Fix bug in PerformanceLogContext

PerformanceLogContext threw NullPointerException when multiple threads
tried to add an event to the PerformanceLogContext. The cause for this
is that the ThreadLocal was initialized only in the class constructor
for the first thread; for subsequent threads it was null.

To fix this initialize eventRecords for each thread.

Change-Id: I18ef67dff8f0488e3ad28c9bbc18ce73d5168cf9
Signed-off-by: Alexa Panfil <alexapizza@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/logging/PerformanceLogContextTest.java

@@ -1,6 +1,7 @@
 package org.eclipse.jgit.logging;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
 import org.junit.Test;
@@ -37,30 +38,58 @@ public void testCleanEvents() {
 	}
 
 	@Test
-	public void testAddEventsTwoThreads() {
-		TestRunnable thread1 = new TestRunnable("record1", 1);
-		TestRunnable thread2 = new TestRunnable("record2", 2);
+	public void testAddEventsTwoThreads() throws InterruptedException {
+		TestRunnable runnable1 = new TestRunnable("record1", 1);
+		TestRunnable runnable2 = new TestRunnable("record2", 2);
 
-		new Thread(thread1).start();
-		new Thread(thread2).start();
+		Thread thread1 = new Thread(runnable1);
+		Thread thread2 = new Thread(runnable2);
+
+		thread1.start();
+		thread2.start();
+
+		thread1.join();
+		thread2.join();
+		assertEquals(1, runnable1.getEventRecordsCount());
+		assertEquals(1, runnable2.getEventRecordsCount());
+		assertFalse(runnable1.isThrown());
+		assertFalse(runnable2.isThrown());
 	}
 
 	private static class TestRunnable implements Runnable {
 		private String name;
+
 		private long durationMs;
 
+		private long eventRecordsCount;
+
+		private boolean thrown = false;
+
 		public TestRunnable(String name, long durationMs) {
 			this.name = name;
 			this.durationMs = durationMs;
 		}
 
+		public boolean isThrown() {
+			return thrown;
+		}
+
+		public long getEventRecordsCount() {
+			return eventRecordsCount;
+		}
+
 		@Override
 		public void run() {
 			PerformanceLogRecord record = new PerformanceLogRecord(name,
 					durationMs);
-			PerformanceLogContext.getInstance().addEvent(record);
-			assertEquals(1, PerformanceLogContext.getInstance()
-					.getEventRecords().size());
+			try {
+				PerformanceLogContext.getInstance().addEvent(record);
+				eventRecordsCount = PerformanceLogContext.getInstance()
+						.getEventRecords().size();
+				PerformanceLogContext.getInstance().cleanEvents();
+			} catch (Exception e) {
+				thrown = true;
+			}
 		}
 	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/logging/PerformanceLogContext.java

@@ -24,10 +24,10 @@ public class PerformanceLogContext {
 	private static final PerformanceLogContext INSTANCE = new PerformanceLogContext();
 
 	/** List that stores events as performance logs. */
-	private final ThreadLocal<List<PerformanceLogRecord>> eventRecords = new ThreadLocal<>();
+	private static final ThreadLocal<List<PerformanceLogRecord>> eventRecords = ThreadLocal
+			.withInitial(ArrayList::new);
 
 	private PerformanceLogContext() {
-		eventRecords.set(new ArrayList<>());
 	}
 
 	/**
@@ -62,6 +62,6 @@ public void addEvent(PerformanceLogRecord record) {
 	 * Removes all of the existing records from the current list of events.
 	 */
 	public void cleanEvents() {
-		eventRecords.get().clear();
+		eventRecords.remove();
 	}
 }