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

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Atomic LongFieldUpdater紹介と関数リスト
AtomicLongFieldUpdaterは「クラスの「volatile long」タイプを指定したメンバー」を原子更新することができます。これは反射原理に基づいて実現される。
Atomic LongFieldUpdater関数一覧

//            ,     。
protected AtomicLongFieldUpdater()
//                               。
long addAndGet(T obj, long delta)
//       ==    ,                               。
abstract boolean compareAndSet(T obj, long expect, long update)
//                         1。
long decrementAndGet(T obj)
//                         。
abstract long get(T obj)
//                               。
long getAndAdd(T obj, long delta)
//                         1。
long getAndDecrement(T obj)
//                          1。
long getAndIncrement(T obj)
//                           ,     。
long getAndSet(T obj, long newValue)
//                         1。
long incrementAndGet(T obj)
//                          。
abstract void lazySet(T obj, long newValue)
//                     。
static <U> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName)
//                        。
abstract void set(T obj, long newValue)
//       ==    ,                               。
abstract boolean weakCompareAndSet(T obj, long expect, long update)
Atomic LongFieldUpdaterの例

// LongTest.java   
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
public class LongFieldTest {
  public static void main(String[] args) {
    //   Person class  
    Class cls = Person.class; 
    //   AtomicLongFieldUpdater  ,     “class  ” “long          ”
    AtomicLongFieldUpdater mAtoLong = AtomicLongFieldUpdater.newUpdater(cls, "id");
    Person person = new Person(12345678L);
    //   person "id"  ,  id   12345678L,    1000。
    mAtoLong.compareAndSet(person, 12345678L, 1000);
    System.out.println("id="+person.getId());
  }
}
class Person {
  volatile long id;
  public Person(long id) {
    this.id = id;
  }
  public void setId(long id) {
    this.id = id;
  }
  public long getId() {
    return id;
  }
}
実行結果:
id=1000
AtomicLongFieldUpdaterソース分析(JDK 1.7.0_に基づく。40)
Atomic LongFieldUpdater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 java.lang.reflect.*;
 import sun.misc.Unsafe;
 import sun.reflect.CallerSensitive;
 import sun.reflect.Reflection;
 /**
  * A reflection-based utility that enables atomic updates to
  * designated {@code volatile} reference fields of designated
  * classes. This class is designed for use in atomic data structures
  * in which several reference fields of the same node are
  * independently subject to atomic updates. For example, a tree node
  * might be declared as
  *
  * <pre> {@code
  * class Node {
  *  private volatile Node left, right;
  *
  *  private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater =
  *   AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
  *  private static AtomicReferenceFieldUpdater<Node, Node> rightUpdater =
  *   AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right");
  *
  *  Node getLeft() { return left; }
  *  boolean compareAndSetLeft(Node expect, Node update) {
  *   return leftUpdater.compareAndSet(this, expect, update);
  *  }
  *  // ... and so on
  * }}</pre>
  *
  * <p>Note that the guarantees of the {@code compareAndSet}
  * method in this class are weaker than in other atomic classes.
  * Because this class cannot ensure that all uses of the field
  * are appropriate for purposes of atomic access, it can
  * guarantee atomicity only with respect to other invocations of
  * {@code compareAndSet} and {@code set} on the same updater.
  *
  * @since .
  * @author Doug Lea
  * @param <T> The type of the object holding the updatable field
  * @param <V> The type of the field
  */
 public abstract class AtomicReferenceFieldUpdater<T, V> {
   /**
    * Creates and returns an updater for objects with the given field.
    * The Class arguments are needed to check that reflective types and
    * generic types match.
    *
    * @param tclass the class of the objects holding the field.
    * @param vclass the class of the field
    * @param fieldName the name of the field to be updated.
    * @return the updater
    * @throws IllegalArgumentException if the field is not a volatile reference type.
    * @throws RuntimeException with a nested reflection-based
    * exception if the class does not hold field or is the wrong type.
    */
   @CallerSensitive
   public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) {
     return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass,
                             vclass,
                             fieldName,
                             Reflection.getCallerClass());
   }
   /**
   * Protected do-nothing constructor for use by subclasses.
   */
   protected AtomicReferenceFieldUpdater() {
   }
   /**
   * Atomically sets the field of the given object managed by this updater
   * to the given updated value if the current value {@code ==} the
   * expected value. This method is guaranteed to be atomic with respect to
   * other calls to {@code compareAndSet} and {@code set}, but not
   * necessarily with respect to other changes in the field.
   *
   * @param obj An object whose field to conditionally set
   * @param expect the expected value
   * @param update the new value
   * @return true if successful.
   */
   public abstract boolean compareAndSet(T obj, V expect, V update);
   /**
   * Atomically sets the field of the given object managed by this updater
   * to the given updated value if the current value {@code ==} the
   * expected value. This method is guaranteed to be atomic with respect to
   * other calls to {@code compareAndSet} and {@code set}, but not
   * necessarily with respect to other changes in the field.
   *
   * <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 obj An object whose field to conditionally set
   * @param expect the expected value
   * @param update the new value
   * @return true if successful.
   */
   public abstract boolean weakCompareAndSet(T obj, V expect, V update);
   /**
   * Sets the field of the given object managed by this updater to the
   * given updated value. This operation is guaranteed to act as a volatile
   * store with respect to subsequent invocations of {@code compareAndSet}.
   *
   * @param obj An object whose field to set
   * @param newValue the new value
   */
   public abstract void set(T obj, V newValue);
   /**
   * Eventually sets the field of the given object managed by this
   * updater to the given updated value.
   *
   * @param obj An object whose field to set
   * @param newValue the new value
   * @since 1.6
   */
   public abstract void lazySet(T obj, V newValue);
   /**
   * Gets the current value held in the field of the given object managed
   * by this updater.
   *
   * @param obj An object whose field to get
   * @return the current value
   */
   public abstract V get(T obj);
   /**
   * Atomically sets the field of the given object managed by this updater
   * to the given value and returns the old value.
   *
   * @param obj An object whose field to get and set
   * @param newValue the new value
   * @return the previous value
   */
   public V getAndSet(T obj, V newValue) {
     for (;;) {
       V current = get(obj);
       if (compareAndSet(obj, current, newValue))
         return current;
     }
   }
   private static final class AtomicReferenceFieldUpdaterImpl<T,V>
     extends AtomicReferenceFieldUpdater<T,V> {
     private static final Unsafe unsafe = Unsafe.getUnsafe();
     private final long offset;
     private final Class<T> tclass;
     private final Class<V> vclass;
     private final Class cclass;
     /*
     * Internal type checks within all update methods contain
     * internal inlined optimizations checking for the common
     * cases where the class is final (in which case a simple
     * getClass comparison suffices) or is of type Object (in
     * which case no check is needed because all objects are
     * instances of Object). The Object case is handled simply by
     * setting vclass to null in constructor. The targetCheck and
     * updateCheck methods are invoked when these faster
     * screenings fail.
     */
     AtomicReferenceFieldUpdaterImpl(Class<T> tclass,
                     Class<V> vclass,
                     String fieldName,
                     Class<?> caller) {
       Field field = null;
       Class fieldClass = null;
       int modifiers = 0;
       try {
         field = tclass.getDeclaredField(fieldName);
         modifiers = field.getModifiers();
         sun.reflect.misc.ReflectUtil.ensureMemberAccess(
           caller, tclass, null, modifiers);
         sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
         fieldClass = field.getType();
       } catch (Exception ex) {
         throw new RuntimeException(ex);
       }
       if (vclass != fieldClass)
         throw new ClassCastException();
       if (!Modifier.isVolatile(modifiers))
         throw new IllegalArgumentException("Must be volatile type");
       this.cclass = (Modifier.isProtected(modifiers) &&
              caller != tclass) ? caller : null;
       this.tclass = tclass;
       if (vclass == Object.class)
         this.vclass = null;
       else
         this.vclass = vclass;
       offset = unsafe.objectFieldOffset(field);
     }
     void targetCheck(T obj) {
       if (!tclass.isInstance(obj))
         throw new ClassCastException();
       if (cclass != null)
         ensureProtectedAccess(obj);
     }
     void updateCheck(T obj, V update) {
       if (!tclass.isInstance(obj) ||
         (update != null && vclass != null && !vclass.isInstance(update)))
         throw new ClassCastException();
       if (cclass != null)
         ensureProtectedAccess(obj);
     }
     public boolean compareAndSet(T obj, V expect, V update) {
       if (obj == null || obj.getClass() != tclass || cclass != null ||
         (update != null && vclass != null &&
         vclass != update.getClass()))
         updateCheck(obj, update);
       return unsafe.compareAndSwapObject(obj, offset, expect, update);
     }
     public boolean weakCompareAndSet(T obj, V expect, V update) {
       // same implementation as strong form for now
       if (obj == null || obj.getClass() != tclass || cclass != null ||
         (update != null && vclass != null &&
         vclass != update.getClass()))
         updateCheck(obj, update);
       return unsafe.compareAndSwapObject(obj, offset, expect, update);
     }
     public void set(T obj, V newValue) {
       if (obj == null || obj.getClass() != tclass || cclass != null ||
         (newValue != null && vclass != null &&
         vclass != newValue.getClass()))
         updateCheck(obj, newValue);
       unsafe.putObjectVolatile(obj, offset, newValue);
     }
     public void lazySet(T obj, V newValue) {
       if (obj == null || obj.getClass() != tclass || cclass != null ||
         (newValue != null && vclass != null &&
         vclass != newValue.getClass()))
         updateCheck(obj, newValue);
       unsafe.putOrderedObject(obj, offset, newValue);
     }
     public V get(T obj) {
       if (obj == null || obj.getClass() != tclass || cclass != null)
         targetCheck(obj);
       return (V)unsafe.getObjectVolatile(obj, offset);
     }
     private void ensureProtectedAccess(T obj) {
       if (cclass.isInstance(obj)) {
         return;
       }
       throw new RuntimeException(
         new IllegalAccessException("Class " +
           cclass.getName() +
           " can not access a protected member of class " +
           tclass.getName() +
           " using an instance of " +
           obj.getClass().getName()
         )
       );
     }
   }
 }
   LongFieldTest.javaの流れを分析します。
1.newUpdater()
newUpdaterのソースコードは以下の通りです。

public static <U> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
  Class<?> caller = Reflection.getCallerClass();
  if (AtomicLong.VM_SUPPORTS_LONG_CAS)
    return new CASUpdater<U>(tclass, fieldName, caller);
  else
    return new LockedUpdater<U>(tclass, fieldName, caller);
}
説明:newUpdater()の役割は、AtomicInteger FieldUpdaterタイプのオブジェクトを取得することである。
それは実際に戻ってきたのはCASUpdaterオブジェクトまたはLockedUpdaterオブジェクトです。具体的にどのクラスに戻るかは、JVMがlongタイプのCAS関数をサポートしているかによって決まります。CASUpdaterとLockedUpdaterはいずれもAtomicInteger FieldUpdaterのサブクラスであり、それらの実現は類似している。次にCASUPEDARで説明します。 
CASUpdater類のソースコードは以下の通りです。

public boolean compareAndSet(T obj, long expect, long update) {
  if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
  return unsafe.compareAndSwapLong(obj, offset, expect, update);
}
説明:実際にCAS関数で操作します。クラスのlongオブジェクトの値がexpectであれば、その値をudateに設定します。