src/java.base/share/classes/java/io/BufferedInputStream.java

rev 17627 : 8185362: Replace use of AtomicReferenceFieldUpdater from BufferedInputStream with Unsafe
Reviewed-by: shade, martin

*** 22,32 ****
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.io;
! import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
  
  /**
   * A <code>BufferedInputStream</code> adds
   * functionality to another input stream-namely,
   * the ability to buffer the input and to
--- 22,33 ----
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package java.io;
! 
! import jdk.internal.misc.Unsafe;
  
  /**
   * A <code>BufferedInputStream</code> adds
   * functionality to another input stream-namely,
   * the ability to buffer the input and to
*** 58,84 ****
       * Attempts to allocate larger arrays may result in
       * OutOfMemoryError: Requested array size exceeds VM limit
       */
      private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
  
      /**
       * The internal buffer array where the data is stored. When necessary,
       * it may be replaced by another array of
       * a different size.
       */
!     protected volatile byte buf[];
! 
!     /**
!      * Atomic updater to provide compareAndSet for buf. This is
!      * necessary because closes can be asynchronous. We use nullness
!      * of buf[] as primary indicator that this stream is closed. (The
!      * "in" field is also nulled out on close.)
!      */
!     private static final
!         AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
!         AtomicReferenceFieldUpdater.newUpdater
!         (BufferedInputStream.class,  byte[].class, "buf");
  
      /**
       * The index one greater than the index of the last valid byte in
       * the buffer.
       * This value is always
--- 59,85 ----
       * Attempts to allocate larger arrays may result in
       * OutOfMemoryError: Requested array size exceeds VM limit
       */
      private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
  
+     private static final Unsafe U = Unsafe.getUnsafe();
+ 
+     private static final long BUF_OFFSET
+             = U.objectFieldOffset(BufferedInputStream.class, "buf");
+ 
      /**
       * The internal buffer array where the data is stored. When necessary,
       * it may be replaced by another array of
       * a different size.
       */
!     /*
!      * We null this out with a CAS on close(), which is necessary since
!      * closes can be asynchronous. We use nullness of buf[] as primary
!      * indicator that this stream is closed. (The "in" field is also
!      * nulled out on close.)
!      */
!     protected volatile byte[] buf;
  
      /**
       * The index one greater than the index of the last valid byte in
       * the buffer.
       * This value is always
*** 228,240 ****
              } else {            /* grow buffer */
                  int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
                          pos * 2 : MAX_BUFFER_SIZE;
                  if (nsz > marklimit)
                      nsz = marklimit;
!                 byte nbuf[] = new byte[nsz];
                  System.arraycopy(buffer, 0, nbuf, 0, pos);
!                 if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
                      // Can't replace buf if there was an async close.
                      // Note: This would need to be changed if fill()
                      // is ever made accessible to multiple threads.
                      // But for now, the only way CAS can fail is via close.
                      // assert buf == null;
--- 229,241 ----
              } else {            /* grow buffer */
                  int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
                          pos * 2 : MAX_BUFFER_SIZE;
                  if (nsz > marklimit)
                      nsz = marklimit;
!                 byte[] nbuf = new byte[nsz];
                  System.arraycopy(buffer, 0, nbuf, 0, pos);
!                 if (!U.compareAndSetObject(this, BUF_OFFSET, buffer, nbuf)) {
                      // Can't replace buf if there was an async close.
                      // Note: This would need to be changed if fill()
                      // is ever made accessible to multiple threads.
                      // But for now, the only way CAS can fail is via close.
                      // assert buf == null;
*** 474,484 ****
       * @exception  IOException  if an I/O error occurs.
       */
      public void close() throws IOException {
          byte[] buffer;
          while ( (buffer = buf) != null) {
!             if (bufUpdater.compareAndSet(this, buffer, null)) {
                  InputStream input = in;
                  in = null;
                  if (input != null)
                      input.close();
                  return;
--- 475,485 ----
       * @exception  IOException  if an I/O error occurs.
       */
      public void close() throws IOException {
          byte[] buffer;
          while ( (buffer = buf) != null) {
!             if (U.compareAndSetObject(this, BUF_OFFSET, buffer, null)) {
                  InputStream input = in;
                  in = null;
                  if (input != null)
                      input.close();
                  return;