Category : C Source Code
Archive   : TASK_C.ZIP
Filename : TSETUP.C

/*****************************************************
File: TSETUP.C John M. DLugosz
function to set up a new thread.
Companion to TSW.ASM
*****************************************************/

static void task_return ()
{ /* 'called' then thread function returns */
exit(0);
}

/* /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\ */

unsigned setup_thread (thread, arg, workspace, size)
void (far *thread)(); /* function to startup */
void far *arg; /* argument to (*thread)() */
unsigned near *workspace; /* stack for new thread */
int size; /* size of workspace in bytes */
{
/* set up stack on workspace so it can be "returned" to.
switching to this task will then start up the passed function.

how to set up the stack:
+4 workspace+(size of stack) is beyond end
+3 task argument 'arg'
+2 task return 'task_return'
+1 return from do_tswitch 'thread'
saveSP saved SI,DI,
saved BP

everything being put on the stack is a far pointer, so make
the stack an array of such. The odd word (saved BP) is skipped
over after the cast in the return statement by subtracting 2.
*/

void far * near *saveSP= (void far * near *)workspace;

saveSP += (size/(sizeof *saveSP)) -4; /* see chart above */
saveSP[1]= thread;
saveSP[2]= task_return;
saveSP[3]= arg;
return (unsigned)saveSP -2;
}