--- a/src/share/classes/java/util/concurrent/atomic/AtomicReferenceArray.java Tue Nov 15 09:57:58 2011 +0000
+++ b/src/share/classes/java/util/concurrent/atomic/AtomicReferenceArray.java Wed Nov 30 22:10:30 2011 +0000
@@ -34,8 +34,9 @@
*/
package java.util.concurrent.atomic;
+import java.lang.reflect.Array;
+import java.util.Arrays;
import sun.misc.Unsafe;
-import java.util.*;
/**
* An array of object references in which elements may be updated
@@ -49,15 +50,37 @@ public class AtomicReferenceArray<E> imp
public class AtomicReferenceArray<E> implements java.io.Serializable {
private static final long serialVersionUID = -6209656149925076980L;
- private static final Unsafe unsafe = Unsafe.getUnsafe();
- private static final int base = unsafe.arrayBaseOffset(Object[].class);
- private static final int scale = unsafe.arrayIndexScale(Object[].class);
- private final Object[] array;
-
- private long rawIndex(int i) {
+ private static final Unsafe unsafe;
+ private static final int base;
+ private static final int shift;
+ private static final long arrayFieldOffset;
+ private final Object[] array; // must have exact type Object[]
+
+ static {
+ int scale;
+ try {
+ unsafe = Unsafe.getUnsafe();
+ arrayFieldOffset = unsafe.objectFieldOffset
+ (AtomicReferenceArray.class.getDeclaredField("array"));
+ base = unsafe.arrayBaseOffset(Object[].class);
+ scale = unsafe.arrayIndexScale(Object[].class);
+ } catch (Exception e) {
+ throw new Error(e);
+ }
+ if ((scale & (scale - 1)) != 0)
+ throw new Error("data type scale not a power of two");
+ shift = 31 - Integer.numberOfLeadingZeros(scale);
+ }
+
+ private long checkedByteOffset(int i) {
if (i < 0 || i >= array.length)
throw new IndexOutOfBoundsException("index " + i);
- return base + (long) i * scale;
+
+ return byteOffset(i);
+ }
+
+ private static long byteOffset(int i) {
+ return ((long) i << shift) + base;
}
/**
@@ -66,9 +89,6 @@ public class AtomicReferenceArray<E> imp
*/
public AtomicReferenceArray(int length) {
array = new Object[length];
- // must perform at least one volatile write to conform to JMM
- if (length > 0)
- unsafe.putObjectVolatile(array, rawIndex(0), null);
}
/**
@@ -79,18 +99,8 @@ public class AtomicReferenceArray<E> imp
* @throws NullPointerException if array is null
*/
public AtomicReferenceArray(E[] array) {
- if (array == null)
- throw new NullPointerException();
- int length = array.length;
- this.array = new Object[length];
- if (length > 0) {
- int last = length-1;
- for (int i = 0; i < last; ++i)
- this.array[i] = array[i];
- // Do the last write as volatile
- E e = array[last];
- unsafe.putObjectVolatile(this.array, rawIndex(last), e);
- }
+ // Visibility guaranteed by final field guarantees
+ this.array = Arrays.copyOf(array, array.length, Object[].class);
}
/**
@@ -109,7 +119,11 @@ public class AtomicReferenceArray<E> imp
* @return the current value
*/
public final E get(int i) {
- return (E) unsafe.getObjectVolatile(array, rawIndex(i));
+ return getRaw(checkedByteOffset(i));
+ }
+
+ private E getRaw(long offset) {
+ return (E) unsafe.getObjectVolatile(array, offset);
}
/**
@@ -119,7 +133,7 @@ public class AtomicReferenceArray<E> imp
* @param newValue the new value
*/
public final void set(int i, E newValue) {
- unsafe.putObjectVolatile(array, rawIndex(i), newValue);
+ unsafe.putObjectVolatile(array, checkedByteOffset(i), newValue);
}
/**
@@ -130,7 +144,7 @@ public class AtomicReferenceArray<E> imp
* @since 1.6
*/
public final void lazySet(int i, E newValue) {
- unsafe.putOrderedObject(array, rawIndex(i), newValue);
+ unsafe.putOrderedObject(array, checkedByteOffset(i), newValue);
}
@@ -143,9 +157,10 @@ public class AtomicReferenceArray<E> imp
* @return the previous value
*/
public final E getAndSet(int i, E newValue) {
+ long offset = checkedByteOffset(i);
while (true) {
- E current = get(i);
- if (compareAndSet(i, current, newValue))
+ E current = getRaw(offset);
+ if (compareAndSetRaw(offset, current, newValue))
return current;
}
}
@@ -153,6 +168,7 @@ public class AtomicReferenceArray<E> imp
/**
* Atomically sets the element at position {@code i} to the given
* updated value if the current value {@code ==} the expected value.
+ *
* @param i the index
* @param expect the expected value
* @param update the new value
@@ -160,8 +176,11 @@ public class AtomicReferenceArray<E> imp
* the actual value was not equal to the expected value.
*/
public final boolean compareAndSet(int i, E expect, E update) {
- return unsafe.compareAndSwapObject(array, rawIndex(i),
- expect, update);
+ return compareAndSetRaw(checkedByteOffset(i), expect, update);
+ }
+
+ private boolean compareAndSetRaw(long offset, E expect, E update) {
+ return unsafe.compareAndSwapObject(array, offset, expect, update);
}
/**
@@ -186,9 +205,33 @@ public class AtomicReferenceArray<E> imp
* @return the String representation of the current values of array.
*/
public String toString() {
- if (array.length > 0) // force volatile read
- get(0);
- return Arrays.toString(array);
+ int iMax = array.length - 1;
+ if (iMax == -1)
+ return "[]";
+
+ StringBuilder b = new StringBuilder();
+ b.append('[');
+ for (int i = 0; ; i++) {
+ b.append(getRaw(byteOffset(i)));
+ if (i == iMax)
+ return b.append(']').toString();
+ b.append(',').append(' ');
+ }
+ }
+
+ /**
+ * Reconstitutes the instance from a stream (that is, deserializes it).
+ * @param s the stream
+ */
+ private void readObject(java.io.ObjectInputStream s)
+ throws java.io.IOException, ClassNotFoundException {
+ // Note: This must be changed if any additional fields are defined
+ Object a = s.readFields().get("array", null);
+ if (a == null || !a.getClass().isArray())
+ throw new java.io.InvalidObjectException("Not array type");
+ if (a.getClass() != Object[].class)
+ a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class);
+ unsafe.putObjectVolatile(this, arrayFieldOffset, a);
}
}