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Merge pull request #84 from urbit/jon/hamt-preserve-no-lw

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hamt: preserve() traversal_stack uses rust stack
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Edward Amsden 2023-09-14 12:56:38 -05:00 committed by GitHub
commit 1b1c36bec5
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1 changed files with 13 additions and 5 deletions
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18
rust/ares/src/hamt.rs
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@ -437,17 +437,25 @@ impl<T: Copy + Preserve> Preserve for Hamt<T> {
let dest_buffer = stack.struct_alloc_in_previous_frame(self.0.size());
copy_nonoverlapping(self.0.buffer, dest_buffer, self.0.size());
self.0.buffer = dest_buffer;
*(stack.push::<(Stem<T>, u32)>()) = (self.0, 0);
// Here we're using the Rust stack since the array is a fixed
// size. Thus it will be cleaned up if the Rust thread running
// this is killed, and is therefore not an issue vs. if it were allocated
// on the heap.
//
// In the past, this traversal stack was allocated in NockStack, but
// exactly the right way to do this is less clear with the split stack.
let mut traversal_stack: [Option<(Stem<T>, u32)>; 6] = [None; 6];
traversal_stack[0] = Some((self.0, 0));
let mut traversal_depth = 1;
'preserve: loop {
if traversal_depth == 0 {
break;
}
let (stem, mut position) = *(stack.top::<(Stem<T>, u32)>());
let (stem, mut position) = traversal_stack[traversal_depth - 1]
.expect("Attempted to access uninitialized array element");
// can we loop over the size and count leading 0s remaining in the bitmap?
'preserve_stem: loop {
if position >= 32 {
stack.pop::<(Stem<T>, u32)>();
traversal_depth -= 1;
continue 'preserve;
}
@ -472,8 +480,8 @@ impl<T: Copy + Preserve> Preserve for Hamt<T> {
};
*(stem.buffer.add(idx) as *mut Entry<T>) = Entry { stem: new_stem };
assert!(traversal_depth <= 5); // will increment
(*(stack.top::<(Stem<T>, u32)>())).1 = position + 1;
*(stack.push::<(Stem<T>, u32)>()) = (new_stem, 0);
traversal_stack[traversal_depth - 1].unwrap().1 = position + 1;
traversal_stack[traversal_depth] = Some((new_stem, 0));
traversal_depth += 1;
continue 'preserve;
} else {