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/* Test harness for stack-copying conext switching.
* Assumes stack grows toward lower addresses.
*/
#include "tra.h"
Label mainlabel;
static void swtch0(Ctxt*, Ctxt*);
static void swtch1(Ctxt*);
static void swtch2(Ctxt*);
/* the abort() calls keep smart compilers from optimizing the tail recursion */
static void
switchctxt(Ctxt *cur, Ctxt *nxt)
{
/*
* save the current stack position and registers
* the first time through. swtch0 won't return.
*/
if(setlabel(&cur->label)==0){
swtch0(cur, nxt);
abort();
}
}
static void
swtch0(Ctxt *cur, Ctxt *nxt)
{
uchar *lo, *hi;
int n;
/* save the stack for the current thread */
lo = (uchar*)cur->label.sp;
hi = (uchar*)mainlabel.sp;
n = hi-lo;
cur->stk = emalloc(n);
memmove(cur->stk, lo, n);
/* switch to the next thread */
swtch1(nxt);
abort();
}
static void
swtch1(Ctxt *nxt)
{
uchar buf[64]; /* take up stack space */
/* recurse until we're out of the area the new stack will occupy. */
if(nxt->label.sp < (ulong)buf)
swtch1(nxt);
/* do the copy */
swtch2(nxt);
abort();
}
static void
swtch2(Ctxt *nxt)
{
uchar *lo, *hi;
int n;
/* put the next stack in place */
lo = (uchar*)nxt->label.sp;
hi = (uchar*)mainlabel.sp;
n = hi-lo;
memmove(lo, nxt->stk, n);
free(nxt->stk);
nxt->stk = nil;
/* hop to it */
gotolabel(&nxt->label);
abort();
}
Ctxt ml, pl;
void
printthread(void *a)
{
printf("printthread runs, arg is %d\n", (int)a);
switchctxt(&pl, &ml);
}
int
main(int argc, char **argv)
{
setlabel(&mainlabel);
initctxt(&pl, printthread, (void*)12345);
printf("main runs\n");
switchctxt(&ml, &pl);
printf("main runs again\n");
return 0;
}
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