test/loops/LockLoops.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/
 */
/*
 * A simple test program. Feel free to play.
 */

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.*;

public final class LockLoops {
    static final ExecutorService pool = Executors.newCachedThreadPool();
    static final LoopHelpers.SimpleRandom rng = new LoopHelpers.SimpleRandom();
    static boolean print = false;
    static boolean doBuiltin = true;
    static boolean doReadWrite = true;
    static boolean doSemaphore = true;
    static boolean doStampedLock = true;
    static boolean doFair = true;

    public static void main(String[] args) throws Exception {
        int maxThreads = 100;
        int iters = 1000000;
        int replications = 1;

        if (args.length > 0)
            maxThreads = Integer.parseInt(args[0]);

        if (args.length > 1)
            iters = Integer.parseInt(args[1]);

        if (args.length > 2)
            replications = Integer.parseInt(args[2]);

        rng.setSeed(3122688L);

        print = false;
        System.out.println("Warmup...");
        oneTest(3, 10000);
        Thread.sleep(1000);
        oneTest(2, 10000);
        Thread.sleep(100);
        oneTest(1, 100000);
        Thread.sleep(100);
        oneTest(1, 100000);
        Thread.sleep(1000);
        print = true;

        for (int i = 1; i <= maxThreads; ++i) {
            for (int j = 0; j < replications; ++j) {
                System.out.println("Threads:" + i);
                oneTest(i, iters / i);
                Thread.sleep(100);
            }
        }
        pool.shutdown();
    }

    static void oneTest(int nthreads, int iters) throws Exception {
        int v = rng.next();

        if (print)
            System.out.print("No shared vars        ");
        new NoLockLoop().test(v, nthreads, iters * 10);
        Thread.sleep(10);

        if (print)
            System.out.print("No Lock + volatile    ");
        new NoLockVolatileLoop().test(v, nthreads, iters);
        Thread.sleep(10);

        if (doBuiltin) {
            if (print)
                System.out.print("builtin lock          ");
            new BuiltinLockLoop().test(v, nthreads, iters);
            Thread.sleep(10);
        }

        if (print)
            System.out.print("ReentrantLock         ");
        new ReentrantLockLoop().test(v, nthreads, iters);
        Thread.sleep(10);

        if (doReadWrite) {
            if (print)
                System.out.print("ReentrantWriteLock    ");
            new ReentrantWriteLockLoop().test(v, nthreads, iters);
            Thread.sleep(10);

            if (print)
                System.out.print("ReentrantReadWriteLock");
            new ReentrantReadWriteLockLoop().test(v, nthreads, iters);
            Thread.sleep(10);
        }

        if (doSemaphore) {
            if (print)
                System.out.print("Semaphore             ");
            new SemaphoreLoop().test(v, nthreads, iters);
            Thread.sleep(10);

            if (print)
                System.out.print("FairSemaphore         ");
            new FairSemaphoreLoop().test(v, nthreads, iters);
            Thread.sleep(10);
        }

        if (doFair) {
            if (print)
                System.out.print("FairReentrantLock     ");
            new FairReentrantLockLoop().test(v, nthreads, iters);
            Thread.sleep(10);

            if (doReadWrite) {
                if (print)
                    System.out.print("FairRWriteLock         ");
                new FairReentrantWriteLockLoop().test(v, nthreads, iters);
                Thread.sleep(10);

                if (print)
                    System.out.print("FairRReadWriteLock     ");
                new FairReentrantReadWriteLockLoop().test(v, nthreads, iters);
                Thread.sleep(10);
            }
        }

        if (doStampedLock) {
            if (print)
                System.out.print("StampedLockWrite   ");
            new StampedLockWriteLoop().test(v, nthreads, iters);
            Thread.sleep(10);

            if (print)
                System.out.print("StampedLockRead    ");
            new StampedLockReadLoop().test(v, nthreads, iters);
            Thread.sleep(10);

            if (print)
                System.out.print("StampedLockReadWrite");
            new StampedLockReadLoop().test(v, nthreads, iters);
            Thread.sleep(10);
        }
    }

    abstract static class LockLoop implements Runnable {
        int v;
        int iters;
        volatile int result;
        final LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
        CyclicBarrier barrier;

        final void test(int initialValue, int nthreads, int iters) throws Exception {
            v = initialValue;
            this.iters = iters;
            barrier = new CyclicBarrier(nthreads+1, timer);
            for (int i = 0; i < nthreads; ++i)
                pool.execute(this);
            barrier.await();
            barrier.await();
            long time = timer.getTime();
            if (print) {
                long tpi = time / (iters * nthreads);
                System.out.print("\t" + LoopHelpers.rightJustify(tpi) + " ns per update");
                //                double secs = (double) time / 1000000000.0;
                //                System.out.print("\t " + secs + "s run time");
                System.out.println();
            }

            if (result == 0) // avoid overoptimization
                System.out.println("useless result: " + result);
        }
        abstract int loop(int n);
        public final void run() {
            try {
                barrier.await();
                result += loop(iters);
                barrier.await();
            }
            catch (Exception ie) {
                return;
            }
        }

    }

    private static class BuiltinLockLoop extends LockLoop {
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                synchronized (this) {
                    v = LoopHelpers.compute1(v);
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class NoLockLoop extends LockLoop {
        final int loop(int n) {
            int sum = 0;
            int y = v;
            while (n-- > 0) {
                y = LoopHelpers.compute1(y);
                sum += LoopHelpers.compute2(y);
            }
            return sum;
        }
    }

    private static class NoLockVolatileLoop extends LockLoop {
        private volatile int vv;
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                int y = LoopHelpers.compute1(vv);
                vv = y;
                sum += LoopHelpers.compute2(y);
            }
            return sum;
        }
    }

    private static class ReentrantLockLoop extends LockLoop {
        private final ReentrantLock lock = new ReentrantLock();
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                lock.lock();
                try {
                    v = LoopHelpers.compute1(v);
                }
                finally {
                    lock.unlock();
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class FairReentrantLockLoop extends LockLoop {
        private final ReentrantLock lock = new ReentrantLock(true);
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                lock.lock();
                try {
                    v = LoopHelpers.compute1(v);
                }
                finally {
                    lock.unlock();
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class ReentrantWriteLockLoop extends LockLoop {
        private final Lock lock = new ReentrantReadWriteLock().writeLock();
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                lock.lock();
                try {
                    v = LoopHelpers.compute1(v);
                }
                finally {
                    lock.unlock();
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class ReentrantReadWriteLockLoop extends LockLoop {
        private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                int x;
                lock.readLock().lock();
                try {
                    x = LoopHelpers.compute1(v);
                }
                finally {
                    lock.readLock().unlock();
                }
                lock.writeLock().lock();
                try {
                    v = x;
                }
                finally {
                    lock.writeLock().unlock();
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class FairReentrantWriteLockLoop extends LockLoop {
        final Lock lock = new ReentrantReadWriteLock(true).writeLock();
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                lock.lock();
                try {
                    v = LoopHelpers.compute1(v);
                }
                finally {
                    lock.unlock();
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class SemaphoreLoop extends LockLoop {
        private final Semaphore sem = new Semaphore(1, false);
        final int loop(int n) {
            int sum = 0;
            try {
                while (n-- > 0) {
                    sem.acquire();
                    try {
                        v = LoopHelpers.compute1(v);
                    }
                    finally {
                        sem.release();
                    }
                    sum += LoopHelpers.compute2(v);
                }
            }
            catch (InterruptedException ie) {
                return sum;
            }
            return sum;
        }
    }

    private static class FairSemaphoreLoop extends LockLoop {
        private final Semaphore sem = new Semaphore(1, true);
        final int loop(int n) {
            int sum = 0;
            try {
                while (n-- > 0) {
                    sem.acquire();
                    try {
                        v = LoopHelpers.compute1(v);
                    }
                    finally {
                        sem.release();
                    }
                    sum += LoopHelpers.compute2(v);
                }
            }
            catch (InterruptedException ie) {
                return sum;
            }
            return sum;
        }
    }

    private static class FairReentrantReadWriteLockLoop extends LockLoop {
        private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                int x;
                lock.readLock().lock();
                try {
                    x = LoopHelpers.compute1(v);
                }
                finally {
                    lock.readLock().unlock();
                }
                lock.writeLock().lock();
                try {
                    v = x;
                }
                finally {
                    lock.writeLock().unlock();
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class StampedLockWriteLoop extends LockLoop {
        private final StampedLock lock = new StampedLock();
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                long stamp = lock.writeLock();
                try {
                    v = LoopHelpers.compute1(v);
                }
                finally {
                    lock.unlockWrite(stamp);
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class StampedLockReadLoop extends LockLoop {
        private final StampedLock lock = new StampedLock();
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                long stamp = lock.readLock();
                try {
                    v = LoopHelpers.compute1(v);
                }
                finally {
                    lock.unlockRead(stamp);
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }

    private static class StampedLockReadWriteLoop extends LockLoop {
        private final StampedLock lock = new StampedLock();
        final int loop(int n) {
            int sum = 0;
            while (n-- > 0) {
                int x;
                long stamp = lock.readLock();
                try {
                    x = LoopHelpers.compute1(v);
                }
                finally {
                    lock.unlockRead(stamp);
                }
                stamp = lock.writeLock();
                try {
                    v = x;
                } finally {
                    lock.unlockWrite(stamp);
                }
                sum += LoopHelpers.compute2(v);
            }
            return sum;
        }
    }
}
Revision:	1.13
Committed:	Wed Jun 8 20:11:01 2016 UTC (7 years, 11 months ago) by jsr166
Branch:	MAIN
Changes since 1.12:	+30 -0 lines
Log Message:	add StampedLockReadWriteLoop
#	User	Rev	Content
1	dl	1.1	/*
2	dl	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	jsr166	1.7	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.2	*/
6			/*
7	dl	1.1	* A simple test program. Feel free to play.
8			*/
9
10	jsr166	1.9	import java.util.*;
11	dl	1.1	import java.util.concurrent.*;
12			import java.util.concurrent.locks.*;
13
14			public final class LockLoops {
15			static final ExecutorService pool = Executors.newCachedThreadPool();
16			static final LoopHelpers.SimpleRandom rng = new LoopHelpers.SimpleRandom();
17			static boolean print = false;
18			static boolean doBuiltin = true;
19			static boolean doReadWrite = true;
20			static boolean doSemaphore = true;
21	jsr166	1.12	static boolean doStampedLock = true;
22	jsr166	1.8	static boolean doFair = true;
23	dl	1.1
24			public static void main(String[] args) throws Exception {
25			int maxThreads = 100;
26			int iters = 1000000;
27			int replications = 1;
28
29	jsr166	1.3	if (args.length > 0)
30	dl	1.1	maxThreads = Integer.parseInt(args[0]);
31
32	jsr166	1.3	if (args.length > 1)
33	dl	1.1	iters = Integer.parseInt(args[1]);
34
35	jsr166	1.3	if (args.length > 2)
36	dl	1.1	replications = Integer.parseInt(args[2]);
37
38			rng.setSeed(3122688L);
39
40			print = false;
41			System.out.println("Warmup...");
42			oneTest(3, 10000);
43			Thread.sleep(1000);
44			oneTest(2, 10000);
45			Thread.sleep(100);
46			oneTest(1, 100000);
47			Thread.sleep(100);
48			oneTest(1, 100000);
49			Thread.sleep(1000);
50			print = true;
51
52			for (int i = 1; i <= maxThreads; ++i) {
53			for (int j = 0; j < replications; ++j) {
54			System.out.println("Threads:" + i);
55			oneTest(i, iters / i);
56			Thread.sleep(100);
57			}
58			}
59			pool.shutdown();
60			}
61
62			static void oneTest(int nthreads, int iters) throws Exception {
63			int v = rng.next();
64
65			if (print)
66			System.out.print("No shared vars ");
67			new NoLockLoop().test(v, nthreads, iters * 10);
68			Thread.sleep(10);
69
70			if (print)
71			System.out.print("No Lock + volatile ");
72			new NoLockVolatileLoop().test(v, nthreads, iters);
73			Thread.sleep(10);
74
75			if (doBuiltin) {
76			if (print)
77			System.out.print("builtin lock ");
78			new BuiltinLockLoop().test(v, nthreads, iters);
79			Thread.sleep(10);
80			}
81
82			if (print)
83			System.out.print("ReentrantLock ");
84			new ReentrantLockLoop().test(v, nthreads, iters);
85			Thread.sleep(10);
86
87			if (doReadWrite) {
88			if (print)
89			System.out.print("ReentrantWriteLock ");
90			new ReentrantWriteLockLoop().test(v, nthreads, iters);
91			Thread.sleep(10);
92
93			if (print)
94			System.out.print("ReentrantReadWriteLock");
95			new ReentrantReadWriteLockLoop().test(v, nthreads, iters);
96			Thread.sleep(10);
97			}
98
99			if (doSemaphore) {
100			if (print)
101			System.out.print("Semaphore ");
102			new SemaphoreLoop().test(v, nthreads, iters);
103			Thread.sleep(10);
104
105			if (print)
106			System.out.print("FairSemaphore ");
107			new FairSemaphoreLoop().test(v, nthreads, iters);
108			Thread.sleep(10);
109			}
110
111			if (doFair) {
112			if (print)
113			System.out.print("FairReentrantLock ");
114			new FairReentrantLockLoop().test(v, nthreads, iters);
115			Thread.sleep(10);
116
117			if (doReadWrite) {
118			if (print)
119			System.out.print("FairRWriteLock ");
120			new FairReentrantWriteLockLoop().test(v, nthreads, iters);
121			Thread.sleep(10);
122
123			if (print)
124			System.out.print("FairRReadWriteLock ");
125			new FairReentrantReadWriteLockLoop().test(v, nthreads, iters);
126			Thread.sleep(10);
127			}
128			}
129	jsr166	1.12
130			if (doStampedLock) {
131			if (print)
132			System.out.print("StampedLockWrite ");
133			new StampedLockWriteLoop().test(v, nthreads, iters);
134			Thread.sleep(10);
135
136			if (print)
137			System.out.print("StampedLockRead ");
138			new StampedLockReadLoop().test(v, nthreads, iters);
139			Thread.sleep(10);
140	jsr166	1.13
141			if (print)
142			System.out.print("StampedLockReadWrite");
143			new StampedLockReadLoop().test(v, nthreads, iters);
144			Thread.sleep(10);
145	jsr166	1.12	}
146	dl	1.1	}
147
148	jsr166	1.6	abstract static class LockLoop implements Runnable {
149	dl	1.1	int v;
150			int iters;
151			volatile int result;
152			final LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
153			CyclicBarrier barrier;
154
155			final void test(int initialValue, int nthreads, int iters) throws Exception {
156			v = initialValue;
157			this.iters = iters;
158			barrier = new CyclicBarrier(nthreads+1, timer);
159	jsr166	1.3	for (int i = 0; i < nthreads; ++i)
160	dl	1.1	pool.execute(this);
161			barrier.await();
162			barrier.await();
163			long time = timer.getTime();
164			if (print) {
165			long tpi = time / (iters * nthreads);
166			System.out.print("\t" + LoopHelpers.rightJustify(tpi) + " ns per update");
167	jsr166	1.4	// double secs = (double) time / 1000000000.0;
168	dl	1.1	// System.out.print("\t " + secs + "s run time");
169			System.out.println();
170			}
171
172			if (result == 0) // avoid overoptimization
173			System.out.println("useless result: " + result);
174			}
175			abstract int loop(int n);
176			public final void run() {
177			try {
178	jsr166	1.3	barrier.await();
179	dl	1.1	result += loop(iters);
180			barrier.await();
181			}
182	jsr166	1.3	catch (Exception ie) {
183			return;
184	dl	1.1	}
185			}
186
187			}
188
189			private static class BuiltinLockLoop extends LockLoop {
190			final int loop(int n) {
191			int sum = 0;
192			while (n-- > 0) {
193	jsr166	1.5	synchronized (this) {
194	dl	1.1	v = LoopHelpers.compute1(v);
195			}
196			sum += LoopHelpers.compute2(v);
197			}
198			return sum;
199			}
200			}
201
202			private static class NoLockLoop extends LockLoop {
203			final int loop(int n) {
204			int sum = 0;
205			int y = v;
206			while (n-- > 0) {
207			y = LoopHelpers.compute1(y);
208			sum += LoopHelpers.compute2(y);
209			}
210			return sum;
211			}
212			}
213
214			private static class NoLockVolatileLoop extends LockLoop {
215	jsr166	1.6	private volatile int vv;
216	dl	1.1	final int loop(int n) {
217			int sum = 0;
218			while (n-- > 0) {
219			int y = LoopHelpers.compute1(vv);
220			vv = y;
221			sum += LoopHelpers.compute2(y);
222			}
223			return sum;
224			}
225			}
226
227			private static class ReentrantLockLoop extends LockLoop {
228	jsr166	1.6	private final ReentrantLock lock = new ReentrantLock();
229	dl	1.1	final int loop(int n) {
230			int sum = 0;
231			while (n-- > 0) {
232			lock.lock();
233			try {
234			v = LoopHelpers.compute1(v);
235			}
236			finally {
237			lock.unlock();
238			}
239			sum += LoopHelpers.compute2(v);
240			}
241			return sum;
242			}
243			}
244
245			private static class FairReentrantLockLoop extends LockLoop {
246	jsr166	1.6	private final ReentrantLock lock = new ReentrantLock(true);
247	dl	1.1	final int loop(int n) {
248			int sum = 0;
249			while (n-- > 0) {
250			lock.lock();
251			try {
252			v = LoopHelpers.compute1(v);
253			}
254			finally {
255			lock.unlock();
256			}
257			sum += LoopHelpers.compute2(v);
258			}
259			return sum;
260			}
261			}
262
263			private static class ReentrantWriteLockLoop extends LockLoop {
264	jsr166	1.6	private final Lock lock = new ReentrantReadWriteLock().writeLock();
265	dl	1.1	final int loop(int n) {
266			int sum = 0;
267			while (n-- > 0) {
268			lock.lock();
269			try {
270			v = LoopHelpers.compute1(v);
271			}
272			finally {
273			lock.unlock();
274			}
275			sum += LoopHelpers.compute2(v);
276			}
277			return sum;
278			}
279			}
280
281			private static class ReentrantReadWriteLockLoop extends LockLoop {
282	jsr166	1.6	private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
283	dl	1.1	final int loop(int n) {
284			int sum = 0;
285			while (n-- > 0) {
286			int x;
287			lock.readLock().lock();
288			try {
289			x = LoopHelpers.compute1(v);
290			}
291			finally {
292			lock.readLock().unlock();
293			}
294			lock.writeLock().lock();
295			try {
296			v = x;
297			}
298			finally {
299			lock.writeLock().unlock();
300			}
301			sum += LoopHelpers.compute2(v);
302			}
303			return sum;
304			}
305			}
306
307			private static class FairReentrantWriteLockLoop extends LockLoop {
308			final Lock lock = new ReentrantReadWriteLock(true).writeLock();
309			final int loop(int n) {
310			int sum = 0;
311			while (n-- > 0) {
312			lock.lock();
313			try {
314			v = LoopHelpers.compute1(v);
315			}
316			finally {
317			lock.unlock();
318			}
319			sum += LoopHelpers.compute2(v);
320			}
321			return sum;
322			}
323			}
324
325			private static class SemaphoreLoop extends LockLoop {
326	jsr166	1.6	private final Semaphore sem = new Semaphore(1, false);
327	dl	1.1	final int loop(int n) {
328			int sum = 0;
329			try {
330			while (n-- > 0) {
331			sem.acquire();
332			try {
333			v = LoopHelpers.compute1(v);
334			}
335			finally {
336			sem.release();
337			}
338			sum += LoopHelpers.compute2(v);
339			}
340			}
341			catch (InterruptedException ie) {
342			return sum;
343			}
344			return sum;
345			}
346			}
347	jsr166	1.12
348	dl	1.1	private static class FairSemaphoreLoop extends LockLoop {
349	jsr166	1.6	private final Semaphore sem = new Semaphore(1, true);
350	dl	1.1	final int loop(int n) {
351			int sum = 0;
352			try {
353			while (n-- > 0) {
354			sem.acquire();
355			try {
356			v = LoopHelpers.compute1(v);
357			}
358			finally {
359			sem.release();
360			}
361			sum += LoopHelpers.compute2(v);
362			}
363			}
364			catch (InterruptedException ie) {
365			return sum;
366			}
367			return sum;
368			}
369			}
370
371			private static class FairReentrantReadWriteLockLoop extends LockLoop {
372	jsr166	1.6	private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
373	dl	1.1	final int loop(int n) {
374			int sum = 0;
375			while (n-- > 0) {
376			int x;
377			lock.readLock().lock();
378			try {
379			x = LoopHelpers.compute1(v);
380			}
381			finally {
382			lock.readLock().unlock();
383			}
384			lock.writeLock().lock();
385			try {
386			v = x;
387			}
388			finally {
389			lock.writeLock().unlock();
390			}
391			sum += LoopHelpers.compute2(v);
392			}
393			return sum;
394			}
395			}
396	jsr166	1.12
397			private static class StampedLockWriteLoop extends LockLoop {
398			private final StampedLock lock = new StampedLock();
399			final int loop(int n) {
400			int sum = 0;
401			while (n-- > 0) {
402			long stamp = lock.writeLock();
403			try {
404			v = LoopHelpers.compute1(v);
405			}
406			finally {
407			lock.unlockWrite(stamp);
408			}
409			sum += LoopHelpers.compute2(v);
410			}
411			return sum;
412			}
413			}
414
415			private static class StampedLockReadLoop extends LockLoop {
416			private final StampedLock lock = new StampedLock();
417			final int loop(int n) {
418			int sum = 0;
419			while (n-- > 0) {
420			long stamp = lock.readLock();
421			try {
422			v = LoopHelpers.compute1(v);
423			}
424			finally {
425			lock.unlockRead(stamp);
426			}
427			sum += LoopHelpers.compute2(v);
428			}
429			return sum;
430			}
431			}
432	jsr166	1.13
433			private static class StampedLockReadWriteLoop extends LockLoop {
434			private final StampedLock lock = new StampedLock();
435			final int loop(int n) {
436			int sum = 0;
437			while (n-- > 0) {
438			int x;
439			long stamp = lock.readLock();
440			try {
441			x = LoopHelpers.compute1(v);
442			}
443			finally {
444			lock.unlockRead(stamp);
445			}
446			stamp = lock.writeLock();
447			try {
448			v = x;
449			} finally {
450			lock.unlockWrite(stamp);
451			}
452			sum += LoopHelpers.compute2(v);
453			}
454			return sum;
455			}
456			}
457	dl	1.1	}