Shared Hell

[Christopher Wright]

Denis Koroskin wrote:
> 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:

Why can't you use a non-shared method on a shared object? The compiler 
could insert locking on the caller side.

Why can't you use a shared method on a non-shared object? The compiler 
could, as an optimization, duplicate the method, minus the 
synchronization. Or it could leave in the locking, which is expensive 
but correct.