class Program
    {
     static void Main(string[] args)
    {
    const string MutexName ="CSharpThreadingCookbook";
    using (var m = new Mutex(false, MutexName))
    {
    if (!m.WaitOne(TimeSpan.FromSeconds(5), false))
    {
     Console.WriteLine("Second instance is running!");
    }
    else {
     Console.WriteLine("Runing!");
     Console.ReadLine();
     m.ReleaseMutex();
    }
   }
  }
 }

static SemaphoreSlim _semaphore = new SemaphoreSlim(4);

   static void AccessDatabase(string name, int seconds) {
   Console.WriteLine("{0} waits to access a database",name);
   _semaphore.Wait();
   Console.WriteLine("{0} was granted an access to a database",name);
   Thread.Sleep(TimeSpan.FromSeconds(seconds));
   Console.WriteLine("{0} is completed",name);
   _semaphore.Release();

  }

static void Main(string[] args)
   {
   for (int i = 1; i <= 6; i++) {
    string threadName ="Thread" + i;
    int secondsToWait = 2 + 2 * i;
    var t = new Thread(() => AccessDatabase(threadName, secondsToWait));
    t.Start();
   }
   Console.ReadKey();
  }

private staticAutoResetEvent _workerEvent=new AutoResetEvent(false);
   private staticAutoResetEvent _mainEvent =new AutoResetEvent(false);
   static void Process(int seconds)
   {
    Console.WriteLine("Starting a long running work... ");
    Thread.Sleep(TimeSpan.FromSeconds(seconds));
    Console.WriteLine("Work is done!");
    _workerEvent.Set();
    Console.WriteLine("Waiting for a main thread to complete its work");
    _mainEvent.WaitOne();
    Console.WriteLine("starting second operation... ");
    Thread.Sleep(TimeSpan.FromSeconds(seconds));
    Console.WriteLine("Work is done!");
    _workerEvent.Set();
  }

static void Main(string[] args)
   {
    var t = new Thread(() => Process(10));
    t.Start();
    Console.WriteLine("Waiting for a main thread to complete its work");
    _workerEvent.WaitOne();
    Console.WriteLine("First operation is completed!");
    Console.WriteLine("Performing an operation on a main thread");
    Thread.Sleep(TimeSpan.FromSeconds(5));
    _mainEvent.Set();
    Console.WriteLine("Now running the second operation on a second thread");
    _workerEvent.WaitOne();
    Console.WriteLine("Second operation is completed!");
  }