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Subject: Re: [boost] [coroutine] : My Confusion
From: Christopher Kormanyos (e_float_at_[hidden])
Date: 2012-05-09 17:12:37

>> Where is the low-level assembly that does the *nuts-and-bolts*
>> of the context switching?

> boost.context contains struct fcontext_t storing the
> architecture+ABI specific stuff (registers) and functions
> make_fcontext() and jump_fcontext(). The first function
> is used to set up a fcontext_t and the second one is used
> to jump from one context to another one.
> Both functions are written in assembler.

OK. Thanks Oliver. I *really* appreciate what you are doing
with context and coroutine. I haven't fully comprehended
the depths of your fascinating development, but I sort of get it.

I know it's wayyy too late in the game for any top-level
requirements. But I would recommend inserting a potentially
user-customizable functional element between the context-save
and the context-restore.

Maybe you already have it and I'm a dummy who can't see it.

Do you know why I suggest this?

Because we could specialize the functional element to
implement a simple (nearly portable) time-slicing cooperative
multitasking scheduler simply using a container filled with
(coroutine + timer) objects. You already have a yield() function.
And I do see some evidence of events and waiting.
With a scheduling element and a potential sleep_for() function
we could essentially get a robust cooperative multitasking scheduler
*right off the rack* from boost.

And this is the kind of thing that I, personally, would definitely
want to adapt to other architectures.

Back in the day, I spent about 5 years, off-and-on writing
multitasking schedulers. I eventually ended up at your
design---but with scheduling and sleep_for(), but not in the
cool boost-way that you have. And these schedulers are still
running and being produced in tens of millions of products
to this very day.

> Template coroutine aggregates two fcontext's.
> One to store the relevant registers form the calling context
> and the second struct contains the register stuff of the to
> called context (coroutines context, coroutine's funtion).

>> Or am I just totally confused here? Are you doing it in
>> a high-level abstraction that I simply don't understand?
>> Are you using proprocessor macros to do the context switch?

> it's assembler code (no inline assembler).
Yeah. It's the only way to do it.

>> Where is the assembler stuff?
> libs/context/src/asm/...

OK. I Got it. Thanks so much for the clarifications.

Well, I need to get back to my other math projects and
the pesky day job. I am looking forward to any progress
with Boost.Coroutine.

Thanks again for this contribution.

Best regards, Chris.

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