Export (0) Print
Expand All

ThreadPool.GetMaxThreads Method

Retrieves the number of requests to the thread pool that can be active concurrently. All requests above that number remain queued until thread pool threads become available.

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

'Declaration
Public Shared Sub GetMaxThreads ( _
	<OutAttribute> ByRef workerThreads As Integer, _
	<OutAttribute> ByRef completionPortThreads As Integer _
)

Parameters

workerThreads
Type: System.Int32

The maximum number of worker threads in the thread pool.

completionPortThreads
Type: System.Int32

The maximum number of asynchronous I/O threads in the thread pool.

When GetMaxThreads returns, the variable specified by workerThreads contains the maximum number of worker threads allowed in the thread pool, and the variable specified by completionPortThreads contains the maximum number of asynchronous I/O threads allowed in the thread pool.

You can use the GetAvailableThreads method to determine the actual number of threads in the thread pool at any given time.

You can use the SetMaxThreads to set the maximum number of worker threads and asynchronous I/O threads in the thread pool.

You can queue as many thread pool requests as system memory allows. If there are more requests than thread pool threads, the additional requests remain queued until thread pool threads become available.

The following code example shows how to retrieve a count of the maximum and available number of threads in the thread pool. A work item is queued that uses FileStream to asynchronously write to two files. The callback methods are timed to overlap. A worker thread handles the work item and, depending on the speed and number of processors on the computer, one or two completion port threads handle the write operations.

Imports Microsoft.VisualBasic
Imports System
Imports System.IO
Imports System.Security.Permissions
Imports System.Threading

Public Class Test


    <MTAThread> _
    Shared Sub Main()
        Dim mainEvent As New AutoResetEvent(False)
        Dim workerThreads As Integer  
        Dim portThreads As Integer 

        ThreadPool.GetMaxThreads(workerThreads, portThreads)
        Console.WriteLine(vbCrLf & "Maximum worker threads: " & _
            vbTab & "{0}" & vbCrLf & "Maximum completion port " & _
            "threads: {1}", workerThreads, portThreads)

        ThreadPool.GetAvailableThreads(workerThreads, portThreads)
        Console.WriteLine(vbCrLf & "Available worker threads: " & _
            vbTab & "{0}" & vbCrLf & "Available completion port " & _
            "threads: {1}" & vbCrLf, workerThreads, portThreads)

        ThreadPool.QueueUserWorkItem(AddressOf _
            ThreadPoolTest.WorkItemMethod, mainEvent)

        ' Since ThreadPool threads are background threads,  
        ' wait for the work item to signal before ending Main.
        mainEvent.WaitOne(5000, False)
    End Sub 

End Class 

Public Class ThreadPoolTest

    ' Maintains state information to be passed to EndWriteCallback. 
    ' This information allows the callback to end the asynchronous 
    ' write operation and signal when it is finished. 
    Class State
        Public fStream As FileStream
        Public autoEvent As AutoResetEvent

        Public Sub New(aFileStream As FileStream, anEvent As AutoResetEvent)
            fStream   = aFileStream
            autoEvent = anEvent
        End Sub 
    End Class    

    Private Sub New 
    End Sub 

    Shared Sub WorkItemMethod(mainEvent As Object)

        Console.WriteLine(vbCrLf & "Starting WorkItem." & vbCrLf)
        Dim autoEvent As New AutoResetEvent(False)

        ' Create some data. 
        Const ArraySize As Integer  = 10000
        Const BufferSize As Integer =  1000
        Dim byteArray As Byte() = New Byte(ArraySize){}
        Dim randomGenerator As New Random()
        randomGenerator.NextBytes(byteArray)

        ' Create two files and two State objects.  
        Dim fileWriter1 As FileStream = _
            New FileStream("C:\Test1111.dat", FileMode.Create, _
            FileAccess.ReadWrite, FileShare.ReadWrite, _
            BufferSize, True)
        Dim fileWriter2 As FileStream = _
            New FileStream("C:\Test2222.dat", FileMode.Create, _
            FileAccess.ReadWrite, FileShare.ReadWrite, _
            BufferSize, True)
        Dim stateInfo1 As New State(fileWriter1, autoEvent)
        Dim stateInfo2 As New State(fileWriter2, autoEvent)

        ' Asynchronously write to the files.
        fileWriter1.BeginWrite(byteArray, 0, byteArray.Length, _
            AddressOf EndWriteCallback, stateInfo1)
        fileWriter2.BeginWrite(byteArray, 0, byteArray.Length, _
            AddressOf EndWriteCallback, stateInfo2)

        ' Wait for the callbacks to signal.
        autoEvent.WaitOne()
        autoEvent.WaitOne()

        fileWriter1.Close()
        fileWriter2.Close()
        Console.WriteLine(vbCrLf & "Ending WorkItem." & vbCrLf)

        ' Signal Main that the work item is finished. 
        DirectCast(mainEvent, AutoResetEvent).Set()

    End Sub 

    Shared Sub EndWriteCallback(asyncResult As IAsyncResult)

        Console.WriteLine("Starting EndWriteCallback.")

        Dim stateInfo As State = _
            DirectCast(asyncResult.AsyncState, State)
        Dim workerThreads As Integer  
        Dim portThreads As Integer  
        Try
            ThreadPool.GetAvailableThreads(workerThreads, portThreads)
            Console.WriteLine(vbCrLf & "Available worker " & _
                "threads:" & vbTab & "{0}" & vbCrLf & "Available " & _
                "completion port threads: {1}" & vbCrLf, _
                workerThreads, portThreads)

            stateInfo.fStream.EndWrite(asyncResult)

            ' Sleep so the other thread has a chance to run 
            ' before the current thread ends.
            Thread.Sleep(1500)
        Finally 

            ' Signal that the current thread is finished.
            stateInfo.autoEvent.Set()
            Console.WriteLine("Ending EndWriteCallback.")
        End Try 

    End Sub 
End Class

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Show:
© 2014 Microsoft