/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
*
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* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent.atomic;
import java.util.function.
UnaryOperator;
import java.util.function.
BinaryOperator;
import java.util.
Arrays;
import java.lang.reflect.
Array;
import sun.misc.
Unsafe;
/**
* An array of object references in which elements may be updated
* atomically. See the {@link java.util.concurrent.atomic} package
* specification for description of the properties of atomic
* variables.
* @since 1.5
* @author Doug Lea
* @param <E> The base class of elements held in this array
*/
public class
AtomicReferenceArray<E> implements java.io.
Serializable {
private static final long
serialVersionUID = -6209656149925076980L;
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 {
try {
unsafe =
Unsafe.
getUnsafe();
arrayFieldOffset =
unsafe.
objectFieldOffset
(
AtomicReferenceArray.class.
getDeclaredField("array"));
base =
unsafe.
arrayBaseOffset(
Object[].class);
int
scale =
unsafe.
arrayIndexScale(
Object[].class);
if ((
scale & (
scale - 1)) != 0)
throw new
Error("data type scale not a power of two");
shift = 31 -
Integer.
numberOfLeadingZeros(
scale);
} catch (
Exception e) {
throw new
Error(
e);
}
}
private long
checkedByteOffset(int
i) {
if (
i < 0 ||
i >=
array.length)
throw new
IndexOutOfBoundsException("index " +
i);
return
byteOffset(
i);
}
private static long
byteOffset(int
i) {
return ((long)
i <<
shift) +
base;
}
/**
* Creates a new AtomicReferenceArray of the given length, with all
* elements initially null.
*
* @param length the length of the array
*/
public
AtomicReferenceArray(int
length) {
array = new
Object[
length];
}
/**
* Creates a new AtomicReferenceArray with the same length as, and
* all elements copied from, the given array.
*
* @param array the array to copy elements from
* @throws NullPointerException if array is null
*/
public
AtomicReferenceArray(E[]
array) {
// Visibility guaranteed by final field guarantees
this.
array =
Arrays.
copyOf(
array,
array.length,
Object[].class);
}
/**
* Returns the length of the array.
*
* @return the length of the array
*/
public final int
length() {
return
array.length;
}
/**
* Gets the current value at position {@code i}.
*
* @param i the index
* @return the current value
*/
public final E
get(int
i) {
return
getRaw(
checkedByteOffset(
i));
}
@
SuppressWarnings("unchecked")
private E
getRaw(long
offset) {
return (E)
unsafe.
getObjectVolatile(
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, E
newValue) {
unsafe.
putObjectVolatile(
array,
checkedByteOffset(
i),
newValue);
}
/**
* Eventually sets the element at position {@code i} to the given value.
*
* @param i the index
* @param newValue the new value
* @since 1.6
*/
public final void
lazySet(int
i, E
newValue) {
unsafe.
putOrderedObject(
array,
checkedByteOffset(
i),
newValue);
}
/**
* Atomically sets the element at position {@code i} to the given
* value and returns the old value.
*
* @param i the index
* @param newValue the new value
* @return the previous value
*/
@
SuppressWarnings("unchecked")
public final E
getAndSet(int
i, E
newValue) {
return (E)
unsafe.
getAndSetObject(
array,
checkedByteOffset(
i),
newValue);
}
/**
* 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 {@code true} if successful. False return indicates that
* the actual value was not equal to the expected value.
*/
public final boolean
compareAndSet(int
i, E
expect, E
update) {
return
compareAndSetRaw(
checkedByteOffset(
i),
expect,
update);
}
private boolean
compareAndSetRaw(long
offset, E
expect, E
update) {
return
unsafe.
compareAndSwapObject(
array,
offset,
expect,
update);
}
/**
* Atomically sets the element at position {@code i} to the given
* updated value if the current value {@code ==} the expected value.
*
* <p><a href="package-summary.html#weakCompareAndSet">May fail
* spuriously and does not provide ordering guarantees</a>, so is
* only rarely an appropriate alternative to {@code compareAndSet}.
*
* @param i the index
* @param expect the expected value
* @param update the new value
* @return {@code true} if successful
*/
public final boolean
weakCompareAndSet(int
i, E
expect, E
update) {
return
compareAndSet(
i,
expect,
update);
}
/**
* Atomically updates the element at index {@code i} with the results
* of applying the given function, returning the previous value. The
* function should be side-effect-free, since it may be re-applied
* when attempted updates fail due to contention among threads.
*
* @param i the index
* @param updateFunction a side-effect-free function
* @return the previous value
* @since 1.8
*/
public final E
getAndUpdate(int
i,
UnaryOperator<E>
updateFunction) {
long
offset =
checkedByteOffset(
i);
E
prev,
next;
do {
prev =
getRaw(
offset);
next =
updateFunction.
apply(
prev);
} while (!
compareAndSetRaw(
offset,
prev,
next));
return
prev;
}
/**
* Atomically updates the element at index {@code i} with the results
* of applying the given function, returning the updated value. The
* function should be side-effect-free, since it may be re-applied
* when attempted updates fail due to contention among threads.
*
* @param i the index
* @param updateFunction a side-effect-free function
* @return the updated value
* @since 1.8
*/
public final E
updateAndGet(int
i,
UnaryOperator<E>
updateFunction) {
long
offset =
checkedByteOffset(
i);
E
prev,
next;
do {
prev =
getRaw(
offset);
next =
updateFunction.
apply(
prev);
} while (!
compareAndSetRaw(
offset,
prev,
next));
return
next;
}
/**
* Atomically updates the element at index {@code i} with the
* results of applying the given function to the current and
* given values, returning the previous value. The function should
* be side-effect-free, since it may be re-applied when attempted
* updates fail due to contention among threads. The function is
* applied with the current value at index {@code i} as its first
* argument, and the given update as the second argument.
*
* @param i the index
* @param x the update value
* @param accumulatorFunction a side-effect-free function of two arguments
* @return the previous value
* @since 1.8
*/
public final E
getAndAccumulate(int
i, E
x,
BinaryOperator<E>
accumulatorFunction) {
long
offset =
checkedByteOffset(
i);
E
prev,
next;
do {
prev =
getRaw(
offset);
next =
accumulatorFunction.
apply(
prev,
x);
} while (!
compareAndSetRaw(
offset,
prev,
next));
return
prev;
}
/**
* Atomically updates the element at index {@code i} with the
* results of applying the given function to the current and
* given values, returning the updated value. The function should
* be side-effect-free, since it may be re-applied when attempted
* updates fail due to contention among threads. The function is
* applied with the current value at index {@code i} as its first
* argument, and the given update as the second argument.
*
* @param i the index
* @param x the update value
* @param accumulatorFunction a side-effect-free function of two arguments
* @return the updated value
* @since 1.8
*/
public final E
accumulateAndGet(int
i, E
x,
BinaryOperator<E>
accumulatorFunction) {
long
offset =
checkedByteOffset(
i);
E
prev,
next;
do {
prev =
getRaw(
offset);
next =
accumulatorFunction.
apply(
prev,
x);
} while (!
compareAndSetRaw(
offset,
prev,
next));
return
next;
}
/**
* Returns the String representation of the current values of array.
* @return the String representation of the current values of array
*/
public
String toString() {
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).
*/
private void
readObject(java.io.
ObjectInputStream s)
throws java.io.
IOException,
ClassNotFoundException,
java.io.
InvalidObjectException {
// 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);
}
}