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WaitHandle.WaitAny Method (WaitHandle[], TimeSpan, Boolean)

.NET Framework 1.1

Waits for any of the elements in the specified array to receive a signal, using a TimeSpan to measure the time interval and specifying whether to exit the synchronization domain before the wait.

[Visual Basic]
Overloads Public Shared Function WaitAny( _
   ByVal waitHandles() As WaitHandle, _
   ByVal timeout As TimeSpan, _
   ByVal exitContext As Boolean _
) As Integer
[C#]
public static int WaitAny(
 WaitHandle[] waitHandles,
 TimeSpan timeout,
 bool exitContext
);
[C++]
public: static int WaitAny(
 WaitHandle* waitHandles[],
 TimeSpan timeout,
 bool exitContext
);
[JScript]
public static function WaitAny(
   waitHandles : WaitHandle[],
 timeout : TimeSpan,
 exitContext : Boolean
) : int;

Parameters

waitHandles
A WaitHandle array containing the objects for which the current instance will wait.
timeout
The number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds to wait indefinitely.
exitContext
true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it; otherwise, false.

Return Value

The array index of the object that satisfied the wait, or WaitTimeout if no object satisfied the wait and a time interval equivalent to timeout has passed.

Exceptions

Exception Type Condition
ArgumentNullException The waitHandles parameter is a null reference (Nothing in Visual Basic) or one or more of the objects in the waitHandles array is a null reference (Nothing).
NotSupportedException The number of objects in waitHandles is greater than the system permits.
ApplicationException waitHandles is an array with no elements.
ArgumentOutOfRangeException timeout is a negative number other than -1 milliseconds, which represents an infinite time-out.

Remarks

This method returns when the wait terminates, either when any of the handles are signaled or when a time-out occurs. If more than one object becomes signaled during the call, the return value is the array index of the signaled object with the smallest index value of all the signaled objects. On some implementations, if more that 64 handles are passed, a NotSupportedException is thrown. If the array contains duplicates, the call will fail.

Note   If a thread exits or aborts without explicitly releasing a Mutex, and that Mutex is included in a WaitAny on another thread, the index returned by WaitAny will be the correct value plus 128. To guard against this, check the index before using it, with C# code such as if (index >= 128) index -= 128; or Visual Basic code such as If index >= 128 Then index -= 128.

Example

[Visual Basic, C#, C++] The following code example demonstrates how to use the thread pool to simultaneously search for a file on multiple disks. For space considerations, only the root directory of each disk is searched.

[Visual Basic] 
Imports Microsoft.VisualBasic
Imports System
Imports System.IO
Imports System.Threading

Public Class Test
    Shared Sub Main()
        Dim search As New Search()
        search.FindFile("SomeFile.dat")
    End Sub    
End Class

Public Class Search

    ' Maintain state information to pass to FindCallback.
    Class State
        Public autoEvent As AutoResetEvent 
        Public fileName As String         

        Sub New(anEvent As AutoResetEvent, fName As String)
            autoEvent = anEvent
            fileName = fName
        End Sub
    End Class

    Dim autoEvents() As AutoResetEvent
    Dim diskLetters() As String

    Sub New()

        ' Retrieve an array of disk letters.
        diskLetters = Environment.GetLogicalDrives()

        autoEvents = New AutoResetEvent(diskLetters.Length - 1) {}
        For i As Integer = 0 To diskLetters.Length - 1
            autoEvents(i) = New AutoResetEvent(False)
        Next i
    End Sub    
    
    ' Search for fileName in the root directory of all disks.
    Sub FindFile(fileName As String)
        For i As Integer = 0 To diskLetters.Length - 1
            Console.WriteLine("Searching for {0} on {1}.", _
                fileName, diskLetters(i))
        
            ThreadPool.QueueUserWorkItem(AddressOf FindCallback, _ 
                New State(autoEvents(i), diskLetters(i) & fileName))
        Next i

        ' Wait for the first instance of the file to be found.
        Dim index As Integer = WaitHandle.WaitAny( _
            autoEvents, New TimeSpan(0, 0, 3), False)
        If index = WaitHandle.WaitTimeout
            Console.WriteLine(vbCrLf & "{0} not found.", fileName)
        Else
            Console.WriteLine(vbCrLf & "{0} found on {1}.", _
                fileName, diskLetters(index))
        End If
    End Sub

    ' Search for stateInfo.fileName.
    Sub FindCallback(state As Object)
        Dim stateInfo As State = DirectCast(state, State)

        ' Signal if the file is found.
        If File.Exists(stateInfo.fileName) Then
            stateInfo.autoEvent.Set()
        End If
    End Sub

End Class

[C#] 
using System;
using System.IO;
using System.Threading;

class Test
{
    static void Main()
    {
        Search search = new Search();
        search.FindFile("SomeFile.dat");
    }
}

class Search
{
    // Maintain state information to pass to FindCallback.
    class State
    {
        public AutoResetEvent autoEvent;
        public string         fileName;

        public State(AutoResetEvent autoEvent, string fileName)
        {
            this.autoEvent    = autoEvent;
            this.fileName     = fileName;
        }
    }

    AutoResetEvent[] autoEvents;
    String[] diskLetters;

    public Search()
    {
        // Retrieve an array of disk letters.
        diskLetters = Environment.GetLogicalDrives();

        autoEvents = new AutoResetEvent[diskLetters.Length];
        for(int i = 0; i < diskLetters.Length; i++)
        {
            autoEvents[i] = new AutoResetEvent(false);
        }
    }

    // Search for fileName in the root directory of all disks.
    public void FindFile(string fileName)
    {
        for(int i = 0; i < diskLetters.Length; i++)
        {
            Console.WriteLine("Searching for {0} on {1}.",
                fileName, diskLetters[i]);
            ThreadPool.QueueUserWorkItem(
                new WaitCallback(FindCallback), 
                new State(autoEvents[i], diskLetters[i] + fileName));
        }

        // Wait for the first instance of the file to be found.
        int index = WaitHandle.WaitAny(
            autoEvents, new TimeSpan(0, 0, 3), false);
        if(index == WaitHandle.WaitTimeout)
        {
            Console.WriteLine("\n{0} not found.", fileName);
        }
        else
        {
            Console.WriteLine("\n{0} found on {1}.", fileName,
                diskLetters[index]);
        }
    }

    // Search for stateInfo.fileName.
    void FindCallback(object state)
    {
        State stateInfo = (State)state;

        // Signal if the file is found.
        if(File.Exists(stateInfo.fileName))
        {
            stateInfo.autoEvent.Set();
        }
    }
}

[C++] 
#using <mscorlib.dll>
using namespace System;
using namespace System::IO;
using namespace System::Threading;

__gc class Search
{
    // Maintain state information to pass to FindCallback.
    __gc class State
    {
    public:
        AutoResetEvent* autoEvent;
        String*         fileName;

        State(AutoResetEvent* autoEvent, String* fileName) : 
            autoEvent(autoEvent), fileName(fileName) {}
    };

    AutoResetEvent* autoEvents __gc[];
    String* diskLetters __gc[];

    // Search for stateInfo->fileName.
    void FindCallback(Object* state)
    {
        State* stateInfo = dynamic_cast<State*>(state);

        // Signal if the file is found.
        if(File::Exists(stateInfo->fileName))
        {
            stateInfo->autoEvent->Set();
        }
    }

public:
    Search()
    {
        // Retrieve an array of disk letters.
        diskLetters = Environment::GetLogicalDrives();

        autoEvents = new AutoResetEvent* __gc[diskLetters->Length];
        for(int i = 0; i < diskLetters->Length; i++)
        {
            autoEvents[i] = new AutoResetEvent(false);
        }
    }

    // Search for fileName in the root directory of all disks.
    void FindFile(String* fileName)
    {
        for(int i = 0; i < diskLetters->Length; i++)
        {
            Console::WriteLine("Searching for {0} on {1}.",
                fileName, diskLetters[i]);
            ThreadPool::QueueUserWorkItem(new WaitCallback(
                this, &Search::FindCallback), new State(autoEvents[i],
                String::Concat(diskLetters[i], fileName)));
        }

        // Wait for the first instance of the file to be found.
        int index = WaitHandle::WaitAny(
            autoEvents, TimeSpan(0, 0, 3), false);
        if(index == WaitHandle::WaitTimeout)
        {
            Console::WriteLine(S"\n{0} not found.", fileName);
        }
        else
        {
            Console::WriteLine(S"\n{0} found on {1}.", fileName,
                diskLetters[index]);
        }
    }
};

void main()
{
    Search* search = new Search();
    search->FindFile(S"SomeFile.dat");
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

WaitHandle Class | WaitHandle Members | System.Threading Namespace | WaitHandle.WaitAny Overload List

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