[dmd-internals] non-PODs again

[Johannes Pfau]

Am 08.03.2013 19:54, schrieb Walter Bright:
>
> On 3/8/2013 4:40 AM, Johannes Pfau wrote:
>>
>> So please explain what's illegal in this concrete example #2.
>
> If it lives in a register, then exception handling recovery won't work 
> on it.
It only lives in the register for a very short time though. 
"User-exceptions" can't happen at that time at all*. The only thing that 
can happen is a memory/access violation exception if we call a invalid 
function pointer or if we have a stack overflow in the called function.

A code example for that: https://gist.github.com/jpf91/5123683

But do you really think it's important that we support recovering from 
these errors? On posix these generate signals anyway (there's 
etc.linux.memoryerror which turns that into exceptions, but that doesn't 
work here and is more a hack than in any way supported). For windows 
this creates access violations errors and there's usually no guarantee 
that you can recover safely from these.

We already argue that you can't safely recover from OutOfMemoryErrors, 
but you can recover from stack overflow / access violations? I think we 
even had documented somewhere that destructors might not be called when 
"Errors" are thrown.


(* The dtor is also not called if we throw in the postblit. At that time 
the value is not yet moved into the register. But that is not only when 
calling a function: even in simple cases if a postblit fails with 
exceptions the dtor is not run for copies so I take it this is intentional)
https://gist.github.com/jpf91/5123738

-- 
Johannes Pfau