import org.apache.cassandra.metrics.HintedHandoffMetrics; //导入依赖的package包/类
private HintsService()
{
    File hintsDirectory = DatabaseDescriptor.getHintsDirectory();
    int maxDeliveryThreads = DatabaseDescriptor.getMaxHintsDeliveryThreads();

    catalog = HintsCatalog.load(hintsDirectory, createDescriptorParams());
    writeExecutor = new HintsWriteExecutor(catalog);

    int bufferSize = Math.max(DatabaseDescriptor.getMaxMutationSize() * 2, MIN_BUFFER_SIZE);
    bufferPool = new HintsBufferPool(bufferSize, writeExecutor::flushBuffer);

    isDispatchPaused = new AtomicBoolean(true);
    dispatchExecutor = new HintsDispatchExecutor(hintsDirectory, maxDeliveryThreads, isDispatchPaused);

    // periodically empty the current content of the buffers
    int flushPeriod = DatabaseDescriptor.getHintsFlushPeriodInMS();
    triggerFlushingFuture = ScheduledExecutors.optionalTasks.scheduleWithFixedDelay(() -> writeExecutor.flushBufferPool(bufferPool),
                                                                                    flushPeriod,
                                                                                    flushPeriod,
                                                                                    TimeUnit.MILLISECONDS);
    metrics = new HintedHandoffMetrics();
}