Java synchronization on static and nonstatic methods

Question

I'm little confused about behaviour for synhronization (static and non static method).

For example:

1.

    class MyClass  {
  ...
  public synchronized static someMethod() {
    ...
  }
  public static someMethod2() {
    ...
  }

  ...
}

So if thread A call someMethod1(), does thread B have lock on someMethod2()?

2.

     class MyClass  {
  ...
  public synchronized someMethod() {
    ...
  }
  public someMethod2() {
    ...
  }

  ...
}

If we have MyClass a = new MyClass(),thread A call method someMethod(),does thread have lock on someMethod2()?

shmosel · Accepted Answer · 2017-08-09 21:26:34Z

1

The answer to both is no. Synchronization is a cooperative mechanism. Synchronizing on an instance or class doesn't prevent other threads from calling another method unless that method also synchronizes on the same monitor.

answered Aug 9, 2017 at 21:26

shmosel

51k7 gold badges81 silver badges147 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ivan Pronin · Accepted Answer · 2017-08-09 21:28:54Z

0

In both of your questions the answer is No: thread B won't be locked on method someMethod2 since this method is not synchronized. Synchronization and related locks will be working only when both threads will call someMethod.

The only difference in this case is the target that will be locked. A synchronized method uses the method receiver as a lock (i.e. this for non static methods, and the enclosing class for static methods)

edited Aug 9, 2017 at 21:28

answered Aug 9, 2017 at 21:22

Ivan Pronin

1,91617 silver badges15 bronze badges

2 Comments

shmosel Over a year ago

Synchronization doesn't block invocation of unsynchronized methods.

Ivan Pronin Over a year ago

Thanks, modified the answer. I didnt understand the question correctly

kapandron · Accepted Answer · 2017-08-09 21:29:38Z

0

No, another method is free to lock in these cases. A thread can get a lock for the static method when another thread lock non static method of the class. These methods have different monitors.

When a static method is synchronized it's synchronize on a class. That means while execution of a static method the whole class is blocked. So other static synchronized methods are also blocked. In other case when a not static method is synchronized it's synchronize on an instance. All synchronized methods of only this specific object are blocked.

edited Aug 9, 2017 at 21:29

answered Aug 9, 2017 at 21:23

kapandron

4,2102 gold badges29 silver badges42 bronze badges

1 Comment

shmosel Over a year ago

But the other method is not synchronized.

Collectives™ on Stack Overflow

Java synchronization on static and nonstatic methods

3 Answers 3

Comments

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related