Java多线程:线程死锁
2017-02-28 17:02
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发生死锁的原因一般是两个对象的锁相互等待造成的。
下面用一个实例来构造这种情况:
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package basic.e_deadlock;
import org.apache.log4j.Logger;
public class TestDeadLock {
public static void main(String[] args) {
DeadlockRisk dead = new DeadlockRisk();
MyThread t1 = new MyThread(dead, 1, 2, "线程1");
MyThread t2 = new MyThread(dead, 3, 4, "线程2");
MyThread t3 = new MyThread(dead, 5, 6, "线程3");
MyThread t4 = new MyThread(dead, 7, 8, "线程4");
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, String threadName) {
this.dead = dead;
this.a = a;
this.b = b;
this.setName(threadName);
}
@Override
public void run() {
dead.read();
dead.write(a, b);
}
}
class DeadlockRisk {
private static Logger logger = Logger.getLogger(DeadlockRisk.class);
private static class Resource {
public int value;
}
private Resource resourceA = new Resource();
private Resource resourceB = new Resource();
public void read() {
logger.debug("===========read begin===========");
synchronized (resourceA) {
logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceA 的锁!");
synchronized (resourceB) {
logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceB 的锁!");
}
}
logger.debug("===========read end=============");
}
public void write(int a, int b) {
logger.debug("===========write begin===========");
synchronized (resourceB) {
logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceB 的锁!");
synchronized (resourceA) {
logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceA 的锁!");
resourceA.value = a;
resourceB.value = b;
}
}
logger.debug("===========write end=============");
}
}
执行结果:
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0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程3] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceA 的锁!
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceB 的锁!
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end=============
0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceA 的锁!
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being===========
1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceB 的锁!
1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end=============
1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being===========
1 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - write():线程1获取了resourceB 的锁!
1 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - read():线程4获取了resourceA 的锁!
注意:此时线程1在等待resourceB的资源,线程2在等待resourceA的资源。两个线程在相互等待,出现死锁。
下面用一个实例来构造这种情况:
[java] view
plain copy
print?
package basic.e_deadlock;
import org.apache.log4j.Logger;
public class TestDeadLock {
public static void main(String[] args) {
DeadlockRisk dead = new DeadlockRisk();
MyThread t1 = new MyThread(dead, 1, 2, "线程1");
MyThread t2 = new MyThread(dead, 3, 4, "线程2");
MyThread t3 = new MyThread(dead, 5, 6, "线程3");
MyThread t4 = new MyThread(dead, 7, 8, "线程4");
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, String threadName) {
this.dead = dead;
this.a = a;
this.b = b;
this.setName(threadName);
}
@Override
public void run() {
dead.read();
dead.write(a, b);
}
}
class DeadlockRisk {
private static Logger logger = Logger.getLogger(DeadlockRisk.class);
private static class Resource {
public int value;
}
private Resource resourceA = new Resource();
private Resource resourceB = new Resource();
public void read() {
logger.debug("===========read begin===========");
synchronized (resourceA) {
logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceA 的锁!");
synchronized (resourceB) {
logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceB 的锁!");
}
}
logger.debug("===========read end=============");
}
public void write(int a, int b) {
logger.debug("===========write begin===========");
synchronized (resourceB) {
logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceB 的锁!");
synchronized (resourceA) {
logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceA 的锁!");
resourceA.value = a;
resourceB.value = b;
}
}
logger.debug("===========write end=============");
}
}
执行结果:
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plain copy
print?
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程3] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin===========
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceA 的锁!
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceB 的锁!
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end=============
0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceA 的锁!
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being===========
1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceB 的锁!
1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end=============
1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being===========
1 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - write():线程1获取了resourceB 的锁!
1 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - read():线程4获取了resourceA 的锁!
注意:此时线程1在等待resourceB的资源,线程2在等待resourceA的资源。两个线程在相互等待,出现死锁。
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