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    * and other copyright owners as documented in the project's IP log.
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  package org.eclipse.jgit.lib;
  
  import static org.junit.Assert.assertEquals;
  import static org.junit.Assert.assertFalse;
  import static org.junit.Assert.assertNull;
  import static org.junit.Assert.assertTrue;
  import static org.junit.Assert.fail;
  
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.TimeUnit;
  
  import org.junit.Test;
  
  public class ThreadSafeProgressMonitorTest {
  	@Test
  	public void testFailsMethodsOnBackgroundThread()
  			throws InterruptedException {
  		final MockProgressMonitor mock = new MockProgressMonitor();
  		final ThreadSafeProgressMonitor pm = new ThreadSafeProgressMonitor(mock);
  
  		runOnThread(() -> {
  			try {
  				pm.start(1);
  				fail("start did not fail on background thread");
  			} catch (IllegalStateException notMainThread) {
  				// Expected result
  			}
  
  			try {
  				pm.beginTask("title", 1);
  				fail("beginTask did not fail on background thread");
  			} catch (IllegalStateException notMainThread) {
  				// Expected result
  			}
  
  			try {
  				pm.endTask();
  				fail("endTask did not fail on background thread");
  			} catch (IllegalStateException notMainThread) {
  				// Expected result
  			}
  		});
  
  		// Ensure we didn't alter the mock above when checking threads.
  		assertNull(mock.taskTitle);
  		assertEquals(0, mock.value);
  	}
  
  	@Test
  	public void testMethodsOkOnMainThread() {
  		final MockProgressMonitor mock = new MockProgressMonitor();
  		final ThreadSafeProgressMonitor pm = new ThreadSafeProgressMonitor(mock);
  
  		pm.start(1);
  		assertEquals(1, mock.value);
  
 		pm.beginTask("title", 42);
 		assertEquals("title", mock.taskTitle);
 		assertEquals(42, mock.value);
 
 		pm.update(1);
 		pm.pollForUpdates();
 		assertEquals(43, mock.value);
 
 		pm.update(2);
 		pm.pollForUpdates();
 		assertEquals(45, mock.value);
 
 		pm.endTask();
 		assertNull(mock.taskTitle);
 		assertEquals(0, mock.value);
 	}
 
 	@Test
 	public void testUpdateOnBackgroundThreads() throws InterruptedException {
 		final MockProgressMonitor mock = new MockProgressMonitor();
 		final ThreadSafeProgressMonitor pm = new ThreadSafeProgressMonitor(mock);
 
 		pm.startWorker();
 
 		final CountDownLatch doUpdate = new CountDownLatch(1);
 		final CountDownLatch didUpdate = new CountDownLatch(1);
 		final CountDownLatch doEndWorker = new CountDownLatch(1);
 
 		final Thread bg = new Thread() {
 			@Override
 			public void run() {
 				assertFalse(pm.isCancelled());
 
 				await(doUpdate);
 				pm.update(2);
 				didUpdate.countDown();
 
 				await(doEndWorker);
 				pm.update(1);
 				pm.endWorker();
 			}
 		};
 		bg.start();
 
 		pm.pollForUpdates();
 		assertEquals(0, mock.value);
 		doUpdate.countDown();
 
 		await(didUpdate);
 		pm.pollForUpdates();
 		assertEquals(2, mock.value);
 
 		doEndWorker.countDown();
 		pm.waitForCompletion();
 		assertEquals(3, mock.value);
 	}
 
 	private static void await(CountDownLatch cdl) {
 		try {
 			assertTrue("latch released", cdl.await(1000, TimeUnit.MILLISECONDS));
 		} catch (InterruptedException ie) {
 			fail("Did not expect to be interrupted");
 		}
 	}
 
 	private static void runOnThread(Runnable task) throws InterruptedException {
 		Thread t = new Thread(task);
 		t.start();
 		t.join(1000);
 		assertFalse("thread has stopped", t.isAlive());
 	}
 
 	private static class MockProgressMonitor implements ProgressMonitor {
 		String taskTitle;
 
 		int value;
 
 		@Override
 		public void update(int completed) {
 			value += completed;
 		}
 
 		@Override
 		public void start(int totalTasks) {
 			value = totalTasks;
 		}
 
 		@Override
 		public void beginTask(String title, int totalWork) {
 			taskTitle = title;
 			value = totalWork;
 		}
 
 		@Override
 		public void endTask() {
 			taskTitle = null;
 			value = 0;
 		}
 
 		@Override
 		public boolean isCancelled() {
 			return false;
 		}
 	}
 }