[Harbour] Asynchronous procedures

[Mindaugas Kavaliauskas]

Mindaugas Kavaliauskas wrote:
> It's compilers job to process language structures such as loops and ifs 
> to machine code. And the code could be written to be a single thread 
> code. So, the question (a little bit philosophical) is, why compiler can 
> not help to write this single thread code?


Hi,


I've made a try to implement my ideas. Instead of long descriptions I 
present it by sample code:
-------------------------------------
PROC main()
LOCAL hContext

    DO WHILE fctxIsContext( hContext := semithread( hContext, 100 ) )
       IF INKEY(0) == 27;  EXIT
       ENDIF
    ENDDO

    /* Let's print some more and pass a different param */
    IF fctxIsContext( hContext );  semithread( hContext, "hello" )
    ENDIF

    ? "main() exit"
RETURN

FUNC semithread( hContext, xParam )
LOCAL nInc, nIndex, nCount

    ? "semithread()"

    /* We assume xParam indicates count. Let's save it in local
       variable, since locals are saved in function context */
    nCount := xParam

    nInc := 0
    FOR nIndex := 1 TO nCount
       ? nIndex
       nInc++
       IF nInc >= 10
          nInc := 0
          RETURN_CONTEXT
          ? "saved nCount:", nCount, "passed param:", xParam
       ENDIF
    NEXT

    ? "semithread() exit"
RETURN NIL
-------------------------------------


The idea is implemented in this way:
- write RETURN_CONTEXT instead of RETURN, if you want function to return 
it's execution context. Pass this context as a first parameter to 
function to continue execution;
- compile .prg code to .hrb file;
- compile .hrb file to .c code. I've mentioned, it's compiler's job to 
generate code. Of cause, I was not going to write a new compiler, I just 
take compiled Harbour code (.hrb file), change it and generate .c 
output. .hrb output is also implemented;
- link fctx.c module to your application.

The implementation is not complete, there are issues related to the 
usage of BEGIN/END SEQUENCE, etc., but you can use it if you like :) 
Read comments and source of fctx.c, if you are interested in 
implementation details.


Best regards,
Mindaugas


P.S. almost forgot to say the main thing - you'll find it at 
http://www.dbtopas.lt/hrb/fctx.zip