Add raw struct variant of AdaptiveWeightedAverage

Author: Thomas Schrott

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/AdaptiveWeightedAverage.java

@@ -24,8 +24,11 @@
  */
 package com.oracle.svm.core.genscavenge;
 
+import static com.oracle.svm.core.Uninterruptible.CALLED_FROM_UNINTERRUPTIBLE_CODE;
+
 import org.graalvm.word.UnsignedWord;
 
+import com.oracle.svm.core.Uninterruptible;
 import com.oracle.svm.core.util.UnsignedUtils;
 
 /**
@@ -101,7 +104,8 @@ protected double computeAdaptiveAverage(double sample, double avg) {
         return expAvg(avg, sample, adaptiveWeight);
     }
 
-    private static double expAvg(double avg, double sample, double adaptiveWeight) {
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+    static double expAvg(double avg, double sample, double adaptiveWeight) {
         assert adaptiveWeight > 0 && adaptiveWeight <= 100 : "weight must be a percentage";
         return (100.0 - adaptiveWeight) * avg / 100.0 + adaptiveWeight * sample / 100.0;
     }

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/AdaptiveWeightedAverageStruct.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2025, 2025, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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 com.oracle.svm.core.genscavenge;
+
+import static com.oracle.svm.core.Uninterruptible.CALLED_FROM_UNINTERRUPTIBLE_CODE;
+import static com.oracle.svm.core.genscavenge.AdaptiveWeightedAverage.OLD_THRESHOLD;
+
+import org.graalvm.nativeimage.c.struct.RawField;
+import org.graalvm.nativeimage.c.struct.RawStructure;
+import org.graalvm.word.PointerBase;
+import org.graalvm.word.UnsignedWord;
+
+import com.oracle.svm.core.Uninterruptible;
+import com.oracle.svm.core.jdk.UninterruptibleUtils;
+import com.oracle.svm.core.util.UnsignedUtils;
+
+/**
+ * This class provides a raw structure implementation of {@link AdaptiveWeightedAverage}. For
+ * further information see {@link AdaptiveWeightedAverage}.
+ */
+class AdaptiveWeightedAverageStruct {
+
+    @RawStructure
+    interface Data extends PointerBase {
+
+        @RawField
+        void setWeight(double weight);
+
+        @RawField
+        double getWeight();
+
+        @RawField
+        void setAverage(double average);
+
+        @RawField
+        double getAverage();
+
+        @RawField
+        void setSampleCount(long sampleCount);
+
+        @RawField
+        long getSampleCount();
+
+        @RawField
+        void setIsOld(boolean isOld);
+
+        @RawField
+        boolean getIsOld();
+    }
+
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+    static void initialize(Data data, double weight) {
+        initialize(data, weight, 0);
+    }
+
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+    static void initialize(Data data, double weight, double avg) {
+        assert weight > 0 && weight <= 100;
+        data.setWeight(weight);
+        data.setAverage(avg);
+    }
+
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+    public static double getAverage(Data data) {
+        return data.getAverage();
+    }
+
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+    public static void sample(Data data, double value) {
+        data.setSampleCount(data.getSampleCount() + 1);
+        if (!data.getIsOld() && data.getSampleCount() > OLD_THRESHOLD) {
+            data.setIsOld(true);
+        }
+        data.setAverage(computeAdaptiveAverage(data, value, data.getAverage()));
+    }
+
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+    public static void sample(Data data, UnsignedWord value) {
+        sample(data, UnsignedUtils.toDouble(value));
+    }
+
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+    protected static double computeAdaptiveAverage(Data data, double sample, double avg) {
+        /*
+         * We smoothen the samples by not using weight directly until we've had enough data to make
+         * it meaningful. We'd like the first weight used to be 1, the second to be 1/2, etc until
+         * we have OLD_THRESHOLD/weight samples.
+         */
+        double countWeight = 0;
+        if (!data.getIsOld()) { // avoid division by zero if the counter wraps
+            countWeight = OLD_THRESHOLD / (double) data.getSampleCount();
+        }
+        double adaptiveWeight = UninterruptibleUtils.Math.max(data.getWeight(), countWeight);
+        return AdaptiveWeightedAverage.expAvg(avg, sample, adaptiveWeight);
+    }
+
+}

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/UninterruptibleUtils.java

@@ -427,6 +427,18 @@ public static long max(long a, long b) {
             return (a >= b) ? a : b;
         }
 
+        @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
+        public static double max(double a, double b) {
+            if (a != a) {
+                return a;   // a is NaN
+            }
+            if ((a == 0.0d) && (b == 0.0d) && (Double.doubleToRawLongBits(a) == Double.doubleToRawLongBits(-0.0d))) {
+                // Raw conversion ok since NaN can't map to -0.0.
+                return b;
+            }
+            return (a >= b) ? a : b;
+        }
+
         @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
         public static int clamp(int value, int min, int max) {
             assert min <= max;