How to synchronize 3 C # threads

There is a task. Training, so that the issues of optimality of the decision fade into the background. There are 3 threads that need to be synchronized. The first thread collects information about files and folders. It works cyclically and recursively. Having found the information, it should stop and let threads 2 and 3 write it to a file and memory. When streams 2 and 3 have finished recording, stream 1 resumes operation and searches for the next file (folder). There should be 3 threads. Writing each found file in a new stream is not an option.
The questions are as follows:
1. Which mechanism is better to use for synchronization of threads: AutoResetEvent (its own for each of the two threads - see the code), ManualResetEvent or Semaphore.
2. How do I fix the code so that the threads start and stop when needed? I would be grateful for an explanation of why this is so, because with the Set (), Reset (), Wait () methods I played for a long time, but without success.
3. How to organize the stopping of secondary flows after the end of the primary work? I equated the null primary stream, but I think this is not the best idea.
4. And I would be grateful for an explanation of how to solve similar problems in normal, non-educational projects.
5. Is it necessary in this example to read information by secondary flows in the critical section? As I assume, the information in the reading process will not change, since the main thread waits for the completion of the secondary ones, and there is no need for a critical section.

Code:

private Queue<Nested3> collection; static int counter=100; object locked; Thread SearcherThread; Thread Handler1Thread; Thread Handler2Thread; static WaitHandle[] events; private class Nested3 { public int Val; public bool IsHandled; public Nested3(int val) { this.Val = val; IsHandled = false; } } public ARETest() { collection = new Queue<Nested3>(); events = new WaitHandle[] { new AutoResetEvent(false), new AutoResetEvent(false) }; SearcherThread = new Thread(Searcher); SearcherThread.Start(); Handler1Thread = new Thread(Handler1); Handler2Thread = new Thread(Handler2); locked = new object(); } private void Searcher() { // Очередь для двух задач в двух разных потоках. ThreadPool.QueueUserWorkItem(new WaitCallback(Handler1), events[0]); ThreadPool.QueueUserWorkItem(new WaitCallback(Handler2), events[1]); for (int i = 0; i < 3; i++) { Thread.Sleep(2); // имитация поиска Monitor.Enter(locked); // применение класса Monitor для создания критической секции обусловлено условием задачи collection.Enqueue(new Nested3(++counter)); // Найден первый пакет информации для записи вторичными потками Monitor.Exit(locked); (events[0] as AutoResetEvent).Set(); // запуск вторичных потоков (events[1] as AutoResetEvent).Set(); (events[0] as AutoResetEvent).Reset(); // сброс в несигнальное состояние (events[1] as AutoResetEvent).Reset(); // Ожидание пока все задачи завершаться. WaitHandle.WaitAll(events); Monitor.Enter(locked); // Очистка очереди от записанной информации collection.Dequeue(); Monitor.Exit(locked); if (i<2) Searcher(); // Рекурсивный вызов } SearcherThread = null; // Запуск последнего прохода цикла вторичными потоками (events[0] as AutoResetEvent).Set(); (events[1] as AutoResetEvent).Set(); } private void Handler1(object state) { var auto = (AutoResetEvent)state; do { auto.WaitOne(); // здесь я хочу чтобы потоки ждали сигнала от первичного потока Thread.Sleep(15); // имитация записи в файл auto.Set(); // Здесь вторичный поток должен дать первичному сигнал, что он закончил итерацию } while (SearcherThread != null); } private void Handler2(Object state) // работает аналогично предыдущему методу, но с другой задержкой { var auto = (AutoResetEvent)state; do { auto.WaitOne(); // здесь я хочу чтобы потоки ждали сигнала от первичного потока Thread.Sleep(15); // имитация записи в файл auto.Set(); // Здесь вторичный поток должен дать первичному сигнал, что он закончил итерацию } while (SearcherThread != null); } }