[fpc-devel] Comparison FPC 2.6.2 - Delphi 7

[Michael Van Canneyt]

On Mon, 4 Mar 2013, Michael Schnell wrote:

> On 03/04/2013 09:49 AM, Michael Van Canneyt wrote:
>>  The solution must work on ALL platforms...
>
> Of course.
>
> I don't remember ever having seen a system (Windows, Linux, x86, ARM, NIOS 
> (similar top MIPS) ) where the C compiler does a library call when accessing 
> a threadvar. Usually a register is dedicated for this purpose that is loaded 
> with a thread specific value by the OS. I do know C compiler implementations 
> that don't support threadvars at all and thus are unable to support FUTEX and 
> with that low level thread synchronization is a lot slower as always a 
> userland/system switch is necessary. Here hardware (atomic instructions) and 
> the OS implementation (e.g. "Atomic Region" to overcome such limitations for 
> userland) comes into play.
>
> I remember from a discussion some years ago that fpc uses a (supposedly 
> arch/platform depending) library call with any access to to a threadvar 
> instead of using the appropriate (arch/platform depending) register. But I 
> did not recheck recently.

We use pthreads on non-windows, and GetTLS/SetTLS on Windows.

Michael.