concurrent/atomic/AtomicLongFieldUpdater.java

/*
 * 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 sun.misc.Unsafe;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.security.AccessController;
import java.security.PrivilegedExceptionAction;
import java.security.PrivilegedActionException;

/**
 * A reflection-based utility that enables atomic updates to
 * designated {@code volatile long} 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 {@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 1.5
 * @author Doug Lea
 * @param <T> The type of the object holding the updatable field
 */
public abstract class AtomicLongFieldUpdater<T> {
    /**
     * Creates and returns 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 long type
     * @throws RuntimeException with a nested reflection-based
     * exception if the class does not hold field or is the wrong type,
     * or the field is inaccessible to the caller according to Java language
     * access control
     */
    public static <U> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
        if (AtomicLong.VM_SUPPORTS_LONG_CAS)
            return new CASUpdater<U>(tclass, fieldName);
        else
            return new LockedUpdater<U>(tclass, fieldName);
    }

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

    /**
     * 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
     * @throws ClassCastException if {@code obj} is not an instance
     * of the class possessing the field established in the constructor
     */
    public abstract boolean compareAndSet(T obj, long expect, long 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">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
     * @throws ClassCastException if {@code obj} is not an instance
     * of the class possessing the field established in the constructor
     */
    public abstract boolean weakCompareAndSet(T obj, long expect, long 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, long 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, long 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 long 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 long getAndSet(T obj, long newValue) {
        for (;;) {
            long current = get(obj);
            if (compareAndSet(obj, current, newValue))
                return current;
        }
    }

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

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

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

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

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

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

    private static class CASUpdater<T> extends AtomicLongFieldUpdater<T> {
        private static final Unsafe unsafe = Unsafe.getUnsafe();
        private final long offset;
        private final Class<T> tclass;
        private final Class<?> cclass;

        CASUpdater(final Class<T> tclass, final String fieldName) {
            final Field field;
            final Class<?> caller;
            final int modifiers;
            try {
                field = AccessController.doPrivileged(
                    new PrivilegedExceptionAction<Field>() {
                        public Field run() throws NoSuchFieldException {
                            return tclass.getDeclaredField(fieldName);
                        }
                    });
                caller = sun.reflect.Reflection.getCallerClass(3);
                modifiers = field.getModifiers();
                sun.reflect.misc.ReflectUtil.ensureMemberAccess(
                    caller, tclass, null, modifiers);
                ClassLoader cl = tclass.getClassLoader();
                ClassLoader ccl = caller.getClassLoader();
                if ((ccl != null) && (ccl != cl) &&
                    ((cl == null) || !isAncestor(cl, ccl))) {
                  sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
                }
            } catch (PrivilegedActionException pae) {
                throw new RuntimeException(pae.getException());
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }

            Class<?> fieldt = field.getType();
            if (fieldt != long.class)
                throw new IllegalArgumentException("Must be long 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);
        }

        private void fullCheck(T obj) {
            if (!tclass.isInstance(obj))
                throw new ClassCastException();
            if (cclass != null)
                ensureProtectedAccess(obj);
        }

        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);
        }

        public boolean weakCompareAndSet(T obj, long expect, long update) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            return unsafe.compareAndSwapLong(obj, offset, expect, update);
        }

        public void set(T obj, long newValue) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            unsafe.putLongVolatile(obj, offset, newValue);
        }

        public void lazySet(T obj, long newValue) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            unsafe.putOrderedLong(obj, offset, newValue);
        }

        public long get(T obj) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            return unsafe.getLongVolatile(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()
                )
            );
        }
    }


    private static class LockedUpdater<T> extends AtomicLongFieldUpdater<T> {
        private static final Unsafe unsafe = Unsafe.getUnsafe();
        private final long offset;
        private final Class<T> tclass;
        private final Class<?> cclass;

        LockedUpdater(final Class<T> tclass, final String fieldName) {
            Field field = null;
            Class<?> caller = null;
            int modifiers = 0;
            try {
                field = AccessController.doPrivileged(
                    new PrivilegedExceptionAction<Field>() {
                        public Field run() throws NoSuchFieldException {
                            return tclass.getDeclaredField(fieldName);
                        }
                    });
                caller = sun.reflect.Reflection.getCallerClass(3);
                modifiers = field.getModifiers();
                sun.reflect.misc.ReflectUtil.ensureMemberAccess(
                    caller, tclass, null, modifiers);
                ClassLoader cl = tclass.getClassLoader();
                ClassLoader ccl = caller.getClassLoader();
                if ((ccl != null) && (ccl != cl) &&
                    ((cl == null) || !isAncestor(cl, ccl))) {
                  sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
                }
            } catch (PrivilegedActionException pae) {
                throw new RuntimeException(pae.getException());
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }

            Class<?> fieldt = field.getType();
            if (fieldt != long.class)
                throw new IllegalArgumentException("Must be long 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);
        }

        private void fullCheck(T obj) {
            if (!tclass.isInstance(obj))
                throw new ClassCastException();
            if (cclass != null)
                ensureProtectedAccess(obj);
        }

        public boolean compareAndSet(T obj, long expect, long update) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            synchronized (this) {
                long v = unsafe.getLong(obj, offset);
                if (v != expect)
                    return false;
                unsafe.putLong(obj, offset, update);
                return true;
            }
        }

        public boolean weakCompareAndSet(T obj, long expect, long update) {
            return compareAndSet(obj, expect, update);
        }

        public void set(T obj, long newValue) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            synchronized (this) {
                unsafe.putLong(obj, offset, newValue);
            }
        }

        public void lazySet(T obj, long newValue) {
            set(obj, newValue);
        }

        public long get(T obj) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            synchronized (this) {
                return unsafe.getLong(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()
                )
            );
        }
    }

    /**
     * Returns true if the second classloader can be found in the first
     * classloader's delegation chain.
     * Equivalent to the inaccessible: first.isAncestor(second).
     */
    private static boolean isAncestor(ClassLoader first, ClassLoader second) {
        ClassLoader acl = first;
        do {
            acl = acl.getParent();
            if (second == acl) {
                return true;
            }
        } while (acl != null);
        return false;
    }
}
Revision:	1.3
Committed:	Tue Feb 5 19:54:07 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+4 -4 lines
Log Message:	javadoc style
#	User	Rev	Content
1	dl	1.1	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain, as explained at
4			* http://creativecommons.org/publicdomain/zero/1.0/
5			*/
6
7			package java.util.concurrent.atomic;
8			import sun.misc.Unsafe;
9			import java.lang.reflect.Field;
10			import java.lang.reflect.Modifier;
11			import java.security.AccessController;
12			import java.security.PrivilegedExceptionAction;
13			import java.security.PrivilegedActionException;
14
15			/**
16			* A reflection-based utility that enables atomic updates to
17			* designated {@code volatile long} fields of designated classes.
18			* This class is designed for use in atomic data structures in which
19			* several fields of the same node are independently subject to atomic
20			* updates.
21			*
22			* <p>Note that the guarantees of the {@code compareAndSet}
23			* method in this class are weaker than in other atomic classes.
24			* Because this class cannot ensure that all uses of the field
25			* are appropriate for purposes of atomic access, it can
26			* guarantee atomicity only with respect to other invocations of
27			* {@code compareAndSet} and {@code set} on the same updater.
28			*
29			* @since 1.5
30			* @author Doug Lea
31			* @param <T> The type of the object holding the updatable field
32			*/
33			public abstract class AtomicLongFieldUpdater<T> {
34			/**
35			* Creates and returns an updater for objects with the given field.
36			* The Class argument is needed to check that reflective types and
37			* generic types match.
38			*
39			* @param tclass the class of the objects holding the field
40	jsr166	1.3	* @param fieldName the name of the field to be updated
41	dl	1.1	* @return the updater
42			* @throws IllegalArgumentException if the field is not a
43	jsr166	1.3	* volatile long type
44	dl	1.1	* @throws RuntimeException with a nested reflection-based
45			* exception if the class does not hold field or is the wrong type,
46			* or the field is inaccessible to the caller according to Java language
47			* access control
48			*/
49			public static <U> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
50			if (AtomicLong.VM_SUPPORTS_LONG_CAS)
51			return new CASUpdater<U>(tclass, fieldName);
52			else
53			return new LockedUpdater<U>(tclass, fieldName);
54			}
55
56			/**
57			* Protected do-nothing constructor for use by subclasses.
58			*/
59			protected AtomicLongFieldUpdater() {
60			}
61
62			/**
63			* Atomically sets the field of the given object managed by this updater
64			* to the given updated value if the current value {@code ==} the
65			* expected value. This method is guaranteed to be atomic with respect to
66			* other calls to {@code compareAndSet} and {@code set}, but not
67			* necessarily with respect to other changes in the field.
68			*
69			* @param obj An object whose field to conditionally set
70			* @param expect the expected value
71			* @param update the new value
72	jsr166	1.2	* @return true if successful
73	dl	1.1	* @throws ClassCastException if {@code obj} is not an instance
74	jsr166	1.3	* of the class possessing the field established in the constructor
75	dl	1.1	*/
76			public abstract boolean compareAndSet(T obj, long expect, long update);
77
78			/**
79			* Atomically sets the field of the given object managed by this updater
80			* to the given updated value if the current value {@code ==} the
81			* expected value. This method is guaranteed to be atomic with respect to
82			* other calls to {@code compareAndSet} and {@code set}, but not
83			* necessarily with respect to other changes in the field.
84			*
85			* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
86			* and does not provide ordering guarantees, so is only rarely an
87			* appropriate alternative to {@code compareAndSet}.
88			*
89			* @param obj An object whose field to conditionally set
90			* @param expect the expected value
91			* @param update the new value
92	jsr166	1.2	* @return true if successful
93	dl	1.1	* @throws ClassCastException if {@code obj} is not an instance
94	jsr166	1.3	* of the class possessing the field established in the constructor
95	dl	1.1	*/
96			public abstract boolean weakCompareAndSet(T obj, long expect, long update);
97
98			/**
99			* Sets the field of the given object managed by this updater to the
100			* given updated value. This operation is guaranteed to act as a volatile
101			* store with respect to subsequent invocations of {@code compareAndSet}.
102			*
103			* @param obj An object whose field to set
104			* @param newValue the new value
105			*/
106			public abstract void set(T obj, long newValue);
107
108			/**
109			* Eventually sets the field of the given object managed by this
110			* updater to the given updated value.
111			*
112			* @param obj An object whose field to set
113			* @param newValue the new value
114			* @since 1.6
115			*/
116			public abstract void lazySet(T obj, long newValue);
117
118			/**
119			* Gets the current value held in the field of the given object managed
120			* by this updater.
121			*
122			* @param obj An object whose field to get
123			* @return the current value
124			*/
125			public abstract long get(T obj);
126
127			/**
128			* Atomically sets the field of the given object managed by this updater
129			* to the given value and returns the old value.
130			*
131			* @param obj An object whose field to get and set
132			* @param newValue the new value
133			* @return the previous value
134			*/
135			public long getAndSet(T obj, long newValue) {
136			for (;;) {
137			long current = get(obj);
138			if (compareAndSet(obj, current, newValue))
139			return current;
140			}
141			}
142
143			/**
144			* Atomically increments by one the current value of the field of the
145			* given object managed by this updater.
146			*
147			* @param obj An object whose field to get and set
148			* @return the previous value
149			*/
150			public long getAndIncrement(T obj) {
151			for (;;) {
152			long current = get(obj);
153			long next = current + 1;
154			if (compareAndSet(obj, current, next))
155			return current;
156			}
157			}
158
159			/**
160			* Atomically decrements by one the current value of the field of the
161			* given object managed by this updater.
162			*
163			* @param obj An object whose field to get and set
164			* @return the previous value
165			*/
166			public long getAndDecrement(T obj) {
167			for (;;) {
168			long current = get(obj);
169			long next = current - 1;
170			if (compareAndSet(obj, current, next))
171			return current;
172			}
173			}
174
175			/**
176			* Atomically adds the given value to the current value of the field of
177			* the given object managed by this updater.
178			*
179			* @param obj An object whose field to get and set
180			* @param delta the value to add
181			* @return the previous value
182			*/
183			public long getAndAdd(T obj, long delta) {
184			for (;;) {
185			long current = get(obj);
186			long next = current + delta;
187			if (compareAndSet(obj, current, next))
188			return current;
189			}
190			}
191
192			/**
193			* Atomically increments by one the current value of the field of the
194			* given object managed by this updater.
195			*
196			* @param obj An object whose field to get and set
197			* @return the updated value
198			*/
199			public long incrementAndGet(T obj) {
200			for (;;) {
201			long current = get(obj);
202			long next = current + 1;
203			if (compareAndSet(obj, current, next))
204			return next;
205			}
206			}
207
208			/**
209			* Atomically decrements by one the current value of the field of the
210			* given object managed by this updater.
211			*
212			* @param obj An object whose field to get and set
213			* @return the updated value
214			*/
215			public long decrementAndGet(T obj) {
216			for (;;) {
217			long current = get(obj);
218			long next = current - 1;
219			if (compareAndSet(obj, current, next))
220			return next;
221			}
222			}
223
224			/**
225			* Atomically adds the given value to the current value of the field of
226			* the given object managed by this updater.
227			*
228			* @param obj An object whose field to get and set
229			* @param delta the value to add
230			* @return the updated value
231			*/
232			public long addAndGet(T obj, long delta) {
233			for (;;) {
234			long current = get(obj);
235			long next = current + delta;
236			if (compareAndSet(obj, current, next))
237			return next;
238			}
239			}
240
241			private static class CASUpdater<T> extends AtomicLongFieldUpdater<T> {
242			private static final Unsafe unsafe = Unsafe.getUnsafe();
243			private final long offset;
244			private final Class<T> tclass;
245			private final Class<?> cclass;
246
247			CASUpdater(final Class<T> tclass, final String fieldName) {
248			final Field field;
249			final Class<?> caller;
250			final int modifiers;
251			try {
252			field = AccessController.doPrivileged(
253			new PrivilegedExceptionAction<Field>() {
254			public Field run() throws NoSuchFieldException {
255			return tclass.getDeclaredField(fieldName);
256			}
257			});
258			caller = sun.reflect.Reflection.getCallerClass(3);
259			modifiers = field.getModifiers();
260			sun.reflect.misc.ReflectUtil.ensureMemberAccess(
261			caller, tclass, null, modifiers);
262			ClassLoader cl = tclass.getClassLoader();
263			ClassLoader ccl = caller.getClassLoader();
264			if ((ccl != null) && (ccl != cl) &&
265			((cl == null) \|\| !isAncestor(cl, ccl))) {
266			sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
267			}
268			} catch (PrivilegedActionException pae) {
269			throw new RuntimeException(pae.getException());
270			} catch (Exception ex) {
271			throw new RuntimeException(ex);
272			}
273
274			Class<?> fieldt = field.getType();
275			if (fieldt != long.class)
276			throw new IllegalArgumentException("Must be long type");
277
278			if (!Modifier.isVolatile(modifiers))
279			throw new IllegalArgumentException("Must be volatile type");
280
281			this.cclass = (Modifier.isProtected(modifiers) &&
282			caller != tclass) ? caller : null;
283			this.tclass = tclass;
284			offset = unsafe.objectFieldOffset(field);
285			}
286
287			private void fullCheck(T obj) {
288			if (!tclass.isInstance(obj))
289			throw new ClassCastException();
290			if (cclass != null)
291			ensureProtectedAccess(obj);
292			}
293
294			public boolean compareAndSet(T obj, long expect, long update) {
295			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
296			return unsafe.compareAndSwapLong(obj, offset, expect, update);
297			}
298
299			public boolean weakCompareAndSet(T obj, long expect, long update) {
300			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
301			return unsafe.compareAndSwapLong(obj, offset, expect, update);
302			}
303
304			public void set(T obj, long newValue) {
305			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
306			unsafe.putLongVolatile(obj, offset, newValue);
307			}
308
309			public void lazySet(T obj, long newValue) {
310			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
311			unsafe.putOrderedLong(obj, offset, newValue);
312			}
313
314			public long get(T obj) {
315			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
316			return unsafe.getLongVolatile(obj, offset);
317			}
318
319			private void ensureProtectedAccess(T obj) {
320			if (cclass.isInstance(obj)) {
321			return;
322			}
323			throw new RuntimeException(
324			new IllegalAccessException("Class " +
325			cclass.getName() +
326			" can not access a protected member of class " +
327			tclass.getName() +
328			" using an instance of " +
329			obj.getClass().getName()
330			)
331			);
332			}
333			}
334
335
336			private static class LockedUpdater<T> extends AtomicLongFieldUpdater<T> {
337			private static final Unsafe unsafe = Unsafe.getUnsafe();
338			private final long offset;
339			private final Class<T> tclass;
340			private final Class<?> cclass;
341
342			LockedUpdater(final Class<T> tclass, final String fieldName) {
343			Field field = null;
344			Class<?> caller = null;
345			int modifiers = 0;
346			try {
347			field = AccessController.doPrivileged(
348			new PrivilegedExceptionAction<Field>() {
349			public Field run() throws NoSuchFieldException {
350			return tclass.getDeclaredField(fieldName);
351			}
352			});
353			caller = sun.reflect.Reflection.getCallerClass(3);
354			modifiers = field.getModifiers();
355			sun.reflect.misc.ReflectUtil.ensureMemberAccess(
356			caller, tclass, null, modifiers);
357			ClassLoader cl = tclass.getClassLoader();
358			ClassLoader ccl = caller.getClassLoader();
359			if ((ccl != null) && (ccl != cl) &&
360			((cl == null) \|\| !isAncestor(cl, ccl))) {
361			sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
362			}
363			} catch (PrivilegedActionException pae) {
364			throw new RuntimeException(pae.getException());
365			} catch (Exception ex) {
366			throw new RuntimeException(ex);
367			}
368
369			Class<?> fieldt = field.getType();
370			if (fieldt != long.class)
371			throw new IllegalArgumentException("Must be long type");
372
373			if (!Modifier.isVolatile(modifiers))
374			throw new IllegalArgumentException("Must be volatile type");
375
376			this.cclass = (Modifier.isProtected(modifiers) &&
377			caller != tclass) ? caller : null;
378			this.tclass = tclass;
379			offset = unsafe.objectFieldOffset(field);
380			}
381
382			private void fullCheck(T obj) {
383			if (!tclass.isInstance(obj))
384			throw new ClassCastException();
385			if (cclass != null)
386			ensureProtectedAccess(obj);
387			}
388
389			public boolean compareAndSet(T obj, long expect, long update) {
390			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
391			synchronized (this) {
392			long v = unsafe.getLong(obj, offset);
393			if (v != expect)
394			return false;
395			unsafe.putLong(obj, offset, update);
396			return true;
397			}
398			}
399
400			public boolean weakCompareAndSet(T obj, long expect, long update) {
401			return compareAndSet(obj, expect, update);
402			}
403
404			public void set(T obj, long newValue) {
405			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
406			synchronized (this) {
407			unsafe.putLong(obj, offset, newValue);
408			}
409			}
410
411			public void lazySet(T obj, long newValue) {
412			set(obj, newValue);
413			}
414
415			public long get(T obj) {
416			if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
417			synchronized (this) {
418			return unsafe.getLong(obj, offset);
419			}
420			}
421
422			private void ensureProtectedAccess(T obj) {
423			if (cclass.isInstance(obj)) {
424			return;
425			}
426			throw new RuntimeException(
427			new IllegalAccessException("Class " +
428			cclass.getName() +
429			" can not access a protected member of class " +
430			tclass.getName() +
431			" using an instance of " +
432			obj.getClass().getName()
433			)
434			);
435			}
436			}
437
438			/**
439			* Returns true if the second classloader can be found in the first
440			* classloader's delegation chain.
441			* Equivalent to the inaccessible: first.isAncestor(second).
442			*/
443			private static boolean isAncestor(ClassLoader first, ClassLoader second) {
444			ClassLoader acl = first;
445			do {
446			acl = acl.getParent();
447			if (second == acl) {
448			return true;
449			}
450			} while (acl != null);
451			return false;
452			}
453			}