Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!ucsd!pacbell.com!tandem!netcom!resnicks
From: resnicks@netcom.COM (Steve Resnick)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Multi-thread on Ms-dos
Message-ID: <1991Mar29.201258.10170@netcom.COM>
Date: 29 Mar 91 20:12:58 GMT
References: <104499@unix.cis.pitt.edu> <1991Mar22.155529.22@cpqhou.uucp> <10592@uwm.edu>
Distribution: comp.sys.ibm.pc.programmer,comp.sys.ibm.pc.misc
Organization: Netcom - Online Communication Services  UNIX System {408 241-9760 guest}
Lines: 70

In article <10592@uwm.edu> markh@csd4.csd.uwm.edu (Mark William Hopkins) writes:
>In article <104499@unix.cis.pitt.edu> bill@hpb.cis.pitt.edu (Bill Broadly) writes:
>>	I need a small C program that allows running more that
>>one thread, using setjmp, and longjmp, on a ms-dos machine.  Nothing 
>>pre-emptive needed.  
>
>In article <1991Mar22.155529.22@cpqhou.uucp> pipkinsj@cpqhou.UUCP (Jeff Pipkins @Adv Dev@SE hou ) writes:
>>This is a nice thought, but it doesn't work.  I actually tried this scenario,
>>but the problem is that all threads have the same stack.  As soon as any
>>one of them do a longjmp(), it throws away a piece of the stack.
>
>You'll have to elaborate on this one.  The longjmp() routine saves the current
>stack pointer, and whether a part of the stack is thrown away or not, when
>you start up the next thread with another longjmp() the stack pointer is
>switched there over to another completely different part of the stack segment
>before the previous part of the stack segment has had a chance to get corrupted.
>

If you don't switch stacks, anything which uses a reasonable amount of 
stack space will get munged pretty badly. I wrote a multi-thread thingy 
with Turbo C and assembler. The assembly piece is used to launch the new
routine with a new stack. The assembler (for large model code) is:

-------------------- Cut Here ---------- Cut Here --------------------------
.model 	large
EXTRN	_EndTask:FAR
.code
PUBLIC	_StartTask
;
; Usage: StartTask( void far (*entrypt)(void),char far * Stack)
;
; StartTask sets up a new stack for a particular task, and then calls the
; task entry point. If the newly created task returns, EndTask() is called
; to invalidate the current task, and no more processing occurs.
;
_StartTask	PROC
	PUSH	BP
	MOV	BP,SP			; Save current stack frame
	MOV	AX,[BP+12]		; Segment Address of New Stack
	MOV	BX,[BP+10]		; Offset Address of New Stack
	MOV	CX,[BP+8]		; Segment Address of entry point
	MOV	DX,[BP+6]		; Offset Address of entry point
	MOV	SS,AX			; Select new stack segment 
	MOV	SP,BX			; And set new stack pointer
	MOV	AX,offset CEtsk		; Get IP Value for dummy return
	PUSH	CS			; Make return segment point to here
	PUSH	AX			; Make return offset  point to CEtsk
	PUSH	CX			; Push return CS
	PUSH	DX			; Push Return IP
	RET
CEtsk:	CALL	far ptr _EndTask	; EndTask is a routine which 
					; invalidates the current thread.
_StartTask	ENDP
	END
	

-----------------------------------------------------------------------------
Have fun! :)
Steve
 	

-- 
-------------------------------------------------------------------------------
	resnicks@netcom.com, steve@camphq, IFNA:	1:143/105.0, 
USNail: 530 Lawrence Expressway, Suite 374 
        Sunnyvale, Ca 94086
- In real life: Steve Resnick. Flames, grammar and spelling errors >/dev/null
0x2b |~ 0x2b, THAT is the question.
The Asylum OS/2 BBS - (408)263-8017 12/2400,8,1 - Running Maximus CBCS 1.2
-------------------------------------------------------------------------------