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Coalesce tombstones on delete_key to reduce all map slots from being filled on insertion

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This is a bodge and will need to be replaced with an actual solution involving backward shift deletion rather than relying on tombstone slots in the first place.
This commit is contained in:
gingerBill
2022-12-06 19:55:17 +00:00
parent f9f4551e8d
commit 27130259cc
1 changed files with 50 additions and 7 deletions
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57
core/runtime/dynamic_map_internal.odin
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@@ -230,6 +230,8 @@ map_data :: #force_inline proc "contextless" (m: Raw_Map) -> uintptr {
Map_Hash :: uintptr
TOMBSTONE_MASK :: 1<<(size_of(Map_Hash)*8 - 1)
// Procedure to check if a slot is empty for a given hash. This is represented
// by the zero value to make the zero value useful. This is a procedure just
// for prose reasons.
@@ -241,14 +243,12 @@ map_hash_is_empty :: #force_inline proc "contextless" (hash: Map_Hash) -> bool {
@(require_results)
map_hash_is_deleted :: #force_no_inline proc "contextless" (hash: Map_Hash) -> bool {
// The MSB indicates a tombstone
N :: size_of(Map_Hash)*8 - 1
return hash >> N != 0
return hash & TOMBSTONE_MASK != 0
}
@(require_results)
map_hash_is_valid :: #force_inline proc "contextless" (hash: Map_Hash) -> bool {
// The MSB indicates a tombstone
N :: size_of(Map_Hash)*8 - 1
return (hash != 0) & (hash >> N == 0)
return (hash != 0) & (hash & TOMBSTONE_MASK == 0)
}
@@ -627,15 +627,58 @@ map_exists_dynamic :: proc "contextless" (m: Raw_Map, #no_alias info: ^Map_Info,
@(require_results)
map_erase_dynamic :: #force_inline proc "contextless" (#no_alias m: ^Raw_Map, #no_alias info: ^Map_Info, k: uintptr) -> (old_k, old_v: uintptr, ok: bool) {
MASK :: 1 << (size_of(Map_Hash)*8 - 1)
index := map_lookup_dynamic(m^, info, k) or_return
ks, vs, hs, _, _ := map_kvh_data_dynamic(m^, info)
hs[index] |= MASK
hs[index] |= TOMBSTONE_MASK
old_k = map_cell_index_dynamic(ks, info.ks, index)
old_v = map_cell_index_dynamic(vs, info.vs, index)
m.len -= 1
ok = true
{ // coalesce tombstones
// HACK NOTE(bill): This is an ugly bodge but it is coalescing the tombstone slots
// TODO(bill): we should do backward shift deletion and not rely on tombstone slots
mask := (uintptr(1)<<map_log2_cap(m^)) - 1
curr_index := uintptr(index)
// TODO(bill): determine a good value for this empirically
// if we do not implement backward shift deletion
PROBE_COUNT :: 8
for i in 0..<PROBE_COUNT {
next_index := (curr_index + 1) & mask
if next_index == index {
// looped around
break
}
// if the next element is empty or has zero probe distance, then any lookup
// will always fail on the next, so we can clear both of them
hash := hs[next_index]
if map_hash_is_empty(hash) || map_probe_distance(m^, hash, next_index) == 0 {
hs[curr_index] = 0
return
}
// now the next element will have a probe count of at least one,
// so it can use the delete slot instead
hs[curr_index] = hs[next_index]
mem_copy_non_overlapping(
rawptr(map_cell_index_dynamic(ks, info.ks, curr_index)),
rawptr(map_cell_index_dynamic(ks, info.ks, next_index)),
int(info.ks.size_of_type),
)
mem_copy_non_overlapping(
rawptr(map_cell_index_dynamic(vs, info.vs, curr_index)),
rawptr(map_cell_index_dynamic(vs, info.vs, next_index)),
int(info.vs.size_of_type),
)
curr_index = next_index
}
hs[curr_index] |= TOMBSTONE_MASK
}
return
}