Atomics benchmark

Benchmark to show cost of Atomic vs AtomicFieldUpdater

Author: dougqh

internal-api/src/jmh/java/datadog/trace/util/AtomicsBenchmark.java

@@ -0,0 +1,161 @@
+package datadog.trace.util;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
+import java.util.function.Supplier;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Threads;
+import org.openjdk.jmh.annotations.Warmup;
+
+/**
+ * <ul>
+ * <li>(RECOMMENDED) AtomicFieldUpdater - especially, when containing object is frequently constructed
+ * <li>Atomic - usually, performs similarly to AtomicFieldUpdater - worse inside commonly constructed objects
+ * </ul>
+ * 
+ * Instead of introucing an Atomic field into a class, a volatile field with an AtomicFieldUpdater is preferred when possible.
+ * <ul>Types with AtomicFieldUpdaters are...
+ * <li>int
+ * <li>long
+ * <li>reference (e.g. Object types)
+ * </ul>
+ * 
+ * While the performance of Atomic is on par with AtomicFieldUpdater (and sometimes slightly better) inside a frequently 
+ * constructed object, the impact of the extra allocation on garbage collection is detrimental to the application as a whole.
+ * 
+ * <code> Java 17 - MacBook M1 - 8 threads
+ * Benchmark                                                                Mode  Cnt           Score           Error   Units
+ * AtomicsBenchmark.atomicFieldUpdater_construction                        thrpt    6  4442811623.924 ± 293568588.782   ops/s
+ * AtomicsBenchmark.atomicFieldUpdater_construction:gc.alloc.rate.norm     thrpt    6          16.000 ±         0.001    B/op
+
+ * AtomicsBenchmark.atomicFieldUpdater_get                                 thrpt    6  1849238178.083 ±  29719143.488   ops/s
+ * AtomicsBenchmark.atomicFieldUpdater_get:gc.alloc.rate.norm              thrpt    6          ≈ 10⁻⁶                    B/op
+
+ * AtomicsBenchmark.atomicFieldUpdater_getVolatile                         thrpt    6  1814698391.230 ±  54378746.492   ops/s
+ * AtomicsBenchmark.atomicFieldUpdater_getVolatile:gc.alloc.rate.norm      thrpt    6          ≈ 10⁻⁶                    B/op
+
+ * AtomicsBenchmark.atomicFieldUpdater_incrementAndGet                     thrpt    6    15871753.651 ±    432451.444   ops/s
+ * AtomicsBenchmark.atomicFieldUpdater_incrementAndGet:gc.alloc.rate.norm  thrpt    6          ≈ 10⁻⁴                    B/op
+
+ * AtomicsBenchmark.atomic_construction                                    thrpt    6  2532095943.171 ±  87644803.894   ops/s
+ * AtomicsBenchmark.atomic_construction:gc.alloc.rate.norm                 thrpt    6          32.000 ±         0.001    B/op
+
+ * AtomicsBenchmark.atomic_incrementAndGet                                 thrpt    6    16416635.546 ±    751137.083   ops/s
+ * AtomicsBenchmark.atomic_incrementAndGet:gc.alloc.rate.norm              thrpt    6          ≈ 10⁻⁴                    B/op
+
+ * AtomicsBenchmark.atomic_read                                            thrpt    6  1943297600.062 ±  43802387.143   ops/s
+ * AtomicsBenchmark.atomic_read:gc.alloc.rate.norm                         thrpt    6          ≈ 10⁻⁶                    B/op
+ */
+@Fork(2)
+@Warmup(iterations=2)
+@Measurement(iterations=3)
+@Threads(8)
+public class AtomicsBenchmark {
+  static int SIZE = 32;
+  
+  static final class AtomicHolder {
+	final AtomicInteger atomic;
+	
+	AtomicHolder(int num) {
+	  this.atomic = new AtomicInteger(num);
+	}
+	
+	int get() {
+	  return this.atomic.get();
+	}
+	
+	int incrementAndGet() {
+	  return this.atomic.incrementAndGet();
+	}
+  }
+  
+  static final class FieldHolder {
+	static final AtomicIntegerFieldUpdater<FieldHolder> AFU_FIELD = AtomicIntegerFieldUpdater.newUpdater(FieldHolder.class, "field");
+	
+	volatile int field;
+	
+	FieldHolder(int num) {
+	  this.field = num;
+	}
+	
+	int getVolatile() {
+	  return this.field;
+	}
+	
+	int get() {
+	  return AFU_FIELD.get(this);
+	}
+	
+	int incrementAndGet() {
+	  return AFU_FIELD.incrementAndGet(this);
+	}
+  }
+  
+  static final AtomicHolder[] atomicHolders = init(() -> {
+	AtomicHolder[] holders = new AtomicHolder[SIZE];
+    for ( int i = 0; i < holders.length; ++i ) {
+      holders[i] = new AtomicHolder(i * 2);
+    }
+    return holders;
+  });
+  
+  static final FieldHolder[] fieldHolders = init(() -> {
+	  FieldHolder[] holders = new FieldHolder[SIZE];
+    for ( int i = 0; i < holders.length; ++i ) {
+      holders[i] = new FieldHolder(i * 2);
+    }
+    return holders;
+  });
+  
+  static final <T> T init(Supplier<T> supplier) {
+	return supplier.get();
+  }
+  
+  static int sharedLookupIndex = 0;
+  
+  static <T> T next(T[] holders) {
+	int localIndex = ++sharedLookupIndex;
+	if ( localIndex >= holders.length ) {
+	  sharedLookupIndex = localIndex = 0;
+	}
+	return holders[localIndex];
+  }
+  
+  @Benchmark
+  public Object atomic_construction() {
+	return new AtomicHolder(0);
+  }
+  
+  @Benchmark
+  public int atomic_incrementAndGet() {
+	return next(atomicHolders).incrementAndGet();  
+  }
+  
+  @Benchmark
+  public Object atomic_read() {
+	return next(atomicHolders).get();
+  }
+  
+  @Benchmark
+  public Object atomicFieldUpdater_construction() {
+	return new FieldHolder(0);
+  }
+  
+  @Benchmark
+  public Object atomicFieldUpdater_getVolatile() {
+	return next(fieldHolders).getVolatile();
+  }
+  
+  @Benchmark
+  public Object atomicFieldUpdater_get() {
+	return next(fieldHolders).get();
+  }
+  
+  @Benchmark
+  public int atomicFieldUpdater_incrementAndGet() {
+	return next(fieldHolders).incrementAndGet();
+  }
+}