Re: GNAT and Tasklets

[Peter Chapin <PChapin@vtc.vsc.edu>]

On Fri, 19 Dec 2014, vincent.diemunsch@gmail.com wrote:

> Ada have created the task abstraction to deal with parallelism...

I haven't tried any parallel programming with Ada but I have used both 
OpenMP and "direct" pthreads calls in parallel C programs. Creating and 
managing threads manually is a major pain compared to what OpenMP does. 
Sure it's possible to use threads directly but it clutters the program's 
logic and it's tricky to get it both right and efficient at the same time.

Ada's tasking features are a lot nicer than pthreads, but I agree with the 
point others have made that they are the wrong tool for writing parallel 
code... at least writing parallel code without extreme pain. Tasks are 
good for large, relatively independent chunks of logic that need to 
execute concurrently such as different control loops in an embedded 
system. However, when writing parallel code that will execute over highly 
regular data structures such as large matrices, explicit tasks are just a 
distraction. In such applications the existence of tasks is an 
implementation detail, not a design element.

Trying to use explicit tasks for parallel programming is a kind of 
abstraction inversion: using a high level construct to implement some low 
level functionality. Sure it is possible but the result is ugly and 
inefficient.

Peter