ojluni/src/main/java/java/util/concurrent/atomic/AtomicReferenceArray.java - platform/libcore.git - Git at Google

 /*
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this
  * particular file as subject to the "Classpath" exception as provided
  * by Oracle in the LICENSE file that accompanied this code.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */

 /*
  * This file is available under and governed by the GNU General Public
  * License version 2 only, as published by the Free Software Foundation.
  * However, the following notice accompanied the original version of this
  * file:
  *
  * 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.lang.reflect.Array;
 import java.util.Arrays;
 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 {
         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 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));
     }

     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
      */
     public final E getAndSet(int i, E newValue) {
         long offset = checkedByteOffset(i);
         while (true) {
             E current = getRaw(offset);
             if (compareAndSetRaw(offset, current, newValue))
                 return current;
         }
     }

     /**
      * 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, 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>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}.
      *
      * @param i the index
      * @param expect the expected value
      * @param update the new value
      * @return true if successful.
      */
     public final boolean weakCompareAndSet(int i, E expect, E update) {
         return compareAndSet(i, expect, update);
     }

     /**
      * 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).
      * @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);
     }

 }
	/*
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	/*
	* This file is available under and governed by the GNU General Public
	* License version 2 only, as published by the Free Software Foundation.
	* However, the following notice accompanied the original version of this
	* file:
	*
	* 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.lang.reflect.Array;
	import java.util.Arrays;
	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 {
	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 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));
	}

	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
	*/
	public final E getAndSet(int i, E newValue) {
	long offset = checkedByteOffset(i);
	while (true) {
	E current = getRaw(offset);
	if (compareAndSetRaw(offset, current, newValue))
	return current;
	}
	}

	/**
	* 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, 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>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}.
	*
	* @param i the index
	* @param expect the expected value
	* @param update the new value
	* @return true if successful.
	*/
	public final boolean weakCompareAndSet(int i, E expect, E update) {
	return compareAndSet(i, expect, update);
	}

	/**
	* 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).
	* @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);
	}

	}