From dc4e239722e51e90b13ac2c14d59c845246df658 Mon Sep 17 00:00:00 2001
From: Trask Stalnaker <trask.stalnaker@gmail.com>
Date: Mon, 30 Aug 2021 09:02:27 -0700
Subject: [PATCH] Add span names cache (#4004)

* Add span names cache

* Simplify
---
 .../instrumentation/api/caching/Cache.java    |  2 ++
 .../instrumentation/api/tracer/SpanNames.java | 24 +++++++++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/instrumentation-api-caching/src/main/java/io/opentelemetry/instrumentation/api/caching/Cache.java b/instrumentation-api-caching/src/main/java/io/opentelemetry/instrumentation/api/caching/Cache.java
index 0a12f43862eb..2eaf273a39fa 100644
--- a/instrumentation-api-caching/src/main/java/io/opentelemetry/instrumentation/api/caching/Cache.java
+++ b/instrumentation-api-caching/src/main/java/io/opentelemetry/instrumentation/api/caching/Cache.java
@@ -6,6 +6,7 @@
 package io.opentelemetry.instrumentation.api.caching;
 
 import java.util.function.Function;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /** A cache from keys to values. */
 public interface Cache<K, V> {
@@ -25,6 +26,7 @@ static CacheBuilder newBuilder() {
    * Returns the cached value associated with the provided {@code key} if present, or {@code null}
    * otherwise.
    */
+  @Nullable
   V get(K key);
 
   /** Puts the {@code value} into the cache for the {@code key}. */
diff --git a/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/tracer/SpanNames.java b/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/tracer/SpanNames.java
index dad2a2bd3cf1..7c17e99674d8 100644
--- a/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/tracer/SpanNames.java
+++ b/instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/tracer/SpanNames.java
@@ -6,9 +6,21 @@
 package io.opentelemetry.instrumentation.api.tracer;
 
 import java.lang.reflect.Method;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 public final class SpanNames {
+
+  private static final ClassValue<Map<String, String>> spanNameCaches =
+      new ClassValue<Map<String, String>>() {
+        @Override
+        protected Map<String, String> computeValue(Class<?> clazz) {
+          // the cache is naturally bounded by the number of methods in a class
+          return new ConcurrentHashMap<>();
+        }
+      };
+
   /**
    * This method is used to generate a span name based on a method. Anonymous classes are named
    * based on their parent.
@@ -29,8 +41,16 @@ public static String fromMethod(Class<?> clazz, @Nullable Method method) {
    * This method is used to generate a span name based on a method. Anonymous classes are named
    * based on their parent.
    */
-  public static String fromMethod(Class<?> cl, String methodName) {
-    return ClassNames.simpleName(cl) + "." + methodName;
+  public static String fromMethod(Class<?> clazz, String methodName) {
+    Map<String, String> spanNameCache = spanNameCaches.get(clazz);
+    // not using computeIfAbsent, because it would require a capturing (allocating) lambda
+    String spanName = spanNameCache.get(methodName);
+    if (spanName != null) {
+      return spanName;
+    }
+    spanName = ClassNames.simpleName(clazz) + "." + methodName;
+    spanNameCache.put(methodName, spanName);
+    return spanName;
   }
 
   private SpanNames() {}