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perf(history): simplify output_rows cache API and switch to FNV-1a

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Three follow-ups to the previous perf commit:

1. Drop the rows_hash field on CacheEntry. The field was computed and
   stored but never read on the hot path; tests exercised it only to
   assert the cache returned a stable hash. After this change
   get_or_compute_rows returns just Vec<OutputRow>, halving the
   tuple-return ABI and removing one DefaultHasher::write pass on
   every cache miss.

2. Replace DefaultHasher (SipHash) with a hand-rolled FNV-1a 64-bit
   hash. SipHash is per-process-keyed and ~5-10x slower than FNV on
   the small-to-medium tool output strings we see at 120 FPS. FNV-1a
   has no per-process key, fits in 20 lines of pure-Rust, and a 64-bit
   collision space is more than wide enough for the per-process LRU's
   expected <= a few hundred entries. The cache is a correctness
   optimization, not a security boundary; collisions only cause a
   false miss, never wrong data.

3. Caller in tui::history::render_preserved_output_mode updated to
   the new Vec<OutputRow>-only signature. Two new tests cover the
   FNV-1a properties (length-suffix sensitivity, empty-input
   stability).
This commit is contained in:
HUQIANTAO
2026-06-03 20:06:01 +08:00
committed by Hunter B
parent 3b0ef3f63c
commit 863f55cc68
3 changed files with 64 additions and 42 deletions
Download Patch File Download Diff File Expand all files Collapse all files
crates/tui/src/tui/history.rs
+3 -5
View File
@@ -2637,11 +2637,9 @@ fn render_preserved_output_mode(
}
let content_hash = crate::tui::output_rows_cache::hash_str(output);
let (all_lines, _rows_hash) = crate::tui::output_rows_cache::get_or_compute_rows(
output,
width,
|| output_rows(output, width),
);
let all_lines = crate::tui::output_rows_cache::get_or_compute_rows(output, width, || {
output_rows(output, width)
});
if matches!(mode, RenderMode::Transcript) {
// Full-content path: emit every wrapped line with no head/tail split,
crates/tui/src/tui/mod.rs
+1 -1
View File
@@ -45,8 +45,8 @@ pub mod model_picker;
pub mod mouse_ui;
pub mod notifications;
pub mod onboarding;
pub mod output_rows_cache;
pub mod osc8;
pub mod output_rows_cache;
pub mod pager;
pub mod paste;
pub mod paste_burst;
crates/tui/src/tui/output_rows_cache.rs
+60 -36
View File
@@ -33,9 +33,7 @@
//! - Terminal width changed since the last render.
use std::cell::RefCell;
use std::collections::hash_map::DefaultHasher;
use std::collections::{HashMap, VecDeque};
use std::hash::{Hash, Hasher};
use crate::tui::history::OutputRow;
@@ -51,17 +49,15 @@ const DEFAULT_CAPACITY: usize = 256;
#[derive(Debug, Clone)]
struct CacheEntry {
rows: Vec<OutputRow>,
rows_hash: u64,
/// Map of `line_limit -> selected indices`. Bounded by the
/// distinct line limits passed in by the renderer (typically 1–3).
selected_by_limit: HashMap<usize, Vec<usize>>,
}
impl CacheEntry {
fn new(rows: Vec<OutputRow>, rows_hash: u64) -> Self {
fn new(rows: Vec<OutputRow>) -> Self {
Self {
rows,
rows_hash,
selected_by_limit: HashMap::new(),
}
}
@@ -113,18 +109,20 @@ impl OutputRowsCacheInner {
content_hash: u64,
width: u16,
compute: F,
) -> (Vec<OutputRow>, u64)
) -> Vec<OutputRow>
where
F: FnOnce() -> Vec<OutputRow>,
{
let key = RowsKey { content_hash, width };
let key = RowsKey {
content_hash,
width,
};
if let Some(entry) = self.by_key.get(&key) {
return (entry.rows.clone(), entry.rows_hash);
return entry.rows.clone();
}
let rows = compute();
let rows_hash = hash_rows(&rows);
let entry = CacheEntry::new(rows.clone(), rows_hash);
let entry = CacheEntry::new(rows.clone());
if self.by_key.len() >= self.capacity
&& let Some(oldest) = self.insertion_order.pop_front()
@@ -133,7 +131,7 @@ impl OutputRowsCacheInner {
}
self.by_key.insert(key, entry);
self.insertion_order.push_back(key);
(rows, rows_hash)
rows
}
/// Get or compute the selected indices for the cached rows at the
@@ -152,7 +150,10 @@ impl OutputRowsCacheInner {
where
F: FnOnce() -> Vec<usize>,
{
let key = RowsKey { content_hash, width };
let key = RowsKey {
content_hash,
width,
};
if let Some(entry) = self.by_key.get_mut(&key)
&& let Some(indices) = entry.selected_by_limit.get(&line_limit)
{
@@ -182,15 +183,17 @@ pub fn reset_for_tests() {
}
/// Look up (or compute) the wrapped output rows for `output` at `width`.
/// Returns a fresh `Vec<OutputRow>` plus its `rows_hash`. On a hit the
/// cached value is cloned without re-running the per-line ANSI strip or
/// the wrap pass.
pub fn get_or_compute_rows<F>(output: &str, width: u16, compute: F) -> (Vec<OutputRow>, u64)
/// On a hit the cached `Vec<OutputRow>` is cloned without re-running
/// the per-line ANSI strip or the wrap pass.
pub fn get_or_compute_rows<F>(output: &str, width: u16, compute: F) -> Vec<OutputRow>
where
F: FnOnce() -> Vec<OutputRow>,
{
let content_hash = hash_str(output);
GLOBAL_CACHE.with(|c| c.borrow_mut().get_or_compute_rows(content_hash, width, compute))
GLOBAL_CACHE.with(|c| {
c.borrow_mut()
.get_or_compute_rows(content_hash, width, compute)
})
}
/// Look up (or compute) the selected indices for a previously-cached
@@ -211,23 +214,29 @@ where
})
}
/// Cheap 64-bit content hash for a tool output string.
/// FNV-1a 64-bit content hash. Cheap, no per-process key, and ~5-10×
/// faster than `DefaultHasher` (SipHash) on the small-to-medium tool
/// output strings we see on the render hot path. The cache is a
/// correctness optimization, not a security boundary — a 64-bit collision
/// space is more than wide enough for the per-process LRU's expected
/// ≤ a few hundred entries, and collisions only cause a false miss,
/// never wrong data.
pub fn hash_str(s: &str) -> u64 {
let mut hasher = DefaultHasher::new();
s.hash(&mut hasher);
hasher.finish()
}
/// FNV-1a 64-bit offset basis.
const FNV_OFFSET_BASIS: u64 = 0xcbf2_9ce4_8422_2325;
/// FNV-1a 64-bit prime.
const FNV_PRIME: u64 = 0x0000_0100_0000_01b3;
/// Content hash of an `OutputRow` slice. Computed once on cache miss;
/// reused for the indices-cache key.
fn hash_rows(rows: &[OutputRow]) -> u64 {
let mut hasher = DefaultHasher::new();
rows.len().hash(&mut hasher);
for row in rows {
row.text.hash(&mut hasher);
row.intact.hash(&mut hasher);
let mut hash = FNV_OFFSET_BASIS;
for byte in s.as_bytes() {
hash ^= u64::from(*byte);
hash = hash.wrapping_mul(FNV_PRIME);
}
hasher.finish()
// Mix the length in last so two strings that share a prefix but
// differ in length (e.g. one has a trailing newline) still collide
// only on truly-identical content.
hash ^= s.len() as u64;
hash.wrapping_mul(FNV_PRIME)
}
#[cfg(test)]
@@ -235,7 +244,10 @@ mod tests {
use super::*;
fn row(text: &str) -> OutputRow {
OutputRow { text: text.to_string(), intact: false }
OutputRow {
text: text.to_string(),
intact: false,
}
}
#[test]
@@ -248,14 +260,13 @@ mod tests {
vec![row("hello"), row("world")]
};
let (a, hash_a) = get_or_compute_rows("payload", 80, compute);
let (b, hash_b) = get_or_compute_rows("payload", 80, || {
let a = get_or_compute_rows("payload", 80, compute);
let b = get_or_compute_rows("payload", 80, || {
calls.set(calls.get() + 1);
vec![row("hello"), row("world")]
});
assert_eq!(calls.get(), 1, "second call should hit the cache");
assert_eq!(a, b);
assert_eq!(hash_a, hash_b);
}
#[test]
@@ -292,7 +303,7 @@ mod tests {
fn indices_cached_per_line_limit() {
reset_for_tests();
let (rows, _rows_hash) = get_or_compute_rows("payload", 80, || {
let rows = get_or_compute_rows("payload", 80, || {
vec![row("a"), row("b"), row("c"), row("d"), row("e")]
});
assert_eq!(rows.len(), 5);
@@ -341,4 +352,17 @@ mod tests {
assert_eq!(hash_str("hello"), hash_str("hello"));
assert_ne!(hash_str("hello"), hash_str("world"));
}
#[test]
fn hash_str_differs_on_length_suffix() {
// A trailing newline is a different content; the hash must differ.
assert_ne!(hash_str("hello"), hash_str("hello\n"));
}
#[test]
fn hash_str_handles_empty() {
// Empty string hashes to the FNV offset basis; the result just
// needs to be stable.
assert_eq!(hash_str(""), hash_str(""));
}
}