synchronize within a static method - Is this a class level lock?

Question

public static void getResult(HttpSession session) {
    synchronized(session) {
     ....
    }
}

Here synchronized block is on session, but the method is a static one. Does this result in a class level locking?

Just a little tip: it makes no sense for a getter with a void return type to exist. — aballaci, Jun 19 '20 at 13:43
did not put the whole logic here. actually returns a value, but did not share here. — programmer, Jun 19 '20 at 13:50

score 2 · Answer 1 · answered Jun 19 '20 at 13:08

2

A thread will take a lock on the session object you have used in synchronized(session). In your case it does not matter if the method is static or not, in both case lock, will be on the session object.

answered Jun 19 '20 at 13:08

Amit Bera

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score 0 · Answer 2 · answered Jun 19 '20 at 13:31

To answer your question: Is this a class level lock? The answer is hmm, no :)

Different threads here can sync on different objects as the lock is brought as parameter to the method.

A couple of examples:

public class DemoClass
{
    //Method is static
    public synchronized static void demoMethod(){

    }
}

or

public class DemoClass
{
    public void demoMethod()
    {
        //Acquire lock on .class reference
        synchronized (DemoClass.class)
        {
            //other thread safe code
        }
    }
}

or

public class DemoClass
{
    private final static Object lock = new Object();

    public void demoMethod()
    {
        //Lock object is static
        synchronized (lock)
        {
            //other thread safe code
        }
    }
}

Syncronisation brings overhead to your program. In a web application it is one of the responsabilities that the Application Container takes for you. Eventhough you could span own threads in a web app, it is discouraged.

synchronize within a static method - Is this a class level lock?

2 Answers2