HDFS-7615. Remove longReadLock. Contributed by Kihwal Lee.

(cherry picked from commit 44eed6cbc9)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -250,6 +250,8 @@ Release 2.7.0 - UNRELEASED
     HDFS-7454. Reduce memory footprint for AclEntries in NameNode.
     (Vinayakumar B via wheat9)
 
+    HDFS-7615. Remove longReadLock (kihwal)
+
   BUG FIXES
 
     HDFS-6741. Improve permission denied message when

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -1456,47 +1456,20 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
     this.fsLock.readLock().lock();
   }
   @Override
-  public void longReadLockInterruptibly() throws InterruptedException {
-    this.fsLock.longReadLock().lockInterruptibly();
-    try {
-      this.fsLock.readLock().lockInterruptibly();
-    } catch (InterruptedException ie) {
-      // In the event we're interrupted while getting the normal FSNS read lock,
-      // release the long read lock.
-      this.fsLock.longReadLock().unlock();
-      throw ie;
-    }
-  }
-  @Override
-  public void longReadUnlock() {
-    this.fsLock.readLock().unlock();
-    this.fsLock.longReadLock().unlock();
-  }
-  @Override
   public void readUnlock() {
     this.fsLock.readLock().unlock();
   }
   @Override
   public void writeLock() {
-    this.fsLock.longReadLock().lock();
     this.fsLock.writeLock().lock();
   }
   @Override
   public void writeLockInterruptibly() throws InterruptedException {
-    this.fsLock.longReadLock().lockInterruptibly();
-    try {
     this.fsLock.writeLock().lockInterruptibly();
-    } catch (InterruptedException ie) {
-      // In the event we're interrupted while getting the normal FSNS write
-      // lock, release the long read lock.
-      this.fsLock.longReadLock().unlock();
-      throw ie;
-    }
   }
   @Override
   public void writeUnlock() {
     this.fsLock.writeLock().unlock();
-    this.fsLock.longReadLock().unlock();
   }
   @Override
   public boolean hasWriteLock() {
@@ -6915,11 +6888,6 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
     return fsLock.coarseLock;
   }
   
-  @VisibleForTesting
-  public ReentrantLock getLongReadLockForTests() {
-    return fsLock.longReadLock;
-  }
-
   @VisibleForTesting
   public ReentrantLock getCpLockForTests() {
     return cpLock;

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystemLock.java

@@ -34,24 +34,6 @@ class FSNamesystemLock implements ReadWriteLock {
   @VisibleForTesting
   protected ReentrantReadWriteLock coarseLock;
   
-  /**
-   * When locking the FSNS for a read that may take a long time, we take this
-   * lock before taking the regular FSNS read lock. All writers also take this
-   * lock before taking the FSNS write lock. Regular (short) readers do not
-   * take this lock at all, instead relying solely on the synchronization of the
-   * regular FSNS lock.
-   * 
-   * This scheme ensures that:
-   * 1) In the case of normal (fast) ops, readers proceed concurrently and
-   *    writers are not starved.
-   * 2) In the case of long read ops, short reads are allowed to proceed
-   *    concurrently during the duration of the long read.
-   * 
-   * See HDFS-5064 for more context.
-   */
-  @VisibleForTesting
-  protected final ReentrantLock longReadLock = new ReentrantLock(true);
-  
   FSNamesystemLock(boolean fair) {
     this.coarseLock = new ReentrantReadWriteLock(fair);
   }
@@ -66,10 +48,6 @@ class FSNamesystemLock implements ReadWriteLock {
     return coarseLock.writeLock();
   }
 
-  public Lock longReadLock() {
-    return longReadLock;
-  }
-  
   public int getReadHoldCount() {
     return coarseLock.getReadHoldCount();
   }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/RwLock.java

@@ -22,15 +22,6 @@ public interface RwLock {
   /** Acquire read lock. */
   public void readLock();
   
-  /**
-   * Acquire the long read lock, unless interrupted while waiting. The long
-   * read lock should also serve to block all concurrent writers.
-   **/
-  void longReadLockInterruptibly() throws InterruptedException;
-  
-  /** Release the long read lock. */
-  public void longReadUnlock();
-
   /** Release read lock. */
   public void readUnlock();