perf: reduce hashmap allocations (#1178)

* chore: reduce hashmap allocations

Signed-off-by: Todd Baert <[email protected]>

CONTRIBUTING.md

@@ -35,10 +35,13 @@ mvn test -P e2e
 There is a small JMH benchmark suite for testing allocations that can be run with:
 
 ```sh
-mvn -P benchmark test-compile jmh:benchmark -Djmh.f=1  -Djmh.prof='dev.openfeature.sdk.benchmark.AllocationProfiler'
+mvn -P benchmark clean compile test-compile jmh:benchmark -Djmh.f=1  -Djmh.prof='dev.openfeature.sdk.benchmark.AllocationProfiler'
 ```
 
 If you are concerned about the repercussions of a change on memory usage, run this an compare the results to the committed. `benchmark.txt` file.
+Note that the ONLY MEANINGFUL RESULTS of this benchmark are the `totalAllocatedBytes` and the `totalAllocatedInstances`.
+The `run` score, and maven task time are not relevant since this benchmark is purely memory-related and has nothing to do with speed.
+You can also view the heap breakdown to see which objects are taking up the most memory.
 
 ## Releasing
 

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

@@ -2,6 +2,7 @@
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Collections;
 
 @SuppressWarnings({ "PMD.BeanMembersShouldSerialize", "checkstyle:MissingJavadocType" })
 abstract class AbstractStructure implements Structure {
@@ -18,7 +19,15 @@ public boolean isEmpty() {
     }
 
     AbstractStructure(Map<String, Value> attributes) {
-        this.attributes = new HashMap<>(attributes);
+        this.attributes = attributes;
+    }
+
+    /**
+     * Returns an unmodifiable representation of the internal attribute map.
+     * @return immutable map
+     */
+    public Map<String, Value> asUnmodifiableMap() {
+        return Collections.unmodifiableMap(attributes);
     }
 
     /**

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

@@ -1,5 +1,9 @@
 package dev.openfeature.sdk;
 
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.function.Function;
+
 /**
  * The EvaluationContext is a container for arbitrary contextual data
  * that can be used as a basis for dynamic evaluation.
@@ -19,4 +23,39 @@ public interface EvaluationContext extends Structure {
      * @return resulting merged context
      */
     EvaluationContext merge(EvaluationContext overridingContext);
+
+    /**
+     * Recursively merges the overriding map into the base Value map.
+     * The base map is mutated, the overriding map is not.
+     * Null maps will cause no-op.
+     * 
+     * @param newStructure function to create the right structure(s) for Values
+     * @param base base map to merge
+     * @param overriding overriding map to merge
+     */
+    static void mergeMaps(Function<Map<String, Value>, Structure> newStructure,
+            Map<String, Value> base,
+            Map<String, Value> overriding) {
+
+        if (base == null) {
+            return;
+        }
+        if (overriding == null || overriding.isEmpty()) {
+            return;
+        }
+
+        for (Entry<String, Value> overridingEntry : overriding.entrySet()) {
+            String key = overridingEntry.getKey();
+            if (overridingEntry.getValue().isStructure() && base.containsKey(key) && base.get(key).isStructure()) {
+                Structure mergedValue = base.get(key).asStructure();
+                Structure overridingValue = overridingEntry.getValue().asStructure();
+                Map<String, Value> newMap = mergedValue.asMap();
+                mergeMaps(newStructure, newMap,
+                        overridingValue.asUnmodifiableMap());
+                base.put(key, new Value(newStructure.apply(newMap)));
+            } else {
+                base.put(key, overridingEntry.getValue());
+            }
+        }
+    }
 }

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

@@ -3,14 +3,16 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Function;
+
 import dev.openfeature.sdk.internal.ExcludeFromGeneratedCoverageReport;
 import lombok.ToString;
 import lombok.experimental.Delegate;
 
 /**
  * The EvaluationContext is a container for arbitrary contextual data
  * that can be used as a basis for dynamic evaluation.
- * The ImmutableContext is an EvaluationContext implementation which is threadsafe, and whose attributes can
+ * The ImmutableContext is an EvaluationContext implementation which is
+ * threadsafe, and whose attributes can
  * not be modified after instantiation.
  */
 @ToString
@@ -21,7 +23,8 @@ public final class ImmutableContext implements EvaluationContext {
     private final ImmutableStructure structure;
 
     /**
-     * Create an immutable context with an empty targeting_key and attributes provided.
+     * Create an immutable context with an empty targeting_key and attributes
+     * provided.
      */
     public ImmutableContext() {
         this(new HashMap<>());
@@ -42,7 +45,7 @@ public ImmutableContext(String targetingKey) {
      * @param attributes evaluation context attributes
      */
     public ImmutableContext(Map<String, Value> attributes) {
-        this("", attributes);
+        this(null, attributes);
     }
 
     /**
@@ -53,9 +56,7 @@ public ImmutableContext(Map<String, Value> attributes) {
      */
     public ImmutableContext(String targetingKey, Map<String, Value> attributes) {
         if (targetingKey != null && !targetingKey.trim().isEmpty()) {
-            final Map<String, Value> actualAttribs = new HashMap<>(attributes);
-            actualAttribs.put(TARGETING_KEY, new Value(targetingKey));
-            this.structure = new ImmutableStructure(actualAttribs);
+            this.structure = new ImmutableStructure(targetingKey, attributes);
         } else {
             this.structure = new ImmutableStructure(attributes);
         }
@@ -71,31 +72,33 @@ public String getTargetingKey() {
     }
 
     /**
-     * Merges this EvaluationContext object with the passed EvaluationContext, overriding in case of conflict.
+     * Merges this EvaluationContext object with the passed EvaluationContext,
+     * overriding in case of conflict.
      *
      * @param overridingContext overriding context
      * @return new, resulting merged context
      */
     @Override
     public EvaluationContext merge(EvaluationContext overridingContext) {
         if (overridingContext == null || overridingContext.isEmpty()) {
-            return new ImmutableContext(this.asMap());
+            return new ImmutableContext(this.asUnmodifiableMap());
         }
         if (this.isEmpty()) {
-            return new ImmutableContext(overridingContext.asMap());
+            return new ImmutableContext(overridingContext.asUnmodifiableMap());
         }
 
-        return new ImmutableContext(
-                this.merge(ImmutableStructure::new, this.asMap(), overridingContext.asMap()));
+        Map<String, Value> attributes = this.asMap();
+        EvaluationContext.mergeMaps(ImmutableStructure::new, attributes,
+                overridingContext.asUnmodifiableMap());
+        return new ImmutableContext(attributes);
     }
 
     @SuppressWarnings("all")
     private static class DelegateExclusions {
         @ExcludeFromGeneratedCoverageReport
-        public <T extends Structure> Map<String, Value> merge(Function<Map<String, Value>, Structure> newStructure, 
+        public <T extends Structure> Map<String, Value> merge(Function<Map<String, Value>, Structure> newStructure,
                 Map<String, Value> base,
                 Map<String, Value> overriding) {
-
             return null;
         }
     }

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

@@ -36,7 +36,11 @@ public ImmutableStructure() {
      * @param attributes attributes.
      */
     public ImmutableStructure(Map<String, Value> attributes) {
-        super(copyAttributes(attributes));
+        super(copyAttributes(attributes, null));
+    }
+
+    protected ImmutableStructure(String targetingKey, Map<String, Value> attributes) {
+        super(copyAttributes(attributes, targetingKey));
     }
 
     @Override
@@ -62,11 +66,18 @@ public Map<String, Value> asMap() {
     }
 
     private static Map<String, Value> copyAttributes(Map<String, Value> in) {
+        return copyAttributes(in, null);
+    }
+
+    private static Map<String, Value> copyAttributes(Map<String, Value> in, String targetingKey) {
         Map<String, Value> copy = new HashMap<>();
         for (Entry<String, Value> entry : in.entrySet()) {
             copy.put(entry.getKey(),
                     Optional.ofNullable(entry.getValue()).map((Value val) -> val.clone()).orElse(null));
         }
+        if (targetingKey != null) {
+            copy.put(EvaluationContext.TARGETING_KEY, new Value(targetingKey));
+        }
         return copy;
     }
 

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

@@ -33,7 +33,7 @@ public MutableContext(String targetingKey) {
     }
 
     public MutableContext(Map<String, Value> attributes) {
-        this("", attributes);
+        this(null, new HashMap<>(attributes));
     }
 
     /**
@@ -44,7 +44,7 @@ public MutableContext(Map<String, Value> attributes) {
      * @param attributes   evaluation context attributes
      */
     public MutableContext(String targetingKey, Map<String, Value> attributes) {
-        this.structure = new MutableStructure(attributes);
+        this.structure = new MutableStructure(new HashMap<>(attributes));
         if (targetingKey != null && !targetingKey.trim().isEmpty()) {
             this.structure.attributes.put(TARGETING_KEY, new Value(targetingKey));
         }
@@ -121,9 +121,10 @@ public EvaluationContext merge(EvaluationContext overridingContext) {
             return overridingContext;
         }
 
-        Map<String, Value> merged = this.merge(
-                MutableStructure::new, this.asMap(), overridingContext.asMap());
-        return new MutableContext(merged);
+        Map<String, Value> attributes = this.asMap();
+        EvaluationContext.mergeMaps(
+                MutableStructure::new, attributes, overridingContext.asUnmodifiableMap());
+        return new MutableContext(attributes);
     }
 
     /**