content: /*
   * 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.arrow.memory;
  
  import java.io.IOException;
  import java.net.URL;
  import java.util.Enumeration;
  import java.util.LinkedHashSet;
  import java.util.Set;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Static method to ensure we have a RootAllocator on the classpath and report which one is used.
   */
  final class CheckAllocator {
    private static final Logger logger = LoggerFactory.getLogger(CheckAllocator.class);
    // unique package names needed by JPMS module naming
    private static final String ALLOCATOR_PATH_CORE =
        "org/apache/arrow/memory/DefaultAllocationManagerFactory.class";
    private static final String ALLOCATOR_PATH_UNSAFE =
        "org/apache/arrow/memory/unsafe/DefaultAllocationManagerFactory.class";
    private static final String ALLOCATOR_PATH_NETTY =
        "org/apache/arrow/memory/netty/DefaultAllocationManagerFactory.class";
  
    private CheckAllocator() {}
  
    static String check() {
      Set<URL> urls = scanClasspath();
      URL rootAllocator = assertOnlyOne(urls);
      reportResult(rootAllocator);
      if (rootAllocator.getPath().contains("memory-core")
          || rootAllocator.getPath().contains("/org/apache/arrow/memory/core/")) {
        return "org.apache.arrow.memory.DefaultAllocationManagerFactory";
      } else if (rootAllocator.getPath().contains("memory-unsafe")
          || rootAllocator.getPath().contains("/org/apache/arrow/memory/unsafe/")) {
        return "org.apache.arrow.memory.unsafe.DefaultAllocationManagerFactory";
      } else if (rootAllocator.getPath().contains("memory-netty")
          || rootAllocator.getPath().contains("/org/apache/arrow/memory/netty/")) {
        return "org.apache.arrow.memory.netty.DefaultAllocationManagerFactory";
      } else {
        throw new IllegalStateException(
            "Unknown allocation manager type to infer. Current: " + rootAllocator.getPath());
      }
    }
  
    @SuppressWarnings("URLEqualsHashCode")
    private static Set<URL> scanClasspath() {
      // LinkedHashSet appropriate here because it preserves insertion order
      // during iteration
      Set<URL> allocatorPathSet = new LinkedHashSet<>();
      try {
        ClassLoader allocatorClassLoader = CheckAllocator.class.getClassLoader();
        Enumeration<URL> paths;
        if (allocatorClassLoader == null) {
          paths = ClassLoader.getSystemResources(ALLOCATOR_PATH_CORE);
          if (!paths.hasMoreElements()) {
            paths = ClassLoader.getSystemResources(ALLOCATOR_PATH_UNSAFE);
          }
          if (!paths.hasMoreElements()) {
            paths = ClassLoader.getSystemResources(ALLOCATOR_PATH_NETTY);
          }
        } else {
          paths = allocatorClassLoader.getResources(ALLOCATOR_PATH_CORE);
          if (!paths.hasMoreElements()) {
            paths = allocatorClassLoader.getResources(ALLOCATOR_PATH_UNSAFE);
          }
          if (!paths.hasMoreElements()) {
            paths = allocatorClassLoader.getResources(ALLOCATOR_PATH_NETTY);
          }
        }
        while (paths.hasMoreElements()) {
          URL path = paths.nextElement();
          allocatorPathSet.add(path);
        }
      } catch (IOException ioe) {
        logger.error("Error getting resources from path", ioe);
      }
      return allocatorPathSet;
    }
  
    private static void reportResult(URL rootAllocator) {
      String path = rootAllocator.getPath();
      String subPath = path.substring(path.indexOf("memory"));
      logger.info("Using DefaultAllocationManager at {}", subPath);
    }
  
    private static URL assertOnlyOne(Set<URL> urls) {
      if (urls.size() > 1) {
        logger.warn("More than one DefaultAllocationManager on classpath. Choosing first found");
      }
      if (urls.isEmpty()) {
        throw new RuntimeException(
            "No DefaultAllocationManager found on classpath. Can't allocate Arrow buffers."
                + " Please consider adding arrow-memory-netty or arrow-memory-unsafe as a dependency.");
      }
      return urls.iterator().next();
    }
  }
  