Xref: news2.mv.net comp.os.msdos.djgpp:1584
From: vogelsan AT i50s20 DOT ira DOT uka DOT de (Holger Vogelsang)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Multi-threads?
Date: 1 Mar 1996 08:50:20 GMT
Organization: IMA Karlsruhe
Lines: 111
Sender: vogelsan AT i50s20 (Holger Vogelsang)
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To: Tom Sgouros <tomss AT conan DOT ids DOT net>
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

>Has anyone who reads this come up with any kind of hack to do rudimentary 
>multi-threading on a DOS-box? Or can anyone point me to a possible 
>solution to the porting of a multi-threading application?

Here is very simple solution for two processes, using longjmp,
setjmp for task switching (without preemption).#include <stdio.h>
This can be expanded for many processes by modifying the "scheduler"
lwp_switch. This examples works under DJGPP 1.x and DJGPP 2.0.
The stack size for each process is set to 2000 bytes in this example.

Hope this helps.


#include <setjmp.h>
#include <stdio.h>

#define DEFAULT_STACK_SIZE 2000

jmp_buf context[ 2 ];
short   running_proc = 0;


void lwp_switch() {
                  
    if( !setjmp( context[ running_proc ] )) {
        running_proc++;
    	running_proc %= 2;
    	longjmp( context[ running_proc ], 1 );
    	}               
}	
    	

         
void Proc1() {
	  
    long i = 0;
         
    printf( "Proc 1 started\n" );
    while( 1 ) { 
        printf( "count1 = %d\n", i++ );         
        lwp_switch();
        }    	
}
    		          
void Proc2() {
	  
    long i = 0x800000;
         
    printf( "Proc 2 started\n" );
    while( 1 ) {
        printf( "count2 = %d\n", i-- ); 
        lwp_switch();
        } 
}
    		          
    		          

void InitProcs() {

    setjmp( context[ 0 ] );
    setjmp( context[ 1 ] );

        /*
            define entry point and stack
        */

        /*
            first: DJGPP 2.0
        */
#if defined(DJGPP) && (DJGPP >= 2) 
    context[ 0 ][ 0 ].__eip = (unsigned long)Proc1;
    context[ 0 ][ 0 ].__esp = (unsigned long)malloc( DEFAULT_STACK_SIZE ) +
                              DEFAULT_STACK_SIZE - sizeof( double );
							
    context[ 1 ][ 0 ].__eip = (unsigned long)Proc2;
    context[ 1 ][ 0 ].__esp = (unsigned long)malloc( DEFAULT_STACK_SIZE ) +
                              DEFAULT_STACK_SIZE - sizeof( double );
#else					
        /*
            DJGPP 1.x
        */
    context[ 0 ][ 0 ].eip = (unsigned long)Proc1;
    context[ 0 ][ 0 ].esp = (unsigned long)malloc( DEFAULT_STACK_SIZE ) +
                            DEFAULT_STACK_SIZE - sizeof( double );
							
    context[ 1 ][ 0 ].eip = (unsigned long)Proc2;
    context[ 1 ][ 0 ].esp = (unsigned long)malloc( DEFAULT_STACK_SIZE ) +
                            DEFAULT_STACK_SIZE - sizeof( double );
#endif

    longjmp( context[ 0 ], 1 );
}


void main() {

    InitProcs():
    
        /*
            should never return
        */
}


 
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Holger Vogelsang
Institut fuer Mikrorechner und Automation, Universitaet Karlsruhe 
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