[GitHub] [hbase] zhaoyim commented on a change in pull request #746: HBASE-23195 FSDataInputStreamWrapper unbuffer can NOT invoke the clas…

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zhaoyim commented on a change in pull request #746: HBASE-23195 FSDataInputStreamWrapper unbuffer can NOT invoke the clas…
URL: https://github.com/apache/hbase/pull/746#discussion_r341441861
 
 

 ##########
 File path: hbase-server/src/main/java/org/apache/hadoop/hbase/io/FSDataInputStreamWrapper.java
 ##########
 @@ -270,22 +271,18 @@ public void unbuffer() {
       if (this.instanceOfCanUnbuffer == null) {
         // To ensure we compute whether the stream is instance of CanUnbuffer only once.
         this.instanceOfCanUnbuffer = false;
-        Class<?>[] streamInterfaces = streamClass.getInterfaces();
-        for (Class c : streamInterfaces) {
-          if (c.getCanonicalName().toString().equals("org.apache.hadoop.fs.CanUnbuffer")) {
-            try {
-              this.unbuffer = streamClass.getDeclaredMethod("unbuffer");
-            } catch (NoSuchMethodException | SecurityException e) {
-              if (isLogTraceEnabled) {
-                LOG.trace("Failed to find 'unbuffer' method in class " + streamClass
-                    + " . So there may be a TCP socket connection "
-                    + "left open in CLOSE_WAIT state.", e);
-              }
-              return;
+        if (CanUnbuffer.class.isAssignableFrom(streamClass)) {
 
 Review comment:
   @Apache9 Good question! Because here we cast the sub class to parent class/interface, generally if want to check the up cast, we use `isAssignableFrom`. Also here the logic we want to judge the Class inheritance relationship, NOT the instance. Through use `(wrappedStream instanceof CanUnbuffer)` should get the same results, but I prefer `isAssignableFrom`.

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