Michael Schnell wrote:
On 03/20/2015 11:09 PM, Mark Morgan Lloyd wrote:
Efficient implementation of coroutines requires CPU-specific code in
the RTL and possibly the compiler. However
http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html suggests a
way that coroutines can be implemented in a portable fashion in C, how
can this be done in Object Pascal?
Lazarus seems to supports a similar concept by using events and
"Application.ProcessMessages". it might not be especially efficient,
though.
My tentative solution simplifies to the excerpt below, which I think is
reasonably efficient.
..
// Check that we're not trying to jump into exception blocks etc. Valid
// line numbers are known to be > 0, the assertion is CPU-specific.
if state.line > 0 then begin
SetJmp(sanity);
Assert(PtrUInt(state.env.sp) shr 1 xor PtrUInt(state.env.bp) =
PtrUInt(sanity.sp) shr 1 xor PtrUInt(sanity.bp),
'Bad stack frame at xfer to line ' +
IntToStr(state.line - 1));
LongJmp(state.env, state.line)
end;
if SetJmp(state.env) = 0 then begin
state.line := StrToInt( (*$I %LINE% *) );
exit('A')
end;
if SetJmp(state.env) = 0 then begin
..
Pity about the StrToInt(), which in principle could be resolved at
compilation time.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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