atomicintegerfieldupdater.java

JAVA的一些源码 JAVA2 STANDARD EDITION DEVELOPMENT KIT 5.0

/*
 * @(#)AtomicIntegerFieldUpdater.java	1.7 05/08/09
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util.concurrent.atomic;
import sun.misc.Unsafe;
import java.lang.reflect.*;

/**
 * A reflection-based utility that enables atomic updates to
 * designated <tt>volatile int</tt> fields of designated classes.
 * This class is designed for use in atomic data structures in which
 * several fields of the same node are independently subject to atomic
 * updates.
 *
 * <p> Note that the guarantees of the <tt>compareAndSet</tt> 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 and volatile
 * semantics only with respect to other invocations of
 * <tt>compareAndSet</tt> and <tt>set</tt>.
 * @since 1.5
 * @author Doug Lea
 * @param <T> The type of the object holding the updatable field
 */
public abstract class  AtomicIntegerFieldUpdater<T>  {
    /**
     * Creates an updater for objects with the given field.  The Class
     * argument is needed to check that reflective types and generic
     * types match.
     * @param tclass the class of the objects holding the field
     * @param fieldName the name of the field to be updated.
     * @return the updater
     * @throws IllegalArgumentException if the field is not a
     * volatile integer type.
     * @throws RuntimeException with a nested reflection-based
     * exception if the class does not hold field or is the wrong type.
     */
    public static <U> AtomicIntegerFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
        return new AtomicIntegerFieldUpdaterImpl<U>(tclass, fieldName);
    }

    /**
     * Protected do-nothing constructor for use by subclasses.
     */
    protected AtomicIntegerFieldUpdater() {
    }

    /**
     * Atomically set the value of the field of the given object managed
     * by this Updater to the given updated value if the current value
     * <tt>==</tt> the expected value. This method is guaranteed to be
     * atomic with respect to other calls to <tt>compareAndSet</tt> and
     * <tt>set</tt>, 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.
     * @throws ClassCastException if <tt>obj</tt> is not an instance
     * of the class possessing the field established in the constructor.
     */

    public abstract boolean compareAndSet(T obj, int expect, int update);

    /**
     * Atomically set the value of the field of the given object managed
     * by this Updater to the given updated value if the current value
     * <tt>==</tt> the expected value. This method is guaranteed to be
     * atomic with respect to other calls to <tt>compareAndSet</tt> and
     * <tt>set</tt>, but not necessarily with respect to other
     * changes in the field, and may fail spuriously.
     * @param obj An object whose field to conditionally set
     * @param expect the expected value
     * @param update the new value
     * @return true if successful.
     * @throws ClassCastException if <tt>obj</tt> is not an instance
     * of the class possessing the field established in the constructor.
     */

    public abstract boolean weakCompareAndSet(T obj, int expect, int update);

    /**
     * Set the field of the given object managed by this updater. This
     * operation is guaranteed to act as a volatile store with respect
     * to subsequent invocations of <tt>compareAndSet</tt>.
     * @param obj An object whose field to set
     * @param newValue the new value
     */
    public abstract void set(T obj, int newValue);

    /**
     * Get the current value held in the field by the given object.
     * @param obj An object whose field to get
     * @return the current value
     */
    public abstract int get(T obj);

    /**
     * Set to the given value and return the old value.
     *
     * @param obj An object whose field to get and set
     * @param newValue the new value
     * @return the previous value
     */
    public int getAndSet(T obj, int newValue) {
        for (;;) {
            int current = get(obj);
            if (compareAndSet(obj, current, newValue))
                return current;
        }
    }

    /**
     * Atomically increment by one the current value.
     * @param obj An object whose field to get and set
     * @return the previous value;
     */
    public int getAndIncrement(T obj) {
        for (;;) {
            int current = get(obj);
            int next = current + 1;
            if (compareAndSet(obj, current, next))
                return current;
        }
    }


    /**
     * Atomically decrement by one the current value.
     * @param obj An object whose field to get and set
     * @return the previous value;
     */
    public int getAndDecrement(T obj) {
        for (;;) {
            int current = get(obj);
            int next = current - 1;
            if (compareAndSet(obj, current, next))
                return current;
        }
    }


    /**
     * Atomically add the given value to current value.
     * @param obj An object whose field to get and set
     * @param delta the value to add
     * @return the previous value;
     */
    public int getAndAdd(T obj, int delta) {
        for (;;) {
            int current = get(obj);
            int next = current + delta;
            if (compareAndSet(obj, current, next))
                return current;
        }
    }

    /**
     * Atomically increment by one the current value.
     * @param obj An object whose field to get and set
     * @return the updated value;
     */
    public int incrementAndGet(T obj) {
        for (;;) {
            int current = get(obj);
            int next = current + 1;
            if (compareAndSet(obj, current, next))
                return next;
        }
    }


    /**
     * Atomically decrement by one the current value.
     * @param obj An object whose field to get and set
     * @return the updated value;
     */
    public int decrementAndGet(T obj) {
        for (;;) {
            int current = get(obj);
            int next = current - 1;
            if (compareAndSet(obj, current, next))
                return next;
        }
    }


    /**
     * Atomically add the given value to current value.
     * @param obj An object whose field to get and set
     * @param delta the value to add
     * @return the updated value;
     */
    public int addAndGet(T obj, int delta) {
        for (;;) {
            int current = get(obj);
            int next = current + delta;
            if (compareAndSet(obj, current, next))
                return next;
        }
    }

    /**
     * Standard hotspot implementation using intrinsics
     */
    private static class AtomicIntegerFieldUpdaterImpl<T> extends AtomicIntegerFieldUpdater<T> {
        private static final Unsafe unsafe =  Unsafe.getUnsafe();
        private final long offset;
        private final Class<T> tclass;
        private final Class cclass;

        AtomicIntegerFieldUpdaterImpl(Class<T> tclass, String fieldName) {
            Field field = null;
	    Class caller = null;
	    int modifiers = 0;
            try {
                field = tclass.getDeclaredField(fieldName);
		caller = sun.reflect.Reflection.getCallerClass(3);
		modifiers = field.getModifiers();
                sun.reflect.misc.ReflectUtil.ensureMemberAccess(
                    caller, tclass, null, modifiers); 
		sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
            } catch(Exception ex) {
                throw new RuntimeException(ex);
            }

            Class fieldt = field.getType();
            if (fieldt != int.class)
                throw new IllegalArgumentException("Must be integer type");
            
            if (!Modifier.isVolatile(modifiers))
                throw new IllegalArgumentException("Must be volatile type");
         
	    this.cclass = (Modifier.isProtected(modifiers) &&
			   caller != tclass) ? caller : null;
            this.tclass = tclass;
            offset = unsafe.objectFieldOffset(field);
        }

        public boolean compareAndSet(T obj, int expect, int update) {
            if (!tclass.isInstance(obj))
                throw new ClassCastException();
	    if (cclass != null)
	        ensureProtectedAccess(obj);
            return unsafe.compareAndSwapInt(obj, offset, expect, update);
        }

        public boolean weakCompareAndSet(T obj, int expect, int update) {
            if (!tclass.isInstance(obj))
                throw new ClassCastException();
	    if (cclass != null)
	        ensureProtectedAccess(obj);
            return unsafe.compareAndSwapInt(obj, offset, expect, update);
        }

        public void set(T obj, int newValue) {
            if (!tclass.isInstance(obj))
                throw new ClassCastException();
	    if (cclass != null)
	        ensureProtectedAccess(obj);
            unsafe.putIntVolatile(obj, offset, newValue);
        }

        public final int get(T obj) {
            if (!tclass.isInstance(obj))
                throw new ClassCastException();
	    if (cclass != null)
	        ensureProtectedAccess(obj);
            return unsafe.getIntVolatile(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()
		)
	    );
	}
    }
}