Extract expiring memoizing supplier as a separate utility and run end offset refreshes in the current thread. (#36075)

Author: sjvanrossum

sdks/java/core/src/main/java/org/apache/beam/sdk/util/ExpiringMemoizingSerializableSupplier.java

@@ -0,0 +1,101 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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
+ *
+ *     http://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.apache.beam.sdk.util;
+
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.time.Duration;
+import java.util.concurrent.atomic.AtomicLongFieldUpdater;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+/**
+ * A thread-safe {@link SerializableSupplier} that wraps a {@link SerializableSupplier} and retains
+ * the supplier's result for the provided period. Lightweight locking and synchronization is used to
+ * guarantee mutual exclusivity and visibility of updates at the expense of single nanosecond
+ * precision.
+ *
+ * <p>The initial value and subsequently retained values are considered transient and will not be
+ * serialized.
+ */
+public final class ExpiringMemoizingSerializableSupplier<T extends @Nullable Object>
+    implements SerializableSupplier<T> {
+  // TODO(sjvanrossum): Replace with VarHandle after JDK 8 support is dropped.
+  @SuppressWarnings("rawtypes")
+  private static final AtomicLongFieldUpdater<ExpiringMemoizingSerializableSupplier>
+      DEADLINE_NANOS =
+          AtomicLongFieldUpdater.newUpdater(
+              ExpiringMemoizingSerializableSupplier.class, "deadlineNanos");
+
+  private final SerializableSupplier<T> supplier;
+  private final long periodNanos;
+  private transient T value;
+  private transient volatile long deadlineNanos;
+
+  public ExpiringMemoizingSerializableSupplier(
+      SerializableSupplier<T> supplier, Duration period, T initialValue, Duration initialDelay) {
+    this.supplier = supplier; // final store
+    this.periodNanos = period.toNanos(); // final store
+    this.value = initialValue; // normal store
+
+    // Ordered stores may be reordered with subsequent loads.
+    // The default value of deadlineNanos permits an indefinite initial expiration depending on the
+    // clock's state.
+    this.deadlineNanos =
+        System.nanoTime() + initialDelay.toNanos()
+            & ~1L; // volatile store (sequentially consistent release)
+  }
+
+  @Override
+  public T get() {
+    final long deadlineNanos = this.deadlineNanos; // volatile load (acquire)
+    final long nowNanos;
+    final T result;
+
+    /*
+     * Sacrificing 1ns precision to pack the lock state into the low bit of deadlineNanos is deemed acceptable.
+     * Subsequent loads and stores are prevented from reordering before a volatile load.
+     * Preceeding loads and stores are prevented from reordering after an ordered store.
+     * A store to value can't be reordered after a store to deadlineNanos
+     * A store to deadlineNanos can be reordered after a load of deadlineNanos.
+     * The returned value will be as old as or younger than deadlineNanos.
+     */
+    if ((deadlineNanos & 1L) == 0
+        && deadlineNanos - (nowNanos = System.nanoTime()) <= 0L
+        && DEADLINE_NANOS
+            .compareAndSet( // volatile load/store (sequentially consistent acquire/release)
+                this, deadlineNanos, deadlineNanos | 1L)) {
+      try {
+        this.value = result = supplier.get(); // normal store
+      } finally {
+        DEADLINE_NANOS.lazySet(this, (nowNanos + periodNanos) & ~1L); // ordered store (release)
+      }
+    } else {
+      result = this.value; // normal load
+    }
+
+    return result;
+  }
+
+  private void readObject(ObjectInputStream is) throws IOException, ClassNotFoundException {
+    is.defaultReadObject();
+
+    // Immediate initial expiration prevents a load of value before it is initialized.
+    this.deadlineNanos =
+        System.nanoTime() & ~1L; // volatile store (sequentially consistent release)
+  }
+}

sdks/java/core/src/test/java/org/apache/beam/sdk/util/ExpiringMemoizingSerializableSupplierTest.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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
+ *
+ *     http://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.apache.beam.sdk.util;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertThrows;
+
+import java.time.Duration;
+import java.util.Arrays;
+import java.util.Iterator;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class ExpiringMemoizingSerializableSupplierTest {
+
+  @Test
+  public void testSupplierIsSerializable() {
+    final ExpiringMemoizingSerializableSupplier<?> instance =
+        new ExpiringMemoizingSerializableSupplier<>(
+            Object::new, Duration.ZERO, null, Duration.ZERO);
+
+    // Instances must be serializable.
+    SerializableUtils.ensureSerializable(instance);
+  }
+
+  @Test
+  public void testSameValueAfterConstruction() {
+    final Object initialValue = new Object();
+    final ExpiringMemoizingSerializableSupplier<Object> instance =
+        new ExpiringMemoizingSerializableSupplier<>(
+            Object::new, Duration.ofHours(1), initialValue, Duration.ofHours(1));
+
+    // Construction initializes deadlineNanos for delayed expiration.
+    // The supplied value must not be observed as uninitialized
+    // The supplied value is referentially equal to initialValue.
+    final Object instanceValue = instance.get();
+    assertNotNull(instanceValue);
+    assertSame(initialValue, instanceValue);
+  }
+
+  @SuppressWarnings("unchecked")
+  @Test
+  public void testDistinctValuesAfterDeserialization() throws Exception {
+    final Object initialValue = new Object();
+    final ExpiringMemoizingSerializableSupplier<Object> instance =
+        new ExpiringMemoizingSerializableSupplier<>(
+            Object::new, Duration.ofHours(1), initialValue, Duration.ofHours(1));
+
+    // Deserialized instances must be referentially distinct for the purpose of this test.
+    final byte[] serialized = SerializableUtils.serializeToByteArray(instance);
+    final ExpiringMemoizingSerializableSupplier<Object> deserialized1 =
+        (ExpiringMemoizingSerializableSupplier<Object>)
+            SerializableUtils.deserializeFromByteArray(serialized, "instance");
+    final ExpiringMemoizingSerializableSupplier<Object> deserialized2 =
+        (ExpiringMemoizingSerializableSupplier<Object>)
+            SerializableUtils.deserializeFromByteArray(serialized, "instance");
+    assertNotSame(instance, deserialized1);
+    assertNotSame(instance, deserialized2);
+    assertNotSame(deserialized1, deserialized2);
+
+    // Deserialization initializes deadlineNanos for immediate expiration.
+    // Supplied values must not be observed as uninitialized.
+    // The initial and supplied values are all referentially distinct.
+    final Object deserialized1Value = deserialized1.get();
+    final Object deserialized2Value = deserialized2.get();
+    assertNotNull(deserialized1Value);
+    assertNotNull(deserialized2Value);
+    assertNotSame(initialValue, deserialized1Value);
+    assertNotSame(initialValue, deserialized2Value);
+    assertNotSame(deserialized1Value, deserialized2Value);
+  }
+
+  @Test
+  public void testProgressAfterException() throws Exception {
+    final Object initialValue = new Object();
+    final Object terminalValue = new Object();
+    final Iterator<?> suppliedValues =
+        Arrays.asList(new Object(), new RuntimeException(), new Object()).iterator();
+    final ExpiringMemoizingSerializableSupplier<?> instance =
+        new ExpiringMemoizingSerializableSupplier<>(
+            () -> {
+              if (!suppliedValues.hasNext()) {
+                return terminalValue;
+              }
+              final Object value = suppliedValues.next();
+              if (value instanceof RuntimeException) {
+                throw (RuntimeException) value;
+              }
+              return value;
+            },
+            Duration.ZERO,
+            initialValue,
+            Duration.ZERO);
+
+    // The initial value expires immediately and must not be observed.
+    final Object instanceValue = instance.get();
+    assertNotSame(initialValue, instanceValue);
+
+    // An exception must be thrown for the purpose of this test.
+    assertThrows(RuntimeException.class, instance::get);
+
+    // Exceptions must not lock the instance state.
+    // The supplied value is referentially distinct from instanceValue for the purpose of this test.
+    // Note that parallelly observed supplied values may be referentially equal to instanceValue.
+    final Object intermediateValue = instance.get();
+    assertNotSame(instanceValue, intermediateValue);
+
+    // The supplied value is referentially equal to terminalValue for the purpose of this test.
+    assertSame(terminalValue, instance.get());
+  }
+
+  @Test
+  public void testInitialValueVisibilityOnDifferentThread() throws Exception {
+    final Object initialValue = new Object();
+    final Object[] valueHolder = new Object[] {new Object()};
+    final ExpiringMemoizingSerializableSupplier<Object> instance =
+        new ExpiringMemoizingSerializableSupplier<>(
+            Object::new, Duration.ZERO, initialValue, Duration.ofHours(1));
+
+    // Initialization of value and deadlineNanos must be visible on other threads.
+    // The initial value must be supplied for delayed expiration.
+    final Thread t = new Thread(() -> valueHolder[0] = instance.get());
+    t.start();
+    t.join();
+    final Object observedValue = valueHolder[0];
+    assertNotNull(observedValue);
+    assertSame(initialValue, observedValue);
+  }
+
+  @Test
+  public void testIntermediateValueVisibilityOnDifferentThread() throws Exception {
+    final Object intermediateValue = new Object();
+    final Object[] valueHolder = new Object[] {new Object()};
+    final ExpiringMemoizingSerializableSupplier<Object> instance =
+        new ExpiringMemoizingSerializableSupplier<>(
+            () -> intermediateValue, Duration.ofHours(1), new Object(), Duration.ZERO);
+
+    // Initialization of value and deadlineNanos must be visible on other threads.
+    // The intermediate value must be supplied for immediate expiration.
+    final Thread t = new Thread(() -> valueHolder[0] = instance.get());
+    t.start();
+    t.join();
+    final Object observedValue = valueHolder[0];
+    assertNotNull(observedValue);
+    assertSame(intermediateValue, observedValue);
+  }
+}