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
     * @param <U> the type of instances of tclass
     * @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><a href="package-summary.html#weakCompareAndSet">May fail
     * spuriously and does not provide ordering guarantees</a>, 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:	1.6
Committed:	Sun Jan 18 20:17:32 2015 UTC (9 years, 5 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.5:	+1 -0 lines
Log Message:	exactly one blank line before and after package statements
#	Content
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
9	import sun.misc.Unsafe;
10	import java.lang.reflect.Field;
11	import java.lang.reflect.Modifier;
12	import java.security.AccessController;
13	import java.security.PrivilegedExceptionAction;
14	import java.security.PrivilegedActionException;
15
16	/**
17	* A reflection-based utility that enables atomic updates to
18	* designated {@code volatile long} fields of designated classes.
19	* This class is designed for use in atomic data structures in which
20	* several fields of the same node are independently subject to atomic
21	* updates.
22	*
23	* <p>Note that the guarantees of the {@code compareAndSet}
24	* method in this class are weaker than in other atomic classes.
25	* Because this class cannot ensure that all uses of the field
26	* are appropriate for purposes of atomic access, it can
27	* guarantee atomicity only with respect to other invocations of
28	* {@code compareAndSet} and {@code set} on the same updater.
29	*
30	* @since 1.5
31	* @author Doug Lea
32	* @param <T> The type of the object holding the updatable field
33	*/
34	public abstract class AtomicLongFieldUpdater<T> {
35	/**
36	* Creates and returns an updater for objects with the given field.
37	* The Class argument is needed to check that reflective types and
38	* generic types match.
39	*
40	* @param tclass the class of the objects holding the field
41	* @param fieldName the name of the field to be updated
42	* @param <U> the type of instances of tclass
43	* @return the updater
44	* @throws IllegalArgumentException if the field is not a
45	* volatile long type
46	* @throws RuntimeException with a nested reflection-based
47	* exception if the class does not hold field or is the wrong type,
48	* or the field is inaccessible to the caller according to Java language
49	* access control
50	*/
51	public static <U> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
52	if (AtomicLong.VM_SUPPORTS_LONG_CAS)
53	return new CASUpdater<U>(tclass, fieldName);
54	else
55	return new LockedUpdater<U>(tclass, fieldName);
56	}
57
58	/**
59	* Protected do-nothing constructor for use by subclasses.
60	*/
61	protected AtomicLongFieldUpdater() {
62	}
63
64	/**
65	* Atomically sets the field of the given object managed by this updater
66	* to the given updated value if the current value {@code ==} the
67	* expected value. This method is guaranteed to be atomic with respect to
68	* other calls to {@code compareAndSet} and {@code set}, but not
69	* necessarily with respect to other changes in the field.
70	*
71	* @param obj An object whose field to conditionally set
72	* @param expect the expected value
73	* @param update the new value
74	* @return true if successful
75	* @throws ClassCastException if {@code obj} is not an instance
76	* of the class possessing the field established in the constructor
77	*/
78	public abstract boolean compareAndSet(T obj, long expect, long update);
79
80	/**
81	* Atomically sets the field of the given object managed by this updater
82	* to the given updated value if the current value {@code ==} the
83	* expected value. This method is guaranteed to be atomic with respect to
84	* other calls to {@code compareAndSet} and {@code set}, but not
85	* necessarily with respect to other changes in the field.
86	*
87	* <p><a href="package-summary.html#weakCompareAndSet">May fail
88	* spuriously and does not provide ordering guarantees</a>, so is
89	* only rarely an appropriate alternative to {@code compareAndSet}.
90	*
91	* @param obj An object whose field to conditionally set
92	* @param expect the expected value
93	* @param update the new value
94	* @return true if successful
95	* @throws ClassCastException if {@code obj} is not an instance
96	* of the class possessing the field established in the constructor
97	*/
98	public abstract boolean weakCompareAndSet(T obj, long expect, long update);
99
100	/**
101	* Sets the field of the given object managed by this updater to the
102	* given updated value. This operation is guaranteed to act as a volatile
103	* store with respect to subsequent invocations of {@code compareAndSet}.
104	*
105	* @param obj An object whose field to set
106	* @param newValue the new value
107	*/
108	public abstract void set(T obj, long newValue);
109
110	/**
111	* Eventually sets the field of the given object managed by this
112	* updater to the given updated value.
113	*
114	* @param obj An object whose field to set
115	* @param newValue the new value
116	* @since 1.6
117	*/
118	public abstract void lazySet(T obj, long newValue);
119
120	/**
121	* Gets the current value held in the field of the given object managed
122	* by this updater.
123	*
124	* @param obj An object whose field to get
125	* @return the current value
126	*/
127	public abstract long get(T obj);
128
129	/**
130	* Atomically sets the field of the given object managed by this updater
131	* to the given value and returns the old value.
132	*
133	* @param obj An object whose field to get and set
134	* @param newValue the new value
135	* @return the previous value
136	*/
137	public long getAndSet(T obj, long newValue) {
138	for (;;) {
139	long current = get(obj);
140	if (compareAndSet(obj, current, newValue))
141	return current;
142	}
143	}
144
145	/**
146	* Atomically increments by one the current value of the field of the
147	* given object managed by this updater.
148	*
149	* @param obj An object whose field to get and set
150	* @return the previous value
151	*/
152	public long getAndIncrement(T obj) {
153	for (;;) {
154	long current = get(obj);
155	long next = current + 1;
156	if (compareAndSet(obj, current, next))
157	return current;
158	}
159	}
160
161	/**
162	* Atomically decrements by one the current value of the field of the
163	* given object managed by this updater.
164	*
165	* @param obj An object whose field to get and set
166	* @return the previous value
167	*/
168	public long getAndDecrement(T obj) {
169	for (;;) {
170	long current = get(obj);
171	long next = current - 1;
172	if (compareAndSet(obj, current, next))
173	return current;
174	}
175	}
176
177	/**
178	* Atomically adds the given value to the current value of the field of
179	* the given object managed by this updater.
180	*
181	* @param obj An object whose field to get and set
182	* @param delta the value to add
183	* @return the previous value
184	*/
185	public long getAndAdd(T obj, long delta) {
186	for (;;) {
187	long current = get(obj);
188	long next = current + delta;
189	if (compareAndSet(obj, current, next))
190	return current;
191	}
192	}
193
194	/**
195	* Atomically increments by one the current value of the field of the
196	* given object managed by this updater.
197	*
198	* @param obj An object whose field to get and set
199	* @return the updated value
200	*/
201	public long incrementAndGet(T obj) {
202	for (;;) {
203	long current = get(obj);
204	long next = current + 1;
205	if (compareAndSet(obj, current, next))
206	return next;
207	}
208	}
209
210	/**
211	* Atomically decrements by one the current value of the field of the
212	* given object managed by this updater.
213	*
214	* @param obj An object whose field to get and set
215	* @return the updated value
216	*/
217	public long decrementAndGet(T obj) {
218	for (;;) {
219	long current = get(obj);
220	long next = current - 1;
221	if (compareAndSet(obj, current, next))
222	return next;
223	}
224	}
225
226	/**
227	* Atomically adds the given value to the current value of the field of
228	* the given object managed by this updater.
229	*
230	* @param obj An object whose field to get and set
231	* @param delta the value to add
232	* @return the updated value
233	*/
234	public long addAndGet(T obj, long delta) {
235	for (;;) {
236	long current = get(obj);
237	long next = current + delta;
238	if (compareAndSet(obj, current, next))
239	return next;
240	}
241	}
242
243	private static class CASUpdater<T> extends AtomicLongFieldUpdater<T> {
244	private static final Unsafe unsafe = Unsafe.getUnsafe();
245	private final long offset;
246	private final Class<T> tclass;
247	private final Class<?> cclass;
248
249	CASUpdater(final Class<T> tclass, final String fieldName) {
250	final Field field;
251	final Class<?> caller;
252	final int modifiers;
253	try {
254	field = AccessController.doPrivileged(
255	new PrivilegedExceptionAction<Field>() {
256	public Field run() throws NoSuchFieldException {
257	return tclass.getDeclaredField(fieldName);
258	}
259	});
260	caller = sun.reflect.Reflection.getCallerClass(3);
261	modifiers = field.getModifiers();
262	sun.reflect.misc.ReflectUtil.ensureMemberAccess(
263	caller, tclass, null, modifiers);
264	ClassLoader cl = tclass.getClassLoader();
265	ClassLoader ccl = caller.getClassLoader();
266	if ((ccl != null) && (ccl != cl) &&
267	((cl == null) \|\| !isAncestor(cl, ccl))) {
268	sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
269	}
270	} catch (PrivilegedActionException pae) {
271	throw new RuntimeException(pae.getException());
272	} catch (Exception ex) {
273	throw new RuntimeException(ex);
274	}
275
276	Class<?> fieldt = field.getType();
277	if (fieldt != long.class)
278	throw new IllegalArgumentException("Must be long type");
279
280	if (!Modifier.isVolatile(modifiers))
281	throw new IllegalArgumentException("Must be volatile type");
282
283	this.cclass = (Modifier.isProtected(modifiers) &&
284	caller != tclass) ? caller : null;
285	this.tclass = tclass;
286	offset = unsafe.objectFieldOffset(field);
287	}
288
289	private void fullCheck(T obj) {
290	if (!tclass.isInstance(obj))
291	throw new ClassCastException();
292	if (cclass != null)
293	ensureProtectedAccess(obj);
294	}
295
296	public boolean compareAndSet(T obj, long expect, long update) {
297	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
298	return unsafe.compareAndSwapLong(obj, offset, expect, update);
299	}
300
301	public boolean weakCompareAndSet(T obj, long expect, long update) {
302	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
303	return unsafe.compareAndSwapLong(obj, offset, expect, update);
304	}
305
306	public void set(T obj, long newValue) {
307	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
308	unsafe.putLongVolatile(obj, offset, newValue);
309	}
310
311	public void lazySet(T obj, long newValue) {
312	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
313	unsafe.putOrderedLong(obj, offset, newValue);
314	}
315
316	public long get(T obj) {
317	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
318	return unsafe.getLongVolatile(obj, offset);
319	}
320
321	private void ensureProtectedAccess(T obj) {
322	if (cclass.isInstance(obj)) {
323	return;
324	}
325	throw new RuntimeException(
326	new IllegalAccessException("Class " +
327	cclass.getName() +
328	" can not access a protected member of class " +
329	tclass.getName() +
330	" using an instance of " +
331	obj.getClass().getName()
332	)
333	);
334	}
335	}
336
337
338	private static class LockedUpdater<T> extends AtomicLongFieldUpdater<T> {
339	private static final Unsafe unsafe = Unsafe.getUnsafe();
340	private final long offset;
341	private final Class<T> tclass;
342	private final Class<?> cclass;
343
344	LockedUpdater(final Class<T> tclass, final String fieldName) {
345	Field field = null;
346	Class<?> caller = null;
347	int modifiers = 0;
348	try {
349	field = AccessController.doPrivileged(
350	new PrivilegedExceptionAction<Field>() {
351	public Field run() throws NoSuchFieldException {
352	return tclass.getDeclaredField(fieldName);
353	}
354	});
355	caller = sun.reflect.Reflection.getCallerClass(3);
356	modifiers = field.getModifiers();
357	sun.reflect.misc.ReflectUtil.ensureMemberAccess(
358	caller, tclass, null, modifiers);
359	ClassLoader cl = tclass.getClassLoader();
360	ClassLoader ccl = caller.getClassLoader();
361	if ((ccl != null) && (ccl != cl) &&
362	((cl == null) \|\| !isAncestor(cl, ccl))) {
363	sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
364	}
365	} catch (PrivilegedActionException pae) {
366	throw new RuntimeException(pae.getException());
367	} catch (Exception ex) {
368	throw new RuntimeException(ex);
369	}
370
371	Class<?> fieldt = field.getType();
372	if (fieldt != long.class)
373	throw new IllegalArgumentException("Must be long type");
374
375	if (!Modifier.isVolatile(modifiers))
376	throw new IllegalArgumentException("Must be volatile type");
377
378	this.cclass = (Modifier.isProtected(modifiers) &&
379	caller != tclass) ? caller : null;
380	this.tclass = tclass;
381	offset = unsafe.objectFieldOffset(field);
382	}
383
384	private void fullCheck(T obj) {
385	if (!tclass.isInstance(obj))
386	throw new ClassCastException();
387	if (cclass != null)
388	ensureProtectedAccess(obj);
389	}
390
391	public boolean compareAndSet(T obj, long expect, long update) {
392	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
393	synchronized (this) {
394	long v = unsafe.getLong(obj, offset);
395	if (v != expect)
396	return false;
397	unsafe.putLong(obj, offset, update);
398	return true;
399	}
400	}
401
402	public boolean weakCompareAndSet(T obj, long expect, long update) {
403	return compareAndSet(obj, expect, update);
404	}
405
406	public void set(T obj, long newValue) {
407	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
408	synchronized (this) {
409	unsafe.putLong(obj, offset, newValue);
410	}
411	}
412
413	public void lazySet(T obj, long newValue) {
414	set(obj, newValue);
415	}
416
417	public long get(T obj) {
418	if (obj == null \|\| obj.getClass() != tclass \|\| cclass != null) fullCheck(obj);
419	synchronized (this) {
420	return unsafe.getLong(obj, offset);
421	}
422	}
423
424	private void ensureProtectedAccess(T obj) {
425	if (cclass.isInstance(obj)) {
426	return;
427	}
428	throw new RuntimeException(
429	new IllegalAccessException("Class " +
430	cclass.getName() +
431	" can not access a protected member of class " +
432	tclass.getName() +
433	" using an instance of " +
434	obj.getClass().getName()
435	)
436	);
437	}
438	}
439
440	/**
441	* Returns true if the second classloader can be found in the first
442	* classloader's delegation chain.
443	* Equivalent to the inaccessible: first.isAncestor(second).
444	*/
445	private static boolean isAncestor(ClassLoader first, ClassLoader second) {
446	ClassLoader acl = first;
447	do {
448	acl = acl.getParent();
449	if (second == acl) {
450	return true;
451	}
452	} while (acl != null);
453	return false;
454	}
455	}