8285447: StackWalker minimal batch size should be optimized for getCallerClass

Reviewed-by: simonis

Author: Mandy Chung

src/java.base/share/classes/java/lang/StackStreamFactory.java

@@ -69,10 +69,12 @@ private StackStreamFactory() {}
     // lazily add subclasses when they are loaded.
     private static final Set<Class<?>> stackWalkImplClasses = init();
 
+    // Number of elements in the buffer reserved for VM to use
+    private static final int RESERVED_ELEMENTS = 1;
+    private static final int MIN_BATCH_SIZE    = RESERVED_ELEMENTS + 2;
     private static final int SMALL_BATCH       = 8;
     private static final int BATCH_SIZE        = 32;
     private static final int LARGE_BATCH_SIZE  = 256;
-    private static final int MIN_BATCH_SIZE    = SMALL_BATCH;
 
     // These flags must match the values maintained in the VM
     @Native private static final int DEFAULT_MODE              = 0x0;
@@ -196,7 +198,7 @@ protected AbstractStackWalker(StackWalker walker, int mode, int maxDepth) {
         protected abstract int batchSize(int lastBatchFrameCount);
 
         /*
-         * Returns the next batch size, always >= minimum batch size (32)
+         * Returns the next batch size, always >= minimum batch size
          *
          * Subclass may override this method if the minimum batch size is different.
          */
@@ -538,8 +540,7 @@ protected void initFrameBuffer() {
         protected int batchSize(int lastBatchFrameCount) {
             if (lastBatchFrameCount == 0) {
                 // First batch, use estimateDepth if not exceed the large batch size
-                // and not too small
-                int initialBatchSize = Math.max(walker.estimateDepth(), SMALL_BATCH);
+                int initialBatchSize = Math.max(walker.estimateDepth()+RESERVED_ELEMENTS, MIN_BATCH_SIZE);
                 return Math.min(initialBatchSize, LARGE_BATCH_SIZE);
             } else {
                 if (lastBatchFrameCount > BATCH_SIZE) {
@@ -747,19 +748,31 @@ protected Integer consumeFrames() {
             return n;
         }
 
+        /*
+         * Typically finding the caller class only needs to walk two stack frames
+         * 0: StackWalker::getCallerClass
+         * 1: API
+         * 2: caller class
+         *
+         * So start the initial batch size with the minimum size.
+         */
         @Override
         protected void initFrameBuffer() {
-            this.frameBuffer = new ClassFrameBuffer(walker, getNextBatchSize());
+            this.frameBuffer = new ClassFrameBuffer(walker, MIN_BATCH_SIZE);
         }
 
         @Override
         protected int batchSize(int lastBatchFrameCount) {
-            return MIN_BATCH_SIZE;
+            // this method is only called when the caller class is not found in
+            // the first batch. getCallerClass may be invoked via core reflection.
+            // So increase the next batch size as there may be implementation-specific
+            // frames before reaching the caller class's frame.
+            return SMALL_BATCH;
         }
 
         @Override
         protected int getNextBatchSize() {
-            return MIN_BATCH_SIZE;
+            return SMALL_BATCH;
         }
     }
 
@@ -785,7 +798,7 @@ protected void initFrameBuffer() {
      * Each specialized AbstractStackWalker subclass may subclass the FrameBuffer.
      */
     abstract static class FrameBuffer<F> {
-        static final int START_POS = 2;     // 0th and 1st elements are reserved
+        static final int START_POS = RESERVED_ELEMENTS;
 
         // buffers for VM to fill stack frame info
         int currentBatchSize;    // current batch size

test/micro/org/openjdk/bench/java/lang/CallerClassBench.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.openjdk.bench.java.lang;
+
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+@Warmup(iterations = 5, time = 1)
+@Measurement(iterations = 5, time = 1)
+@Fork(value = 3, jvmArgsAppend = {"-Xmx1g", "-Xms1g"})
+@State(Scope.Benchmark)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MICROSECONDS)
+public class CallerClassBench {
+    static final StackWalker INST = StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE);
+
+    @Benchmark
+    public Class<?> getCallerClass() {
+        return INST.getCallerClass();
+    }
+}

test/micro/org/openjdk/bench/java/lang/StackWalkBench.java

@@ -310,16 +310,6 @@ public void run() {
         }
     }
 
-    /**
-     * StackWalker.getCallerClass()
-     */
-    @Benchmark
-    public void getCallerClass(Blackhole bh) {
-        final StackWalker sw = walker(walker);
-        Class<?> c = sw.getCallerClass();
-        bh.consume(c);
-    }
-
     /**
      * StackWalker.getCallerClass() with generated call stack of
      * the given depth.