I thought because AmigaOS can create multiple tasks, and have them running in parallel, that that was multithreading.. Can someone explain what the multithreading ability thats going to be in later versions of AmigaOS actually is?

I don't know what they specifically have in mind but I sure hope they will include some common threading API wrappers along with whatever they dream up. For example, pthreads immediately comes to mind for easing UN*X ports. Another nice to have would be the Boost Thread library because it seems very clean and it is a serious contender for the next C++ standard. Those that like to play down low can use the native ExecSG thread API but I know I would like to stick to something a bit higher up to keep the code more "thread neutral" if there is such a thing.

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ExecSG Team Lead

AFAIK The difference between a process and a thread is that threads have resources from the parent process that are shared between the threads.

The most important difference between a thread and a process is the cost. On the AmigaOS, the cost of context switching is already extremely low and the lack of memory protection enables you to share almost all the resources between them. Therefore, AmigaOS doesn't really need threads in its current incarnation. When the cost of process context switching rises and process resources cannot be easily shared without further costs, the need for threads rises. Threads are always lower cost and hopefully a bit easier to use when compared to processes.

There have been many attempts at creating thread libraries based on AmigaOS processes in the past to ease porting efforts, etc.

I even created a thread library myself in the past but got stuck when I found out C++ exceptions could not jump thread boundaries and required compiler modifications to do so.

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I'm by no means an expert but a thread would be a subdivision of a task and would get a fraction of the allocated time quantum of the parent task.

AmigaOS doesn't have threads, just tasks and processes (which are tasks initiated via DOS I believe).

Multithreading will be introduced in 4.1, we already have a design document for it by Hans-Joerg Frieden.

We need it for efficient SMP and other reasons.

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I'm by no means an expert but a thread would be a subdivision of a task and would get a fraction of the allocated time quantum of the parent task.

AmigaOS doesn't have threads, just tasks and processes (which are tasks initiated via DOS I believe).

Multithreading will be introduced in 4.1, we already have a design document for it by Hans-Joerg Frieden.

We need it for efficient SMP and other reasons.

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Quote:

I'm by no means an expert but a thread would be a subdivision of a task and would get a fraction of the allocated time quantum of the parent task.

Very much so. A thread is usually a separate execution unit within a task or process, running in the same address space. This is currently still a bit theoretical, since everything runs in the same address space anyway, but this difference will become more important later.

A very important point, however, is the time allocated to threads vs. tasks - all threads of a single task will run in that task's time quantum. Otherwise a multi-threaded application would get considerably more time than a single-threaded application.

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AmigaOS is multitasking, which means that it can switch between tasks and execute code for them in allocated time slots at a sufficient speed such that to the user it appears that all programs are running at the same time. That's not to be confused with multi-threading though, which is a completely different thing.

As I understand it multi-threading only has a use when applied to a computer which has more than one processor. With most multi-processor machines where the OS only uses single threading you don't get a TRUE "multi-processing effect" because you can still only really do one job at a time - that's why you don't get double the speed from the machine when you add a second processor to it. Instead you only get a relatively small gain from the addition of a second processor with a single threaded OS.
With multi-threading the program execution is done in a different way and allows multiple processors to actually do different jobs so that they are ALMOST "multi-processing". As I understand it you never get pure multi-processing with a computer in the same way that you never get pure multi-tasking, but an OS that uses multi-threads is able to multi-process much much more efficiently than a single threaded OS due to the way the operating system handles the code.

This is my understanding of the subject based on what I have read up on myself a while ago, back when AmigaOS was reported to be taking the form of BeOS for future development. (BeOS was of course a multi-threaded OS) I'm not an expert and if I'm wrong with anything I'm happy to be corrected - but I hope that helps :)

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As I understand it multi-threading only has a use when applied to a computer which has more than one processor.

No, not at all. There are two major implications, process time and access rights.

Process time is assigned to tasks. If an application spawns subtasks to do its work, then it essentially is multiple programs. If you have a program that spawns ten sub-tasks vs. one that does all its processing in a single task, then the sub-task program will get time times the computing time. If the sub-tasked program is a compiler and the single-tasked program is a web browser, you will not like the result.

OTOH, if the compiler only used threads, the time would be evenly split among the compiler and the browser.

Secondly, ownership. When a process on the Amiga opens a socket or a message port, it will allocate a signal for this. A signal is task-local, meaning that if this program spawns sub-tasks, they cannot use this message port or socket because the a message arriving at the message port would signal the first task, not the sub task. Thread OTOH *can* use the tasks resources. With isolated address spaces things become even more obvious.

Finally, if we are to go multi-CPU at one point (and we *will* go multi-CPU), then we need the programs to take advantage of this

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@Rogue

Any hints at possible threading APIs? As I kind of hinted at above, I'm looking forward to porting Boost.Threads over to AmigaOS 4.x when the time comes.

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ExecSG Team Lead

Hi Rogue

I think you will save a lot of time writing the documentation for OS4 just by collecting all your answers to technical questions asked in forums.

Keep up the good work.

BTW, Can I be a betatester?? ... pretty please.

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