void
MR_print_zones(FILE *fp, const MR_MemoryZones *zones)
{
while (zones != NULL) {
MR_print_zone(fp, zones->MR_zones_head);
zones = zones->MR_zones_tail;
}
}
static MR_MemoryZone *
MR_rewind_nondetstack_segments(MR_Word *maxfr)
{
MR_MemoryZone *zone_to_reuse;
MR_MemoryZone *zone;
MR_Word *limit;
MR_MemoryZones *list;
zone_to_reuse = NULL;
for (;;) {
zone = MR_CONTEXT(MR_ctxt_nondetstack_zone);
limit = (MR_Word *) zone->MR_zone_end;
if (maxfr >= zone->MR_zone_min && maxfr < limit) {
break;
}
#ifdef MR_DEBUG_STACK_SEGMENTS
printf("\nfreeing zone\n");
MR_print_zone(stdout, zone);
#endif
// If there are several currently unneeded segments, this algorithm
// reuses the zone of the topmost segment (the first segment in the
// list from the top), since its contents are more likely to have been
// recently referred to, and thus more likely to be in the cache.
//
// However, reusing the zone of the bottom-most unneeded segment
// would look conceptually a bit neater in that it would preserve
// the follows/precedes relationship between the zones.
if (zone_to_reuse == NULL) {
zone_to_reuse = zone;
} else {
MR_release_zone(zone);
}
list = MR_CONTEXT(MR_ctxt_prev_nondetstack_zones);
assert(list != NULL);
MR_CONTEXT(MR_ctxt_nondetstack_zone) = list->MR_zones_head;
MR_CONTEXT(MR_ctxt_prev_nondetstack_zones) = list->MR_zones_tail;
MR_GC_free_attrib(list);
}
#ifdef MR_DEBUG_STACK_SEGMENTS
if (zone_to_reuse == NULL) {
printf("\nno old nondet segment zone available for reuse\n");
} else {
printf("\nreturning zone of old nondet segment for reuse: %p\n",
zone_to_reuse);
}
#endif
return zone_to_reuse;
}
MR_Word *
MR_new_nondetstack_segment(MR_Word *maxfr, int incr)
{
MR_Word *sentinel_maxfr;
MR_Word *old_maxfr;
MR_Word *old_curfr;
MR_MemoryZone *new_cur_zone;
MR_MemoryZones *new_prev_zones;
old_maxfr = maxfr;
old_curfr = MR_curfr;
#ifdef MR_DEBUG_STACK_SEGMENTS
printf("\nadding new nondet stack segment");
printf("\ncontext: %p", &MR_ENGINE(MR_eng_context));
printf("\nold maxfr: ");
MR_printnondetstack(stdout, old_maxfr);
printf("\nold curfr: ");
MR_printnondetstack(stdout, old_curfr);
printf("\n");
#endif
new_cur_zone = MR_rewind_nondetstack_segments(maxfr);
if (new_cur_zone == NULL) {
// There is no old segment to reuse in the nondet stack itself,
// so allocate a new one (possibly one that was freed earlier).
//
// Note that we perform explicit overflow checks, so redzones
// would just waste space.
new_cur_zone = MR_create_or_reuse_zone("nondetstack_segment",
MR_nondetstack_size, 0, 0, MR_default_handler);
}
#ifdef MR_DEBUG_STACK_SEGMENTS
printf("\nbefore creating new nondet segment:\n");
MR_print_zone(stdout, MR_CONTEXT(MR_ctxt_nondetstack_zone));
printf("\n");
#endif
new_prev_zones = MR_GC_malloc_uncollectable_attrib(sizeof(MR_MemoryZones),
MR_ALLOC_SITE_RUNTIME);
new_prev_zones->MR_zones_head = MR_CONTEXT(MR_ctxt_nondetstack_zone);
new_prev_zones->MR_zones_tail = MR_CONTEXT(MR_ctxt_prev_nondetstack_zones);
MR_CONTEXT(MR_ctxt_prev_nondetstack_zones) = new_prev_zones;
MR_CONTEXT(MR_ctxt_nondetstack_zone) = new_cur_zone;
MR_CONTEXT(MR_ctxt_maxfr) = new_cur_zone->MR_zone_min;
MR_maxfr_word = (MR_Word) MR_CONTEXT(MR_ctxt_maxfr);
#ifdef MR_DEBUG_STACK_SEGMENTS
printf("\nafter creating new nondet segment\n");
printf("new maxfr: ");
MR_printnondetstack(stdout, MR_maxfr);
printf("\nnew cur zone:\n");
MR_print_zone(stdout, MR_CONTEXT(MR_ctxt_nondetstack_zone));
printf("new prev zones:\n");
MR_print_zones(stdout, MR_CONTEXT(MR_ctxt_prev_nondetstack_zones));
printf("\n");
fflush(stdout);
#endif
// The stack trace tracing code needs to know the size of each nondet
// stack frame, since it uses the size to classify frames as temp or
// ordinary. The size is given by the difference in address between
// the address of the frame and the address of the previous frame.
// This difference would yield an incorrect size and hence an incorrect
// frame classification if a temp frame were allowed to have a frame
// on a different segment as its immediate predecessor.
//
// We prevent this by putting an ordinary (i.e. non-temp) frame at the
// bottom of every new nondet stack segment as a sentinel. We hand-build
// this frame, since it is not an "ordinary" ordinary frame. It is not
// created by a call, so it has no meaningful success continuation,
// and since it does not make any calls, no other frame's success
// continuation can point to it either.
//
// We store three pieces of information in the sentinel frame.
//
// - The maxfr at the time the sentinel frame was created, which we store
// in the prevfr slot. This is actually the address of the logically
// previous frame, so we are using the slot for its intended purpose,
// but the difference between the addresses of the two frames is NOT
// the size of the sentinel frame.
//
// - The curfr at the time the sentinel frame was created, which we store
// in the succfr slot. This is NOT actually the frame of the success
// continuation; we can store it there because this frame HAS no
// meaningful success continuation, so the slot is not needed for its
// intended purpose.
//
// - The address of the MR_MemoryZone structure of the zone containing
// the sentinel frame, which we store in framevar 1. This is used by
// the code of MR_pop_nondetstack_segment.
sentinel_maxfr = MR_maxfr + (MR_NONDET_FIXED_SIZE + 1);
MR_prevfr_slot_word(sentinel_maxfr) = (MR_Word) old_maxfr;
MR_succfr_slot_word(sentinel_maxfr) = (MR_Word) old_curfr;
MR_succip_slot_word(sentinel_maxfr) =
(MR_Word) MR_ENTRY(MR_do_not_reached);
MR_redofr_slot_word(sentinel_maxfr) = (MR_Word) sentinel_maxfr;
MR_redoip_slot_word(sentinel_maxfr) =
(MR_Word) MR_ENTRY(MR_pop_nondetstack_segment);
MR_based_framevar(sentinel_maxfr, 1) = (MR_Word) new_cur_zone;
#ifdef MR_DEBUG_STACK_SEGMENTS
printf("creating sentinel frame:\n");
printf("sentinel_maxfr: ");
MR_printnondetstack(stdout, sentinel_maxfr);
printf("\nsentinel frame's prevfr slot: ");
MR_printnondetstack(stdout, MR_prevfr_slot(sentinel_maxfr));
printf("\nsentinel frame's succfr slot: ");
MR_printnondetstack(stdout, MR_succfr_slot(sentinel_maxfr));
printf("\nsentinel frame's redofr slot: ");
MR_printnondetstack(stdout, MR_redofr_slot(sentinel_maxfr));
printf("\n");
#endif
// Reserve space for the new nondet stack frame on top of the
// sentinel frame.
MR_maxfr_word = (MR_Word) (sentinel_maxfr + incr);
#ifdef MR_DEBUG_STACK_SEGMENTS
printf("after creating sentinel frame and reserving %d words:\n", incr);
printf("new maxfr: ");
MR_printnondetstack(stdout, MR_maxfr);
printf("\n");
fflush(stdout);
#endif
return MR_maxfr;
}
