[GitHub] [flink-statefun] igalshilman commented on a change in pull request #25: [FLINK-16106] Add PersistedList state primitive

[GitBox <gi...@apache.org>]

igalshilman commented on a change in pull request #25: [FLINK-16106] Add PersistedList state primitive
URL: https://github.com/apache/flink-statefun/pull/25#discussion_r380502824
 
 

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 File path: statefun-sdk/src/main/java/org/apache/flink/statefun/sdk/state/PersistedAppendingBuffer.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.flink.statefun.sdk.state;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import javax.annotation.Nullable;
+import org.apache.flink.statefun.sdk.StatefulFunction;
+import org.apache.flink.statefun.sdk.annotations.ForRuntime;
+import org.apache.flink.statefun.sdk.annotations.Persisted;
+
+/**
+ * A {@link PersistedAppendingBuffer} is an append-only buffer registered within {@link
+ * StatefulFunction}s and is persisted and maintained by the system for fault-tolerance. Persisted
+ * elements in the buffer may only be updated with bulk replacements.
+ *
+ * <p>Created persisted buffers must be registered by using the {@link Persisted} annotation. Please
+ * see the class-level Javadoc of {@link StatefulFunction} for an example on how to do that.
+ *
+ * @see StatefulFunction
+ * @param <E> type of the list elements.
+ */
+public final class PersistedAppendingBuffer<E> {
+  private final String name;
+  private final Class<E> elementType;
+  private AppendingBufferAccessor<E> accessor;
+
+  private PersistedAppendingBuffer(
+      String name, Class<E> elementType, AppendingBufferAccessor<E> accessor) {
+    this.name = Objects.requireNonNull(name);
+    this.elementType = Objects.requireNonNull(elementType);
+    this.accessor = Objects.requireNonNull(accessor);
+  }
+
+  /**
+   * Creates a {@link PersistedAppendingBuffer} instance that may be used to access persisted state
+   * managed by the system. Access to the persisted buffer is identified by an unique name and type
+   * of the elements. These may not change across multiple executions of the application.
+   *
+   * @param name the unique name of the persisted buffer state
+   * @param elementType the type of the elements of this {@code PersistedAppendingBuffer}.
+   * @param <E> the type of the elements.
+   * @return a {@code PersistedAppendingBuffer} instance.
+   */
+  public static <E> PersistedAppendingBuffer<E> of(String name, Class<E> elementType) {
+    return new PersistedAppendingBuffer<>(name, elementType, new NonFaultTolerantAccessor<>());
+  }
+
+  /**
+   * Returns the unique name of the persisted buffer.
+   *
+   * @return unique name of the persisted buffer.
+   */
+  public String name() {
+    return name;
+  }
+
+  /**
+   * Returns the type of the persisted buffer elements.
+   *
+   * @return the type of the persisted buffer elements.
+   */
+  public Class<E> elementType() {
+    return elementType;
+  }
+
+  /**
+   * Appends an element to the persisted buffer.
+   *
+   * <p>If {@code null} is passed in, then this method has no effect and the persisted buffer
+   * remains the same.
+   *
+   * @param element the element to add to the persisted buffer.
+   */
+  public void append(@Nullable E element) {
+    if (element != null) {
+      accessor.append(element);
+    }
+  }
+
+  /**
+   * Adds all elements of a list to the persisted buffer.
+   *
+   * <p>If {@code null} or an empty list is passed in, then this method has no effect and the
+   * persisted buffer remains the same.
+   *
+   * @param elements a list of elements to add to the persisted buffer.
+   */
+  public void appendAll(@Nullable List<E> elements) {
+    if (elements != null && !elements.isEmpty()) {
+      accessor.appendAll(elements);
+    }
+  }
+
+  /**
+   * Replace the elements in the persisted buffer with the provided list of elements.
+   *
+   * <p>If an empty list or {@code null} is passed in, this method will have the same effect as
+   * {@link #clear()}.
+   *
+   * @param elements list of elements to replace the elements in the persisted buffer with.
+   */
+  public void replaceWith(@Nullable List<E> elements) {
+    if (elements != null && !elements.isEmpty()) {
+      accessor.replaceWith(elements);
+    } else {
+      accessor.clear();
+    }
+  }
+
+  /**
+   * Gets the elements of the persisted buffer as an {@link Iterable}.
+   *
+   * <p>This may return {@code null} if the buffer is empty or had been cleared (with {@link
+   * #clear()}).
+   *
+   * <p>Note that any modifications to the view does not modify the elements in the persisted
+   * buffer. To modify elements in the persisted buffer, you must use {@link #replaceWith(List)}.
+   *
+   * @return a modifiable view, as an {@link Iterable}, of the elements of the persisted buffer, or
 
 Review comment:
   Is it modifiable or unmodifiable?

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