Avoid allocations when advice doesn't remove any attributes (open-telemetry#6629)

Author: jack-berg

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/view/AdviceAttributesProcessor.java

@@ -23,11 +23,28 @@ final class AdviceAttributesProcessor extends AttributesProcessor {
 
   @Override
   public Attributes process(Attributes incoming, Context context) {
+    // Exit early to avoid allocations if the incoming attributes do not have extra keys to be
+    // filtered
+    if (!hasExtraKeys(incoming)) {
+      return incoming;
+    }
     AttributesBuilder builder = incoming.toBuilder();
     builder.removeIf(key -> !attributeKeys.contains(key));
     return builder.build();
   }
 
+  /** Returns true if {@code attributes} has keys not contained in {@link #attributeKeys}. */
+  private boolean hasExtraKeys(Attributes attributes) {
+    boolean[] result = {false};
+    attributes.forEach(
+        (key, value) -> {
+          if (!result[0] && !attributeKeys.contains(key)) {
+            result[0] = true;
+          }
+        });
+    return result[0];
+  }
+
   @Override
   public boolean usesContext() {
     return false;

sdk/metrics/src/test/java/io/opentelemetry/sdk/metrics/internal/view/AdviceAttributesProcessorTest.java

@@ -24,6 +24,19 @@ void doesNotUseContext() {
     assertThat(new AdviceAttributesProcessor(emptyList()).usesContext()).isFalse();
   }
 
+  @Test
+  void noExtraAttributes() {
+    AttributesProcessor processor =
+        new AdviceAttributesProcessor(asList(stringKey("abc"), stringKey("def")));
+
+    Attributes result =
+        processor.process(
+            Attributes.builder().put(stringKey("abc"), "abc").put(stringKey("def"), "def").build(),
+            Context.root());
+
+    assertThat(result).containsOnly(entry(stringKey("abc"), "abc"), entry(stringKey("def"), "def"));
+  }
+
   @Test
   void removeUnwantedAttributes() {
     AttributesProcessor processor =