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8185362: Replace use of AtomicReferenceFieldUpdater from BufferedInputStream with Unsafe

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Reviewed-by: shade, martin, sherman
This commit is contained in:
Claes Redestad 2017-08-22 07:52:40 +02:00
parent a0682e8231
commit 01c44cfed8
1 changed files with 21 additions and 15 deletions
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36
jdk/src/java.base/share/classes/java/io/BufferedInputStream.java
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@ -24,7 +24,8 @@
*/
package java.io;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import jdk.internal.misc.Unsafe;
/**
* A <code>BufferedInputStream</code> adds
@ -60,23 +61,28 @@ class BufferedInputStream extends FilterInputStream {
*/
private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
/**
* As this class is used early during bootstrap, it's motivated to use
* Unsafe.compareAndSetObject instead of AtomicReferenceFieldUpdater
* (or VarHandles) to reduce dependencies and improve startup time.
*/
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.
*/
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.)
/*
* 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.)
*/
private static final
AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
AtomicReferenceFieldUpdater.newUpdater
(BufferedInputStream.class, byte[].class, "buf");
protected volatile byte[] buf;
/**
* The index one greater than the index of the last valid byte in
@ -230,9 +236,9 @@ class BufferedInputStream extends FilterInputStream {
pos * 2 : MAX_BUFFER_SIZE;
if (nsz > marklimit)
nsz = marklimit;
byte nbuf[] = new byte[nsz];
byte[] nbuf = new byte[nsz];
System.arraycopy(buffer, 0, nbuf, 0, pos);
if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
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.
@ -476,7 +482,7 @@ class BufferedInputStream extends FilterInputStream {
public void close() throws IOException {
byte[] buffer;
while ( (buffer = buf) != null) {
if (bufUpdater.compareAndSet(this, buffer, null)) {
if (U.compareAndSetObject(this, BUF_OFFSET, buffer, null)) {
InputStream input = in;
in = null;
if (input != null)