feat(json): Improve structure performance

components/json/build.gradle.kts

@@ -1 +1,9 @@
+plugins {
+  id("me.champeau.jmh")
+}
+
 apply(from = "$rootDir/gradle/java.gradle")
+
+jmh {
+  version = "1.28"
+}

components/json/src/jmh/java/datadog/json/JsonWriterBenchmark.java

@@ -0,0 +1,106 @@
+package datadog.json;
+
+import static java.util.concurrent.TimeUnit.MICROSECONDS;
+import static org.openjdk.jmh.annotations.Mode.AverageTime;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.infra.Blackhole;
+
+@BenchmarkMode(AverageTime)
+@OutputTimeUnit(MICROSECONDS)
+@Fork(value = 1)
+@SuppressWarnings("unused")
+public class JsonWriterBenchmark {
+  @Benchmark
+  public void writeSimpleArray(Blackhole blackhole) {
+    try (JsonWriter writer = new JsonWriter()) {
+      writer
+          .beginArray()
+          .beginObject()
+          .name("true")
+          .value(true)
+          .endObject()
+          .beginObject()
+          .name("false")
+          .value(false)
+          .endObject()
+          .endArray();
+      blackhole.consume(writer.toString());
+    }
+  }
+
+  @Benchmark
+  public void writeComplexArray(Blackhole blackhole) {
+    try (JsonWriter writer = new JsonWriter()) {
+      writer
+          .beginArray()
+          .value("first level")
+          .beginArray()
+          .value("second level")
+          .beginArray()
+          .value("third level")
+          .beginObject()
+          .name("key")
+          .value("value")
+          .endObject()
+          .beginObject()
+          .name("key")
+          .value("value")
+          .endObject()
+          .endArray() // second level
+          .beginObject()
+          .name("key")
+          .value("value")
+          .endObject()
+          .endArray() // first level
+          .beginObject()
+          .name("key")
+          .value("value")
+          .endObject()
+          .value("last value")
+          .endArray();
+      blackhole.consume(writer.toString());
+    }
+  }
+
+  @Benchmark
+  public void writeComplexObject(Blackhole blackhole) {
+    try (JsonWriter writer = new JsonWriter()) {
+      writer
+          .beginObject()
+          .name("attrs")
+          .beginObject()
+          .name("attr1")
+          .value("value1")
+          .name("attr2")
+          .value("value2")
+          .endObject()
+          .name("data")
+          .beginArray()
+          .beginObject()
+          .name("x")
+          .value(1)
+          .name("y")
+          .value(12.3)
+          .endObject()
+          .beginObject()
+          .name("x")
+          .value(2)
+          .name("y")
+          .value(4.56)
+          .endObject()
+          .beginObject()
+          .name("x")
+          .value(3)
+          .name("y")
+          .value(789)
+          .endObject()
+          .endArray()
+          .endObject();
+      blackhole.consume(writer.toString());
+    }
+  }
+}

components/json/src/main/java/datadog/json/SafeJsonStructure.java

@@ -1,20 +1,19 @@
 package datadog.json;
 
-import static java.util.stream.Collectors.joining;
-
-import java.util.ArrayDeque;
-import java.util.Deque;
+import java.util.BitSet;
 
 /**
  * This {@link JsonStructure} performs minimal structure checks to ensure the built JSON is
  * coherent.
  */
 class SafeJsonStructure implements JsonStructure {
-  private final Deque<Boolean> structure;
+  private final BitSet structure;
+  private int depth;
   private boolean complete;
 
   SafeJsonStructure() {
-    this.structure = new ArrayDeque<>();
+    this.structure = new BitSet();
+    this.depth = -1;
     this.complete = false;
   }
 
@@ -23,21 +22,21 @@ public void beginObject() {
     if (this.complete) {
       throw new IllegalStateException("Object is complete");
     }
-    this.structure.add(true);
+    this.structure.set(++this.depth);
   }
 
   @Override
   public boolean objectStarted() {
-    return !this.structure.isEmpty() && this.structure.peekLast();
+    return this.depth >= 0 && this.structure.get(this.depth);
   }
 
   @Override
   public void endObject() {
     if (!objectStarted()) {
       throw new IllegalStateException("Object not started");
     }
-    this.structure.removeLast();
-    if (this.structure.isEmpty()) {
+    this.depth--;
+    if (this.depth < 0) {
       this.complete = true;
     }
   }
@@ -47,21 +46,21 @@ public void beginArray() {
     if (this.complete) {
       throw new IllegalStateException("Object is complete");
     }
-    this.structure.offer(false);
+    this.structure.clear(++this.depth);
   }
 
   @Override
   public boolean arrayStarted() {
-    return !this.structure.isEmpty() && !this.structure.peekLast();
+    return this.depth >= 0 && !this.structure.get(this.depth);
   }
 
   @Override
   public void endArray() {
     if (!arrayStarted()) {
       throw new IllegalStateException("Array not started");
     }
-    this.structure.removeLast();
-    if (this.structure.isEmpty()) {
+    this.depth--;
+    if (this.depth < 0) {
       this.complete = true;
     }
   }
@@ -78,16 +77,13 @@ public void addValue() {
     if (this.complete) {
       throw new IllegalStateException("Object is complete");
     }
-    if (this.structure.isEmpty()) {
+    if (this.depth < 0) {
       this.complete = true;
     }
   }
 
   @Override
   public String toString() {
-    return (this.complete ? "complete" : "")
-        + this.structure.stream()
-            .map(b -> b ? "object start" : "array start")
-            .collect(joining(","));
+    return (this.complete ? "complete" : "") + this.structure;
   }
 }