[fpc-pascal] Threading vs Parallelism ?

Mark Morgan Lloyd markMLl.fpc-pascal at telemetry.co.uk
Thu Apr 20 12:29:11 CEST 2017

On 20/04/17 10:22, Marco van de Voort wrote:
> In our previous episode, Mark Morgan Lloyd said:> > They are not really threads. They must be scheduled within threads.> > https://msdn.microsoft.com/en-us/library/windows/desktop/ms682661(v=vs.85).aspx> > from the article they don't seem to have that many advantages, except toconvert existing manual m:n scheduling apps.> > Which effectively makes them coroutines, but since they're MS-only > they're nonportable.
> What exactly makes them coroutines? Maybe that they  implement a local stackconcept.

Yes, exactly. Which I think is an abstraction that FPC doesn't have. 
Even Turbo Pascal interrupt handlers worked within the same stack, as 
distinct from TopSpeed's IOTRANSFER() which switched.

> But you still would have to integrate that with FPC (exceptionhandling, stack checking), so at the basic level it only saves some asmswitching contexts.

It's interesting that coroutines (Modula-2, perhaps others) precede 
exceptions etc. (C++?). It might turn out that in practice they /have/ 
to be implemented first, otherwise the amount of doctrine that grows up 
around exceptions makes the job implausible.

> But maybe the OS support for stack switching makes things like keeping SEHworking easier. (not that that is enabled by default for 32-bit windows x86)
>> Which is more or less where Ryan started off the > other thread.
> It suddenly occured to me that that piece of code is compatible to nothingin FPC, since the only likely target in FPC (win32 x86) doesn't use SEH.There is a define to enable it though ( -dTEST_WIN32_SEH )

I think I said at the time that he should be looking at (an equivalent 
of) fibers.

Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

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