Question

Is there any way to check how many threads are waiting for a synchronized method to become unlocked?

I would like to know when the thread calls a synchronized method:

1) How many threads are already waiting to call the method?

2) Once the method is called how long it needed to wait for the method to become unlocked?

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Solution:
I solved this using stackers answer:

public class LockedClass {
    public static int count;
    public static void measuringClass() throws IOException{
        long startTime = System.currentTimeMillis();
        count++;
        System.out.println("Threads waiting="+count);
        lockedMethod(startTime);
        count--;
        System.out.println("Threads waiting="+count);
    }
    public static synchronized void lockedMethod(long startTime) throws IOException{
        System.out.println("I spent="+(System.currentTimeMillis()-startTime)+" in the queue");
        Hashtable<String, String> params = new Hashtable<String, String>();
        params.put("param1", "test");
        params.put("param2", "12345678");
        String sessionId = Common.getSession(Common.executeHttpRequest(params));
    }
}

Answer 1

You could transform your code to use a synchronized block instead of synchronized methods, here is my rough draft. I’m not sure whether it matches you second requirement (due to my choppy english)

public class Sync {
    public static int waiting = 0;
    private Object mutex = new Object();

    public void sync() {
        waiting++;
        synchronized (mutex) {
            waiting--;
            long start = System.currentTimeMillis();
            doWhatever();
            System.out.println("duration:"
                    + (System.currentTimeMillis() - start));
        }
    }
}