System.Threading.Timer是否实际上在两个不同的线程中运行？

Question

The code sample below

using System.Threading;

namespace TimerApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("***** Timer Application *****\n");
            Console.WriteLine("In the thread #{0}",     Thread.CurrentThread.ManagedThreadId); 

            // Create the delegate for the Timer type. 
            TimerCallback timerCB = new TimerCallback(ShowTime);

            // Establish timer settings. 
            Timer t = new Timer(
                timerCB,                // The TimerCallback delegate object. 
                "Hello from Main()",    // Any info to pass into the called method (null for no info). 
                0,                      // Amount of time to wait before starting (in milliseconds). 
                1000);                  // Interval of time between calls (in milliseconds). 

            Console.WriteLine("Hit key to terminate...");
            Console.ReadLine(); 
        }

        // Method to show current time... 
        public static void ShowTime(object state)
        {
        Console.WriteLine("From the thread #{0}, it is background?{1}: time is {2}, param is {3}", 
            Thread.CurrentThread.ManagedThreadId, 
            Thread.CurrentThread.IsBackground,
            DateTime.Now.ToLongTimeString(), 
            state.ToString()); 
        }
    }
 } 

produces the following output

***** Timer Application *****

In the thread #1
Hit key to terminate...
From the thread #4, it is background?True: time is 10:37:54 PM, param is Hello from Main()
From the thread #4, it is background?True: time is 10:37:55 PM, param is Hello from Main()
From the thread #5, it is background?True: time is 10:37:56 PM, param is Hello from Main()
From the thread #4, it is background?True: time is 10:37:57 PM, param is Hello from Main()
From the thread #5, it is background?True: time is 10:37:58 PM, param is Hello from Main()
From the thread #4, it is background?True: time is 10:37:59 PM, param is Hello from Main()
From the thread #5, it is background?True: time is 10:38:00 PM, param is Hello from Main()
...
Press any key to continue . . .

Does the System.Threading.Timer make callbacks using several threads at a time?

Answer 1

It makes use of the thread pool, using the first thread that it finds available at each time interval. The timer simply triggers the firing of these threads.

void Main()
{
    System.Threading.Timer timer = new Timer((x) =>
    {
        Console.WriteLine($"{DateTime.Now.TimeOfDay} - Is Thread Pool Thread: {Thread.CurrentThread.IsThreadPoolThread} - Managed Thread Id: {Thread.CurrentThread.ManagedThreadId}");
        Thread.Sleep(5000);

    }, null, 1000, 1000);

    Console.ReadLine();
}

Output

07:19:44.2628607 - Is Thread Pool Thread: True - Managed Thread Id: 10
07:19:45.2639080 - Is Thread Pool Thread: True - Managed Thread Id: 13
07:19:46.2644998 - Is Thread Pool Thread: True - Managed Thread Id: 9
07:19:47.2649563 - Is Thread Pool Thread: True - Managed Thread Id: 8
07:19:48.2660500 - Is Thread Pool Thread: True - Managed Thread Id: 12
07:19:49.2664012 - Is Thread Pool Thread: True - Managed Thread Id: 14
07:19:50.2669635 - Is Thread Pool Thread: True - Managed Thread Id: 15
07:19:51.2679269 - Is Thread Pool Thread: True - Managed Thread Id: 10
07:19:52.2684307 - Is Thread Pool Thread: True - Managed Thread Id: 9
07:19:53.2693090 - Is Thread Pool Thread: True - Managed Thread Id: 13
07:19:54.2839838 - Is Thread Pool Thread: True - Managed Thread Id: 8
07:19:55.2844800 - Is Thread Pool Thread: True - Managed Thread Id: 12
07:19:56.2854568 - Is Thread Pool Thread: True - Managed Thread Id: 15

In the code above we are setting the thread to wait 5 seconds, so after printing out to the console, the thread is kept alive for an additional 5 seconds before completing execution and returning to the Thread Pool.

The timer carries on firing on each second regardless, it's not waiting on the thread it triggered to complete.