ThreadPool
Learn the thread pool with ThreadPool.
ThreadPool
The ThreadPool is a pool of ready threads shared by short tasks in the application. Creating a new Thread each time is costly; the ThreadPool reuses its threads.
ThreadPool.QueueUserWorkItem(callback) enqueues a work item that runs on an idle pool thread. The ThreadPool is not suitable for long work; it can exhaust the pool.
ThreadPool and waiting
There is no guarantee when work enqueued to the ThreadPool will finish. In tests you wait with a signal mechanism such as ManualResetEvent or CountdownEvent.
Production code usually prefers Task.Run; it also uses the ThreadPool but makes waiting easy with await and keeps the code simple.
Exercise ThreadPool with a signal wait
Create a signal with ManualResetEvent done = new ManualResetEvent(false);. Enqueue work with ThreadPool.QueueUserWorkItem(_ => { done.Set(); });. Wait with done.WaitOne();. Finally print Console.WriteLine("Done");.
Show example solution
ManualResetEvent done = new ManualResetEvent(false); ThreadPool.QueueUserWorkItem(_ => { done.Set(); }); done.WaitOne(); Console.WriteLine("Done");
Example solution:
using System;
using System.Threading;
class Program
{
static void Main()
{
ManualResetEvent done = new ManualResetEvent(false);
ThreadPool.QueueUserWorkItem(_ => { done.Set(); });
done.WaitOne();
Console.WriteLine("Done");
}
}Test yourself
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What does ThreadPool.QueueUserWorkItem do?
- Creates a new thread
- Cancels a thread
- Pauses a thread
- Enqueues a work item
Show answer
Enqueues a work item — Correct. QueueUserWorkItem enqueues a work item.
-
The QueueUserWorkItem call
ThreadPool.____(state => { /* iş */ });Show answer
ThreadPool.QueueUserWorkItem(state => { /* iş */ }); -
Match the ThreadPool concepts
- ThreadPool
- Ready thread pool
- QueueUserWorkItem
- Enqueue work
- ManualResetEvent
- Wait with signal
- Task.Run
- ThreadPool + await