WaitHandle.WaitAll Method (WaitHandle())

 

Waits for all the elements in the specified array to receive a signal.

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

Public Shared Function WaitAll (
	waitHandles As WaitHandle()
) As Boolean

Parameters

waitHandles
Type: System.Threading.WaitHandle()

A WaitHandle array containing the objects for which the current instance will wait. This array cannot contain multiple references to the same object.

Return Value

Type: System.Boolean

true when every element in waitHandles has received a signal; otherwise the method never returns.

Exception Condition
ArgumentNullException

The waitHandles parameter is null. -or-

One or more of the objects in the waitHandles array are null.

-or-

waitHandles is an array with no elements and the .NET Framework version is 2.0 or later.

DuplicateWaitObjectException
System_CAPS_noteNote

In the .NET for Windows Store apps or the Portable Class Library, catch the base class exception, ArgumentException, instead.

The waitHandles array contains elements that are duplicates.

NotSupportedException

The number of objects in waitHandles is greater than the system permits.

-or-

The STAThreadAttribute attribute is applied to the thread procedure for the current thread, and waitHandles contains more than one element.

ApplicationException

waitHandles is an array with no elements and the .NET Framework version is 1.0 or 1.1.

AbandonedMutexException

The wait terminated because a thread exited without releasing a mutex. This exception is not thrown on Windows 98 or Windows Millennium Edition.

InvalidOperationException

The waitHandles array contains a transparent proxy for a WaitHandle in another application domain.

AbandonedMutexException is new in the .NET Framework version 2.0. In previous versions, the WaitAll method returns true when a mutex is abandoned. An abandoned mutex often indicates a serious coding error. In the case of a system-wide mutex, it might indicate that an application has been terminated abruptly (for example, by using Windows Task Manager). The exception contains information useful for debugging.

The WaitAll method returns when all the handles are signaled. On some implementations, if more than 64 handles are passed, a NotSupportedException is thrown. If the array contains duplicates, the call fails with a DuplicateWaitObjectException.

System_CAPS_noteNote

The WaitAll method is not supported on threads that have STAThreadAttribute.

Calling this method overload is equivalent to calling the WaitAll(WaitHandle(), Int32, Boolean) method overload and specifying -1 (or Timeout.Infinite) for millisecondsTimeoutand true for exitContext.

The following code example shows how to use the thread pool to asynchronously create and write to a group of files. Each write operation is queued as a work item and signals when it is finished. The main thread waits for all the items to signal and then exits.

Imports System
Imports System.IO
Imports System.Security.Permissions
Imports System.Threading

Public Class Test

    ' WaitHandle.WaitAll requires a multithreaded apartment 
    ' when using multiple wait handles.
    <MTAThreadAttribute> _
    Shared Sub Main()
        Const numberOfFiles As Integer = 5
        Dim dirName As String = "C:\TestTest"
        Dim fileName As String 

        Dim byteArray() As Byte 
        Dim randomGenerator As New Random()

        Dim manualEvents(numberOfFiles - 1) As ManualResetEvent
        Dim stateInfo As State 

        If Directory.Exists(dirName) <> True Then
            Directory.CreateDirectory(dirName)
        End If

        ' Queue the work items that create and write to the files.
        For i As Integer = 0 To numberOfFiles - 1
            fileName = String.Concat( _
                dirName, "\Test", i.ToString(), ".dat")

            ' Create random data to write to the file.
            byteArray = New Byte(1000000){}
            randomGenerator.NextBytes(byteArray)

            manualEvents(i) = New ManualResetEvent(false)

            stateInfo = _ 
                New State(fileName, byteArray, manualEvents(i))

            ThreadPool.QueueUserWorkItem(AddressOf _
                Writer.WriteToFile, stateInfo)
        Next i

        ' Since ThreadPool threads are background threads, 
        ' wait for the work items to signal before exiting.
        WaitHandle.WaitAll(manualEvents)
        Console.WriteLine("Files written - main exiting.")
    End Sub

End Class

' Maintain state to pass to WriteToFile.
Public Class State

    Public fileName As String
    Public byteArray As Byte()
    Public manualEvent As ManualResetEvent

    Sub New(fileName As String, byteArray() As Byte, _
        manualEvent As ManualResetEvent)

        Me.fileName = fileName
        Me.byteArray = byteArray
        Me.manualEvent = manualEvent
    End Sub

End Class

Public Class Writer

    Private Sub New()
    End Sub

    Shared workItemCount As Integer = 0

    Shared Sub WriteToFile(state As Object)
        Dim workItemNumber As Integer = workItemCount
        Interlocked.Increment(workItemCount)
        Console.WriteLine("Starting work item {0}.", _
            workItemNumber.ToString())
        Dim stateInfo As State = CType(state, State)
        Dim fileWriter As FileStream = Nothing

        ' Create and write to the file.
        Try
            fileWriter = New FileStream( _
                stateInfo.fileName, FileMode.Create)
            fileWriter.Write(stateInfo.byteArray, _
                0, stateInfo.byteArray.Length)
        Finally
            If Not fileWriter Is Nothing Then
                fileWriter.Close()
            End If

            ' Signal Main that the work item has finished.
            Console.WriteLine("Ending work item {0}.", _
                workItemNumber.ToString())
            stateInfo.manualEvent.Set()
        End Try
    End Sub

End Class

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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