Github user juliuszsompolski commented on a diff in the pull request:

    https://github.com/apache/spark/pull/20555#discussion_r167646954
  
    --- Diff: core/src/main/java/org/apache/spark/io/ReadAheadInputStream.java 
---
    @@ -258,54 +262,43 @@ public int read(byte[] b, int offset, int len) throws 
IOException {
         if (len == 0) {
           return 0;
         }
    -    stateChangeLock.lock();
    -    try {
    -      return readInternal(b, offset, len);
    -    } finally {
    -      stateChangeLock.unlock();
    -    }
    -  }
    -
    -  /**
    -   * flip the active and read ahead buffer
    -   */
    -  private void swapBuffers() {
    -    ByteBuffer temp = activeBuffer;
    -    activeBuffer = readAheadBuffer;
    -    readAheadBuffer = temp;
    -  }
     
    -  /**
    -   * Internal read function which should be called only from read() api. 
The assumption is that
    -   * the stateChangeLock is already acquired in the caller before calling 
this function.
    -   */
    -  private int readInternal(byte[] b, int offset, int len) throws 
IOException {
    -    assert (stateChangeLock.isLocked());
         if (!activeBuffer.hasRemaining()) {
    -      waitForAsyncReadComplete();
    -      if (readAheadBuffer.hasRemaining()) {
    -        swapBuffers();
    -      } else {
    -        // The first read or activeBuffer is skipped.
    -        readAsync();
    +      // No remaining in active buffer - lock and switch to write ahead 
buffer.
    +      stateChangeLock.lock();
    +      try {
             waitForAsyncReadComplete();
    -        if (isEndOfStream()) {
    -          return -1;
    +        if (!readAheadBuffer.hasRemaining()) {
    +          // The first read or activeBuffer is skipped.
    +          readAsync();
    +          waitForAsyncReadComplete();
    +          if (isEndOfStream()) {
    +            return -1;
    +          }
             }
    +        // Swap the newly read read ahead buffer in place of empty active 
buffer.
    --- End diff --
    
    Other existing places in comments in the file use `read ahead`.


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