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pop AND frames when safe to do so, suspend resizing of AND frames until a proper GC is implemented (#244)

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This commit is contained in:
Mark Thom
2019-11-30 14:08:02 -07:00
parent 3e49db1a29
commit 0eb20a5d8e
4 changed files with 29 additions and 20 deletions
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20
src/prolog/machine/machine_state_impl.rs
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@@ -123,7 +123,7 @@ impl MachineState {
self.flags
}
fn next_global_index(&self) -> usize {
pub(super) fn next_global_index(&self) -> usize {
max(
if self.and_stack.len() > 0 {
self.and_stack[self.e].global_index
@@ -3127,10 +3127,18 @@ impl MachineState {
pub(super) fn allocate(&mut self, num_cells: usize) {
let gi = self.next_global_index();
// let new_e = self.e + 1;
self.p += 1;
if self.e + 1 < self.and_stack.len() {
/*
/* See issue #244 for an example of a program broken (at the
top level) by the inclusion of this code. A proper GC must determine if an
existing AND frame is safe to resize; the check here is not
enough.
*/
if new_e < self.and_stack.len() {
let and_gi = self.and_stack[self.e].global_index;
let or_gi = self
.or_stack
@@ -3139,10 +3147,8 @@ impl MachineState {
.unwrap_or(0);
if and_gi > or_gi {
let new_e = self.e + 1;
self.and_stack[new_e].e = self.e;
self.and_stack[new_e].cp = self.cp.clone();
self.and_stack[new_e].cp = self.cp;
self.and_stack[new_e].global_index = gi;
self.and_stack.resize(new_e, num_cells);
@@ -3151,7 +3157,7 @@ impl MachineState {
return;
}
}
*/
self.and_stack.push(gi, self.e, self.cp.clone(), num_cells);
self.e = self.and_stack.len() - 1;
}
@@ -3353,7 +3359,7 @@ impl MachineState {
self.b = self.or_stack.len();
let b = self.b - 1;
for i in 1..n + 1 {
for i in 1 .. n + 1 {
self.or_stack[b][i] = self.registers[i].clone();
}