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[Jonathan Marler via Digitalmars-d]

On Friday, 11 July 2014 at 18:56:07 UTC, Timon Gehr wrote:
> On 07/10/2014 08:12 PM, Jonathan Marler wrote:
>> So what do people think?
>
> How do you make sure there is at most one thread of each kind?

Good question. First, since the language doesn't support starting 
threads itself (like Go) but instead uses a library, the compiler 
would likely need to be modified to semantically understand 
whenever a line of code is starting a thread (I'm assuming it 
doesn't already).  If this feature were interesting enough I'm 
sure Walter would have an opinion on the right way to accomplish 
this.

Then how do you make sure that every named thread is only started 
once?  The ideal situation would be to verify this at compile 
time.  This is possible in some situations.  If it is not 
possible to verify this at compile time then the compiler could 
generate a synchronized global pointer to every named thread to 
prevent each one from getting started more than once.  However, 
one thought that comes to mind is if the developer cannot change 
the code to be able to verify that the thread is only started 
once at compile-time then maybe their code is poorly designed or 
they are using this feature incorrectly.

This is just a random thought I had after writing this but maybe 
if you could somehow tell the compiler that a section of code 
will only ever be executed once it would help in this analysis. 
@executeonce.  The main function would obviously only be executed 
once, so any function that executes once would need to be called 
at most once and you can directly trace where it is called from 
the main thread.  However I'm not sure how useful this feature 
would be in the general case...I would have to think on it more.