Re: [TUHS] C Threading

[Warner Losh <imp@bsdimp.com>]

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On Fri, Jun 29, 2018 at 10:27 AM, <ron@ronnatalie.com> wrote:

> Thread local storage and starting threads up is largely a rather
> inconsequential implementation detail.   When it comes down to actual
> parallel programming, of which I have done more than a little, the big
> thing
> is thread synchronization.    It's rather hardware dependent.    You can
> pretty much entirely wipe out any parallism gains with a synchronization
> call that results in a context switch or even a serious cache impact.    On
> one side you have machines like the Denelcor HEP where every memory word
> had
> a pair of semaphores on it and the instructions could stall the process
> while waiting for them and the hardware would schedule the other threads.
> On the other hand you have your x86, which you can do a few clever things
> with some atomic operations and inlined assembler but a lot of the
> "standard" (boost, pthread, etc...) synchs will kill you.
>

C11 also defines thread APIs and atomic operations sufficient to do many
types of locking. POSIX layers on threads as well that could be implemented
using those atomics.

Warner

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