticks4, chopsticks5);philosopher4.eating();philosopher4.putDown(chopsticks4, chopsticks5);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.submit(new Runnable() {Overridepublic void run() {try {philosopher5.thinking();philosopher5.takeUp(chopsticks5, chopsticks1);philosopher5.eating();philosopher5.putDown(chopsticks5, chopsticks1);} catch (InterruptedException e) {throw new RuntimeException(e);}}});pool.shutdown();} } 3.如何避免死锁 死锁产生的四个必要条件 互斥使用即当资源被一个线程使用(占有)时别的线程不能使用不可抢占资源请求者不能强制从资源占有者手中夺取资源资源只能由资源占有者主动释放。请求和保持即当资源请求者在请求其他的资源的同时保持对原有资源的占有。循环等待即存在一个等待队列P1占有P2的资源P2占有P3的资源P3占有P1的资源。这样就形成了一个等待环路 当上述四个条件都成立的时候便形成死锁。当然死锁的情况下如果打破上述任何一个条件便可让死锁消失。其中最容易破坏的就是 循环等待. 破坏循环等待 最常用的一种死锁阻止技术就是锁排序. 假设有 N 个线程尝试获取 M 把锁, 就可以针对 M 把锁进行编号(1, 2, 3…M).N 个线程尝试获取锁的时候, 都按照固定的按编号由小到大顺序来获取锁. 这样就可以避免环路等待. 属于理论上的破除死锁的方法.但是这样的方法,并不实用. 更实用的方法,就是尽量避免锁嵌套.(不要在一个加锁的代码中,再去加其他锁…) 可能产生环路等待的代码: package thread4;public class Test2 {public static void main(String[] args) {Object locker1 new Object();Object locker2 new Object();Thread thread1 new Thread() {Overridepublic void run() {synchronized (locker1) {synchronized (locker2) {}}}};thread1.start();Thread thread2 new Thread() {Overridepublic void run() {synchronized (locker2) {synchronized (locker1) {}}}};thread2.start();} }约定好先获取 lock1, 再获取 lock2 , 就不会环路等待锁排序 package thread4;public class Test2 {public static void main(String[] args) {Object locker1 new Object();Object locker2 new Object();Thread thread1 new Thread() {Overridepublic void run() {synchronized (locker1) {synchronized (locker2) {}}}};thread1.start();Thread thread2 new Thread() {Overridepublic void run() {synchronized (locker1) {synchronized (locker2) {}}}};thread2.start();} }