Java線程：并發(fā)協(xié)作-死鎖
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線程發(fā)生死鎖可能性很小，即使看似可能發(fā)生死鎖的代碼，在運(yùn)行時(shí)發(fā)生死鎖的可能性也是小之又小。
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發(fā)生死鎖的原因一般是兩個(gè)對(duì)象的鎖相互等待造成的。
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在《Java線程：線程的同步與鎖》一文中，簡(jiǎn)述死鎖的概念與簡(jiǎn)單例子，但是所給的例子是不完整的，這里給出一個(gè)完整的例子。
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/**
* Java線程：并發(fā)協(xié)作-死鎖
*
* @author Administrator 2009-11-4 22:06:13
*/
public class Test {
???????? public static void main(String[] args) {
????????????????DeadlockRisk dead = new DeadlockRisk();
????????????????MyThread t1 = new MyThread(dead, 1, 2);
????????????????MyThread t2 = new MyThread(dead, 3, 4);
????????????????MyThread t3 = new MyThread(dead, 5, 6);
????????????????MyThread t4 = new MyThread(dead, 7, 8);
????????????????t1.start();
????????????????t2.start();
????????????????t3.start();
????????????????t4.start();
????????}
}
class MyThread extends Thread {
???????? private DeadlockRisk dead;
???????? private int a, b;
????????MyThread(DeadlockRisk dead, int a, int b) {
???????????????? this .dead = dead;
???????????????? this .a = a;
???????????????? this .b = b;
????????}
????????@Override
???????? public void run() {
????????????????dead.read();
????????????????dead.write(a, b);
????????}
}
class DeadlockRisk {
???????? private static class Resource {
???????????????? public int value;
????????}
???????? private Resource resourceA = new Resource();
???????? private Resource resourceB = new Resource();
???????? public int read() {
???????????????? synchronized (resourceA) {
????????????????????????System.out.println( "read():" + Thread.currentThread().getName() + "獲取了resourceA的鎖！" );
???????????????????????? synchronized (resourceB) {
????????????????????????????????System.out.println( "read():" + Thread.currentThread().getName() + "獲取了resourceB的鎖！" );
???????????????????????????????? return resourceB.value + resourceA.value;
????????????????????????}
????????????????}
????????}
???????? public void write( int a, int b) {
???????????????? synchronized (resourceB) {
????????????????????????System.out.println( "write():" + Thread.currentThread().getName() + "獲取了resourceA的鎖！" );
???????????????????????? synchronized (resourceA) {
????????????????????????????????System.out.println( "write():" + Thread.currentThread().getName() + "獲取了resourceB的鎖！" );
????????????????????????????????resourceA.value = a;
????????????????????????????????resourceB.value = b;
????????????????????????}
????????????????}
????????}
}
* Java線程：并發(fā)協(xié)作-死鎖
*
* @author Administrator 2009-11-4 22:06:13
*/
public class Test {
???????? public static void main(String[] args) {
????????????????DeadlockRisk dead = new DeadlockRisk();
????????????????MyThread t1 = new MyThread(dead, 1, 2);
????????????????MyThread t2 = new MyThread(dead, 3, 4);
????????????????MyThread t3 = new MyThread(dead, 5, 6);
????????????????MyThread t4 = new MyThread(dead, 7, 8);
????????????????t1.start();
????????????????t2.start();
????????????????t3.start();
????????????????t4.start();
????????}
}
class MyThread extends Thread {
???????? private DeadlockRisk dead;
???????? private int a, b;
????????MyThread(DeadlockRisk dead, int a, int b) {
???????????????? this .dead = dead;
???????????????? this .a = a;
???????????????? this .b = b;
????????}
????????@Override
???????? public void run() {
????????????????dead.read();
????????????????dead.write(a, b);
????????}
}
class DeadlockRisk {
???????? private static class Resource {
???????????????? public int value;
????????}
???????? private Resource resourceA = new Resource();
???????? private Resource resourceB = new Resource();
???????? public int read() {
???????????????? synchronized (resourceA) {
????????????????????????System.out.println( "read():" + Thread.currentThread().getName() + "獲取了resourceA的鎖！" );
???????????????????????? synchronized (resourceB) {
????????????????????????????????System.out.println( "read():" + Thread.currentThread().getName() + "獲取了resourceB的鎖！" );
???????????????????????????????? return resourceB.value + resourceA.value;
????????????????????????}
????????????????}
????????}
???????? public void write( int a, int b) {
???????????????? synchronized (resourceB) {
????????????????????????System.out.println( "write():" + Thread.currentThread().getName() + "獲取了resourceA的鎖！" );
???????????????????????? synchronized (resourceA) {
????????????????????????????????System.out.println( "write():" + Thread.currentThread().getName() + "獲取了resourceB的鎖！" );
????????????????????????????????resourceA.value = a;
????????????????????????????????resourceB.value = b;
????????????????????????}
????????????????}
????????}
}
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下面死鎖的情況發(fā)生了，真是難得一見啊：
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本文出自 “ 熔 巖 ” 博客，請(qǐng)務(wù)必保留此出處 http://lavasoft.blog.51cto.com/62575/222074
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