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

[Alex Rønne Petersen]

On 29-05-2012 23:38, Andrei Alexandrescu wrote:
> On 5/29/12 5:26 AM, Alex Rønne Petersen wrote:
>> Generalized object monitors is the worst idea in programming language
>> and virtual machine design, ever.
>
> I think that's an exaggeration. Care to elaborate a bit?
>
> Andrei
>

1) You waste an entire word of memory in *every single object you ever 
create*. And for the majority of objects, this word will always be 
zero/null. Not to mention that when you do allocate a monitor, you also 
get the actual memory of that monitor in addition.
2) Anyone can lock on any object meaning it's near impossible to see 
where a deadlock might come from.
3) Encapsulation is completely broken as a result of (2).
4) There's a whole bunch of runtime and GC plumbing (which is even 
broken in druntime right now) to support object monitors. To fix this 
entire mess, we'd need weak references.
5) This whole object monitor model goes against our "thread-local by 
default" model. Synchronization is evil and should be explicit with 
core.sync.mutex.

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