Re: Eliminating Singleton Objects

[John W. Eaton]

On 04/30/2017 11:28 PM, Rik wrote:

> It's true.  I don't think register pressure is going to develop at 2 or 3
> function parameters.  I thought we might already be at the 4-5 parameter
> range in which case another could make a difference.
>
> If the compiler is no longer doing initialization of the singleton, is this
> the cause of certain data race bugs between the interpreter and the GUI
> thread?  Bug #50880 and #50396 both seem to be caused by the GUI looking
> for interpreter static variables that have not been initialized in time.

With the singleton idiom, there is no way for the object to be used 
before it is initialized.  That's the one nice thing about singletons. 
But, with multiple threads, I suppose it's possible that the 
initialization code could be called from two threads simultaneously, and 
that will certainly cause trouble.

> Also, if the pointer to the interpreter really is used all over the code
> base, maybe it does make sense to have it be a global?  I know it is
> generally frowned upon, but it might actually be simpler then re-working
> the API to pass the pointer through to all functions.

For now it will have to remain global because we need a way to access 
the objects like the symbol table and the load path that are singletons. 
 But I would eventually like to eliminate the global because I would 
like to be able to allow a single program to contain multiple 
interpreter objects that are completely independent of one another.  So 
all data for an interpreter instance would need to be owned by the 
interpreter object.  Maybe that's an impossible goal, but for now I'd 
like to aim for it.

jwe