Shared Hell

[Denis Koroskin]

I've recently updated to DMD2.035 (from DMD2.031 because all the later  
versions had issues with imports) and for the first time faced problems  
with shared modifier.

I don't need shared and all my globals are __gshared (they are globally  
unique instances that don't need per-thread copies).

Yet some of methods of the class hierarchy (a root singleton class and  
everything which is accessible through it) are synchronized (well, you  
know why). That's where the problems begin.

Marking a method as synchronized automatically makes it shared (more or  
less obvious). And marking the method shared makes it unable to invoke  
with non-shared instance (and __gshared != shared), meaning that I'm  
unable to use my __gshared variables anymore, making this attribute  
useless for any serious safe programming.

So I started with replacing __gshared with shared and quickly understood  
how viral it is. Not only you mast mark all the members shared (methods  
and field), instantiate classes with shared attribute, you also have to  
create a duplicate all the methods to make them accessible with both  
shared and non-shared (thread-local) instances:

class Array(T)
{
     const(T) opIndex(uint index) const
     {
         return data[index];
     }

     T opIndex(uint index)
     {
         return data[index];
     }

     const(T) opIndex(uint index) shared const
     {
         return data[index];
     }

     shared(T) opIndex(uint index) shared
     {
         return data[index];
     }

     private T[] data;
}

And that's just opIndex. Ooops...

But not only that, every interface now have to specify the same method  
twice, too:

interface Target
{
     bool build();
     bool build() shared;
     void clean();
     void clean() shared;
     bool ready();
     bool ready() shared;
     void setBuildListener(BuildListener buildListener);
     void setBuildListener(shared BuildListener buildListener) shared;
}

That's a bit frustrating. Most importantly, I don't even need shared  
(__gshared was more than enough for me), yet I'm imposed on using it.

Oh, I can't use any of the druntime/Phobos classes (e.g. create an  
instance of shared(Thread)), because none of them are shared-aware.

I think the design needs to be given a second thought before the plane  
takes off because I'm afraid it may painfully crash.