perf: eliminate merge allocation in setHooks by accepting hook sources directly

Signed-off-by: Tobias Ibounig <tobias.ibounig@dynatrace.com>

Author: tobias-ibounig-dt

src/main/java/dev/openfeature/sdk/HookSupport.java

@@ -1,6 +1,7 @@
 package dev.openfeature.sdk;
 
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
@@ -16,19 +17,37 @@ class HookSupport {
     /**
      * Sets the {@link Hook}-{@link HookContext}-{@link Pair} list in the given data object with {@link HookContext}
      * set to null. Filters hooks by supported {@link FlagValueType}.
+     * Sources are iterated in order: provider → options → client → API.
      *
      * @param hookSupportData the data object to modify
-     * @param hooks           the hooks to set
+     * @param providerHooks   provider-level hooks
+     * @param optionHooks     per-evaluation option hooks
+     * @param clientHooks     client-level hooks
+     * @param apiHooks        API-level hooks
      * @param type            the flag value type to filter unsupported hooks
      */
-    public void setHooks(HookSupportData hookSupportData, List<Hook> hooks, FlagValueType type) {
+    public void setHooks(
+            HookSupportData hookSupportData,
+            Collection<Hook> providerHooks,
+            Collection<Hook> optionHooks,
+            Collection<Hook> clientHooks,
+            Collection<Hook> apiHooks,
+            FlagValueType type) {
         List<Pair<Hook, HookContext>> hookContextPairs = new ArrayList<>();
-        for (Hook hook : hooks) {
+        addFilteredHooks(hookContextPairs, providerHooks, type);
+        addFilteredHooks(hookContextPairs, optionHooks, type);
+        addFilteredHooks(hookContextPairs, clientHooks, type);
+        addFilteredHooks(hookContextPairs, apiHooks, type);
+        hookSupportData.hooks = hookContextPairs;
+    }
+
+    private static void addFilteredHooks(
+            List<Pair<Hook, HookContext>> dest, Collection<Hook> source, FlagValueType type) {
+        for (Hook hook : source) {
             if (hook.supportsFlagValueType(type)) {
-                hookContextPairs.add(Pair.of(hook, null));
+                dest.add(Pair.of(hook, null));
             }
         }
-        hookSupportData.hooks = hookContextPairs;
     }
 
     /**

src/main/java/dev/openfeature/sdk/OpenFeatureClient.java

@@ -5,7 +5,6 @@
 import dev.openfeature.sdk.exceptions.GeneralError;
 import dev.openfeature.sdk.exceptions.OpenFeatureError;
 import dev.openfeature.sdk.exceptions.ProviderNotReadyError;
-import dev.openfeature.sdk.internal.ObjectUtils;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -185,9 +184,13 @@ private <T> FlagEvaluationDetails<T> evaluateFlag(
             final var state = stateManager.getState();
 
             // Hooks are initialized as early as possible to enable the execution of error stages
-            var mergedHooks = ObjectUtils.merge(
-                    provider.getProviderHooks(), flagOptions.getHooks(), clientHooks, openfeatureApi.getMutableHooks());
-            hookSupport.setHooks(hookSupportData, mergedHooks, type);
+            hookSupport.setHooks(
+                    hookSupportData,
+                    provider.getProviderHooks(),
+                    flagOptions.getHooks(),
+                    clientHooks,
+                    openfeatureApi.getMutableHooks(),
+                    type);
 
             var sharedHookContext =
                     new SharedHookContext(key, type, this.getMetadata(), provider.getMetadata(), defaultValue);

src/test/java/dev/openfeature/sdk/HookSupportTest.java

@@ -9,6 +9,7 @@
 
 import dev.openfeature.sdk.fixtures.HookFixtures;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -38,7 +39,13 @@ void shouldMergeEvaluationContextsOnBeforeHooksCorrectly() {
         var sharedContext = getBaseHookContextForType(FlagValueType.STRING);
         var hookSupportData = new HookSupportData();
         hookSupportData.evaluationContext = layered;
-        hookSupport.setHooks(hookSupportData, Arrays.asList(hook1, hook2), FlagValueType.STRING);
+        hookSupport.setHooks(
+                hookSupportData,
+                Collections.emptyList(),
+                Collections.emptyList(),
+                Arrays.asList(hook1, hook2),
+                Collections.emptyList(),
+                FlagValueType.STRING);
         hookSupport.setHookContexts(hookSupportData, sharedContext, layered);
 
         hookSupport.executeBeforeHooks(hookSupportData);
@@ -57,7 +64,13 @@ void shouldAlwaysCallGenericHook(FlagValueType flagValueType) {
         Hook<?> genericHook = mockGenericHook();
 
         var hookSupportData = new HookSupportData();
-        hookSupport.setHooks(hookSupportData, List.of(genericHook), flagValueType);
+        hookSupport.setHooks(
+                hookSupportData,
+                Collections.emptyList(),
+                Collections.emptyList(),
+                List.of(genericHook),
+                Collections.emptyList(),
+                flagValueType);
 
         callAllHooks(hookSupportData);
 
@@ -73,7 +86,13 @@ void shouldAlwaysCallGenericHook(FlagValueType flagValueType) {
     void shouldPassDataAcrossStages(FlagValueType flagValueType) {
         var testHook = new TestHookWithData();
         var hookSupportData = new HookSupportData();
-        hookSupport.setHooks(hookSupportData, List.of(testHook), flagValueType);
+        hookSupport.setHooks(
+                hookSupportData,
+                Collections.emptyList(),
+                Collections.emptyList(),
+                List.of(testHook),
+                Collections.emptyList(),
+                flagValueType);
         hookSupport.setHookContexts(
                 hookSupportData,
                 getBaseHookContextForType(flagValueType),
@@ -102,7 +121,13 @@ void shouldIsolateDataBetweenHooks(FlagValueType flagValueType) {
         var testHook2 = new TestHookWithData(2);
 
         var hookSupportData = new HookSupportData();
-        hookSupport.setHooks(hookSupportData, List.of(testHook1, testHook2), flagValueType);
+        hookSupport.setHooks(
+                hookSupportData,
+                Collections.emptyList(),
+                Collections.emptyList(),
+                List.of(testHook1, testHook2),
+                Collections.emptyList(),
+                flagValueType);
         hookSupport.setHookContexts(
                 hookSupportData,
                 getBaseHookContextForType(flagValueType),
@@ -132,7 +157,13 @@ public Optional<EvaluationContext> before(HookContext ctx, Map hints) {
         var layeredEvaluationContext =
                 new LayeredEvaluationContext(evaluationContextWithValue("key", "value"), null, null, null);
         hookSupportData.evaluationContext = layeredEvaluationContext;
-        hookSupport.setHooks(hookSupportData, List.of(recursiveHook, emptyHook), FlagValueType.STRING);
+        hookSupport.setHooks(
+                hookSupportData,
+                Collections.emptyList(),
+                Collections.emptyList(),
+                List.of(recursiveHook, emptyHook),
+                Collections.emptyList(),
+                FlagValueType.STRING);
         hookSupport.setHookContexts(
                 hookSupportData, getBaseHookContextForType(FlagValueType.STRING), layeredEvaluationContext);