Threads-Can someone reply to this que?

[sanjana narayanan]

Hi,
In threads, what is the purpose of getting multiple locks on the same object by the same thread.
Eg: public void run()
{
Synchronized(this)// lock is obtained on 'this' object
{
Synchronized(this) //#2 lock is agin obtained on the 'this' obj
{
--------------
On obtaining the first lock, the thread holds the lock on the object and prevents any other thread from getting a lock on the 'this' object. so when do we go for the #2 lock.
-Sanjana
[ December 25, 2003: Message edited by: sanjana narayanan ]

[Marlene Miller]

Hi Sanjana,
When I read about a thread executing more than one block of synchronized code, I think of synchronized methods being invoked in succession or recursively.

class Data {
   synchronized void m1() {
      m2();
      ... access fields
   }
   synchronized void m2() {
      ... access fields
   }
}

Both methods are synchronized, because m2 might be invoked without invoking m1 first.
Note: I changed the words to correct the error Vad found
[ December 25, 2003: Message edited by: Marlene Miller ]

[Vad Fogel]

Originally posted by Marlene Miller:
When I read about threads having multiple locks on an object, I think of a different kind of example than yours.

Multiple locks on the same object?? Hmm, doesn't any object have only one lock that becomes a subject of multithreaded contest?

[Marlene Miller]

Thank you Vad. You are correct, I am wrong.
An object has a lock. A thread acquires the lock of the object.
I should have said a thread performs multiple lock actions on an object.