src/share/classes/java/util/concurrent/atomic/AtomicLongArray.java
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@@ -45,32 +45,41 @@
* @author Doug Lea
*/
public class AtomicLongArray implements java.io.Serializable {
private static final long serialVersionUID = -2308431214976778248L;
- // setup to use Unsafe.compareAndSwapInt for updates
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final int base = unsafe.arrayBaseOffset(long[].class);
- private static final int scale = unsafe.arrayIndexScale(long[].class);
+ private static final int shift;
private final long[] array;
- private long rawIndex(int i) {
+ static {
+ int scale = unsafe.arrayIndexScale(long[].class);
+ 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;
+ }
+
/**
- * Creates a new AtomicLongArray of given length.
+ * Creates a new AtomicLongArray of the given length, with all
+ * elements initially zero.
*
* @param length the length of the array
*/
public AtomicLongArray(int length) {
array = new long[length];
- // must perform at least one volatile write to conform to JMM
- if (length > 0)
- unsafe.putLongVolatile(array, rawIndex(0), 0);
}
/**
* Creates a new AtomicLongArray with the same length as, and
* all elements copied from, the given array.
@@ -77,22 +86,13 @@
*
* @param array the array to copy elements from
* @throws NullPointerException if array is null
*/
public AtomicLongArray(long[] array) {
- if (array == null)
- throw new NullPointerException();
- int length = array.length;
- this.array = new long[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
- unsafe.putLongVolatile(this.array, rawIndex(last), array[last]);
+ // Visibility guaranteed by final field guarantees
+ this.array = array.clone();
}
- }
/**
* Returns the length of the array.
*
* @return the length of the array
@@ -106,21 +106,25 @@
*
* @param i the index
* @return the current value
*/
public final long get(int i) {
- return unsafe.getLongVolatile(array, rawIndex(i));
+ return getRaw(checkedByteOffset(i));
}
+ private long getRaw(long offset) {
+ return unsafe.getLongVolatile(array, offset);
+ }
+
/**
* Sets the element at position {@code i} to the given value.
*
* @param i the index
* @param newValue the new value
*/
public final void set(int i, long newValue) {
- unsafe.putLongVolatile(array, rawIndex(i), newValue);
+ unsafe.putLongVolatile(array, checkedByteOffset(i), newValue);
}
/**
* Eventually sets the element at position {@code i} to the given value.
*
@@ -127,11 +131,11 @@
* @param i the index
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(int i, long newValue) {
- unsafe.putOrderedLong(array, rawIndex(i), newValue);
+ unsafe.putOrderedLong(array, checkedByteOffset(i), newValue);
}
/**
* Atomically sets the element at position {@code i} to the given value
@@ -140,35 +144,39 @@
* @param i the index
* @param newValue the new value
* @return the previous value
*/
public final long getAndSet(int i, long newValue) {
+ long offset = checkedByteOffset(i);
while (true) {
- long current = get(i);
- if (compareAndSet(i, current, newValue))
+ long current = getRaw(offset);
+ if (compareAndSetRaw(offset, current, newValue))
return current;
}
}
/**
- * Atomically sets the value to the given updated value
- * if the current value {@code ==} the expected value.
+ * 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
* @return true if successful. False return indicates that
* the actual value was not equal to the expected value.
*/
public final boolean compareAndSet(int i, long expect, long update) {
- return unsafe.compareAndSwapLong(array, rawIndex(i),
- expect, update);
+ return compareAndSetRaw(checkedByteOffset(i), expect, update);
}
+ private boolean compareAndSetRaw(long offset, long expect, long update) {
+ return unsafe.compareAndSwapLong(array, offset, expect, update);
+ }
+
/**
- * Atomically sets the value to the given updated value
- * if the current value {@code ==} the expected value.
+ * Atomically sets the element at position {@code i} to the given
+ * updated value if the current value {@code ==} the expected value.
*
* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
* and does not provide ordering guarantees, so is only rarely an
* appropriate alternative to {@code compareAndSet}.
*
@@ -186,45 +194,35 @@
*
* @param i the index
* @return the previous value
*/
public final long getAndIncrement(int i) {
- while (true) {
- long current = get(i);
- long next = current + 1;
- if (compareAndSet(i, current, next))
- return current;
+ return getAndAdd(i, 1);
}
- }
/**
* Atomically decrements by one the element at index {@code i}.
*
* @param i the index
* @return the previous value
*/
public final long getAndDecrement(int i) {
- while (true) {
- long current = get(i);
- long next = current - 1;
- if (compareAndSet(i, current, next))
- return current;
+ return getAndAdd(i, -1);
}
- }
/**
* Atomically adds the given value to the element at index {@code i}.
*
* @param i the index
* @param delta the value to add
* @return the previous value
*/
public final long getAndAdd(int i, long delta) {
+ long offset = checkedByteOffset(i);
while (true) {
- long current = get(i);
- long next = current + delta;
- if (compareAndSet(i, current, next))
+ long current = getRaw(offset);
+ if (compareAndSetRaw(offset, current, current + delta))
return current;
}
}
/**
@@ -232,55 +230,55 @@
*
* @param i the index
* @return the updated value
*/
public final long incrementAndGet(int i) {
- while (true) {
- long current = get(i);
- long next = current + 1;
- if (compareAndSet(i, current, next))
- return next;
+ return addAndGet(i, 1);
}
- }
/**
* Atomically decrements by one the element at index {@code i}.
*
* @param i the index
* @return the updated value
*/
public final long decrementAndGet(int i) {
- while (true) {
- long current = get(i);
- long next = current - 1;
- if (compareAndSet(i, current, next))
- return next;
+ return addAndGet(i, -1);
}
- }
/**
* Atomically adds the given value to the element at index {@code i}.
*
* @param i the index
* @param delta the value to add
* @return the updated value
*/
public long addAndGet(int i, long delta) {
+ long offset = checkedByteOffset(i);
while (true) {
- long current = get(i);
+ long current = getRaw(offset);
long next = current + delta;
- if (compareAndSet(i, current, next))
+ if (compareAndSetRaw(offset, current, next))
return next;
}
}
/**
* Returns the String representation of the current values of array.
- * @return the String representation of the current values of array.
+ * @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(' ');
}
+ }
}