CODEWITHSUNDEEP
javamultithreadingconcurrencylocking
shrinidhisondur
shrinidhisondur

Reputation: 759

Do synchronized methods have locks of their own?

Suppose I have 

class myClass {

    synchronized methodA { };

    synchronized methodB { };
}

Does it mean that there are 2 implicit locks? One for methodA and one for B? I was reading Cracking the Coding Interview by Gayle McDowell, and she says that locking happens at the level of method + object, as opposed to object. I was under the impression that myClass simply has one lock and every synchronized method uses that. Can anyone explain ?

Upvotes: 0

Views: 72

Answers (2)

Evgeny Kiselev
Evgeny Kiselev

Reputation: 216

Both of this methods used same lock. Every object in java has his internal mutex.

synchronized void method() {}

and 

synchronized(this) {}

used same lock.

But if you try synchronized on static method - it will use different locks:

static synchronized method() { // used Class lock ! not object lock
}

Upvotes: 0

ortis
ortis

Reputation: 2223

This

synchronized void methodA 
{
  //code
}

is equivalent to

void methodA 
{
  synchronized(this)
  {
    //code
  }

}

So, synchronized in front of a method will use the instance of the object itself as a lock.

Upvotes: 4

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