Thread.Start

Learn to start threads with Thread.Start and wait with Join.

Start and Join

Thread.Start() begins running a thread; the call returns immediately while the thread runs in the background. Thread.Join() blocks the caller until the target thread finishes.

Used together: Start to begin, Join to wait — this is the basis of simple synchronization. Join accepts a timeout: t.Join(1000) waits at most 1 second.

Ordering with Join

To wait for several threads in sequence, write t1.Join(); t2.Join();. When all Join calls return, the main thread continues.

This is a simple way to gather parallel work and combine results. If a thread never ends, Join waits forever; so for safety, a timeout Join may be preferred.

Exercise Wait for two threads in sequence

Create Thread t1 = new Thread(() => { }); and Thread t2 = new Thread(() => { });. Start both with Start(), then wait with t1.Join(); t2.Join();. Finally print Console.WriteLine("Done");.

Show example solution

Thread t1 = new Thread(() => { }); Thread t2 = new Thread(() => { }); t1.Start(); t2.Start(); t1.Join(); t2.Join(); Console.WriteLine("Done");
Example solution:
using System;
using System.Threading;

class Program
{
    static void Main()
    {
        Thread t1 = new Thread(() => { });
        Thread t2 = new Thread(() => { });
        t1.Start();
        t2.Start();
        t1.Join();
        t2.Join();
        Console.WriteLine("Done");
    }
}

Test yourself

The Join call

t.Start();
t.____();

Show answer

t.Start();
t.Join();

What does Thread.Join() do?
- Starts the thread
- Blocks the caller until the target ends
- Cancels the thread
- Creates a new thread
Show answer

Blocks the caller until the target ends — Correct. Join blocks the caller.
Match the Thread methods

Start()

Starts the thread
Join()

Waits for completion
Join(1000)

Timeout wait
Sleep(500)

Pause for a duration

Next lesson: ThreadPool

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