core: allow attributes to be built multiple times

core/src/jmh/java/io/grpc/AttributesBenchmark.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2017, gRPC Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc;
+
+
+import java.util.concurrent.TimeUnit;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+
+/**
+ * Javadoc.
+ */
+@State(Scope.Benchmark)
+public class AttributesBenchmark {
+
+  public Attributes base = Attributes.EMPTY;
+
+  public Attributes.Key<Object>[] keys;
+  public Attributes withValue = base;
+
+  /**
+   * Javadoc.
+   */
+  @Setup
+  @SuppressWarnings({"unchecked", "rawtypes"})
+  public void setUp() {
+    keys = new Attributes.Key[iterations];
+    for (int i = 0; i < iterations; i++) {
+      keys[i] = Attributes.Key.of("any");
+      withValue = Attributes.newBuilder(withValue).set(keys[i], "yes").build();
+    }
+  }
+
+  @Param({"1", "2", "10"})
+  public int iterations;
+
+  /**
+   * Javadoc.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public Attributes chain() {
+    Attributes attr = base;
+    for (int i = 0; i < iterations; i++) {
+      attr = Attributes.newBuilder(attr).set(keys[i], new Object()).build();
+    }
+    return attr;
+  }
+
+  /**
+   * Javadoc.
+   */
+  @Benchmark
+  @BenchmarkMode(Mode.SampleTime)
+  @OutputTimeUnit(TimeUnit.NANOSECONDS)
+  public Object lookup() {
+    return withValue.get(keys[0]);
+  }
+}

core/src/main/java/io/grpc/Attributes.java

@@ -16,10 +16,13 @@
 
 package io.grpc;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+
 import com.google.common.base.Objects;
-import com.google.common.base.Preconditions;
 import java.util.Collections;
-import java.util.HashMap;
+import java.util.IdentityHashMap;
+import java.util.Map;
+import java.util.Map.Entry;
 import java.util.Set;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
@@ -31,11 +34,13 @@ import javax.annotation.concurrent.Immutable;
 @Immutable
 public final class Attributes {
 
-  private final HashMap<Key<?>, Object> data = new HashMap<Key<?>, Object>();
+  private final Map<Key<?>, Object> data;
 
-  public static final Attributes EMPTY = new Attributes();
+  public static final Attributes EMPTY = new Attributes(Collections.<Key<?>, Object>emptyMap());
 
-  private Attributes() {
+  private Attributes(Map<Key<?>, Object> data) {
+    assert data != null;
+    this.data = data;
   }
 
   /**
@@ -60,14 +65,15 @@ public final class Attributes {
    * Create a new builder that is pre-populated with the content from a given container.
    */
   public static Builder newBuilder(Attributes base) {
-    return newBuilder().setAll(base);
+    checkNotNull(base, "base");
+    return new Builder(base);
   }
 
   /**
    * Create a new builder.
    */
   public static Builder newBuilder() {
-    return new Builder();
+    return new Builder(EMPTY);
   }
 
   /**
@@ -144,30 +150,45 @@ public final class Attributes {
    * The helper class to build an Attributes instance.
    */
   public static final class Builder {
-    private Attributes product;
+    private Attributes base;
+    private Map<Key<?>, Object> newdata;
 
-    private Builder() {
-      this.product = new Attributes();
+    private Builder(Attributes base) {
+      assert base != null;
+      this.base = base;
+    }
+
+    private Map<Key<?>, Object> data(int size) {
+      if (newdata == null) {
+        newdata = new IdentityHashMap<Key<?>, Object>(size);
+      }
+      return newdata;
     }
 
     public <T> Builder set(Key<T> key, T value) {
-      product.data.put(key, value);
+      data(1).put(key, value);
       return this;
     }
 
     public <T> Builder setAll(Attributes other) {
-      product.data.putAll(other.data);
+      data(other.data.size()).putAll(other.data);
       return this;
     }
 
     /**
-     * Build the attributes. Can only be called once.
+     * Build the attributes.
      */
     public Attributes build() {
-      Preconditions.checkState(product != null, "Already built");
-      Attributes result = product;
-      product = null;
-      return result;
+      if (newdata != null) {
+        for (Entry<Key<?>, Object> entry : base.data.entrySet()) {
+          if (!newdata.containsKey(entry.getKey())) {
+            newdata.put(entry.getKey(), entry.getValue());
+          }
+        }
+        base = new Attributes(newdata);
+        newdata = null;
+      }
+      return base;
     }
   }
 }