ThreadPool Class
Assembly: mscorlib (in mscorlib.dll)
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| The HostProtectionAttribute attribute applied to this class has the following Resources property value: Synchronization | ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes. |
Many applications create threads that spend a great deal of time in the sleeping state, waiting for an event to occur. Other threads might enter a sleeping state only to be awakened periodically to poll for a change or update status information. Thread pooling enables you to use threads more efficiently by providing your application with a pool of worker threads that are managed by the system. One thread monitors the status of several wait operations queued to the thread pool. When a wait operation completes, a worker thread from the thread pool executes the corresponding callback function.
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| The threads in the managed thread pool are background threads. That is, their IsBackground properties are true. This means that a ThreadPool thread will not keep an application running after all foreground threads have exited. |
You can also queue work items that are not related to a wait operation to the thread pool. To request that a work item be handled by a thread in the thread pool, call the QueueUserWorkItem method. This method takes as a parameter a reference to the method or delegate that will be called by the thread selected from the thread pool. There is no way to cancel a work item after it has been queued.
Timer-queue timers and registered wait operations also use the thread pool. Their callback functions are queued to the thread pool.
There is one thread pool per process. The thread pool has a default size of 25 threads per available processor. The number of threads in the thread pool can be changed using the SetMaxThreads method. Each thread uses the default stack size and runs at the default priority.
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| Unmanaged code that hosts the .NET Framework can change the size of the thread pool using the CorSetMaxThreads function, defined in the mscoree.h file. |
| Topic | Location |
|---|---|
| How to: Create an Asynchronous HTTP Handler | Building ASP .NET Web Applications |
| How to: Create an Asynchronous HTTP Handler | Building ASP .NET Web Applications |
using System; using System.Threading; public class Example { public static void Main() { // Queue the task. ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc)); Console.WriteLine("Main thread does some work, then sleeps."); // If you comment out the Sleep, the main thread exits before // the thread pool task runs. The thread pool uses background // threads, which do not keep the application running. (This // is a simple example of a race condition.) Thread.Sleep(1000); Console.WriteLine("Main thread exits."); } // This thread procedure performs the task. static void ThreadProc(Object stateInfo) { // No state object was passed to QueueUserWorkItem, so // stateInfo is null. Console.WriteLine("Hello from the thread pool."); } }
import System.*;
import System.Threading.*;
import System.Threading.Thread;
public class Example
{
public static void main(String[] args)
{
// Queue the task.
ThreadPool.QueueUserWorkItem(new WaitCallback(ThreadProc));
Console.WriteLine("Main thread does some work, then sleeps.");
// If you comment out the Sleep, the main thread exits before
// the thread pool task runs. The thread pool uses background
// threads, which do not keep the application running. (This
// is a simple example of a race condition.)
Thread.Sleep(1000);
Console.WriteLine("Main thread exits.");
} //main
// This thread procedure performs the task.
static void ThreadProc(Object stateInfo)
{
// No state object was passed to QueueUserWorkItem, so
// stateInfo is null.
Console.WriteLine("Hello from the thread pool.");
} //ThreadProc
} //Example
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.
Reference
ThreadPool MembersSystem.Threading Namespace
Other Resources
Threads and ThreadingThe Managed Thread Pool
Note