英文:
Java Multi-threading Deadlock or Starvation?
问题
我正在为我的OCP考试学习，试图理解何时会出现线程死锁，或者线程是否处于饥饿状态。在下面的场景中，我有疑问。
public class ThreadTest {
private static int i = 0;
public static void doSomething() {
synchronized(ThreadTest.class) {
while(true) {
System.out.println("count:" + ++i);
}
}
}
public static void main(String args[]) {
new Thread(() -> doSomething()).start();
new Thread(() -> doSomething()).start();
}
}
第一个线程在doSomething()中获取了synchronized ThreadTest类的锁，并进入无限循环，永远不会释放锁。
第二个线程会一直等待，直到资源变为可用（但这永远不会发生）。
在这种情况下，我们在谈论死锁还是饥饿？我认为这是饥饿，因为一个线程无法访问共享资源，而死锁是指线程相互阻塞，无法继续执行。
死锁描述了线程永远被阻塞的情况。
饥饿描述了线程无法定期访问共享资源的情况。
英文:
I am learning for my OCP exam and are trying to understand when we are speaking of a thread deadlock or a thread is in starvation. in case of the scenario below I have doubt.
public class ThreadTest {
private static int i = 0;
public static void doSomething() {
synchronized(ThreadTest.class) {
while(true) {
System.out.println("count:" + ++i)
} }
}
public static void main(String args[]) {
New Thread(() -> doSomething()).start();
New Thread(() -> doSomething()).start();
}}
The first thread to acquires the lock of the synchronized ThreadTest class in doSomething() goes in a infinite loop never releasing the lock.
The second thread keep waiting til the resource becomes available (what never happens).
Are we speaking of a Deadlock in this situation or Starvation? I think about Starvation because one thread is not getting access to a shared resource and for a deadlock threads block each others resources. But just to be sure i ask about it here.
Deadlock describes a situation where threads are blocked forever.
Starvation describes a situation where a thread is unable to gain regular access to shared resources.
答案1
得分: 0
正如评论中指出的那样。死锁发生在以下4个条件同时满足时。它们是：
- 互斥 - B想要A拥有的资源。B不能使用A正在使用的资源（即此处的情况）。
- 持有和等待 - A持有B想要的资源。A还在等待其他人拥有的资源被释放（根据问题陈述，A并未出现这种情况）。
- 不可抢占 - A持有的资源不能被强行夺走（假设在这里成立，因为未有其他说明）。
- 循环等待 - A持有B想要的资源。B持有A想要的资源（在这里没有发生）。
因此我们可以看到，不满足所有条件。因此在这种情况下不能发生死锁。
然而，由于一个无限循环，A永远不会释放锁。因此B将被饿死。
这应该能解决你的疑惑。干杯。
英文:
As pointed out in comment. Deadlock happens when the below 4 conditions happens. Them being :
- Mutual Exclusion - B wants a resource A has. B cannot use the
resource A is using(which is happening here). - Hold and wait - A is holding a resource that B wants. A is also waiting for a resource to be freed that somebody else has(Not happening for A from the probem statement given)
- No Preemption - The resource A is holding cannot be snatched away from it by force(assuming that it is true here because not given other wise).
- Circular Wait - A is holding a resouce B wants. B is holding a resource A wants(Not happening here).
Hence we see here that all the conditions are not met. So a deadlock cannot exist in this situation.
There is however an infinite loop due to which A never gives up the lock. Hence B will be starved.
This should clear your doubt. Cheers
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论