review of std.parallelism

[Michel Fortin]

On 2011-03-19 13:16:02 -0400, dsimcha <dsimcha at yahoo.com> said:

>> * "A goto from inside the parallel foreach loop to a label outside the
>> loop will result in undefined behavior." Would this be a bug in dmd?
> 
> No, it's because a goto of this form has no reasonable, useful 
> semantics.  I should probably mention in the docs that the same applies 
> to labeled break and continue.
> 
> I have no idea what semantics these should have, and even if I did, 
> given the long odds that even one person would actually need them, I 
> think they'd be more trouble than they're worth to implement.  For 
> example, once you break out of a parallel foreach loop to some 
> arbitrary address (and different threads can goto different labels, 
> etc.), well, it's no longer a parallel foreach loop.  It's just a bunch 
> of completely unstructured threading doing god-knows-what.
> 
> Therefore, I slapped undefined behavior on it as a big sign that says, 
> "Just don't do it."  This also has the advantage that, if anyone ever 
> thinks of any good, clearly useful semantics, these will be 
> implementable without breaking code later.

I think an improvement over undefined behaviour would be to throw an exception.

Also, what happens if one of the tasks throws an exception?

-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/