Cache ImmutableKeyValuePairs#hashCode (#5307)

api/all/src/jmh/java/io/opentelemetry/api/common/AttributesBenchmark.java

@@ -25,11 +25,30 @@ public class AttributesBenchmark {
   // pre-allocate the keys & values to remove one possible confounding factor
   private static final List<AttributeKey<String>> keys = new ArrayList<>(10);
   private static final List<String> values = new ArrayList<>(10);
+  private static final List<Attributes> attributes = new ArrayList<>();
 
   static {
     for (int i = 0; i < 10; i++) {
       keys.add(AttributeKey.stringKey("key" + i));
       values.add("value" + i);
+      AttributesBuilder builder = Attributes.builder();
+      for (int j = 0; j <= i; j++) {
+        builder.put(keys.get(j), values.get(j));
+      }
+      attributes.add(builder.build());
+    }
+  }
+
+  @Benchmark
+  @BenchmarkMode({Mode.AverageTime})
+  @Fork(1)
+  @Measurement(iterations = 15, time = 1)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  @Warmup(iterations = 5, time = 1)
+  @SuppressWarnings("ReturnValueIgnored")
+  public void computeHashCode() {
+    for (Attributes attributes : attributes) {
+      attributes.hashCode();
     }
   }
 

api/all/src/main/java/io/opentelemetry/api/internal/ImmutableKeyValuePairs.java

@@ -32,6 +32,7 @@ import javax.annotation.concurrent.Immutable;
 @Immutable
 public abstract class ImmutableKeyValuePairs<K, V> {
   private final Object[] data;
+  private int hashcode;
 
   /**
    * Stores the raw object data directly. Does not do any de-duping or sorting. If you use this
@@ -247,9 +248,13 @@ public abstract class ImmutableKeyValuePairs<K, V> {
 
   @Override
   public int hashCode() {
-    int result = 1;
-    result *= 1000003;
-    result ^= Arrays.hashCode(data);
+    int result = hashcode;
+    if (result == 0) {
+      result = 1;
+      result *= 1000003;
+      result ^= Arrays.hashCode(data);
+      hashcode = result;
+    }
     return result;
   }
 

sdk/metrics/src/jmh/java/io/opentelemetry/sdk/metrics/MetricsBenchmarks.java

@@ -6,9 +6,12 @@
 package io.opentelemetry.sdk.metrics;
 
 import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.common.AttributesBuilder;
 import io.opentelemetry.api.metrics.Meter;
 import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.api.trace.Tracer;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.TimeUnit;
 import org.openjdk.jmh.annotations.Benchmark;
 import org.openjdk.jmh.annotations.BenchmarkMode;
@@ -32,6 +35,22 @@ import org.openjdk.jmh.infra.ThreadParams;
 @Fork(1)
 public class MetricsBenchmarks {
 
+  private static final List<Attributes> ATTRIBUTES_LIST;
+
+  static {
+    int keys = 5;
+    int valuesPerKey = 20;
+
+    ATTRIBUTES_LIST = new ArrayList<>();
+    for (int key = 0; key < keys; key++) {
+      AttributesBuilder builder = Attributes.builder();
+      for (int value = 0; value < valuesPerKey; value++) {
+        builder.put("key_" + key, "value_" + value);
+      }
+      ATTRIBUTES_LIST.add(builder.build());
+    }
+  }
+
   @State(Scope.Thread)
   public static class ThreadState {
 
@@ -65,6 +84,14 @@ public class MetricsBenchmarks {
     }
   }
 
+  @Benchmark
+  @Threads(1)
+  public void recordToMultipleAttributes(ThreadState threadState) {
+    for (Attributes attributes : ATTRIBUTES_LIST) {
+      threadState.op.perform(attributes);
+    }
+  }
+
   @Benchmark
   @Threads(1)
   public void oneThread(ThreadState threadState) {