在Java中检查对对象的锁定

Question

I want to check the lock on an object of the class. I use Thread.holdsLock(this) for this. Is this the Right way?

My question is how I can check if the object is locked for the main method and also check the lock on static methods.

public class CheckLock {
    public static void main(String[] args) throws InterruptedException {
        objectLockClass olc=    new objectLockClass();
        Thread t1=new Thread(olc);
        t1.start();
    }
}

class objectLockClass implements Runnable {

    @Override
    public void run() {
        boolean isLocked = true;
        int counter=0;     
        synchronized (this) {
            while (isLocked) {
                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("lock object in run  : " + Thread.holdsLock(this));
                if (counter==5 ) isLocked=false;
                    counter++;
            }
        }

The output is:

lock object in run  : true
lock object in run  : true
lock object in run  : true
lock object in run  : true
lock object in run  : true
lock object in run  : true

Answer 1

how I can check the object is locked for main method and also check lock on static methods?

An object isn't locked for a method . It's just locked. period. The utility of Java's synchronized keyword is that no two threads will ever be allowed to synchronize on the same object at the same time.

---

It doesn't usually make sense to ask whether some other thread has an object locked. The Thread.holdsLock(foo) method won't tell you that: It only tells whether the calling thread has foo locked. Suppose there was a method, Thread.otherThreadHoldsLock(foo) , and suppose you called it like this:

Object foo = ...;

if (Thread.otherThreadHasLocked(foo)) {
    doSomething();
} else {
    doSomethingElse();
}

It doesn't give you any useful information: This code could call doSomething() with foo locked, or with foo not locked; and it could call doSomethingElse() with foo locked, or with foo not locked. There's no guarantee, because another thread could acquire the lock or release the lock at any time.