Difference between Synchronized Block and Synchronized Method in Thread ?

[Prabhat Ranjan]

Hi ,

Why java has 2 ways to do synchronization ?

which is best and when to use which one ?

please share your views !

Regards,
prabhat

[Paul Clapham]

A method is itself a block of code. So there's no difference between the two things which you mention there.

[Prabhat Ranjan]

yes but my question is

1) public void Synchronized myThread() {


}

2) public void myThread() {

synchronized(this) {

}

}

You don't see any difference between the two ways to sync the threads..

when to use which and why ?

[Venu Chakravorty]

In the first case the thread acquires the lock on the currently executing object i.e. 'this'. BTW it's 'synchronized' not 'Syn...'.
In the second case you can have code that is both thread safe and thread unsafe (if I may call it so) un the same method, moreover you can specify the object whose lock you want to acquire (by replacing the 'this' keyword with it).

[Campbell Ritchie]

Too difficult for "beginning". Moving thread.

[Sebastian Janisch]

Prabhat Ranjan wrote:

1) public void Synchronized myThread() {


}

just for your interest. it's public synchronized void not public void synchronized ...

[Vijitha Kumara]

Prabhat Ranjan wrote:when to use which and why ?

Sometimes to minimize the time the lock is held by a thread you might synchronize a block of code inside the method not the hole method itself.

[Chris Hurst]

A method is itself a block of code. So there's no difference between the two things which you mention there.

The last time I looked (was a while back) at the generated code the first put a flag on the method (ACC_SYNCHRONIZED) the second had the byte code for a synchronized block which would make it less efficient I guess and I would have said the first was far more maintainable / readable.

[Prabhat Ranjan]

Prabhat Ranjan wrote:yes but my question is

1) public void Synchronized myThread() {


}

2) public void myThread() {

synchronized(this) {

}

}

You don't see any difference between the two ways to synchroniz the threads..

when to use which and why ?

[Adam Smolnik]

Hey.

You type in Google words: concurrency open calls

and all will become clear...

Adam

[Chris Hurst]

Use the first one unless you have a good reason not to, as you have written it the first one is the winner.

The second one gives you a finer level of control over how long the lock is held within the method and really requires to be more efficient that you have a mix of code that requires to be synchronised and not within the method.

[Adam Smolnik]

Hey.

Or have a look at:
http://www.informit.com/articles/article.aspx?p=167821

and find "open calls" in this article.

Adam

[suraj august]

Synchronized Method it desired when the object or class (resource )is the same class in which the Synchronized method is there .otherwise use Synchronized block to lock on any arbitrary object which is of some other class