Synchronization Attributes

[CKKwan]

Dear All,

[Synchronization]
Can synchronize a class, any function is called and the entire class
is locked.

[MethodImplAttri bute(MethodImpl Options.Synchro nized)]
Can synchronize a method

What if I need to Lock a class only when specific method is call?

For Example:

public class C
{
public void A() {}
public void B() {}
}

The instance of class C need to be locked when method B() is called,
but not lock when method A() is called.

Certainly I can manually put 'lock(this)' in method B(). But is there
any other way of doing this?

Thanks in advance

[Peter Duniho]

Re: Synchronization Attributes

On Sun, 17 Aug 2008 21:49:28 -0700, CKKwan <ckkwan@my-deja.comwrote:

Dear All,
>
[Synchronization]
Can synchronize a class, any function is called and the entire class
is locked.

No, not at all. That attribute is used for remoting. I admit, I'm not
completely sure of the details, but I can guarantee you that it doesn't
lock "an entire class". I wrote a small test program and confirmed that
multiple threads can still access members of a given class simultaneously
even with that attribute applied to the class.

It appears to me that it handles synchronization across remoting contexts,
whatever those are. It probably ensures synchronization/consistency
across multiple remoting endpoints. But whatever it does, it's definitely
not a general-purpose synchronization mechanism.

[MethodImplAttri bute(MethodImpl Options.Synchro nized)]
Can synchronize a method

No, not precisely. Synchronizes _all_ such labeled methods in a class,
along with anything that explicitly uses the type (when applied to static
members) or instance (when applied to instance members) for locking.

What if I need to Lock a class only when specific method is call?

I'm not convinced the question makes sense. See below...

For Example:
>
public class C
{
public void A() {}
public void B() {}
}
>
The instance of class C need to be locked when method B() is called,
but not lock when method A() is called.

What does it mean to lock "the instance", if you don't want method A() to
participate in the locking? If A() doesn't participate, then at least
some of the instance (i.e method A()) doesn't wind up locked. You can
lock "on the instance", but I wouldn't say that's the same as locking
"_the_ instance".

Certainly I can manually put 'lock(this)' in method B(). But is there
any other way of doing this?

Putting a "lock(this) " in method B() would have the effect of
synchronizing method B() and any other code that is also protected by
locking on the instance. That is, only one thread could be executing any
of those at once.

If that's the effect you want, then why not use that approach? If it's
not the effect you want, then maybe you can try to be more clear about
what effect you do want.

Pete

[sturyuu5eye@gmail.com]

Re: Synchronization Attributes

On Aug 18, 1:20 pm, "Peter Duniho" <NpOeStPe...@nn owslpianmk.com>
wrote:

[MethodImplAttri bute(MethodImpl Options.Synchro nized)]
Can synchronize a method

>
No, not precisely.  Synchronizes _all_ such labeled methods in a class, 
along with anything that explicitly uses the type (when applied to static 
members) or instance (when applied to instance members) for locking.

Oh Pete, you are correct! It lock on the instance. And that is exactly
what I want.

Thanks for the help and sorry for the confusion.

p.s. I wonder why google forced me to use this stupid Id on reply :(

[Peter Duniho]

Re: Synchronization Attributes

On Sun, 17 Aug 2008 23:40:59 -0700, <sturyuu5eye@gm ail.comwrote:

On Aug 18, 1:20 pm, "Peter Duniho" <NpOeStPe...@nn owslpianmk.com>
wrote:
>

[MethodImplAttri bute(MethodImpl Options.Synchro nized)]
Can synchronize a method

>>
>No, not precisely.  Synchronizes _all_ such labeled methods in a class,
> 
>along with anything that explicitly uses the type (when applied to
>static  
>members) or instance (when applied to instance members) for locking.

>
Oh Pete, you are correct! It lock on the instance. And that is exactly
what I want.

For what it's worth, it is generally better to _not_ use the instance for
locking. The instance of your class is exposed to users of the class and
while it would be better for _that_ code to also not use the instance,
there's nothing your class can do to stop it. That means that if your
code uses its own instance for locking, it's risking being blocked for
access to itself by code elsewhere outside your control. This can cause a
variety of problems, including deadlock.

It's better for you to allocate a dummy object instance used solely for
the purpose of locking, and do the locking yourself explicitly rather than
using something like MethodImplOptio ns.Synchronized .

Pete