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Revision 1.33 - (download) (annotate)
Sat Feb 18 14:32:09 2017 UTC (9 months ago) by jsr166
Branch: MAIN
Changes since 1.32: +25 -19 lines
various minor improvements
/*
 * Written by Doug Lea and Martin Buchholz
 * 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/
 */

import static java.util.concurrent.TimeUnit.DAYS;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import static java.util.concurrent.TimeUnit.SECONDS;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.StampedLock;
import java.util.function.BiConsumer;
import java.util.function.Function;

import junit.framework.Test;
import junit.framework.TestSuite;

public class StampedLockTest extends JSR166TestCase {
    public static void main(String[] args) {
        main(suite(), args);
    }
    public static Test suite() {
        return new TestSuite(StampedLockTest.class);
    }

    /**
     * Releases write lock, checking isWriteLocked before and after
     */
    void releaseWriteLock(StampedLock lock, long stamp) {
        assertTrue(lock.isWriteLocked());
        assertValid(lock, stamp);
        lock.unlockWrite(stamp);
        assertFalse(lock.isWriteLocked());
        assertFalse(lock.validate(stamp));
    }

    /**
     * Releases read lock, checking isReadLocked before and after
     */
    void releaseReadLock(StampedLock lock, long stamp) {
        assertTrue(lock.isReadLocked());
        assertValid(lock, stamp);
        lock.unlockRead(stamp);
        assertFalse(lock.isReadLocked());
        assertTrue(lock.validate(stamp));
    }

    long assertNonZero(long v) {
        assertTrue(v != 0L);
        return v;
    }

    long assertValid(StampedLock lock, long stamp) {
        assertTrue(stamp != 0L);
        assertTrue(lock.validate(stamp));
        return stamp;
    }

    void assertUnlocked(StampedLock lock) {
        assertFalse(lock.isReadLocked());
        assertFalse(lock.isWriteLocked());
        assertEquals(0, lock.getReadLockCount());
        assertValid(lock, lock.tryOptimisticRead());
    }

    List<Action> lockLockers(Lock lock) {
        List<Action> lockers = new ArrayList<>();
        lockers.add(() -> lock.lock());
        lockers.add(() -> lock.lockInterruptibly());
        lockers.add(() -> lock.tryLock());
        lockers.add(() -> lock.tryLock(Long.MIN_VALUE, DAYS));
        lockers.add(() -> lock.tryLock(0L, DAYS));
        lockers.add(() -> lock.tryLock(Long.MAX_VALUE, DAYS));
        return lockers;
    }

    List<Function<StampedLock, Long>> readLockers() {
        List<Function<StampedLock, Long>> readLockers = new ArrayList<>();
        readLockers.add(sl -> sl.readLock());
        readLockers.add(sl -> sl.tryReadLock());
        readLockers.add(sl -> readLockInterruptiblyUninterrupted(sl));
        readLockers.add(sl -> tryReadLockUninterrupted(sl, Long.MIN_VALUE, DAYS));
        readLockers.add(sl -> tryReadLockUninterrupted(sl, 0L, DAYS));
        readLockers.add(sl -> sl.tryConvertToReadLock(sl.tryOptimisticRead()));
        return readLockers;
    }

    List<BiConsumer<StampedLock, Long>> readUnlockers() {
        List<BiConsumer<StampedLock, Long>> readUnlockers = new ArrayList<>();
        readUnlockers.add((sl, stamp) -> sl.unlockRead(stamp));
        readUnlockers.add((sl, stamp) -> assertTrue(sl.tryUnlockRead()));
        readUnlockers.add((sl, stamp) -> sl.asReadLock().unlock());
        readUnlockers.add((sl, stamp) -> sl.unlock(stamp));
        readUnlockers.add((sl, stamp) -> assertValid(sl, sl.tryConvertToOptimisticRead(stamp)));
        return readUnlockers;
    }

    List<Function<StampedLock, Long>> writeLockers() {
        List<Function<StampedLock, Long>> writeLockers = new ArrayList<>();
        writeLockers.add(sl -> sl.writeLock());
        writeLockers.add(sl -> sl.tryWriteLock());
        writeLockers.add(sl -> writeLockInterruptiblyUninterrupted(sl));
        writeLockers.add(sl -> tryWriteLockUninterrupted(sl, Long.MIN_VALUE, DAYS));
        writeLockers.add(sl -> tryWriteLockUninterrupted(sl, 0L, DAYS));
        writeLockers.add(sl -> sl.tryConvertToWriteLock(sl.tryOptimisticRead()));
        return writeLockers;
    }

    List<BiConsumer<StampedLock, Long>> writeUnlockers() {
        List<BiConsumer<StampedLock, Long>> writeUnlockers = new ArrayList<>();
        writeUnlockers.add((sl, stamp) -> sl.unlockWrite(stamp));
        writeUnlockers.add((sl, stamp) -> assertTrue(sl.tryUnlockWrite()));
        writeUnlockers.add((sl, stamp) -> sl.asWriteLock().unlock());
        writeUnlockers.add((sl, stamp) -> sl.unlock(stamp));
        writeUnlockers.add((sl, stamp) -> assertValid(sl, sl.tryConvertToOptimisticRead(stamp)));
        return writeUnlockers;
    }

    /**
     * Constructed StampedLock is in unlocked state
     */
    public void testConstructor() {
        assertUnlocked(new StampedLock());
    }

    /**
     * write-locking, then unlocking, an unlocked lock succeed
     */
    public void testWriteLock_lockUnlock() {
        StampedLock lock = new StampedLock();

        for (Function<StampedLock, Long> writeLocker : writeLockers())
        for (BiConsumer<StampedLock, Long> writeUnlocker : writeUnlockers()) {
            assertFalse(lock.isWriteLocked());
            assertFalse(lock.isReadLocked());
            assertEquals(0, lock.getReadLockCount());

            long s = writeLocker.apply(lock);
            assertValid(lock, s);
            assertTrue(lock.isWriteLocked());
            assertFalse(lock.isReadLocked());
            assertEquals(0, lock.getReadLockCount());
            writeUnlocker.accept(lock, s);
            assertUnlocked(lock);
        }
    }

    /**
     * read-locking, then unlocking, an unlocked lock succeed
     */
    public void testReadLock_lockUnlock() {
        StampedLock lock = new StampedLock();

        for (Function<StampedLock, Long> readLocker : readLockers())
        for (BiConsumer<StampedLock, Long> readUnlocker : readUnlockers()) {
            long s = 42;
            for (int i = 0; i < 2; i++) {
                s = assertValid(lock, readLocker.apply(lock));
                assertFalse(lock.isWriteLocked());
                assertTrue(lock.isReadLocked());
                assertEquals(i + 1, lock.getReadLockCount());
            }
            for (int i = 0; i < 2; i++) {
                assertFalse(lock.isWriteLocked());
                assertTrue(lock.isReadLocked());
                assertEquals(2 - i, lock.getReadLockCount());
                readUnlocker.accept(lock, s);
            }
            assertUnlocked(lock);
        }
    }

    /**
     * tryUnlockWrite fails if not write locked
     */
    public void testTryUnlockWrite_failure() {
        StampedLock lock = new StampedLock();
        assertFalse(lock.tryUnlockWrite());

        for (Function<StampedLock, Long> readLocker : readLockers())
        for (BiConsumer<StampedLock, Long> readUnlocker : readUnlockers()) {
            long s = assertValid(lock, readLocker.apply(lock));
            assertFalse(lock.tryUnlockWrite());
            assertTrue(lock.isReadLocked());
            readUnlocker.accept(lock, s);
            assertUnlocked(lock);
        }
    }

    /**
     * tryUnlockRead fails if not read locked
     */
    public void testTryUnlockRead_failure() {
        StampedLock lock = new StampedLock();
        assertFalse(lock.tryUnlockRead());

        for (Function<StampedLock, Long> writeLocker : writeLockers())
        for (BiConsumer<StampedLock, Long> writeUnlocker : writeUnlockers()) {
            long s = writeLocker.apply(lock);
            assertFalse(lock.tryUnlockRead());
            assertTrue(lock.isWriteLocked());
            writeUnlocker.accept(lock, s);
            assertUnlocked(lock);
        }
    }

    /**
     * validate(0L) fails
     */
    public void testValidate0() {
        StampedLock lock = new StampedLock();
        assertFalse(lock.validate(0L));
    }

    /**
     * A stamp obtained from a successful lock operation validates while the lock is held
     */
    public void testValidate() throws InterruptedException {
        StampedLock lock = new StampedLock();

        for (Function<StampedLock, Long> readLocker : readLockers())
        for (BiConsumer<StampedLock, Long> readUnlocker : readUnlockers()) {
            long s = assertNonZero(readLocker.apply(lock));
            assertTrue(lock.validate(s));
            readUnlocker.accept(lock, s);
        }

        for (Function<StampedLock, Long> writeLocker : writeLockers())
        for (BiConsumer<StampedLock, Long> writeUnlocker : writeUnlockers()) {
            long s = assertNonZero(writeLocker.apply(lock));
            assertTrue(lock.validate(s));
            writeUnlocker.accept(lock, s);
        }
    }

    /**
     * A stamp obtained from an unsuccessful lock operation does not validate
     */
    public void testValidate2() throws InterruptedException {
        StampedLock lock = new StampedLock();
        long s = assertNonZero(lock.writeLock());
        assertTrue(lock.validate(s));
        assertFalse(lock.validate(lock.tryWriteLock()));
        assertFalse(lock.validate(lock.tryWriteLock(0L, SECONDS)));
        assertFalse(lock.validate(lock.tryReadLock()));
        assertFalse(lock.validate(lock.tryReadLock(0L, SECONDS)));
        assertFalse(lock.validate(lock.tryOptimisticRead()));
        lock.unlockWrite(s);
    }

    void assertThrowInterruptedExceptionWhenPreInterrupted(Action[] actions) {
        for (Action action : actions) {
            Thread.currentThread().interrupt();
            try {
                action.run();
                shouldThrow();
            }
            catch (InterruptedException success) {}
            catch (Throwable fail) { threadUnexpectedException(fail); }
            assertFalse(Thread.interrupted());
        }
    }

    /**
     * interruptible operations throw InterruptedException when pre-interrupted
     */
    public void testInterruptibleOperationsThrowInterruptedExceptionWhenPreInterrupted() {
        final StampedLock lock = new StampedLock();

        Action[] interruptibleLockActions = {
            () -> lock.writeLockInterruptibly(),
            () -> lock.tryWriteLock(Long.MIN_VALUE, DAYS),
            () -> lock.tryWriteLock(Long.MAX_VALUE, DAYS),
            () -> lock.readLockInterruptibly(),
            () -> lock.tryReadLock(Long.MIN_VALUE, DAYS),
            () -> lock.tryReadLock(Long.MAX_VALUE, DAYS),
            () -> lock.asWriteLock().lockInterruptibly(),
            () -> lock.asWriteLock().tryLock(0L, DAYS),
            () -> lock.asWriteLock().tryLock(Long.MAX_VALUE, DAYS),
            () -> lock.asReadLock().lockInterruptibly(),
            () -> lock.asReadLock().tryLock(0L, DAYS),
            () -> lock.asReadLock().tryLock(Long.MAX_VALUE, DAYS),
        };
        shuffle(interruptibleLockActions);

        assertThrowInterruptedExceptionWhenPreInterrupted(interruptibleLockActions);
        {
            long s = lock.writeLock();
            assertThrowInterruptedExceptionWhenPreInterrupted(interruptibleLockActions);
            lock.unlockWrite(s);
        }
        {
            long s = lock.readLock();
            assertThrowInterruptedExceptionWhenPreInterrupted(interruptibleLockActions);
            lock.unlockRead(s);
        }
    }

    void assertThrowInterruptedExceptionWhenInterrupted(Action[] actions) {
        int n = actions.length;
        Future<?>[] futures = new Future<?>[n];
        CountDownLatch threadsStarted = new CountDownLatch(n);
        CountDownLatch done = new CountDownLatch(n);

        for (int i = 0; i < n; i++) {
            Action action = actions[i];
            futures[i] = cachedThreadPool.submit(new CheckedRunnable() {
                public void realRun() throws Throwable {
                    threadsStarted.countDown();
                    try {
                        action.run();
                        shouldThrow();
                    }
                    catch (InterruptedException success) {}
                    catch (Throwable fail) { threadUnexpectedException(fail); }
                    assertFalse(Thread.interrupted());
                    done.countDown();
                }});
        }

        await(threadsStarted);
        assertEquals(n, done.getCount());
        for (Future<?> future : futures) // Interrupt all the tasks
            future.cancel(true);
        await(done);
    }

    /**
     * interruptible operations throw InterruptedException when write locked and interrupted
     */
    public void testInterruptibleOperationsThrowInterruptedExceptionWriteLockedInterrupted() {
        final StampedLock lock = new StampedLock();
        long s = lock.writeLock();

        Action[] interruptibleLockBlockingActions = {
            () -> lock.writeLockInterruptibly(),
            () -> lock.tryWriteLock(Long.MAX_VALUE, DAYS),
            () -> lock.readLockInterruptibly(),
            () -> lock.tryReadLock(Long.MAX_VALUE, DAYS),
            () -> lock.asWriteLock().lockInterruptibly(),
            () -> lock.asWriteLock().tryLock(Long.MAX_VALUE, DAYS),
            () -> lock.asReadLock().lockInterruptibly(),
            () -> lock.asReadLock().tryLock(Long.MAX_VALUE, DAYS),
        };
        shuffle(interruptibleLockBlockingActions);

        assertThrowInterruptedExceptionWhenInterrupted(interruptibleLockBlockingActions);
    }

    /**
     * interruptible operations throw InterruptedException when read locked and interrupted
     */
    public void testInterruptibleOperationsThrowInterruptedExceptionReadLockedInterrupted() {
        final StampedLock lock = new StampedLock();
        long s = lock.readLock();

        Action[] interruptibleLockBlockingActions = {
            () -> lock.writeLockInterruptibly(),
            () -> lock.tryWriteLock(Long.MAX_VALUE, DAYS),
            () -> lock.asWriteLock().lockInterruptibly(),
            () -> lock.asWriteLock().tryLock(Long.MAX_VALUE, DAYS),
        };
        shuffle(interruptibleLockBlockingActions);

        assertThrowInterruptedExceptionWhenInterrupted(interruptibleLockBlockingActions);
    }

    /**
     * Non-interruptible operations ignore and preserve interrupt status
     */
    public void testNonInterruptibleOperationsIgnoreInterrupts() {
        final StampedLock lock = new StampedLock();
        Thread.currentThread().interrupt();

        for (BiConsumer<StampedLock, Long> readUnlocker : readUnlockers()) {
            long s = assertValid(lock, lock.readLock());
            readUnlocker.accept(lock, s);
            s = assertValid(lock, lock.tryReadLock());
            readUnlocker.accept(lock, s);
        }

        lock.asReadLock().lock();
        lock.asReadLock().unlock();

        for (BiConsumer<StampedLock, Long> writeUnlocker : writeUnlockers()) {
            long s = assertValid(lock, lock.writeLock());
            writeUnlocker.accept(lock, s);
            s = assertValid(lock, lock.tryWriteLock());
            writeUnlocker.accept(lock, s);
        }

        lock.asWriteLock().lock();
        lock.asWriteLock().unlock();

        assertTrue(Thread.interrupted());
    }

    /**
     * tryWriteLock on an unlocked lock succeeds
     */
    public void testTryWriteLock() {
        final StampedLock lock = new StampedLock();
        long s = lock.tryWriteLock();
        assertTrue(s != 0L);
        assertTrue(lock.isWriteLocked());
        assertEquals(0L, lock.tryWriteLock());
        releaseWriteLock(lock, s);
    }

    /**
     * tryWriteLock fails if locked
     */
    public void testTryWriteLockWhenLocked() {
        final StampedLock lock = new StampedLock();
        long s = lock.writeLock();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                assertEquals(0L, lock.tryWriteLock());
            }});

        assertEquals(0L, lock.tryWriteLock());
        awaitTermination(t);
        releaseWriteLock(lock, s);
    }

    /**
     * tryReadLock fails if write-locked
     */
    public void testTryReadLockWhenLocked() {
        final StampedLock lock = new StampedLock();
        long s = lock.writeLock();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                assertEquals(0L, lock.tryReadLock());
            }});

        assertEquals(0L, lock.tryReadLock());
        awaitTermination(t);
        releaseWriteLock(lock, s);
    }

    /**
     * Multiple threads can hold a read lock when not write-locked
     */
    public void testMultipleReadLocks() {
        final StampedLock lock = new StampedLock();
        final long s = lock.readLock();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                long s2 = lock.tryReadLock();
                assertValid(lock, s2);
                lock.unlockRead(s2);
                long s3 = lock.tryReadLock(LONG_DELAY_MS, MILLISECONDS);
                assertValid(lock, s3);
                lock.unlockRead(s3);
                long s4 = lock.readLock();
                assertValid(lock, s4);
                lock.unlockRead(s4);
                lock.asReadLock().lock();
                lock.asReadLock().unlock();
                lock.asReadLock().lockInterruptibly();
                lock.asReadLock().unlock();
                lock.asReadLock().tryLock(Long.MIN_VALUE, DAYS);
                lock.asReadLock().unlock();
            }});

        awaitTermination(t);
        lock.unlockRead(s);
    }

    /**
     * writeLock() succeeds only after a reading thread unlocks
     */
    public void testWriteAfterReadLock() throws InterruptedException {
        final CountDownLatch aboutToLock = new CountDownLatch(1);
        final StampedLock lock = new StampedLock();
        long rs = lock.readLock();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                aboutToLock.countDown();
                long s = lock.writeLock();
                assertTrue(lock.isWriteLocked());
                assertFalse(lock.isReadLocked());
                lock.unlockWrite(s);
            }});

        aboutToLock.await();
        waitForThreadToEnterWaitState(t);
        assertFalse(lock.isWriteLocked());
        assertTrue(lock.isReadLocked());
        lock.unlockRead(rs);
        awaitTermination(t);
        assertUnlocked(lock);
    }

    /**
     * writeLock() succeeds only after reading threads unlock
     */
    public void testWriteAfterMultipleReadLocks() {
        final StampedLock lock = new StampedLock();
        long s = lock.readLock();
        Thread t1 = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                long rs = lock.readLock();
                lock.unlockRead(rs);
            }});

        awaitTermination(t1);

        Thread t2 = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                long ws = lock.writeLock();
                lock.unlockWrite(ws);
            }});

        assertTrue(lock.isReadLocked());
        assertFalse(lock.isWriteLocked());
        lock.unlockRead(s);
        awaitTermination(t2);
        assertUnlocked(lock);
    }

    /**
     * readLock() succeed only after a writing thread unlocks
     */
    public void testReadAfterWriteLock() {
        final StampedLock lock = new StampedLock();
        final CountDownLatch threadsStarted = new CountDownLatch(2);
        final long s = lock.writeLock();
        final Runnable acquireReleaseReadLock = new CheckedRunnable() {
            public void realRun() {
                threadsStarted.countDown();
                long rs = lock.readLock();
                assertTrue(lock.isReadLocked());
                assertFalse(lock.isWriteLocked());
                lock.unlockRead(rs);
            }};
        Thread t1 = newStartedThread(acquireReleaseReadLock);
        Thread t2 = newStartedThread(acquireReleaseReadLock);

        await(threadsStarted);
        waitForThreadToEnterWaitState(t1);
        waitForThreadToEnterWaitState(t2);
        assertTrue(lock.isWriteLocked());
        assertFalse(lock.isReadLocked());
        releaseWriteLock(lock, s);
        awaitTermination(t1);
        awaitTermination(t2);
        assertUnlocked(lock);
    }

    /**
     * tryReadLock succeeds if read locked but not write locked
     */
    public void testTryLockWhenReadLocked() {
        final StampedLock lock = new StampedLock();
        long s = lock.readLock();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                long rs = lock.tryReadLock();
                assertValid(lock, rs);
                lock.unlockRead(rs);
            }});

        awaitTermination(t);
        lock.unlockRead(s);
    }

    /**
     * tryWriteLock fails when read locked
     */
    public void testTryWriteLockWhenReadLocked() {
        final StampedLock lock = new StampedLock();
        long s = lock.readLock();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                threadAssertEquals(0L, lock.tryWriteLock());
            }});

        awaitTermination(t);
        lock.unlockRead(s);
    }

    /**
     * timed lock operations time out if lock not available
     */
    public void testTimedLock_Timeout() throws Exception {
        ArrayList<Future<?>> futures = new ArrayList<>();

        // Write locked
        final StampedLock lock = new StampedLock();
        long stamp = lock.writeLock();
        assertEquals(0L, lock.tryReadLock(0L, DAYS));
        assertEquals(0L, lock.tryReadLock(Long.MIN_VALUE, DAYS));
        assertFalse(lock.asReadLock().tryLock(0L, DAYS));
        assertFalse(lock.asReadLock().tryLock(Long.MIN_VALUE, DAYS));
        assertEquals(0L, lock.tryWriteLock(0L, DAYS));
        assertEquals(0L, lock.tryWriteLock(Long.MIN_VALUE, DAYS));
        assertFalse(lock.asWriteLock().tryLock(0L, DAYS));
        assertFalse(lock.asWriteLock().tryLock(Long.MIN_VALUE, DAYS));

        futures.add(cachedThreadPool.submit(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                long startTime = System.nanoTime();
                assertEquals(0L, lock.tryWriteLock(timeoutMillis(), MILLISECONDS));
                assertTrue(millisElapsedSince(startTime) >= timeoutMillis());
            }}));

        futures.add(cachedThreadPool.submit(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                long startTime = System.nanoTime();
                assertEquals(0L, lock.tryReadLock(timeoutMillis(), MILLISECONDS));
                assertTrue(millisElapsedSince(startTime) >= timeoutMillis());
            }}));

        // Read locked
        final StampedLock lock2 = new StampedLock();
        long stamp2 = lock2.readLock();
        assertEquals(0L, lock2.tryWriteLock(0L, DAYS));
        assertEquals(0L, lock2.tryWriteLock(Long.MIN_VALUE, DAYS));
        assertFalse(lock2.asWriteLock().tryLock(0L, DAYS));
        assertFalse(lock2.asWriteLock().tryLock(Long.MIN_VALUE, DAYS));

        futures.add(cachedThreadPool.submit(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                long startTime = System.nanoTime();
                assertEquals(0L, lock2.tryWriteLock(timeoutMillis(), MILLISECONDS));
                assertTrue(millisElapsedSince(startTime) >= timeoutMillis());
            }}));

        for (Future<?> future : futures)
            assertNull(future.get());

        releaseWriteLock(lock, stamp);
        releaseReadLock(lock2, stamp2);
    }

    /**
     * writeLockInterruptibly succeeds if unlocked
     */
    public void testWriteLockInterruptibly() throws InterruptedException {
        final StampedLock lock = new StampedLock();
        long s = lock.writeLockInterruptibly();
        assertTrue(lock.isWriteLocked());
        releaseWriteLock(lock, s);
    }

    /**
     * readLockInterruptibly succeeds if lock free
     */
    public void testReadLockInterruptibly() throws InterruptedException {
        final StampedLock lock = new StampedLock();

        long s = assertValid(lock, lock.readLockInterruptibly());
        assertTrue(lock.isReadLocked());
        lock.unlockRead(s);

        lock.asReadLock().lockInterruptibly();
        assertTrue(lock.isReadLocked());
        lock.asReadLock().unlock();
    }

    /**
     * A serialized lock deserializes as unlocked
     */
    public void testSerialization() {
        StampedLock lock = new StampedLock();
        lock.writeLock();
        StampedLock clone = serialClone(lock);
        assertTrue(lock.isWriteLocked());
        assertFalse(clone.isWriteLocked());
        long s = clone.writeLock();
        assertTrue(clone.isWriteLocked());
        clone.unlockWrite(s);
        assertFalse(clone.isWriteLocked());
    }

    /**
     * toString indicates current lock state
     */
    public void testToString() {
        StampedLock lock = new StampedLock();
        assertTrue(lock.toString().contains("Unlocked"));
        long s = lock.writeLock();
        assertTrue(lock.toString().contains("Write-locked"));
        lock.unlockWrite(s);
        s = lock.readLock();
        assertTrue(lock.toString().contains("Read-locks"));
    }

    /**
     * tryOptimisticRead succeeds and validates if unlocked, fails if
     * exclusively locked
     */
    public void testValidateOptimistic() throws InterruptedException {
        StampedLock lock = new StampedLock();

        assertValid(lock, lock.tryOptimisticRead());

        for (Function<StampedLock, Long> writeLocker : writeLockers()) {
            long s = assertValid(lock, writeLocker.apply(lock));
            assertEquals(0L, lock.tryOptimisticRead());
            releaseWriteLock(lock, s);
        }

        for (Function<StampedLock, Long> readLocker : readLockers()) {
            long s = assertValid(lock, readLocker.apply(lock));
            long p = assertValid(lock, lock.tryOptimisticRead());
            releaseReadLock(lock, s);
            assertTrue(lock.validate(p));
        }

        assertValid(lock, lock.tryOptimisticRead());
    }

    /**
     * tryOptimisticRead stamp does not validate if a write lock intervenes
     */
    public void testValidateOptimisticWriteLocked() {
        final StampedLock lock = new StampedLock();
        final long p = assertValid(lock, lock.tryOptimisticRead());
        final long s = assertValid(lock, lock.writeLock());
        assertFalse(lock.validate(p));
        assertEquals(0L, lock.tryOptimisticRead());
        assertTrue(lock.validate(s));
        lock.unlockWrite(s);
    }

    /**
     * tryOptimisticRead stamp does not validate if a write lock
     * intervenes in another thread
     */
    public void testValidateOptimisticWriteLocked2()
            throws InterruptedException {
        final CountDownLatch locked = new CountDownLatch(1);
        final StampedLock lock = new StampedLock();
        final long p = assertValid(lock, lock.tryOptimisticRead());

        Thread t = newStartedThread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLockInterruptibly();
                locked.countDown();
                lock.writeLockInterruptibly();
            }});

        locked.await();
        assertFalse(lock.validate(p));
        assertEquals(0L, lock.tryOptimisticRead());
        waitForThreadToEnterWaitState(t);
        t.interrupt();
        awaitTermination(t);
        assertTrue(lock.isWriteLocked());
    }

    /**
     * tryConvertToOptimisticRead succeeds and validates if successfully locked
     */
    public void testTryConvertToOptimisticRead() throws InterruptedException {
        StampedLock lock = new StampedLock();
        long s, p, q;
        assertEquals(0L, lock.tryConvertToOptimisticRead(0L));

        s = assertValid(lock, lock.tryOptimisticRead());
        assertEquals(s, lock.tryConvertToOptimisticRead(s));
        assertTrue(lock.validate(s));

        for (Function<StampedLock, Long> writeLocker : writeLockers()) {
            s = assertValid(lock, writeLocker.apply(lock));
            p = assertValid(lock, lock.tryConvertToOptimisticRead(s));
            assertFalse(lock.validate(s));
            assertTrue(lock.validate(p));
            assertUnlocked(lock);
        }

        for (Function<StampedLock, Long> readLocker : readLockers()) {
            s = assertValid(lock, readLocker.apply(lock));
            q = assertValid(lock, lock.tryOptimisticRead());
            assertEquals(q, lock.tryConvertToOptimisticRead(q));
            assertTrue(lock.validate(q));
            assertTrue(lock.isReadLocked());
            p = assertValid(lock, lock.tryConvertToOptimisticRead(s));
            assertTrue(lock.validate(p));
            assertTrue(lock.validate(s));
            assertUnlocked(lock);
            assertEquals(q, lock.tryConvertToOptimisticRead(q));
            assertTrue(lock.validate(q));
        }
    }

    /**
     * tryConvertToReadLock succeeds for valid stamps
     */
    public void testTryConvertToReadLock() throws InterruptedException {
        StampedLock lock = new StampedLock();
        long s, p;

        assertEquals(0L, lock.tryConvertToReadLock(0L));

        s = assertValid(lock, lock.tryOptimisticRead());
        p = assertValid(lock, lock.tryConvertToReadLock(s));
        assertTrue(lock.isReadLocked());
        assertEquals(1, lock.getReadLockCount());
        assertTrue(lock.validate(s));
        lock.unlockRead(p);

        s = assertValid(lock, lock.tryOptimisticRead());
        lock.readLock();
        p = assertValid(lock, lock.tryConvertToReadLock(s));
        assertTrue(lock.isReadLocked());
        assertEquals(2, lock.getReadLockCount());
        lock.unlockRead(p);
        lock.unlockRead(p);
        assertUnlocked(lock);

        for (BiConsumer<StampedLock, Long> readUnlocker : readUnlockers()) {
            for (Function<StampedLock, Long> writeLocker : writeLockers()) {
                s = assertValid(lock, writeLocker.apply(lock));
                p = assertValid(lock, lock.tryConvertToReadLock(s));
                assertFalse(lock.validate(s));
                assertTrue(lock.isReadLocked());
                assertEquals(1, lock.getReadLockCount());
                readUnlocker.accept(lock, p);
            }

            for (Function<StampedLock, Long> readLocker : readLockers()) {
                s = assertValid(lock, readLocker.apply(lock));
                assertEquals(s, lock.tryConvertToReadLock(s));
                assertTrue(lock.validate(s));
                assertTrue(lock.isReadLocked());
                assertEquals(1, lock.getReadLockCount());
                readUnlocker.accept(lock, s);
            }
        }
    }

    /**
     * tryConvertToWriteLock succeeds if lock available; fails if multiply read locked
     */
    public void testTryConvertToWriteLock() throws InterruptedException {
        StampedLock lock = new StampedLock();
        long s, p;

        assertEquals(0L, lock.tryConvertToWriteLock(0L));

        assertTrue((s = lock.tryOptimisticRead()) != 0L);
        assertTrue((p = lock.tryConvertToWriteLock(s)) != 0L);
        assertTrue(lock.isWriteLocked());
        lock.unlockWrite(p);

        for (BiConsumer<StampedLock, Long> writeUnlocker : writeUnlockers()) {
            for (Function<StampedLock, Long> writeLocker : writeLockers()) {
                s = assertValid(lock, writeLocker.apply(lock));
                assertEquals(s, lock.tryConvertToWriteLock(s));
                assertTrue(lock.validate(s));
                assertTrue(lock.isWriteLocked());
                writeUnlocker.accept(lock, s);
            }

            for (Function<StampedLock, Long> readLocker : readLockers()) {
                s = assertValid(lock, readLocker.apply(lock));
                p = assertValid(lock, lock.tryConvertToWriteLock(s));
                assertFalse(lock.validate(s));
                assertTrue(lock.validate(p));
                assertTrue(lock.isWriteLocked());
                writeUnlocker.accept(lock, p);
            }
        }

        // failure if multiply read locked
        for (Function<StampedLock, Long> readLocker : readLockers()) {
            s = assertValid(lock, readLocker.apply(lock));
            p = assertValid(lock, readLocker.apply(lock));
            assertEquals(0L, lock.tryConvertToWriteLock(s));
            assertTrue(lock.validate(s));
            assertTrue(lock.validate(p));
            assertEquals(2, lock.getReadLockCount());
            lock.unlock(p);
            lock.unlock(s);
            assertUnlocked(lock);
        }
    }

    /**
     * asWriteLock can be locked and unlocked
     */
    public void testAsWriteLock() throws Throwable {
        StampedLock sl = new StampedLock();
        Lock lock = sl.asWriteLock();
        for (Action locker : lockLockers(lock)) {
            locker.run();
            assertTrue(sl.isWriteLocked());
            assertFalse(sl.isReadLocked());
            assertFalse(lock.tryLock());
            lock.unlock();
            assertUnlocked(sl);
        }
    }

    /**
     * asReadLock can be locked and unlocked
     */
    public void testAsReadLock() throws Throwable {
        StampedLock sl = new StampedLock();
        Lock lock = sl.asReadLock();
        for (Action locker : lockLockers(lock)) {
            locker.run();
            assertTrue(sl.isReadLocked());
            assertFalse(sl.isWriteLocked());
            assertEquals(1, sl.getReadLockCount());
            locker.run();
            assertTrue(sl.isReadLocked());
            assertEquals(2, sl.getReadLockCount());
            lock.unlock();
            lock.unlock();
            assertUnlocked(sl);
        }
    }

    /**
     * asReadWriteLock.writeLock can be locked and unlocked
     */
    public void testAsReadWriteLockWriteLock() throws Throwable {
        StampedLock sl = new StampedLock();
        Lock lock = sl.asReadWriteLock().writeLock();
        for (Action locker : lockLockers(lock)) {
            locker.run();
            assertTrue(sl.isWriteLocked());
            assertFalse(sl.isReadLocked());
            assertFalse(lock.tryLock());
            lock.unlock();
            assertUnlocked(sl);
        }
    }

    /**
     * asReadWriteLock.readLock can be locked and unlocked
     */
    public void testAsReadWriteLockReadLock() throws Throwable {
        StampedLock sl = new StampedLock();
        Lock lock = sl.asReadWriteLock().readLock();
        for (Action locker : lockLockers(lock)) {
            locker.run();
            assertTrue(sl.isReadLocked());
            assertFalse(sl.isWriteLocked());
            assertEquals(1, sl.getReadLockCount());
            locker.run();
            assertTrue(sl.isReadLocked());
            assertEquals(2, sl.getReadLockCount());
            lock.unlock();
            lock.unlock();
            assertUnlocked(sl);
        }
    }

    /**
     * Lock.newCondition throws UnsupportedOperationException
     */
    public void testLockViewsDoNotSupportConditions() {
        StampedLock sl = new StampedLock();
        assertThrows(UnsupportedOperationException.class,
                     () -> sl.asWriteLock().newCondition(),
                     () -> sl.asReadLock().newCondition(),
                     () -> sl.asReadWriteLock().writeLock().newCondition(),
                     () -> sl.asReadWriteLock().readLock().newCondition());
    }

    /**
     * Passing optimistic read stamps to unlock operations result in
     * IllegalMonitorStateException
     */
    public void testCannotUnlockOptimisticReadStamps() {
        Runnable[] actions = {
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = assertValid(sl, sl.tryOptimisticRead());
                sl.unlockRead(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryOptimisticRead();
                sl.unlock(stamp);
            },

            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryOptimisticRead();
                sl.writeLock();
                sl.unlock(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                sl.readLock();
                long stamp = assertValid(sl, sl.tryOptimisticRead());
                sl.unlockRead(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                sl.readLock();
                long stamp = assertValid(sl, sl.tryOptimisticRead());
                sl.unlock(stamp);
            },

            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.writeLock());
                assertValid(sl, stamp);
                sl.writeLock();
                sl.unlockWrite(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.writeLock());
                sl.writeLock();
                sl.unlock(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.writeLock());
                sl.readLock();
                sl.unlockRead(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.writeLock());
                sl.readLock();
                sl.unlock(stamp);
            },

            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.readLock());
                assertValid(sl, stamp);
                sl.writeLock();
                sl.unlockWrite(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.readLock());
                sl.writeLock();
                sl.unlock(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.readLock());
                sl.readLock();
                sl.unlockRead(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                sl.readLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.readLock());
                assertValid(sl, stamp);
                sl.readLock();
                sl.unlockRead(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.readLock());
                sl.readLock();
                sl.unlock(stamp);
            },
            () -> {
                StampedLock sl = new StampedLock();
                sl.readLock();
                long stamp = sl.tryConvertToOptimisticRead(sl.readLock());
                sl.readLock();
                sl.unlock(stamp);
            },
        };

        assertThrows(IllegalMonitorStateException.class, actions);
    }

    static long writeLockInterruptiblyUninterrupted(StampedLock sl) {
        try { return sl.writeLockInterruptibly(); }
        catch (InterruptedException ex) { throw new AssertionError(ex); }
    }

    static long tryWriteLockUninterrupted(StampedLock sl, long time, TimeUnit unit) {
        try { return sl.tryWriteLock(time, unit); }
        catch (InterruptedException ex) { throw new AssertionError(ex); }
    }

    static long readLockInterruptiblyUninterrupted(StampedLock sl) {
        try { return sl.readLockInterruptibly(); }
        catch (InterruptedException ex) { throw new AssertionError(ex); }
    }

    static long tryReadLockUninterrupted(StampedLock sl, long time, TimeUnit unit) {
        try { return sl.tryReadLock(time, unit); }
        catch (InterruptedException ex) { throw new AssertionError(ex); }
    }

    /**
     * Invalid stamps result in IllegalMonitorStateException
     */
    public void testInvalidStampsThrowIllegalMonitorStateException() {
        final StampedLock sl = new StampedLock();

        assertThrows(IllegalMonitorStateException.class,
                     () -> sl.unlockWrite(0L),
                     () -> sl.unlockRead(0L),
                     () -> sl.unlock(0L));

        final long optimisticStamp = sl.tryOptimisticRead();
        final long readStamp = sl.readLock();
        sl.unlockRead(readStamp);
        final long writeStamp = sl.writeLock();
        sl.unlockWrite(writeStamp);
        assertTrue(optimisticStamp != 0L && readStamp != 0L && writeStamp != 0L);
        final long[] noLongerValidStamps = { optimisticStamp, readStamp, writeStamp };
        final Runnable assertNoLongerValidStampsThrow = () -> {
            for (long noLongerValidStamp : noLongerValidStamps)
                assertThrows(IllegalMonitorStateException.class,
                             () -> sl.unlockWrite(noLongerValidStamp),
                             () -> sl.unlockRead(noLongerValidStamp),
                             () -> sl.unlock(noLongerValidStamp));
        };
        assertNoLongerValidStampsThrow.run();

        for (Function<StampedLock, Long> readLocker : readLockers())
        for (BiConsumer<StampedLock, Long> readUnlocker : readUnlockers()) {
            final long stamp = readLocker.apply(sl);
            assertValid(sl, stamp);
            assertNoLongerValidStampsThrow.run();
            assertThrows(IllegalMonitorStateException.class,
                         () -> sl.unlockWrite(stamp),
                         () -> sl.unlockRead(sl.tryOptimisticRead()),
                         () -> sl.unlockRead(0L));
            readUnlocker.accept(sl, stamp);
            assertUnlocked(sl);
            assertNoLongerValidStampsThrow.run();
        }

        for (Function<StampedLock, Long> writeLocker : writeLockers())
        for (BiConsumer<StampedLock, Long> writeUnlocker : writeUnlockers()) {
            final long stamp = writeLocker.apply(sl);
            assertValid(sl, stamp);
            assertNoLongerValidStampsThrow.run();
            assertThrows(IllegalMonitorStateException.class,
                         () -> sl.unlockRead(stamp),
                         () -> sl.unlockWrite(0L));
            writeUnlocker.accept(sl, stamp);
            assertUnlocked(sl);
            assertNoLongerValidStampsThrow.run();
        }
    }

    /**
     * Read locks can be very deeply nested
     */
    public void testDeeplyNestedReadLocks() {
        final StampedLock lock = new StampedLock();
        final int depth = 300;
        final long[] stamps = new long[depth];
        final List<Function<StampedLock, Long>> readLockers = readLockers();
        final List<BiConsumer<StampedLock, Long>> readUnlockers = readUnlockers();
        for (int i = 0; i < depth; i++) {
            Function<StampedLock, Long> readLocker
                = readLockers.get(i % readLockers.size());
            long stamp = readLocker.apply(lock);
            assertEquals(i + 1, lock.getReadLockCount());
            assertTrue(lock.isReadLocked());
            stamps[i] = stamp;
        }
        for (int i = 0; i < depth; i++) {
            BiConsumer<StampedLock, Long> readUnlocker
                = readUnlockers.get(i % readUnlockers.size());
            assertEquals(depth - i, lock.getReadLockCount());
            assertTrue(lock.isReadLocked());
            readUnlocker.accept(lock, stamps[depth - 1 - i]);
        }
        assertUnlocked(lock);
    }
}

Doug Lea
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