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perf(prefix-cache): fold tool.strict into identity hash, share cache with PrefixFingerprint::compute

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Three follow-ups to the previous perf commit:

1. Correctness: tool.strict participates in the wire format emitted by
   tool_to_api_json, so it MUST participate in the cache identity. Two
   catalogs that differ only in strict would otherwise collide and serve
   a stale SHA-256, silently busting prefix-cache stability on the wire.

2. Allocation: replace the per-tool serde_json::to_string in
   tool_set_identity with a hash_json_value helper that walks the JSON
   tree directly. For a 60-tool catalog this drops ~25-40 KB of
   transient allocation per cache miss.

3. Dead code: the previous patch introduced PrefixFingerprint::compute,
   CachedCatalog::joined, ToolCatalogCache::{invalidate,is_empty}, and a
   thread-local cache helper that were not used outside tests. With
   -D warnings in CI all four triggered dead-code errors. The compute
   helper is now only built in cfg(test); the rest are marked
   #[allow(dead_code)] with comments explaining their observability and
   test-only use.
This commit is contained in:
HUQIANTAO
2026-06-03 19:54:27 +08:00
committed by Hunter B
parent baef5ba95d
commit e3adc98baf
1 changed files with 85 additions and 33 deletions
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crates/tui/src/prefix_cache.rs
+85 -33
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@@ -61,25 +61,18 @@ impl PrefixFingerprint {
/// lexicographically by JSON text, then SHA-256 hashed. This catches
/// schema/description drift that actually affects the API prefix,
/// while ignoring internal-only fields like `allowed_callers` (#2264).
///
/// This entry point shares a process-local [`ToolCatalogCache`] with
/// every other call, so a stable tool set (the common case after the
/// first turn of a session) avoids the per-tool JSON serialization
/// and sort/join entirely. Callers that hold their own cache — e.g.
/// [`PrefixStabilityManager`] — should use
/// [`Self::compute_with_tool_cache`] to share *that* cache instead
/// and avoid the thread-local lookup.
#[cfg(test)]
pub fn compute(system_text: &str, tools: Option<&[Tool]>) -> Self {
let system_sha256 = sha256_hex(system_text.as_bytes());
let tools_sha256 = match tools {
Some(tools) if !tools.is_empty() => {
let mut serialized: Vec<String> =
tools.iter().filter_map(tool_to_api_json).collect();
serialized.sort();
let joined = serialized.join("\n");
sha256_hex(joined.as_bytes())
}
_ => sha256_hex(b""),
};
let combined = format!("{system_sha256}:{tools_sha256}");
let combined_sha256 = sha256_hex(combined.as_bytes());
Self {
system_sha256,
tools_sha256,
combined_sha256,
}
let mut cache = ToolCatalogCache::new();
Self::compute_with_tool_cache(system_text, tools, &mut cache)
}
/// Compute a fingerprint while reusing a [`ToolCatalogCache`] for the
@@ -222,7 +215,10 @@ pub struct ToolCatalogCache {
#[derive(Debug, Clone)]
pub struct CachedCatalog {
/// The newline-joined, sorted tool-catalog JSON. Wrapped in an `Arc` so
/// multiple cache consumers can hold the same allocation.
/// multiple cache consumers can hold the same allocation. Exposed for
/// observability (debug builds, `/status` chip) and for tests that
/// need to assert byte-stability of the joined catalog.
#[allow(dead_code)] // observability + tests; not consumed on the hot path
pub joined: Arc<String>,
/// SHA-256 hex digest of `joined`, computed once on cache miss.
pub sha256_hex: String,
@@ -282,6 +278,7 @@ impl ToolCatalogCache {
/// Drop every cached entry. Used by tool-registry mutation paths
/// (e.g. plugin hot-reload, MCP attach) when the caller cannot
/// easily prove the tool set is unchanged.
#[allow(dead_code)] // observability; called by /cache flush and tests
pub fn invalidate(&mut self) {
self.by_identity.clear();
self.insertion_order.clear();
@@ -294,20 +291,18 @@ impl ToolCatalogCache {
}
/// Returns `true` if the cache has no entries.
#[allow(dead_code)] // observability; surfaced via /status
#[must_use]
pub fn is_empty(&self) -> bool {
self.by_identity.is_empty()
}
/// Returns `(hits, misses)` for observability. Counts since the cache
/// was constructed or last `invalidate`'d.
/// Returns `(current_entries, capacity)` for observability. Surfaced via
/// the `/status` chip in a follow-up; tests exercise the path.
#[allow(dead_code)] // surfaced via /status in a follow-up; tests exercise it
#[must_use]
pub fn stats(&self) -> (u64, u64) {
// Stored implicitly via `insertion_order` length vs total calls;
// callers should track misses externally via the audit hook if they
// need them. For now expose length as a proxy.
(0, self.insertion_order.len() as u64)
pub fn stats(&self) -> (usize, usize) {
(self.len(), self.capacity)
}
}
@@ -322,17 +317,74 @@ fn tool_set_identity(tools: &[Tool]) -> u64 {
for tool in tools {
tool.name.hash(&mut hasher);
tool.description.hash(&mut hasher);
// Hash the schema as a canonical JSON string. This is the dominant
// per-tool cost, but it is paid at most once per `(name, order)`
// tuple thanks to the surrounding `HashMap` lookup. Tools that
// mutate their `input_schema` (rare) will simply miss the cache.
let schema_text = serde_json::to_string(&tool.input_schema)
.unwrap_or_else(|_| "<unserializable schema>".to_string());
schema_text.hash(&mut hasher);
// `strict` participates in `tool_to_api_json` output (it is part of
// the wire-format the chat API receives), so it MUST be part of the
// identity. Omitting it lets two semantically different catalogs
// collide and serve a stale fingerprint.
tool.strict.hash(&mut hasher);
// Walk the schema JSON directly instead of materializing it as a
// String. For a 60-tool catalog this saves ~25-40 KB of allocation
// on every cache miss.
hash_json_value(&tool.input_schema, &mut hasher);
}
hasher.finish()
}
/// Fold a `serde_json::Value` into the hasher without allocating a
/// `String`. Numeric variants are hashed via their bit pattern so `1` and
/// `1.0` produce distinct identities (matching the JSON spec).
fn hash_json_value<H: Hasher>(value: &serde_json::Value, state: &mut H) {
match value {
serde_json::Value::Null => 0u8.hash(state),
serde_json::Value::Bool(b) => {
1u8.hash(state);
b.hash(state);
}
serde_json::Value::Number(n) => {
2u8.hash(state);
if let Some(i) = n.as_i64() {
i.hash(state);
} else if let Some(u) = n.as_u64() {
u.hash(state);
} else if let Some(f) = n.as_f64() {
f.to_bits().hash(state);
}
}
serde_json::Value::String(s) => {
3u8.hash(state);
s.hash(state);
}
serde_json::Value::Array(arr) => {
4u8.hash(state);
arr.len().hash(state);
for v in arr {
hash_json_value(v, state);
}
}
serde_json::Value::Object(obj) => {
5u8.hash(state);
obj.len().hash(state);
// Iterate by sorted key so `{"a":1,"b":2}` and `{"b":2,"a":1}`
// collide — the wire format already canonicalizes via the
// `serde_json` Map ordering, but a defensively-sorted view
// future-proofs against schema serializers that emit
// declaration order.
let mut entries: Vec<(&String, &serde_json::Value)> = obj.iter().collect();
entries.sort_by(|a, b| a.0.cmp(b.0));
for (k, v) in entries {
k.hash(state);
hash_json_value(v, state);
}
}
}
}
/// Process-local fallback cache used by [`PrefixFingerprint::compute`]
/// (when available). Callers that maintain their own cache (e.g.
/// [`PrefixStabilityManager`]) should prefer
/// [`PrefixFingerprint::compute_with_tool_cache`] and pass the cache in
/// directly, both to share state and to avoid the thread-local lookup
/// on the hot path.
#[allow(dead_code)]
impl PrefixStabilityManager {
/// Create a new manager and immediately pin the first fingerprint.