Re: RFC: Prototype for a user threading library in Ada

[Hadrien Grasland <hadrien.grasland@gmail.com>]

Le samedi 2 juillet 2016 06:36:09 UTC+2, Randy Brukardt a écrit :
> But I don't think that really helps the race and deadlock issues that are 
> the real problem with programming with Ada tasks. I'd like to find some help 
> there, too.

Here's my view of this: people are heavily overusing shared mutable data in multitasking programs, and that is the source of too many data races, which in turn people attempt to fix with locks, thusly killing their performance and introducing deadlocks.

In many cases, better performance and correctness can be easily achieved by moving to asynchronous tasking runtimes, where the runtime internally manages an event-based dependency graph of tasks that can be processed condurrently, and data is kept task-private but can be moved around between tasks.

But shared mutable data is necessary to the efficient implementation of data-parallel algorithms, so it should remain available to expert programmers.

What I would love in the end is some kind of static analysis tool that warns people about shared mutable data in multitasking programs, but gives a way to bypass the warning to people who actually know what they are doing.

But to make this warning useful would also entail introducing a notion of "deferred constants", that is, values which are defined at runtime but will not be modified subsequently. Otherwise, there would be too many false positives about program parameters that are loaded at runtime.