Difference between __gshared and shared.

[via Digitalmars-d]

On Wednesday, 8 July 2015 at 21:15:19 UTC, deadalnix wrote:
> On Wednesday, 8 July 2015 at 12:08:37 UTC, Jonathan M Davis 
> wrote:

>> I know that there are a number of people who get frustrated 
>> with shared and using __gshared instead, but unless you fully 
>> understand what you're doing and how the language works, and 
>> you're _really_ careful, you're going to shoot yourself in the 
>> foot it subtle ways if you do that.
>>
>> - Jonathan M Davis
>
> Amen

What sort of subtle ways? Can you give examples that are not 
effectively the same subtle ways you would encounter with 
pthreads in C/C++? I have been running with the assumption that 
__gshared effectively bypasses TLS, which again, feels sort of 
dirty to use a __ prefixed keyword for that, but, yeah...

I'm not sure why I don't see the magic with synchronized classes. 
To me, they have a fundamental flaw in the fact they are classes. 
While I don't mind much their existence, I would very much 
dislike if that is the only convenient way to use the 
shared/synchronized mechanisms.

Regarding your point about multiple pieces of data being guarded 
by multiple mutexes using the proposed design, we could perhaps 
do it this way:

@lock(mutex) shared {
   int moo;
   float foo;
}


We could implement synchronized classes/structs like this:

struct Foo {
   void cowsay() synchronized(moootex) {
      // your synchronized method implementation
   }

   void cowsay() {
     synchronized(mootex) {
       // no sugar
     }
   }

   @lock(moootex) private shared {
     int m_moo;
     float m_foo;
   }
}

I think we should have avoid Java's non-sense of having to 
declare a class to do anything, and instead find generic ways to 
do things that are useful for multiple paradigms.