如何避免 Java 中的死锁?
javaobject oriented programmingprogramming更新于 2024/5/10 1:14:00
在 Java 中，死锁是一种编程情况，其中两个或多个线程被永久阻塞。至少有两个线程和两个或多个资源时会发生死锁情况。
如何避免死锁
- 避免嵌套锁:死锁主要发生在我们为多个线程提供锁时。如果我们已经为一个线程提供锁，请避免为多个线程提供锁。
- 避免不必要的锁:我们只能锁定那些需要的成员。不必要地锁定可能会导致死锁。
- 使用 Thread.join():当一个线程等待另一个线程完成时，就会出现死锁情况。如果出现这种情况，我们可以使用 Thread.join() 并指定执行所需的最大时间。
示例
public class DeadlockTest {
public static void main(String[] args) throws InterruptedException {
Object obj1 = new Object();
Object obj2 = new Object();
Object obj3 = new Object();
Thread t1 = new Thread(new SyncThread(obj1, obj2), "t1");
Thread t2 = new Thread(new SyncThread(obj2, obj3), "t2");
t1.start();
Thread.sleep(2000);
t2.start();
Thread.sleep(2000);
}
}
class SyncThread implements Runnable {
private Object obj1;
private Object obj2;
public SyncThread(Object o1, Object o2){
this.obj1=o1;
this.obj2=o2;
}
@Override
public void run() {
String name = Thread.currentThread().getName();
System.out.println(name + " acquiring lock on " + obj1);
synchronized (obj1) {
System.out.println(name + " acquired lock on " + obj1);
work();
}
System.out.println(name + " released lock on " + obj1);
System.out.println(name + " acquiring lock on " + obj2);
synchronized (obj2) {
System.out.println(name + " acquired lock on " + obj2);
work();
}
System.out.println(name + " released lock on " + obj2);
System.out.println(name + " finished execution.");
}
private void work() {
try {
Thread.sleep(5000);
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
}
输出
t1 acquiring lock on java.lang.Object@917d8d4 t1 acquired lock on java.lang.Object@917d8d4 t2 acquiring lock on java.lang.Object@5c4b42fb t2 acquired lock on java.lang.Object@5c4b42fb t1 released lock on java.lang.Object@917d8d4 t1 acquiring lock on java.lang.Object@5c4b42fb t1 acquired lock on java.lang.Object@5c4b42fb t2 released lock on java.lang.Object@5c4b42fb t2 acquiring lock on java.lang.Object@528cb702 t2 acquired lock on java.lang.Object@528cb702 t1 released lock on java.lang.Object@5c4b42fb t2 released lock on java.lang.Object@528cb702 t1 finished execution. t2 finished execution.
