[GitHub] [hbase] chenxu14 commented on a change in pull request #583: HBASE-22802 Avoid temp ByteBuffer allocation in FileIOEngine#read

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chenxu14 commented on a change in pull request #583: HBASE-22802 Avoid temp ByteBuffer allocation in FileIOEngine#read
URL: https://github.com/apache/hbase/pull/583#discussion_r321591733
 
 

 ##########
 File path: hbase-common/src/main/java/org/apache/hadoop/hbase/nio/MultiByteBuff.java
 ##########
 @@ -1064,23 +1084,44 @@ public void get(ByteBuffer out, int sourceOffset, int length) {
     return output;
   }
 
+  private int internalRead(ReadableByteChannel channel, long offset,
+      ChannelReader reader) throws IOException {
+    checkRefCount();
+    int total = 0;
+    while (buffsIterator.hasNext()) {
+      ByteBuffer buffer = buffsIterator.next();
+      int len = read(channel, buffer, offset, reader);
+      if (len > 0) {
+        total += len;
+        offset += len;
+      }
+      if (buffer.hasRemaining()) {
+        break;
+      }
+    }
+    return total;
+  }
+
   @Override
   public int read(ReadableByteChannel channel) throws IOException {
+    return internalRead(channel, 0, CHANNEL_READER);
+  }
+
+  @Override
+  public int read(FileChannel channel, long offset) throws IOException {
+    return internalRead(channel, offset, FILE_READER);
+  }
+
+  @Override
+  public int write(FileChannel channel, long offset) throws IOException {
     checkRefCount();
     int total = 0;
-    while (true) {
-      // Read max possible into the current BB
-      int len = channelRead(channel, this.curItem);
-      if (len > 0)
+    while (buffsIterator.hasNext()) {
+      ByteBuffer buffer = buffsIterator.next();
+      while (buffer.hasRemaining()) {
+        int len = channel.write(curItem, offset);
 
 Review comment:
   > Better to use buffer instead of curItem here
   
   nice find, use buffer instead
   
   > maybe we can try to combine the buffsIterator and curItem & curItemIndex into one iterator
   
   I think it's not easy to do that, the curItem is referenced in so many methods, maybe we should keep the current logic to avoid possible BUGs.

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