[GitHub] [beam] cpovirk commented on a change in pull request #16130: [BEAM-13015] Start integrating a process wide cache.

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cpovirk commented on a change in pull request #16130:
URL: https://github.com/apache/beam/pull/16130#discussion_r770933541



##########
File path: sdks/java/harness/src/main/java/org/apache/beam/fn/harness/Caches.java
##########
@@ -0,0 +1,285 @@
+/*
+ * 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.fn.harness;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Objects;
+import java.util.Set;
+import java.util.function.Function;
+import org.apache.beam.sdk.options.PipelineOptions;
+import org.apache.beam.sdk.options.SdkHarnessOptions;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.annotations.VisibleForTesting;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Sets;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.util.concurrent.MoreExecutors;
+import org.cache2k.Cache2kBuilder;
+import org.cache2k.operation.Weigher;
+import org.github.jamm.MemoryMeter;
+
+/** Utility methods used to instantiate and operate over cache instances. */
+@SuppressWarnings("nullness")
+public final class Caches {
+
+  /** A cache that never stores any values. */
+  public static <K, V> Cache<K, V> noop() {
+    return new SubCacheable<K, V>() {
+      @Override
+      public V peek(K key) {
+        return null;
+      }
+
+      @Override
+      public V computeIfAbsent(K key, Function<K, V> loadingFunction) {
+        return loadingFunction.apply(key);
+      }
+
+      @Override
+      public void put(K key, V value) {}
+
+      @Override
+      public void clear() {}
+
+      @Override
+      public void remove(K key) {}
+
+      @Override
+      public Set<K> keys() {
+        return Collections.emptySet();
+      }
+    };
+  }
+
+  /**
+   * Uses the specified {@link PipelineOptions} to configure and return a cache instance based upon
+   * parameters within {@link SdkHarnessOptions}.
+   */
+  public static <K, V> Cache<K, V> fromOptions(PipelineOptions options) {
+    // We specifically use cache2k since it allows for recursive computeIfAbsent calls
+    // preventing deadlock from occurring when a loading function mutates the underlying cache
+    org.cache2k.Cache<Object, Object> cache =
+        Cache2kBuilder.forUnknownTypes()
+            .maximumWeight(
+                options.as(SdkHarnessOptions.class).getMaxCacheMemoryUsageMb() * 1024L * 1024L)
+            .weigher(
+                new Weigher<Object, Object>() {
+                  private final MemoryMeter memoryMeter = MemoryMeter.builder().build();
+
+                  @Override
+                  public int weigh(Object key, Object value) {
+                    long size = memoryMeter.measureDeep(key) + memoryMeter.measureDeep(value);
+                    return size > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) size;
+                  }
+                })
+            .storeByReference(true)
+            .executor(MoreExecutors.directExecutor())
+            .build();
+
+    return (Cache<K, V>) forCache(cache);
+  }
+
+  /**
+   * Returns a view of a cache that operates on keys with a specified key prefix.
+   *
+   * <p>All lookups, insertions, and removals into the parent {@link Cache} will be prefixed by the
+   * specified prefixes.
+   *
+   * <p>Operations which operate over the entire caches contents such as {@link Cache#clear} only
+   * operate over keys with the specified prefixes.
+   */
+  public static <K, V> Cache<K, V> subCache(
+      Cache<?, ?> cache, Object keyPrefix, Object... additionalKeyPrefix) {
+    if (cache instanceof SubCache) {
+      return new SubCache<>(
+          ((SubCache<?, ?>) cache).cache,
+          ((SubCache<?, ?>) cache).keyPrefix.subKey(keyPrefix, additionalKeyPrefix));
+    } else if (cache instanceof SubCacheable) {
+      return new SubCache<>((SubCacheable<?, ?>) cache, CompositeKey.ROOT.subKey(keyPrefix));
+    }
+    throw new UnsupportedOperationException("An unsupported type of cache was passed.");
+  }
+
+  /** A cache that never evicts any values. */
+  public static <K, V> Cache<K, V> eternal() {
+    // We specifically use cache2k since it allows for recursive computeIfAbsent calls

Review comment:
       (Sorry for not replying. As a general rule, I endorse doing what Ben says; the details of our own caching library (let alone the others out there) are mostly beyond me.)




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