android-platform-libcore/luni/src/test/java/tests/api/java/util/concurrent/ReentrantReadWriteLockTest.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/licenses/publicdomain
 * Other contributors include Andrew Wright, Jeffrey Hayes,
 * Pat Fisher, Mike Judd.
 */

package tests.api.java.util.concurrent; // android-added

import junit.framework.*;
import java.util.concurrent.locks.*;
import java.util.concurrent.*;
import static java.util.concurrent.TimeUnit.MILLISECONDS;
import java.io.*;
import java.util.*;

public class ReentrantReadWriteLockTest extends JSR166TestCase {
    public static Test suite() {
        return new TestSuite(ReentrantReadWriteLockTest.class);
    }

    /**
     * A runnable calling lockInterruptibly
     */
    class InterruptibleLockRunnable extends CheckedRunnable {
        final ReentrantReadWriteLock lock;
        InterruptibleLockRunnable(ReentrantReadWriteLock l) { lock = l; }
        public void realRun() throws InterruptedException {
            lock.writeLock().lockInterruptibly();
        }
    }


    /**
     * A runnable calling lockInterruptibly that expects to be
     * interrupted
     */
    class InterruptedLockRunnable extends CheckedInterruptedRunnable {
        final ReentrantReadWriteLock lock;
        InterruptedLockRunnable(ReentrantReadWriteLock l) { lock = l; }
        public void realRun() throws InterruptedException {
            lock.writeLock().lockInterruptibly();
        }
    }

    /**
     * Subclass to expose protected methods
     */
    static class PublicReentrantReadWriteLock extends ReentrantReadWriteLock {
        PublicReentrantReadWriteLock() { super(); }
        public Collection<Thread> getQueuedThreads() {
            return super.getQueuedThreads();
        }
        public Collection<Thread> getWaitingThreads(Condition c) {
            return super.getWaitingThreads(c);
        }
    }

    /**
     * Constructor sets given fairness, and is in unlocked state
     */
    public void testConstructor() {
        ReentrantReadWriteLock rl = new ReentrantReadWriteLock();
        assertFalse(rl.isFair());
        assertFalse(rl.isWriteLocked());
        assertEquals(0, rl.getReadLockCount());
        ReentrantReadWriteLock r2 = new ReentrantReadWriteLock(true);
        assertTrue(r2.isFair());
        assertFalse(r2.isWriteLocked());
        assertEquals(0, r2.getReadLockCount());
        ReentrantReadWriteLock r3 = new ReentrantReadWriteLock(false);
        assertFalse(r3.isFair());
        assertFalse(r3.isWriteLocked());
        assertEquals(0, r3.getReadLockCount());
    }

    /**
     * write-locking and read-locking an unlocked lock succeed
     */
    public void testLock() {
        ReentrantReadWriteLock rl = new ReentrantReadWriteLock();
        rl.writeLock().lock();
        assertTrue(rl.isWriteLocked());
        assertTrue(rl.isWriteLockedByCurrentThread());
        assertTrue(rl.writeLock().isHeldByCurrentThread());
        assertEquals(0, rl.getReadLockCount());
        rl.writeLock().unlock();
        assertFalse(rl.isWriteLocked());
        assertFalse(rl.isWriteLockedByCurrentThread());
        assertFalse(rl.writeLock().isHeldByCurrentThread());
        assertEquals(0, rl.getReadLockCount());
        rl.readLock().lock();
        assertFalse(rl.isWriteLocked());
        assertFalse(rl.isWriteLockedByCurrentThread());
        assertEquals(1, rl.getReadLockCount());
        rl.readLock().unlock();
        assertFalse(rl.isWriteLocked());
        assertFalse(rl.isWriteLockedByCurrentThread());
        assertEquals(0, rl.getReadLockCount());
    }


    /**
     * locking an unlocked fair lock succeeds
     */
    public void testFairLock() {
        ReentrantReadWriteLock rl = new ReentrantReadWriteLock(true);
        rl.writeLock().lock();
        assertTrue(rl.isWriteLocked());
        assertTrue(rl.isWriteLockedByCurrentThread());
        assertTrue(rl.writeLock().isHeldByCurrentThread());
        assertEquals(0, rl.getReadLockCount());
        rl.writeLock().unlock();
        assertFalse(rl.isWriteLocked());
        assertFalse(rl.isWriteLockedByCurrentThread());
        assertFalse(rl.writeLock().isHeldByCurrentThread());
        assertEquals(0, rl.getReadLockCount());
        rl.readLock().lock();
        assertFalse(rl.isWriteLocked());
        assertFalse(rl.isWriteLockedByCurrentThread());
        assertEquals(1, rl.getReadLockCount());
        rl.readLock().unlock();
        assertFalse(rl.isWriteLocked());
        assertFalse(rl.isWriteLockedByCurrentThread());
        assertEquals(0, rl.getReadLockCount());
    }

    /**
     * getWriteHoldCount returns number of recursive holds
     */
    public void testGetWriteHoldCount() {
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        for (int i = 1; i <= SIZE; i++) {
            lock.writeLock().lock();
            assertEquals(i,lock.getWriteHoldCount());
        }
        for (int i = SIZE; i > 0; i--) {
            lock.writeLock().unlock();
            assertEquals(i-1,lock.getWriteHoldCount());
        }
    }

    /**
     * WriteLock.getHoldCount returns number of recursive holds
     */
    public void testGetHoldCount() {
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        for (int i = 1; i <= SIZE; i++) {
            lock.writeLock().lock();
            assertEquals(i,lock.writeLock().getHoldCount());
        }
        for (int i = SIZE; i > 0; i--) {
            lock.writeLock().unlock();
            assertEquals(i-1,lock.writeLock().getHoldCount());
        }
    }

    /**
     * getReadHoldCount returns number of recursive holds
     */
    public void testGetReadHoldCount() {
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        for (int i = 1; i <= SIZE; i++) {
            lock.readLock().lock();
            assertEquals(i,lock.getReadHoldCount());
        }
        for (int i = SIZE; i > 0; i--) {
            lock.readLock().unlock();
            assertEquals(i-1,lock.getReadHoldCount());
        }
    }


    /**
     * write-unlocking an unlocked lock throws IllegalMonitorStateException
     */
    public void testUnlock_IllegalMonitorStateException() {
        ReentrantReadWriteLock rl = new ReentrantReadWriteLock();
        try {
            rl.writeLock().unlock();
            shouldThrow();
        } catch (IllegalMonitorStateException success) {}
    }


    /**
     * write-lockInterruptibly is interruptible
     */
    public void testWriteLockInterruptibly_Interrupted() throws Exception {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lockInterruptibly();
                lock.writeLock().unlock();
                lock.writeLock().lockInterruptibly();
                lock.writeLock().unlock();
            }});

        lock.writeLock().lock();
        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().unlock();
        t.join();
    }

    /**
     * timed write-tryLock is interruptible
     */
    public void testWriteTryLock_Interrupted() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().tryLock(SMALL_DELAY_MS, MILLISECONDS);
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        lock.writeLock().unlock();
        t.join();
    }

    /**
     * read-lockInterruptibly is interruptible
     */
    public void testReadLockInterruptibly_Interrupted() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.readLock().lockInterruptibly();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().unlock();
        t.join();
    }

    /**
     * timed read-tryLock is interruptible
     */
    public void testReadTryLock_Interrupted() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.readLock().tryLock(LONG_DELAY_MS, MILLISECONDS);
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        t.join();
    }


    /**
     * write-tryLock fails if locked
     */
    public void testWriteTryLockWhenLocked() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() {
                threadAssertFalse(lock.writeLock().tryLock());
            }});

        t.start();
        t.join();
        lock.writeLock().unlock();
    }

    /**
     * read-tryLock fails if locked
     */
    public void testReadTryLockWhenLocked() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() {
                threadAssertFalse(lock.readLock().tryLock());
            }});

        t.start();
        t.join();
        lock.writeLock().unlock();
    }

    /**
     * Multiple threads can hold a read lock when not write-locked
     */
    public void testMultipleReadLocks() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.readLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() {
                threadAssertTrue(lock.readLock().tryLock());
                lock.readLock().unlock();
            }});

        t.start();
        t.join();
        lock.readLock().unlock();
    }

    /**
     * A writelock succeeds after reading threads unlock
     */
    public void testWriteAfterMultipleReadLocks() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.readLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.readLock().lock();
                lock.readLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});

        t1.start();
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        lock.readLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }

    /**
     * Readlocks succeed after a writing thread unlocks
     */
    public void testReadAfterWriteLock() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.readLock().lock();
                lock.readLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.readLock().lock();
                lock.readLock().unlock();
            }});

        t1.start();
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }

    /**
     * Read trylock succeeds if write locked by current thread
     */
    public void testReadHoldingWriteLock() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        assertTrue(lock.readLock().tryLock());
        lock.readLock().unlock();
        lock.writeLock().unlock();
    }

    /**
     * Read lock succeeds if write locked by current thread even if
     * other threads are waiting for readlock
     */
    public void testReadHoldingWriteLock2() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.readLock().lock();
                lock.readLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.readLock().lock();
                lock.readLock().unlock();
            }});

        t1.start();
        t2.start();
        lock.readLock().lock();
        lock.readLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.readLock().lock();
        lock.readLock().unlock();
        lock.writeLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }

    /**
     *  Read lock succeeds if write locked by current thread even if
     * other threads are waiting for writelock
     */
    public void testReadHoldingWriteLock3() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});

        t1.start();
        t2.start();
        lock.readLock().lock();
        lock.readLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.readLock().lock();
        lock.readLock().unlock();
        lock.writeLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }


    /**
     *  Write lock succeeds if write locked by current thread even if
     * other threads are waiting for writelock
     */
    public void testWriteHoldingWriteLock4() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});

        t1.start();
        t2.start();
        lock.writeLock().lock();
        lock.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        lock.writeLock().unlock();
        lock.writeLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }


    /**
     * Fair Read trylock succeeds if write locked by current thread
     */
    public void testReadHoldingWriteLockFair() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        lock.writeLock().lock();
        assertTrue(lock.readLock().tryLock());
        lock.readLock().unlock();
        lock.writeLock().unlock();
    }

    /**
     * Fair Read lock succeeds if write locked by current thread even if
     * other threads are waiting for readlock
     */
    public void testReadHoldingWriteLockFair2() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        lock.writeLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.readLock().lock();
                lock.readLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.readLock().lock();
                lock.readLock().unlock();
            }});

        t1.start();
        t2.start();
        lock.readLock().lock();
        lock.readLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.readLock().lock();
        lock.readLock().unlock();
        lock.writeLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }


    /**
     * Fair Read lock succeeds if write locked by current thread even if
     * other threads are waiting for writelock
     */
    public void testReadHoldingWriteLockFair3() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        lock.writeLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});

        t1.start();
        t2.start();
        lock.readLock().lock();
        lock.readLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.readLock().lock();
        lock.readLock().unlock();
        lock.writeLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }


    /**
     * Fair Write lock succeeds if write locked by current thread even if
     * other threads are waiting for writelock
     */
    public void testWriteHoldingWriteLockFair4() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        lock.writeLock().lock();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});
        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() {
                lock.writeLock().lock();
                lock.writeLock().unlock();
            }});

        t1.start();
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(lock.isWriteLockedByCurrentThread());
        assertTrue(lock.getWriteHoldCount() == 1);
        lock.writeLock().lock();
        assertTrue(lock.getWriteHoldCount() == 2);
        lock.writeLock().unlock();
        lock.writeLock().lock();
        lock.writeLock().unlock();
        lock.writeLock().unlock();
        t1.join(MEDIUM_DELAY_MS);
        t2.join(MEDIUM_DELAY_MS);
        assertTrue(!t1.isAlive());
        assertTrue(!t2.isAlive());
    }


    /**
     * Read tryLock succeeds if readlocked but not writelocked
     */
    public void testTryLockWhenReadLocked() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.readLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() {
                threadAssertTrue(lock.readLock().tryLock());
                lock.readLock().unlock();
            }});

        t.start();
        t.join();
        lock.readLock().unlock();
    }



    /**
     * write tryLock fails when readlocked
     */
    public void testWriteTryLockWhenReadLocked() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.readLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() {
                threadAssertFalse(lock.writeLock().tryLock());
            }});

        t.start();
        t.join();
        lock.readLock().unlock();
    }


    /**
     * Fair Read tryLock succeeds if readlocked but not writelocked
     */
    public void testTryLockWhenReadLockedFair() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        lock.readLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() {
                threadAssertTrue(lock.readLock().tryLock());
                lock.readLock().unlock();
            }});

        t.start();
        t.join();
        lock.readLock().unlock();
    }



    /**
     * Fair write tryLock fails when readlocked
     */
    public void testWriteTryLockWhenReadLockedFair() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
        lock.readLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() {
                threadAssertFalse(lock.writeLock().tryLock());
            }});

        t.start();
        t.join();
        lock.readLock().unlock();
    }



    /**
     * write timed tryLock times out if locked
     */
    public void testWriteTryLock_Timeout() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                threadAssertFalse(lock.writeLock().tryLock(1, MILLISECONDS));
            }});

        t.start();
        t.join();
        assertTrue(lock.writeLock().isHeldByCurrentThread());
        lock.writeLock().unlock();
    }

    /**
     * read timed tryLock times out if write-locked
     */
    public void testReadTryLock_Timeout() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lock();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                threadAssertFalse(lock.readLock().tryLock(1, MILLISECONDS));
            }});

        t.start();
        t.join();
        assertTrue(lock.writeLock().isHeldByCurrentThread());
        lock.writeLock().unlock();
    }


    /**
     * write lockInterruptibly succeeds if lock free else is interruptible
     */
    public void testWriteLockInterruptibly() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lockInterruptibly();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lockInterruptibly();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        Thread.sleep(SHORT_DELAY_MS);
        t.join();
        lock.writeLock().unlock();
    }

    /**
     *  read lockInterruptibly succeeds if lock free else is interruptible
     */
    public void testReadLockInterruptibly() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        lock.writeLock().lockInterruptibly();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.readLock().lockInterruptibly();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        t.join();
        lock.writeLock().unlock();
    }

    /**
     * Calling await without holding lock throws IllegalMonitorStateException
     */
    public void testAwait_IllegalMonitor() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        try {
            c.await();
            shouldThrow();
        } catch (IllegalMonitorStateException success) {}
    }

    /**
     * Calling signal without holding lock throws IllegalMonitorStateException
     */
    public void testSignal_IllegalMonitor() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        try {
            c.signal();
            shouldThrow();
        } catch (IllegalMonitorStateException success) {}
    }

    /**
     * awaitNanos without a signal times out
     */
    public void testAwaitNanos_Timeout() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();

        lock.writeLock().lock();
        long t = c.awaitNanos(100);
        assertTrue(t <= 0);
        lock.writeLock().unlock();
    }


    /**
     *  timed await without a signal times out
     */
    public void testAwait_Timeout() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        lock.writeLock().lock();
        assertFalse(c.await(SHORT_DELAY_MS, MILLISECONDS));
        lock.writeLock().unlock();
    }

    /**
     * awaitUntil without a signal times out
     */
    public void testAwaitUntil_Timeout() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        lock.writeLock().lock();
        java.util.Date d = new java.util.Date();
        assertFalse(c.awaitUntil(new java.util.Date(d.getTime() + 10)));
        lock.writeLock().unlock();
    }

    /**
     * await returns when signalled
     */
    public void testAwait() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                c.await();
                lock.writeLock().unlock();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        c.signal();
        lock.writeLock().unlock();
        t.join(SHORT_DELAY_MS);
        assertFalse(t.isAlive());
    }

    /** A helper class for uninterruptible wait tests */
    class UninterruptableThread extends Thread {
        private Lock lock;
        private Condition c;

        public volatile boolean canAwake = false;
        public volatile boolean interrupted = false;
        public volatile boolean lockStarted = false;

        public UninterruptableThread(Lock lock, Condition c) {
            this.lock = lock;
            this.c = c;
        }

        public synchronized void run() {
            lock.lock();
            lockStarted = true;

            while (!canAwake) {
                c.awaitUninterruptibly();
            }

            interrupted = isInterrupted();
            lock.unlock();
        }
    }

    /**
     * awaitUninterruptibly doesn't abort on interrupt
     */
    public void testAwaitUninterruptibly() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        UninterruptableThread thread = new UninterruptableThread(lock.writeLock(), c);

        thread.start();

        while (!thread.lockStarted) {
            Thread.sleep(100);
        }

        lock.writeLock().lock();
        try {
            thread.interrupt();
            thread.canAwake = true;
            c.signal();
        } finally {
            lock.writeLock().unlock();
        }

        thread.join();
        assertTrue(thread.interrupted);
        assertFalse(thread.isAlive());
    }

    /**
     * await is interruptible
     */
    public void testAwait_Interrupt() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                c.await();
                lock.writeLock().unlock();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        t.join(SHORT_DELAY_MS);
        assertFalse(t.isAlive());
    }

    /**
     * awaitNanos is interruptible
     */
    public void testAwaitNanos_Interrupt() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                c.awaitNanos(MILLISECONDS.toNanos(LONG_DELAY_MS));
                lock.writeLock().unlock();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        t.join(SHORT_DELAY_MS);
        assertFalse(t.isAlive());
    }

    /**
     * awaitUntil is interruptible
     */
    public void testAwaitUntil_Interrupt() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t = new Thread(new CheckedInterruptedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                java.util.Date d = new java.util.Date();
                c.awaitUntil(new java.util.Date(d.getTime() + 10000));
                lock.writeLock().unlock();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        t.interrupt();
        t.join(SHORT_DELAY_MS);
        assertFalse(t.isAlive());
    }

    /**
     * signalAll wakes up all threads
     */
    public void testSignalAll() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                c.await();
                lock.writeLock().unlock();
            }});

        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                c.await();
                lock.writeLock().unlock();
            }});

        t1.start();
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        c.signalAll();
        lock.writeLock().unlock();
        t1.join(SHORT_DELAY_MS);
        t2.join(SHORT_DELAY_MS);
        assertFalse(t1.isAlive());
        assertFalse(t2.isAlive());
    }

    /**
     * A serialized lock deserializes as unlocked
     */
    public void testSerialization() throws Exception {
        ReentrantReadWriteLock l = new ReentrantReadWriteLock();
        l.readLock().lock();
        l.readLock().unlock();

        ByteArrayOutputStream bout = new ByteArrayOutputStream(10000);
        ObjectOutputStream out = new ObjectOutputStream(new BufferedOutputStream(bout));
        out.writeObject(l);
        out.close();

        ByteArrayInputStream bin = new ByteArrayInputStream(bout.toByteArray());
        ObjectInputStream in = new ObjectInputStream(new BufferedInputStream(bin));
        ReentrantReadWriteLock r = (ReentrantReadWriteLock) in.readObject();
        r.readLock().lock();
        r.readLock().unlock();
    }

    /**
     * hasQueuedThreads reports whether there are waiting threads
     */
    public void testhasQueuedThreads() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        Thread t1 = new Thread(new InterruptedLockRunnable(lock));
        Thread t2 = new Thread(new InterruptibleLockRunnable(lock));
        assertFalse(lock.hasQueuedThreads());
        lock.writeLock().lock();
        t1.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(lock.hasQueuedThreads());
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(lock.hasQueuedThreads());
        t1.interrupt();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(lock.hasQueuedThreads());
        lock.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        assertFalse(lock.hasQueuedThreads());
        t1.join();
        t2.join();
    }

    /**
     * hasQueuedThread(null) throws NPE
     */
    public void testHasQueuedThreadNPE() {
        final ReentrantReadWriteLock sync = new ReentrantReadWriteLock();
        try {
            sync.hasQueuedThread(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * hasQueuedThread reports whether a thread is queued.
     */
    public void testHasQueuedThread() throws InterruptedException {
        final ReentrantReadWriteLock sync = new ReentrantReadWriteLock();
        Thread t1 = new Thread(new InterruptedLockRunnable(sync));
        Thread t2 = new Thread(new InterruptibleLockRunnable(sync));
        assertFalse(sync.hasQueuedThread(t1));
        assertFalse(sync.hasQueuedThread(t2));
        sync.writeLock().lock();
        t1.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(sync.hasQueuedThread(t1));
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(sync.hasQueuedThread(t1));
        assertTrue(sync.hasQueuedThread(t2));
        t1.interrupt();
        Thread.sleep(SHORT_DELAY_MS);
        assertFalse(sync.hasQueuedThread(t1));
        assertTrue(sync.hasQueuedThread(t2));
        sync.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        assertFalse(sync.hasQueuedThread(t1));
        Thread.sleep(SHORT_DELAY_MS);
        assertFalse(sync.hasQueuedThread(t2));
        t1.join();
        t2.join();
    }


    /**
     * getQueueLength reports number of waiting threads
     */
    public void testGetQueueLength() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        Thread t1 = new Thread(new InterruptedLockRunnable(lock));
        Thread t2 = new Thread(new InterruptibleLockRunnable(lock));
        assertEquals(0, lock.getQueueLength());
        lock.writeLock().lock();
        t1.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertEquals(1, lock.getQueueLength());
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertEquals(2, lock.getQueueLength());
        t1.interrupt();
        Thread.sleep(SHORT_DELAY_MS);
        assertEquals(1, lock.getQueueLength());
        lock.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        assertEquals(0, lock.getQueueLength());
        t1.join();
        t2.join();
    }

    /**
     * getQueuedThreads includes waiting threads
     */
    public void testGetQueuedThreads() throws InterruptedException {
        final PublicReentrantReadWriteLock lock = new PublicReentrantReadWriteLock();
        Thread t1 = new Thread(new InterruptedLockRunnable(lock));
        Thread t2 = new Thread(new InterruptibleLockRunnable(lock));
        assertTrue(lock.getQueuedThreads().isEmpty());
        lock.writeLock().lock();
        assertTrue(lock.getQueuedThreads().isEmpty());
        t1.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(lock.getQueuedThreads().contains(t1));
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(lock.getQueuedThreads().contains(t1));
        assertTrue(lock.getQueuedThreads().contains(t2));
        t1.interrupt();
        Thread.sleep(SHORT_DELAY_MS);
        assertFalse(lock.getQueuedThreads().contains(t1));
        assertTrue(lock.getQueuedThreads().contains(t2));
        lock.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        assertTrue(lock.getQueuedThreads().isEmpty());
        t1.join();
        t2.join();
    }

    /**
     * hasWaiters throws NPE if null
     */
    public void testHasWaitersNPE() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        try {
            lock.hasWaiters(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * getWaitQueueLength throws NPE if null
     */
    public void testGetWaitQueueLengthNPE() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        try {
            lock.getWaitQueueLength(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }


    /**
     * getWaitingThreads throws NPE if null
     */
    public void testGetWaitingThreadsNPE() {
        final PublicReentrantReadWriteLock lock = new PublicReentrantReadWriteLock();
        try {
            lock.getWaitingThreads(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * hasWaiters throws IAE if not owned
     */
    public void testHasWaitersIAE() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        final ReentrantReadWriteLock lock2 = new ReentrantReadWriteLock();
        try {
            lock2.hasWaiters(c);
            shouldThrow();
        } catch (IllegalArgumentException success) {}
    }

    /**
     * hasWaiters throws IMSE if not locked
     */
    public void testHasWaitersIMSE() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        try {
            lock.hasWaiters(c);
            shouldThrow();
        } catch (IllegalMonitorStateException success) {}
    }


    /**
     * getWaitQueueLength throws IAE if not owned
     */
    public void testGetWaitQueueLengthIAE() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        final ReentrantReadWriteLock lock2 = new ReentrantReadWriteLock();
        try {
            lock2.getWaitQueueLength(c);
            shouldThrow();
        } catch (IllegalArgumentException success) {}
    }

    /**
     * getWaitQueueLength throws IMSE if not locked
     */
    public void testGetWaitQueueLengthIMSE() {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        try {
            lock.getWaitQueueLength(c);
            shouldThrow();
        } catch (IllegalMonitorStateException success) {}
    }


    /**
     * getWaitingThreads throws IAE if not owned
     */
    public void testGetWaitingThreadsIAE() {
        final PublicReentrantReadWriteLock lock = new PublicReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        final PublicReentrantReadWriteLock lock2 = new PublicReentrantReadWriteLock();
        try {
            lock2.getWaitingThreads(c);
            shouldThrow();
        } catch (IllegalArgumentException success) {}
    }

    /**
     * getWaitingThreads throws IMSE if not locked
     */
    public void testGetWaitingThreadsIMSE() {
        final PublicReentrantReadWriteLock lock = new PublicReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        try {
            lock.getWaitingThreads(c);
            shouldThrow();
        } catch (IllegalMonitorStateException success) {}
    }


    /**
     * hasWaiters returns true when a thread is waiting, else false
     */
    public void testHasWaiters() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                threadAssertFalse(lock.hasWaiters(c));
                threadAssertEquals(0, lock.getWaitQueueLength(c));
                c.await();
                lock.writeLock().unlock();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        assertTrue(lock.hasWaiters(c));
        assertEquals(1, lock.getWaitQueueLength(c));
        c.signal();
        lock.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        assertFalse(lock.hasWaiters(c));
        assertEquals(0, lock.getWaitQueueLength(c));
        lock.writeLock().unlock();
        t.join(SHORT_DELAY_MS);
        assertFalse(t.isAlive());
    }

    /**
     * getWaitQueueLength returns number of waiting threads
     */
    public void testGetWaitQueueLength() throws InterruptedException {
        final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                threadAssertFalse(lock.hasWaiters(c));
                threadAssertEquals(0, lock.getWaitQueueLength(c));
                c.await();
                lock.writeLock().unlock();
            }});

        t.start();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        assertTrue(lock.hasWaiters(c));
        assertEquals(1, lock.getWaitQueueLength(c));
        c.signal();
        lock.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        assertFalse(lock.hasWaiters(c));
        assertEquals(0, lock.getWaitQueueLength(c));
        lock.writeLock().unlock();
        t.join(SHORT_DELAY_MS);
        assertFalse(t.isAlive());
    }


    /**
     * getWaitingThreads returns only and all waiting threads
     */
    public void testGetWaitingThreads() throws InterruptedException {
        final PublicReentrantReadWriteLock lock = new PublicReentrantReadWriteLock();
        final Condition c = lock.writeLock().newCondition();
        Thread t1 = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                threadAssertTrue(lock.getWaitingThreads(c).isEmpty());
                c.await();
                lock.writeLock().unlock();
            }});

        Thread t2 = new Thread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                lock.writeLock().lock();
                threadAssertFalse(lock.getWaitingThreads(c).isEmpty());
                c.await();
                lock.writeLock().unlock();
            }});

        lock.writeLock().lock();
        assertTrue(lock.getWaitingThreads(c).isEmpty());
        lock.writeLock().unlock();
        t1.start();
        Thread.sleep(SHORT_DELAY_MS);
        t2.start();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        assertTrue(lock.hasWaiters(c));
        assertTrue(lock.getWaitingThreads(c).contains(t1));
        assertTrue(lock.getWaitingThreads(c).contains(t2));
        c.signalAll();
        lock.writeLock().unlock();
        Thread.sleep(SHORT_DELAY_MS);
        lock.writeLock().lock();
        assertFalse(lock.hasWaiters(c));
        assertTrue(lock.getWaitingThreads(c).isEmpty());
        lock.writeLock().unlock();
        t1.join(SHORT_DELAY_MS);
        t2.join(SHORT_DELAY_MS);
        assertFalse(t1.isAlive());
        assertFalse(t2.isAlive());
    }

    /**
     * toString indicates current lock state
     */
    public void testToString() {
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        String us = lock.toString();
        assertTrue(us.indexOf("Write locks = 0") >= 0);
        assertTrue(us.indexOf("Read locks = 0") >= 0);
        lock.writeLock().lock();
        String ws = lock.toString();
        assertTrue(ws.indexOf("Write locks = 1") >= 0);
        assertTrue(ws.indexOf("Read locks = 0") >= 0);
        lock.writeLock().unlock();
        lock.readLock().lock();
        lock.readLock().lock();
        String rs = lock.toString();
        assertTrue(rs.indexOf("Write locks = 0") >= 0);
        assertTrue(rs.indexOf("Read locks = 2") >= 0);
    }

    /**
     * readLock.toString indicates current lock state
     */
    public void testReadLockToString() {
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        String us = lock.readLock().toString();
        assertTrue(us.indexOf("Read locks = 0") >= 0);
        lock.readLock().lock();
        lock.readLock().lock();
        String rs = lock.readLock().toString();
        assertTrue(rs.indexOf("Read locks = 2") >= 0);
    }

    /**
     * writeLock.toString indicates current lock state
     */
    public void testWriteLockToString() {
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        String us = lock.writeLock().toString();
        assertTrue(us.indexOf("Unlocked") >= 0);
        lock.writeLock().lock();
        String ls = lock.writeLock().toString();
        assertTrue(ls.indexOf("Locked") >= 0);
    }

}