[GitHub] [hbase] huaxiangsun commented on a change in pull request #2523: HBASE-25167 Normalizer support for hot config reloading

[GitBox]

huaxiangsun commented on a change in pull request #2523:
URL: https://github.com/apache/hbase/pull/2523#discussion_r509003475



##########
File path: 
hbase-server/src/main/java/org/apache/hadoop/hbase/master/normalizer/SimpleRegionNormalizer.java
##########
@@ -71,38 +76,81 @@
   static final String MERGE_MIN_REGION_SIZE_MB_KEY = 
"hbase.normalizer.merge.min_region_size.mb";
   static final int DEFAULT_MERGE_MIN_REGION_SIZE_MB = 1;
 
-  private Configuration conf;
   private MasterServices masterServices;
-  private boolean splitEnabled;
-  private boolean mergeEnabled;
-  private int minRegionCount;
-  private Period mergeMinRegionAge;
-  private int mergeMinRegionSizeMb;
+
+  /** Ensure configuration changes are applied atomically. */
+  private final ReadWriteLock configUpdateLock = new ReentrantReadWriteLock();
+  @GuardedBy("configUpdateLock") private Configuration conf;
+  @GuardedBy("configUpdateLock") private boolean splitEnabled;
+  @GuardedBy("configUpdateLock") private boolean mergeEnabled;
+  @GuardedBy("configUpdateLock") private int minRegionCount;
+  @GuardedBy("configUpdateLock") private Period mergeMinRegionAge;
+  @GuardedBy("configUpdateLock") private int mergeMinRegionSizeMb;
 
   public SimpleRegionNormalizer() {
-    splitEnabled = DEFAULT_SPLIT_ENABLED;
-    mergeEnabled = DEFAULT_MERGE_ENABLED;
-    minRegionCount = DEFAULT_MIN_REGION_COUNT;
-    mergeMinRegionAge = Period.ofDays(DEFAULT_MERGE_MIN_REGION_AGE_DAYS);
-    mergeMinRegionSizeMb = DEFAULT_MERGE_MIN_REGION_SIZE_MB;
+    final Lock writeLock = configUpdateLock.writeLock();
+    writeLock.lock();
+    try {
+      splitEnabled = DEFAULT_SPLIT_ENABLED;
+      mergeEnabled = DEFAULT_MERGE_ENABLED;
+      minRegionCount = DEFAULT_MIN_REGION_COUNT;
+      mergeMinRegionAge = Period.ofDays(DEFAULT_MERGE_MIN_REGION_AGE_DAYS);
+      mergeMinRegionSizeMb = DEFAULT_MERGE_MIN_REGION_SIZE_MB;
+    } finally {
+      writeLock.unlock();
+    }
   }
 
   @Override
   public Configuration getConf() {
-    return conf;
+    final Lock readLock = configUpdateLock.readLock();
+    readLock.lock();
+    try {
+      return conf;
+    } finally {
+      readLock.unlock();
+    }
   }
 
   @Override
   public void setConf(final Configuration conf) {
     if (conf == null) {
       return;
     }
-    this.conf = conf;
-    splitEnabled = conf.getBoolean(SPLIT_ENABLED_KEY, DEFAULT_SPLIT_ENABLED);
-    mergeEnabled = conf.getBoolean(MERGE_ENABLED_KEY, DEFAULT_MERGE_ENABLED);
-    minRegionCount = parseMinRegionCount(conf);
-    mergeMinRegionAge = parseMergeMinRegionAge(conf);
-    mergeMinRegionSizeMb = parseMergeMinRegionSizeMb(conf);
+
+    final Lock readLock = configUpdateLock.readLock();
+    final Lock writeLock = configUpdateLock.writeLock();
+    writeLock.lock(); // "a writer can acquire the read lock, but not 
vice-versa."
+    readLock.lock();

Review comment:
       Why is readLock.lock() called here? Thought writeLock is enough.




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