### Question:
RealtimeSegmentStatsHistory implements Serializable { public static synchronized RealtimeSegmentStatsHistory deserialzeFrom(File inFile) throws IOException, ClassNotFoundException { if (inFile.exists()) { try (FileInputStream is = new FileInputStream(inFile); ObjectInputStream obis = new ObjectInputStream(is)) { RealtimeSegmentStatsHistory history = (RealtimeSegmentStatsHistory) (obis.readObject()); history.normalize(); return history; } } else { return new RealtimeSegmentStatsHistory(inFile.getAbsolutePath()); } } private  RealtimeSegmentStatsHistory(String historyFilePath); @VisibleForTesting static int getMaxNumEntries(); @VisibleForTesting static int getDefaultEstAvgColSize(); @VisibleForTesting static int getDefaultEstCardinality(); @VisibleForTesting static void setMaxNumEntries(int maxNumEntries); int getCursor(); int getArraySize(); boolean isFull(); synchronized boolean isEmpty(); synchronized void setMinIntervalBetweenUpdatesMillis(long millis); synchronized void addSegmentStats(SegmentStats segmentStats); synchronized int getEstimatedCardinality(@Nonnull String columnName); synchronized int getEstimatedAvgColSize(@Nonnull String columnName); synchronized int getEstimatedRowsToIndex(); SegmentStats getSegmentStatsAt(int index); @Override String toString(); static synchronized RealtimeSegmentStatsHistory deserialzeFrom(File inFile); static void main(String[] args); static Logger LOGGER; }### Answer:
@Test public void testMultiThreadedUse() throws Exception { final int numThreads = 8; final int numIterations = 10; final long avgSleepTimeMs = 300; Thread[] threads = new Thread[numThreads]; final String tmpDir = System.getProperty("java.io.tmpdir"); File serializedFile = new File(tmpDir, STATS_FILE_NAME); FileUtils.deleteQuietly(serializedFile); serializedFile.deleteOnExit(); RealtimeSegmentStatsHistory statsHistory = RealtimeSegmentStatsHistory.deserialzeFrom(serializedFile); for (int i = 0; i < numThreads; i++) { threads[i] = new Thread(new StatsUpdater(statsHistory, numIterations, avgSleepTimeMs)); threads[i].start(); } for (int i = 0; i < numThreads; i++) { threads[i].join(); } FileUtils.deleteQuietly(serializedFile); }