Changed the root package from net.sf.briar to org.briarproject.

briar-tests/src/org/briarproject/LockFairnessTest.java

@@ -0,0 +1,161 @@
+package org.briarproject;
+
+import static java.util.concurrent.TimeUnit.SECONDS;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+import org.junit.Test;
+
+public class LockFairnessTest extends BriarTestCase {
+
+	@Test
+	public void testReadersCanShareTheLock() throws Exception {
+		// Use a fair lock
+		final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
+		final CountDownLatch firstReaderHasLock = new CountDownLatch(1);
+		final CountDownLatch firstReaderHasFinished = new CountDownLatch(1);
+		final CountDownLatch secondReaderHasLock = new CountDownLatch(1);
+		final CountDownLatch secondReaderHasFinished = new CountDownLatch(1);
+		// First reader
+		Thread first = new Thread() {
+			@Override
+			public void run() {
+				try {
+					// Acquire the lock
+					lock.readLock().lock();
+					try {
+						// Allow the second reader to acquire the lock
+						firstReaderHasLock.countDown();
+						// Wait for the second reader to acquire the lock
+						assertTrue(secondReaderHasLock.await(10, SECONDS));
+					} finally {
+						// Release the lock
+						lock.readLock().unlock();
+					}
+				} catch(InterruptedException e) {
+					fail();
+				}
+				firstReaderHasFinished.countDown();
+			}
+		};
+		first.start();
+		// Second reader
+		Thread second = new Thread() {
+			@Override
+			public void run() {
+				try {
+					// Wait for the first reader to acquire the lock
+					assertTrue(firstReaderHasLock.await(10, SECONDS));
+					// Acquire the lock
+					lock.readLock().lock();
+					try {
+						// Allow the first reader to release the lock
+						secondReaderHasLock.countDown();
+					} finally {
+						// Release the lock
+						lock.readLock().unlock();
+					}
+				} catch(InterruptedException e) {
+					fail();
+				}
+				secondReaderHasFinished.countDown();
+			}
+		};
+		second.start();
+		// Wait for both readers to finish
+		assertTrue(firstReaderHasFinished.await(10, SECONDS));
+		assertTrue(secondReaderHasFinished.await(10, SECONDS));
+	}
+
+	@Test
+	public void testWritersDoNotStarve() throws Exception {
+		// Use a fair lock
+		final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
+		final CountDownLatch firstReaderHasLock = new CountDownLatch(1);
+		final CountDownLatch firstReaderHasFinished = new CountDownLatch(1);
+		final CountDownLatch secondReaderHasFinished = new CountDownLatch(1);
+		final CountDownLatch writerHasFinished = new CountDownLatch(1);
+		final AtomicBoolean secondReaderHasHeldLock = new AtomicBoolean(false);
+		final AtomicBoolean writerHasHeldLock = new AtomicBoolean(false);
+		// First reader
+		Thread first = new Thread() {
+			@Override
+			public void run() {
+				try {
+					// Acquire the lock
+					lock.readLock().lock();
+					try {
+						// Allow the other threads to acquire the lock
+						firstReaderHasLock.countDown();
+						// Wait for both other threads to wait for the lock
+						while(lock.getQueueLength() < 2) Thread.sleep(10);
+						// No other thread should have acquired the lock
+						assertFalse(secondReaderHasHeldLock.get());
+						assertFalse(writerHasHeldLock.get());
+					} finally {
+						// Release the lock
+						lock.readLock().unlock();
+					}
+				} catch(InterruptedException e) {
+					fail();
+				}
+				firstReaderHasFinished.countDown();
+			}
+		};
+		first.start();
+		// Writer
+		Thread writer = new Thread() {
+			@Override
+			public void run() {
+				try {
+					// Wait for the first reader to acquire the lock
+					assertTrue(firstReaderHasLock.await(10, SECONDS));
+					// Acquire the lock
+					lock.writeLock().lock();
+					try {
+						writerHasHeldLock.set(true);
+						// The second reader should not overtake the writer
+						assertFalse(secondReaderHasHeldLock.get());
+					} finally {
+						lock.writeLock().unlock();
+					}
+				} catch(InterruptedException e) {
+					fail();
+				}
+				writerHasFinished.countDown();
+			}
+		};
+		writer.start();
+		// Second reader
+		Thread second = new Thread() {
+			@Override
+			public void run() {
+				try {
+					// Wait for the first reader to acquire the lock
+					assertTrue(firstReaderHasLock.await(10, SECONDS));
+					// Wait for the writer to wait for the lock
+					while(lock.getQueueLength() < 1) Thread.sleep(10);
+					// Acquire the lock
+					lock.readLock().lock();
+					try {
+						secondReaderHasHeldLock.set(true);
+						// The second reader should not overtake the writer
+						assertTrue(writerHasHeldLock.get());
+					} finally {
+						lock.readLock().unlock();
+					}
+				} catch(InterruptedException e) {
+					fail();
+				}
+				secondReaderHasFinished.countDown();
+			}
+		};
+		second.start();
+		// Wait for all the threads to finish
+		assertTrue(firstReaderHasFinished.await(10, SECONDS));
+		assertTrue(secondReaderHasFinished.await(10, SECONDS));
+		assertTrue(writerHasFinished.await(10, SECONDS));
+	}
+}