[Java] Dekker's algorithm tests.

agrona-concurrency-tests/src/main/java/org/agrona/concurrent/DekkerTests.java

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+/*
+ * Copyright 2014-2024 Real Logic Limited.
+ *
+ * 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
+ *
+ * https://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 org.agrona.concurrent;
+
+import org.openjdk.jcstress.annotations.Actor;
+import org.openjdk.jcstress.annotations.Expect;
+import org.openjdk.jcstress.annotations.JCStressMeta;
+import org.openjdk.jcstress.annotations.JCStressTest;
+import org.openjdk.jcstress.annotations.Outcome;
+import org.openjdk.jcstress.annotations.State;
+import org.openjdk.jcstress.infra.results.JJJJ_Result;
+
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+
+/**
+ * Set of concurrency tests for the Dekker's algorithm.
+ */
+public class DekkerTests
+{
+
+    private static final MethodHandles.Lookup LOOKUP = MethodHandles.lookup();
+
+    DekkerTests()
+    {
+    }
+
+    /**
+     * Expected states.
+     */
+    @Outcome(id = "0, 0, 0, 0", expect = Expect.ACCEPTABLE, desc = "read before write")
+    @Outcome(id = "1, 8, 7, 1", expect = Expect.ACCEPTABLE, desc = "write before read")
+    @Outcome(id = "1, -1, -1, 0", expect = Expect.ACCEPTABLE, desc = "aborted read")
+    public static class ExpectedStates
+    {
+        ExpectedStates()
+        {
+        }
+    }
+
+    /**
+     * Implementation based on volatile access.
+     */
+    @JCStressTest
+    @JCStressMeta(ExpectedStates.class)
+    @State
+    public static class Volatile
+    {
+        private volatile long before;
+        private volatile long after;
+        private int x;
+        private int y;
+
+        Volatile()
+        {
+        }
+
+        /**
+         * Reader thread.
+         *
+         * @param result object.
+         */
+        @Actor
+        public void reader(final JJJJ_Result result)
+        {
+            result.r4 = after;
+
+            result.r2 = x;
+            result.r3 = y;
+            VarHandle.loadLoadFence();
+
+            result.r1 = before;
+            if (result.r1 != result.r4)
+            {
+                result.r2 = -1;
+                result.r3 = -1;
+            }
+        }
+
+        /**
+         * Write thread.
+         */
+        @Actor
+        public void writer()
+        {
+            final long changeNr = before + 1;
+            before = changeNr;
+
+            x = 8;
+            y = 7;
+
+            after = changeNr;
+        }
+    }
+
+    /**
+     * An implementation using {@link VarHandle} API and acquire/release semantics.
+     */
+    @JCStressTest
+    @JCStressMeta(ExpectedStates.class)
+    @State
+    public static class VarHandlesAcquireRelease
+    {
+        private static final VarHandle BEFORE;
+        private static final VarHandle AFTER;
+
+        static
+        {
+            try
+            {
+                BEFORE = LOOKUP.findVarHandle(VarHandlesAcquireRelease.class, "before", long.class);
+                AFTER = LOOKUP.findVarHandle(VarHandlesAcquireRelease.class, "after", long.class);
+            }
+            catch (final NoSuchFieldException | IllegalAccessException e)
+            {
+                throw new RuntimeException(e);
+            }
+        }
+
+        private volatile long before;
+        private volatile long after;
+        private int x;
+        private int y;
+
+        /**
+         * Reader thread.
+         *
+         * @param result object.
+         */
+        @Actor
+        public void reader(final JJJJ_Result result)
+        {
+            result.r4 = (long)AFTER.getAcquire(this);
+
+            result.r2 = x;
+            result.r3 = y;
+            VarHandle.loadLoadFence();
+
+            result.r1 = (long)BEFORE.getAcquire(this);
+            if (result.r1 != result.r4)
+            {
+                result.r2 = -1;
+                result.r3 = -1;
+            }
+        }
+
+        /**
+         * Write thread.
+         */
+        @Actor
+        public void writer()
+        {
+            final long changeNr = (long)BEFORE.get(this) + 1;
+            BEFORE.setRelease(this, changeNr);
+            VarHandle.storeStoreFence();
+
+            x = 8;
+            y = 7;
+
+            AFTER.setRelease(this, changeNr);
+        }
+    }
+
+    /**
+     * An implementation using {@link VarHandle} API and acquire/release semantics with relaxed write barriers.
+     */
+    @JCStressTest
+    @JCStressMeta(ExpectedStates.class)
+    @State
+    public static class VarHandlesAcquireReleasePlainWrite
+    {
+        private static final VarHandle BEFORE;
+        private static final VarHandle AFTER;
+
+        static
+        {
+            try
+            {
+                BEFORE = LOOKUP.findVarHandle(VarHandlesAcquireReleasePlainWrite.class, "before", long.class);
+                AFTER = LOOKUP.findVarHandle(VarHandlesAcquireReleasePlainWrite.class, "after", long.class);
+            }
+            catch (final NoSuchFieldException | IllegalAccessException e)
+            {
+                throw new RuntimeException(e);
+            }
+        }
+
+        private volatile long before;
+        private volatile long after;
+        private int x;
+        private int y;
+
+        /**
+         * Reader thread.
+         *
+         * @param result object.
+         */
+        @Actor
+        public void reader(final JJJJ_Result result)
+        {
+            result.r4 = (long)AFTER.getAcquire(this);
+
+            result.r2 = x;
+            result.r3 = y;
+            VarHandle.loadLoadFence();
+
+            result.r1 = (long)BEFORE.getAcquire(this);
+            if (result.r1 != result.r4)
+            {
+                result.r2 = -1;
+                result.r3 = -1;
+            }
+        }
+
+        /**
+         * Write thread.
+         */
+        @Actor
+        public void writer()
+        {
+            final long changeNr = (long)BEFORE.get(this) + 1;
+            BEFORE.set(this, changeNr);
+            VarHandle.storeStoreFence();
+
+            x = 8;
+            y = 7;
+
+            AFTER.setRelease(this, changeNr);
+        }
+    }
+
+    /**
+     * An implementation using {@link VarHandle} API and acquire/release semantics with relaxed write/read barriers.
+     */
+    @JCStressTest
+    @JCStressMeta(ExpectedStates.class)
+    @State
+    public static class VarHandlesAcquireReleasePlainReadAndWrite
+    {
+        private static final VarHandle BEFORE;
+        private static final VarHandle AFTER;
+
+        static
+        {
+            try
+            {
+                BEFORE = LOOKUP.findVarHandle(VarHandlesAcquireReleasePlainReadAndWrite.class, "before", long.class);
+                AFTER = LOOKUP.findVarHandle(VarHandlesAcquireReleasePlainReadAndWrite.class, "after", long.class);
+            }
+            catch (final NoSuchFieldException | IllegalAccessException e)
+            {
+                throw new RuntimeException(e);
+            }
+        }
+
+        private volatile long before;
+        private volatile long after;
+        private int x;
+        private int y;
+
+        /**
+         * Reader thread.
+         *
+         * @param result object.
+         */
+        @Actor
+        public void reader(final JJJJ_Result result)
+        {
+            result.r4 = (long)AFTER.getAcquire(this);
+
+            result.r2 = x;
+            result.r3 = y;
+            VarHandle.loadLoadFence();
+
+            result.r1 = (long)BEFORE.get(this);
+            if (result.r1 != result.r4)
+            {
+                result.r2 = -1;
+                result.r3 = -1;
+            }
+        }
+
+        /**
+         * Write thread.
+         */
+        @Actor
+        public void writer()
+        {
+            final long changeNr = (long)BEFORE.get(this) + 1;
+            BEFORE.set(this, changeNr);
+            VarHandle.storeStoreFence();
+
+            x = 8;
+            y = 7;
+
+            AFTER.setRelease(this, changeNr);
+        }
+    }
+}