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ThreadPool.SetMinThreads Method

Sets the number of idle threads the thread pool maintains in anticipation of new requests.

Namespace:  System.Threading
Assembly:  mscorlib (in mscorlib.dll)

[SecurityPermissionAttribute(SecurityAction.Demand, ControlThread = true)]
public static bool SetMinThreads(
	int workerThreads,
	int completionPortThreads


Type: System.Int32

The new minimum number of idle worker threads to be maintained by the thread pool.

Type: System.Int32

The new minimum number of idle asynchronous I/O threads to be maintained by the thread pool.

Return Value

Type: System.Boolean
true if the change is successful; otherwise, false.

Idle threads are maintained by the thread pool in order to reduce the time required to satisfy requests for thread pool threads. Separate minimums are maintained for worker threads and asynchronous I/O threads. Idle threads in excess of the minimums are terminated, to save system resources. Maintenance of the idle threads is a background task.


GetMinThreads and SetMinThreads retrieve and set the total number of idle threads maintained by the thread pool, regardless of the number of processors in the computer.

If you specify a negative number or a number larger than the maximum number of active thread pool threads (obtained using GetMaxThreads), SetMinThreads returns false and does not change either of the minimum values.

Caution noteCaution:

Reducing the number of idle threads to less than the number of processors can hurt performance.

When all thread pool threads have been assigned to tasks, the thread pool does not immediately begin creating new idle threads. To avoid unnecessarily allocating stack space for threads, it creates new idle threads at intervals. The interval is currently half a second, although it could change in future versions of the .NET Framework.

If an application is subject to bursts of activity in which large numbers of thread pool tasks are queued, use the SetMinThreads method to increase the minimum number of idle threads. Otherwise, the built-in delay in creating new idle threads could cause a bottleneck. A small increase in the number of idle threads can produce a significant improvement in throughput.


Unnecessarily increasing the number of idle threads can also cause performance problems. Stack space must be allocated for each thread. If too many tasks start at the same time, all of them might appear to be slow. Finding the right balance is a performance-tuning issue.

The following example sets the minimum number of idle worker threads to four, and preserves the original value for the minimum number of idle asynchronous I/O completion threads.

using System;
using System.Threading;

public class Test
    public static void Main()
        int minWorker, minIOC;
        // Get the current settings.
        ThreadPool.GetMinThreads(out minWorker, out minIOC);
        // Change the minimum number of worker threads to four, but 
        // keep the old setting for minimum asynchronous I/O  
        // completion threads. 
        if (ThreadPool.SetMinThreads(4, minIOC))
            // The minimum number of threads was set successfully.
            // The minimum number of threads was not changed.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1