Precalculated attribute set hashes

opentelemetry-sdk/src/attributes/set.rs

@@ -1,3 +1,4 @@
+use std::collections::hash_map::DefaultHasher;
 use std::collections::HashSet;
 use std::{
     cmp::Ordering,
@@ -104,13 +105,13 @@ impl Eq for HashKeyValue {}
 ///
 /// This must implement [Hash], [PartialEq], and [Eq] so it may be used as
 /// HashMap keys and other de-duplication methods.
-#[derive(Clone, Default, Debug, Hash, PartialEq, Eq)]
-pub struct AttributeSet(Vec<HashKeyValue>);
+#[derive(Clone, Default, Debug, PartialEq, Eq)]
+pub struct AttributeSet(Vec<HashKeyValue>, u64);
 
 impl From<&[KeyValue]> for AttributeSet {
     fn from(values: &[KeyValue]) -> Self {
         let mut seen_keys = HashSet::with_capacity(values.len());
-        let mut vec = values
+        let vec = values
             .iter()
             .rev()
             .filter_map(|kv| {
@@ -121,25 +122,34 @@ impl From<&[KeyValue]> for AttributeSet {
                 }
             })
             .collect::<Vec<_>>();
-        vec.sort_unstable();
 
-        AttributeSet(vec)
+        AttributeSet::new(vec)
     }
 }
 
 impl From<&Resource> for AttributeSet {
     fn from(values: &Resource) -> Self {
-        let mut vec = values
+        let vec = values
             .iter()
             .map(|(key, value)| HashKeyValue(KeyValue::new(key.clone(), value.clone())))
             .collect::<Vec<_>>();
-        vec.sort_unstable();
 
-        AttributeSet(vec)
+        AttributeSet::new(vec)
     }
 }
 
 impl AttributeSet {
+    fn new(mut values: Vec<HashKeyValue>) -> Self {
+        values.sort_unstable();
+        let mut hasher = DefaultHasher::new();
+        values.iter().fold(&mut hasher, |mut hasher, item| {
+            item.hash(&mut hasher);
+            hasher
+        });
+
+        AttributeSet(values, hasher.finish())
+    }
+
     /// Returns the number of elements in the set.
     pub fn len(&self) -> usize {
         self.0.len()
@@ -163,3 +173,9 @@ impl AttributeSet {
         self.0.iter().map(|kv| (&kv.0.key, &kv.0.value))
     }
 }
+
+impl Hash for AttributeSet {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        state.write_u64(self.1)
+    }
+}