[GitHub] [flink] carp84 commented on a change in pull request #10447: [FLINK-15084][runtime] Add shared resources tracking to MemoryManager

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carp84 commented on a change in pull request #10447: [FLINK-15084][runtime] Add shared resources tracking to MemoryManager
URL: https://github.com/apache/flink/pull/10447#discussion_r354424986
 
 

 ##########
 File path: flink-runtime/src/main/java/org/apache/flink/runtime/memory/SharedResources.java
 ##########
 @@ -0,0 +1,172 @@
+/*
+ * 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.runtime.memory;
+
+import org.apache.flink.annotation.VisibleForTesting;
+import org.apache.flink.util.function.LongFunctionWithException;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * A map that keeps track of acquired shared resources and handles their allocation disposal.
+ */
+final class SharedResources {
+
+	private final ReentrantLock lock = new ReentrantLock();
+
+	private final HashMap<String, LeasedResource<?>> reservedResources = new HashMap<>();
+
+	/**
+	 * Gets the shared memory resource for the given owner and registers a lease. If the resource
+	 * does not yet exist, it will be created via the given initializer function.
+	 *
+	 * <p>The resource must be released when no longer used. That releases the lease. When all leases are
+	 * released, the resource is disposed.
+	 */
+	<T extends AutoCloseable> ResourceAndSize<T> getOrAllocateSharedResource(
+			String type,
+			Object leaseHolder,
+			LongFunctionWithException<T, Exception> initializer,
+			long sizeForInitialization) throws Exception {
+
+		// We could be stuck on this lock for a while, in cases where another initialization is currently
+		// happening and the initialization is expensive.
+		// We lock interruptibly here to allow for faster exit in case of cancellation errors.
+		try {
+			lock.lockInterruptibly();
+		}
+		catch (InterruptedException e) {
+			Thread.currentThread().interrupt();
+			throw new MemoryAllocationException("Interrupted while acquiring memory");
+		}
+
+		try {
+			// we cannot use "computeIfAbsent()" here because the computing function may throw an exception.
+			@SuppressWarnings("unchecked")
+			LeasedResource<T> resource = (LeasedResource<T>) reservedResources.get(type);
+			if (resource == null) {
+				resource = createResource(initializer, sizeForInitialization);
+				reservedResources.put(type, resource);
+			}
+
+			resource.addLeaseHolder(leaseHolder);
+			return resource;
+		}
+		finally {
+			lock.unlock();
+		}
+	}
+
+	/**
+	 * Releases a lease (identified by the lease holder object) for the given type.
+	 * If no further leases exist, the resource is disposed.
+	 *
+	 * @return True, if this was the last lease holder and the resource was disposed.
+	 */
+	boolean release(String type, Object leaseHolder) throws Exception {
+		lock.lock();
+		try {
+			final LeasedResource resource = reservedResources.get(type);
+			if (resource == null) {
+				return false;
+			}
+
+			if (resource.removeLeaseHolder(leaseHolder)) {
+				reservedResources.remove(type);
+				resource.dispose();
+				return true;
+			}
+
+			return false;
+		}
+		finally {
+			lock.unlock();
+		}
+	}
+
+	@VisibleForTesting
+	int getNumResources() {
+		return reservedResources.size();
+	}
+
+	private static <T extends AutoCloseable> LeasedResource<T> createResource(
+			LongFunctionWithException<T, Exception> initializer,
+			long size) throws Exception {
+
+		final T resource = initializer.apply(size);
+		return new LeasedResource<>(resource, size);
+	}
+
+	// ------------------------------------------------------------------------
+
+	/**
+	 * A resource handle with size.
+	 */
+	interface ResourceAndSize<T extends AutoCloseable> {
+
+		T resourceHandle();
+
+		long size();
+	}
+
+	// ------------------------------------------------------------------------
+
+	private static final class LeasedResource<T extends AutoCloseable> implements ResourceAndSize<T> {
+
+		private final HashSet<Object> leaseHolders = new HashSet<>();
+
+		private final T resourceHandle;
+
+		private final long size;
+
+		private boolean disposed;
+
+		private LeasedResource(T resourceHandle, long size) {
+			this.resourceHandle = resourceHandle;
+			this.size = size;
+		}
+
+		public T resourceHandle() {
+			return resourceHandle;
+		}
+
+		public long size() {
+			return size;
+		}
+
+		void addLeaseHolder(Object leaseHolder) {
+			assert !disposed;
+			leaseHolders.add(leaseHolder);
+		}
+
+		boolean removeLeaseHolder(Object leaseHolder) {
+			assert !disposed;
+			leaseHolders.remove(leaseHolder);
+			return  leaseHolders.isEmpty();
 
 Review comment:
   Minor: double space between `return` and `leaseHolders`

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