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ThreadPool.SetMinThreads(Int32, Int32) Method

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Definition

Namespace:
System.Threading
Assembly:
System.Threading.ThreadPool.dll
Assembly:
mscorlib.dll
Assembly:
netstandard.dll
Source:
ThreadPool.CoreCLR.cs
Source:
ThreadPool.Unix.cs
Source:
ThreadPool.Unix.cs

Sets the minimum number of threads the thread pool creates on demand, as new requests are made, before switching to an algorithm for managing thread creation and destruction.

public:
 static bool SetMinThreads(int workerThreads, int completionPortThreads);
public static bool SetMinThreads (int workerThreads, int completionPortThreads);
static member SetMinThreads : int * int -> bool
Public Shared Function SetMinThreads (workerThreads As Integer, completionPortThreads As Integer) As Boolean

Parameters

workerThreads
Int32

The minimum number of worker threads that the thread pool creates on demand.

completionPortThreads
Int32

The minimum number of asynchronous I/O threads that the thread pool creates on demand.

Returns

Boolean

true if the change is successful; otherwise, false.

Examples

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

using namespace System;
using namespace System::Threading;
int main()
{
   int minWorker;
   int minIOC;
   
   // Get the current settings.
   ThreadPool::GetMinThreads( minWorker, 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.
   }
   else
   {
      
      // The minimum number of threads was not changed.
   }
}

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.
        }
        else
        {
            // The minimum number of threads was not changed.
        }
    }
}

Imports System.Threading

Public Class Test

    <MTAThread> _
    Public Shared Sub Main()
        Dim minWorker, minIOC As Integer
        ' Get the current settings.
        ThreadPool.GetMinThreads(minWorker, 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) Then
            ' The minimum number of threads was set successfully.
        Else
            ' The minimum number of threads was not changed.
        End If
    End Sub
End Class

Remarks

This method is not supported when the Windows thread pool is configured to be used instead of the .NET thread pool. For more information, see the Windows thread pool config setting.

The thread pool provides new worker threads or I/O completion threads on demand until it reaches the minimum for each category. When the minimum is reached, the thread pool can create additional threads in that category or wait until some tasks complete. Beginning with the .NET Framework 4, the thread pool creates and destroys threads in order to optimize throughput, which is defined as the number of tasks that complete per unit of time. Too few threads might not make optimal use of available resources, whereas too many threads could increase resource contention.

When demand is low, the actual number of thread pool threads can fall below the minimum values.

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.

By default, the minimum number of threads is set to the processor count. You can use SetMinThreads to increase the minimum number of threads, such as to temporarily work around issues where some queued work items or tasks block thread pool threads. Those blockages sometimes lead to a situation where all worker or I/O completion threads are blocked (starvation). However, increasing the minimum number of threads might degrade performance in other ways, such as:

  • The thread pool may schedule more worker threads, even when the worker threads are not getting blocked. The oversubscription can cause threads that get scheduled-out to be significantly delayed as they wait in a long queue to get another time slice, delaying some work items or tasks.
  • Worker threads may take more CPU time in dequeuing work items due to having to scan more threads to steal work from.
  • Context switching between threads may increase CPU usage.
  • Garbage collection may take more CPU time in thread stack walking.
  • The process may consume more memory.

Caution

Using the SetMinThreads method to increase the minimum number of threads can cause performance problems as described in the preceding text. In most cases, the thread pool will perform better with its own algorithm for allocating threads. Reducing the minimum to less than the number of processors can also hurt performance.

Applies to

See also