[GitHub] [hadoop] anuengineer commented on a change in pull request #1006: HDDS-1723. Create new OzoneManagerLock class.

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

anuengineer commented on a change in pull request #1006: HDDS-1723. Create new OzoneManagerLock class.
URL: https://github.com/apache/hadoop/pull/1006#discussion_r296819487
 
 

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 File path: hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/lock/OzoneManagerLock.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.hadoop.ozone.om.lock;
+
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.ozone.lock.LockManager;
+
+/**
+ * Provides different locks to handle concurrency in OzoneMaster.
+ * We also maintain lock hierarchy, based on the weight.
+ *
+ * <table>
+ *   <caption></caption>
+ *   <tr>
+ *     <td><b> WEIGHT </b></td> <td><b> LOCK </b></td>
+ *   </tr>
+ *   <tr>
+ *     <td> 0 </td> <td> S3 Bucket Lock </td>
+ *   </tr>
+ *   <tr>
+ *     <td> 1 </td> <td> Volume Lock </td>
+ *   </tr>
+ *   <tr>
+ *     <td> 2 </td> <td> Bucket Lock </td>
+ *   </tr>
+ *   <tr>
+ *     <td> 3 </td> <td> User Lock </td>
+ *   </tr>
+ *   <tr>
+ *     <td> 4 </td> <td> S3 Secret Lock</td>
+ *   </tr>
+ *   <tr>
+ *     <td> 5 </td> <td> Prefix Lock </td>
+ *   </tr>
+ * </table>
+ *
+ * One cannot obtain a lower weight lock while holding a lock with higher
+ * weight. The other way around is possible. <br>
+ * <br>
+ * <p>
+ * For example:
+ * <br>
+ * {@literal ->} acquire volume lock (will work)<br>
+ *   {@literal +->} acquire bucket lock (will work)<br>
+ *     {@literal +-->} acquire s3 bucket lock (will throw Exception)<br>
+ * </p>
+ * <br>
+ */
+
+public class OzoneManagerLock {
+
+  private static final Logger LOG =
+      LoggerFactory.getLogger(OzoneManagerLock.class);
+
+  private final LockManager<String> manager;
+  private final ThreadLocal<Short> lockSet = ThreadLocal.withInitial(
+      () -> Short.valueOf((short)0));
+
+
+  /**
+   * Creates new OzoneManagerLock instance.
+   * @param conf Configuration object
+   */
+  public OzoneManagerLock(Configuration conf) {
+    manager = new LockManager<>(conf);
+  }
+
+  /**
+   * Acquire lock on resource.
+   *
+   * For S3_Bucket, VOLUME, BUCKET type resource, same thread acquiring lock
+   * again is allowed.
+   *
+   * For USER, PREFIX, S3_SECRET type resource, same thread acquiring lock
+   * again is not allowed.
+   *
+   * Special Note for UserLock: Single thread can acquire single user lock/
+   * multi user lock. But not both at the same time.
+   * @param resourceName - Resource name on which user want to acquire lock.
+   * @param resource - Type of the resource.
+   */
+  public void acquireLock(String resourceName, Resource resource) {
+    if (!resource.canLock(lockSet.get())) {
+      String errorMessage = getErrorMessage(resource);
+      LOG.error(errorMessage);
+      throw new RuntimeException(errorMessage);
+    } else {
+      manager.lock(resourceName);
+      lockSet.set(resource.setLock(lockSet.get()));
+    }
+  }
+
+  private String getErrorMessage(Resource resource) {
+    return "Thread '" + Thread.currentThread().getName() + "' cannot " +
+        "acquire " + resource.name + " lock while holding " +
+        getCurrentLocks().toString() + " lock(s).";
+
+  }
+
+  private List<String> getCurrentLocks() {
+    List<String> currentLocks = new ArrayList<>();
+    int i=0;
+    short lockSetVal = lockSet.get();
+    for (Resource value : Resource.values()) {
+      if ((lockSetVal & value.setMask) == value.setMask) {
 
 Review comment:
   nit: this can be moved to a helper function if possible. something like isLevelLocked?(Resource, lockSet); That way, there is a helper function which is available too. Or perhaps move this function into Resource like canlock ? like isLocked ?

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