Java concurrencyのAtomicLongAray原子類動力ノードJava学院の整理

AtomicLongAray紹介と関数リスト 
AtomicLongAray関数一覧

//          AtomicLongArray。
AtomicLongArray(int length)
//                 AtomicLongArray，             。
AtomicLongArray(long[] array)
//                i    。
long addAndGet(int i, long delta)
//       ==    ，                  。
boolean compareAndSet(int i, long expect, long update)
//          i     1。
long decrementAndGet(int i)
//      i     。
long get(int i)
//              i      。
long getAndAdd(int i, long delta)
//          i      1。
long getAndDecrement(int i)
//          i      1。
long getAndIncrement(int i)
//          i          ，     。
long getAndSet(int i, long newValue)
//          i     1。
long incrementAndGet(int i)
//       i          。
void lazySet(int i, long newValue)
//         。
int length()
//     i          。
void set(int i, long newValue)
//                。
String toString()
//       ==    ，                  。
boolean  weakCompareAndSet(int i, long expect, long update)

AtomicLongArayソース分析（JDK 1.7.0_に基づく。40）
AtomicLongArayの完全なソースコード

 /*
  * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
  *
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 /*
  *
  *
  *
  *
  *
  * Written by Doug Lea with assistance from members of JCP JSR-
  * Expert Group and released to the public domain, as explained at
  * http://creativecommons.org/publicdomain/zero/./
  */
 package java.util.concurrent.atomic;
 import sun.misc.Unsafe;
 import java.util.*;
 /**
  * A {@code long} array 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 .
  * @author Doug Lea
  */
 public class AtomicLongArray implements java.io.Serializable {
   private static final long serialVersionUID = -2308431214976778248L;
   private static final Unsafe unsafe = Unsafe.getUnsafe();
   private static final int base = unsafe.arrayBaseOffset(long[].class);
   private static final int shift;
   private final long[] array;
   static {
     int scale = unsafe.arrayIndexScale(long[].class);
     if ((scale & (scale - )) != )
       throw new Error("data type scale not a power of two");
     shift = - Integer.numberOfLeadingZeros(scale);
   }
   private long checkedByteOffset(int i) {
     if (i < || 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 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];
   }
   /**
    * Creates a new AtomicLongArray 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 AtomicLongArray(long[] array) {
     // Visibility guaranteed by final field guarantees
     this.array = array.clone();
   }
   /**
    * 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 long get(int 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, 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, long newValue) {
     unsafe.putOrderedLong(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 long getAndSet(int i, long newValue) {
     long offset = checkedByteOffset(i);
     while (true) {
       long 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, long expect, long 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 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" rel="external nofollow" >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, long expect, long update) {
     return compareAndSet(i, expect, update);
   }
   /**
   * Atomically increments by one the element at index {@code i}.
   *
   * @param i the index
   * @return the previous value
   */
   public final long getAndIncrement(int i) {
     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) {
     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 = getRaw(offset);
       if (compareAndSetRaw(offset, current, current + delta))
         return current;
     }
   }
   /**
   * Atomically increments by one the element at index {@code i}.
   *
   * @param i the index
   * @return the updated value
   */
   public final long incrementAndGet(int i) {
     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) {
     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 = getRaw(offset);
       long next = current + delta;
       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
   */
   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(' ');
     }
   }
 }

AtomicLongArayのコードは簡単で、以下はincrement AndGet()だけを例にとって、AtomicLongの原理を説明します。
increment AndGetのソースコードは以下の通りです。

public final long incrementAndGet(int i) {
  return addAndGet(i, 1);
}

説明：increment AndGet()の役割は、long配列のインデックスiの要素を原子的に1を加算し、1を加算した値を返します。 
addAndGetのソースコードは以下の通りです。

public long addAndGet(int i, long delta) {
  //         
  long offset = checkedByteOffset(i);
  while (true) {
    //   long       offset     
    long current = getRaw(offset);
    //   long  
    long next = current + delta;
    //   CAS  long       offset  。
    if (compareAndSetRaw(offset, current, next))
      return next;
  }
}

説明：addAndGet（）は、まず、配列が境界を越えるかどうかを確認する。境界を越えていない場合は、配列インデックスiの値を先に取得します。iの値はCAS関数で更新される。 
getRawのソースコードは以下の通りです。

private long getRaw(long offset) {
  return unsafe.getLongVolatile(array, offset);
}

説明：unsafeはUnisafe.get Unisafe（）を通じて戻ります。long型配列の要素はUnisafeのCAS関数によって原子操作される。compreAndSetRaw（）はUnisafeのCAS関数を呼び出します。ソースは以下の通りです。

private boolean compareAndSetRaw(long offset, long expect, long update) {
  return unsafe.compareAndSwapLong(array, offset, expect, update);
} 

AtomicLongAray例

 // LongArrayTest.java   
 import java.util.concurrent.atomic.AtomicLongArray;
 public class LongArrayTest {
   public static void main(String[] args){
     //   AtomicLongArray  
     long[] arrLong = new long[] {10, 20, 30, 40, 50};
     AtomicLongArray ala = new AtomicLongArray(arrLong);
     ala.set(0, 100);
     for (int i=0, len=ala.length(); i<len; i++) 
       System.out.printf("get(%d) : %s
", i, ala.get(i));
     System.out.printf("%20s : %s
", "getAndDecrement(0)", ala.getAndDecrement(0));
     System.out.printf("%20s : %s
", "decrementAndGet(1)", ala.decrementAndGet(1));
     System.out.printf("%20s : %s
", "getAndIncrement(2)", ala.getAndIncrement(2));
     System.out.printf("%20s : %s
", "incrementAndGet(3)", ala.incrementAndGet(3));
     System.out.printf("%20s : %s
", "addAndGet(100)", ala.addAndGet(0, 100));
     System.out.printf("%20s : %s
", "getAndAdd(100)", ala.getAndAdd(1, 100));
     System.out.printf("%20s : %s
", "compareAndSet()", ala.compareAndSet(2, 31, 1000));
     System.out.printf("%20s : %s
", "get(2)", ala.get(2));
   }
 }

実行結果:

get(0) : 100
get(1) : 20
get(2) : 30
get(3) : 40
get(4) : 50
 getAndDecrement(0) : 100
 decrementAndGet(1) : 19
 getAndIncrement(2) : 30
 incrementAndGet(3) : 41
   addAndGet(100) : 199
   getAndAdd(100) : 19
   compareAndSet() : true
       get(2) : 1000

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