synchronized (this[.classinfo]) in druntime and phobos

[Alex Rønne Petersen]

On 29-05-2012 01:24, Jonathan M Davis wrote:
> On Tuesday, May 29, 2012 01:11:49 Alex Rønne Petersen wrote:
>> I have no idea how synchronized classes work; they are not a documented
>> feature of the language. We have synchronized functions which
>> synchronize on the this reference. Perhaps synchronized classes just
>> make all functions in a class do this.
>
> Per TDPL, having individually synchronized functions is illegal. Either all
> of the functions in a class are synchronized or none of them are. Putting
> synchronized on a function should actually be illegal. It belongs only on
> classes or in synchronized blocks, never on functions.
>
> Now, unfortuntately, I don't believe that the compiler enforces any of that
> right now, so you end up synchronizing indivdual functions rather than whole
> classes, but the synchronized functions themselves should function the same.
>
>> Either way, this is a fundamental language design fallacy. This is
>> anti-pattern number one when it comes to locking:
>>
>> * http://stackoverflow.com/a/251668/438034
>> * http://msdn.microsoft.com/en-us/library/ms173179.aspx (The lock and
>> SyncLock Keywords section)
>
> Well, then you should probably be arguing about the design of synchronized
> classes/functions rather than synchronized(this). However, given the design of
> synchronized classes, synchronized(this) would probably never be appropriate.
> If you're using a synchronized class, then you don't need it. And if you're
> not using a synchronized class, then you shouldn't be synchronizing your
> class. I would definitely think that synchronized blocks should synchronize on
> something else, since they're trying to lock a much smaller area than an
> entire class.
>
> - Jonathan M Davis

I don't think arguing about them makes sense at this point. Way too much 
code would break if we changed the semantics. I'd consider it a mistake 
and a lesson learned, rather.

But I take it you agree that synchronized (this) and similar 
"uncontrollable" synchronization blocks should be avoided?

-- 
Alex Rønne Petersen
alex at lycus.org
http://lycus.org