using System;
using System.Threading;

class Program
{
    static void Main()
    {
        int workItems = 5;
        ManualResetEvent[] doneEvents = new ManualResetEvent[workItems];
        
        for (int i = 0; i < workItems; i++)
        {
            doneEvents[i] = new ManualResetEvent(false);
            ThreadPool.QueueUserWorkItem(new WaitCallback(DoWork), doneEvents[i]);
        }
        
        // 等待所有工作项完成
        WaitHandle.WaitAll(doneEvents);
        Console.WriteLine("所有工作项已完成");
    }

    static void DoWork(object state)
    {
        ManualResetEvent doneEvent = (ManualResetEvent)state;
        try
        {
            // 执行实际工作
            Console.WriteLine("工作项正在执行...");
            Thread.Sleep(1000); // 模拟工作
        }
        finally
        {
            doneEvent.Set();
        }
    }
}

using System;
using System.Threading;

class Program
{
    static void Main()
    {
        int workItems = 5;
        CountdownEvent countdown = new CountdownEvent(workItems);
        
        for (int i = 0; i < workItems; i++)
        {
            ThreadPool.QueueUserWorkItem(state => 
            {
                try
                {
                    Console.WriteLine("工作项正在执行...");
                    Thread.Sleep(1000); // 模拟工作
                }
                finally
                {
                    countdown.Signal();
                }
            });
        }
        
        countdown.Wait();
        Console.WriteLine("所有工作项已完成");
    }
}

using System;
using System.Threading.Tasks;

class Program
{
    static void Main()
    {
        int workItems = 5;
        Task[] tasks = new Task[workItems];
        
        for (int i = 0; i < workItems; i++)
        {
            tasks[i] = Task.Run(() => 
            {
                Console.WriteLine("工作项正在执行...");
                Task.Delay(1000).Wait(); // 模拟工作
            });
        }
        
        Task.WaitAll(tasks);
        Console.WriteLine("所有工作项已完成");
    }
}