Re: basic question on Ada tasks and running on different cores

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Simon Wright writes on comp.lang.ada:
> One imagines that Ada RTS's will offer the ability to map tasks to
> cores, building on the facilities offered by the OS's to specify
> processor affinities. Whether Ada 2020 will standardise an interface
> to this is to be determined! (ada-auth.org isn't responding at the
> moment, so I can't tell whether there's anything in Ada 2012).

Ada 2012 has an entire clause, D.16, "Multiprocessor Implementation",
devoted to this.  The salient part is:

7/3 For a task type (including the anonymous type of a
single_task_declaration) or subprogram, the following language-defined
representation aspect may be specified:

8/3 CPU

               The aspect CPU is an expression, which shall be of type
               System.Multiprocessors.CPU_Range.

This allows assigning a single CPU to a task; the problem is that the
value of the aspect_specification must be static.  In subclause D.16.1
"Dispatching Domains" we see:

16/3
The type Dispatching_Domain represents a series of processors on which
a task may execute. Each processor is contained within exactly one
Dispatching_Domain. System_Dispatching_Domain contains the processor or
processors on which the environment task executes. At program start-up
all processors are contained within System_Dispatching_Domain.

17/3
For a task type (including the anonymous type of a
single_task_declaration), the following language-defined representation
aspect may be specified:

18/3
Dispatching_Domain

               The value of aspect Dispatching_Domain is an expression,
               which shall be of type
               Dispatching_Domains.Dispatching_Domain. This aspect is
               the domain to which the task (or all objects of the task
               type) are assigned.

This allows assigning any one of a range of CPUs to a task.

-- 
Ludovic Brenta.
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