[GitHub] [hadoop] steveloughran commented on a diff in pull request #5675: HADOOP-18740. S3A prefetch cache blocks should be accessed by RW locks

["steveloughran (via GitHub)" <gi...@apache.org>]

steveloughran commented on code in PR #5675:
URL: https://github.com/apache/hadoop/pull/5675#discussion_r1211811893


##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/SingleFilePerBlockCache.java:
##########
@@ -99,6 +106,32 @@ public String toString() {
           "([%03d] %s: size = %d, checksum = %d)",
           blockNumber, path, size, checksum);
     }
+
+    /**
+     * Take the read or write lock.
+     *
+     * @param lockType type of the lock.
+     */
+    void takeLock(LockType lockType) {
+      if (LockType.READ == lockType) {
+        this.lock.readLock().lock();

Review Comment:
   remove the `this.`



##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/SingleFilePerBlockCache.java:
##########
@@ -99,6 +106,32 @@ public String toString() {
           "([%03d] %s: size = %d, checksum = %d)",
           blockNumber, path, size, checksum);
     }
+
+    /**
+     * Take the read or write lock.
+     *
+     * @param lockType type of the lock.
+     */
+    void takeLock(LockType lockType) {
+      if (LockType.READ == lockType) {
+        this.lock.readLock().lock();
+      } else if (LockType.WRITE == lockType) {
+        this.lock.writeLock().lock();
+      }
+    }
+
+    /**
+     * Release the read or write lock.
+     *
+     * @param lockType type of the lock.
+     */
+    void releaseLock(LockType lockType) {
+      if (LockType.READ == lockType) {
+        this.lock.readLock().unlock();

Review Comment:
   remove the `this.`



##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/impl/prefetch/SingleFilePerBlockCache.java:
##########
@@ -268,12 +310,15 @@ public void close() throws IOException {
     int numFilesDeleted = 0;
 
     for (Entry entry : blocks.values()) {
+      entry.takeLock(Entry.LockType.WRITE);

Review Comment:
   should we be acquiring locks in close()?
   good: no race condition in close
   bad) the usual
   
   also, L303: should closed be atomic?



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