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Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks
Namespace specialNamespaceForOneMethodSignature
Class Task(Of TResult)
Public TValue As TResult
End Class
Class Dummy(Of TResult)
'<snippet01>
Public Function FromAsync(Of TArg1, TArg2, TArg3)(
ByVal beginMethod As Func(Of TArg1, TArg2, TArg3, AsyncCallback, Object, IAsyncResult),
ByVal endMethod As Func(Of IAsyncResult, TResult),
ByVal dataBuffer As TArg1,
ByVal byteOffsetToStartAt As TArg2,
ByVal maxBytesToRead As TArg3,
ByVal stateInfo As Object)
'</snippet01>
Return New Task(Of TResult)
End Function
End Class
End Namespace
Module Module1
Class AsyncResult
Public Sub New()
End Sub
'<snippet07>
Shared Function ReturnTaskFromAsyncResult() As Task(Of String)
Dim ar As IAsyncResult = DoSomethingAsynchronously()
Dim t As Task(Of String) = Task(Of String).Factory.FromAsync(ar, Function(res) CStr(res.AsyncState))
Return t
End Function
'</snippet07>
Private Shared Function DoSomethingAsynchronously() As IAsyncResult
Throw New NotImplementedException
End Function
End Class
'<snippet08>
Class WebDataDownLoader
Dim tcs As New TaskCompletionSource(Of String())
Dim nameToSearch As String
Dim token As CancellationToken
Dim results As New List(Of String)
Dim m_lock As Object
Dim count As Integer
Dim addresses() As String
Shared Sub Main()
Dim downloader As New WebDataDownLoader()
downloader.addresses = {"http://www.msnbc.com", "http://www.yahoo.com", _
"http://www.nytimes.com", "http://www.washingtonpost.com", _
"http://www.latimes.com", "http://www.newsday.com"}
Dim cts As New CancellationTokenSource()
' Create a UI thread from which to cancel the entire operation
Task.Factory.StartNew(Sub()
Console.WriteLine("Press c to cancel")
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
End Sub)
' Using a neutral search term that is sure to get some hits on English web sites.
' Please substitute your favorite search term.
downloader.nameToSearch = "the"
Dim webTask As Task(Of String()) = downloader.GetWordCounts(downloader.addresses, downloader.nameToSearch, cts.Token)
' Do some other work here unless the method has already completed.
If (webTask.IsCompleted = False) Then
' Simulate some work
Thread.SpinWait(5000000)
End If
Dim results As String() = Nothing
Try
results = webTask.Result
Catch ae As AggregateException
For Each ex As Exception In ae.InnerExceptions
If (TypeOf (ex) Is OperationCanceledException) Then
Dim oce As OperationCanceledException = CType(ex, OperationCanceledException)
If oce.CancellationToken = cts.Token Then
Console.WriteLine("Operation canceled by user.")
End If
Else
Console.WriteLine(ex.Message)
End If
Next
Finally
cts.Dispose()
End Try
If (Not results Is Nothing) Then
For Each item As String In results
Console.WriteLine(item)
Next
End If
Console.WriteLine("Press any key to exit")
Console.ReadKey()
End Sub
Public Function GetWordCounts(ByVal urls() As String, ByVal str As String, ByVal token As CancellationToken) As Task(Of String())
Dim webClients() As WebClient
ReDim webClients(urls.Length)
m_lock = New Object()
' If the user cancels the CancellationToken, then we can use the
' WebClient's ability to cancel its own async operations.
token.Register(Sub()
For Each wc As WebClient In webClients
If Not wc Is Nothing Then
wc.CancelAsync()
End If
Next
End Sub)
For i As Integer = 0 To urls.Length - 1
webClients(i) = New WebClient()
' Specify the callback for the DownloadStringCompleted
' event that will be raised by this WebClient instance.
AddHandler webClients(i).DownloadStringCompleted, AddressOf WebEventHandler
Dim address As Uri = Nothing
Try
address = New Uri(urls(i))
' Pass the address, and also use it for the userToken
' to identify the page when the delegate is invoked.
webClients(i).DownloadStringAsync(address, address)
Catch ex As UriFormatException
tcs.TrySetException(ex)
Return tcs.Task
End Try
Next
' Return the underlying Task. The client code
' waits on the Result property, and handles exceptions
' in the try-catch block there.
Return tcs.Task
End Function
Public Sub WebEventHandler(ByVal sender As Object, ByVal args As DownloadStringCompletedEventArgs)
If args.Cancelled = True Then
tcs.TrySetCanceled()
Return
ElseIf Not args.Error Is Nothing Then
tcs.TrySetException(args.Error)
Return
Else
' Split the string into an array of words,
' then count the number of elements that match
' the search term.
Dim words() As String = args.Result.Split(" "c)
Dim NAME As String = nameToSearch.ToUpper()
Dim nameCount = (From word In words.AsParallel()
Where word.ToUpper().Contains(NAME)
Select word).Count()
' Associate the results with the url, and add new string to the array that
' the underlying Task object will return in its Result property.
results.Add(String.Format("{0} has {1} instances of {2}", args.UserState, nameCount, nameToSearch))
End If
SyncLock (m_lock)
count = count + 1
If (count = addresses.Length) Then
tcs.TrySetResult(results.ToArray())
End If
End SyncLock
End Sub
'</snippet08>
End Class
'<snippet09>
Class Calculator
Public Function BeginCalculate(ByVal decimalPlaces As Integer, ByVal ac As AsyncCallback, ByVal state As Object) As IAsyncResult
Console.WriteLine("Calling BeginCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Dim myTask = Task(Of String).Factory.StartNew(Function(obj) Compute(decimalPlaces), state)
myTask.ContinueWith(Sub(antedecent) ac(myTask))
End Function
Private Function Compute(ByVal decimalPlaces As Integer)
Console.WriteLine("Calling compute on thread {0}", Thread.CurrentThread.ManagedThreadId)
' Simulating some heavy work.
Thread.SpinWait(500000000)
' Actual implemenation left as exercise for the reader.
' Several examples are available on the Web.
Return "3.14159265358979323846264338327950288"
End Function
Public Function EndCalculate(ByVal ar As IAsyncResult) As String
Console.WriteLine("Calling EndCalculate on thread {0}", Thread.CurrentThread.ManagedThreadId)
Return CType(ar, Task(Of String)).Result
End Function
End Class
Class CalculatorClient
Shared decimalPlaces As Integer
Shared Sub Main()
Dim calc As New Calculator
Dim places As Integer = 35
Dim callback As New AsyncCallback(AddressOf PrintResult)
Dim ar As IAsyncResult = calc.BeginCalculate(places, callback, calc)
' Do some work on this thread while the calulator is busy.
Console.WriteLine("Working...")
Thread.SpinWait(500000)
Console.ReadLine()
End Sub
Public Shared Sub PrintResult(ByVal result As IAsyncResult)
Dim c As Calculator = CType(result.AsyncState, Calculator)
Dim piString As String = c.EndCalculate(result)
Console.WriteLine("Calling PrintResult on thread {0}; result = {1}",
Thread.CurrentThread.ManagedThreadId, piString)
End Sub
End Class
'</snippet09>
Class FileStreamDemo
Shared Sub Main()
Dim fsd As New FileStreamDemo()
fsd.ShowCallingFromAsync()
End Sub
'<snippet03>
Const MAX_FILE_SIZE As Integer = 14000000
Shared Function GetFileStringAsync(ByVal path As String) As Task(Of String)
Dim fi As New FileInfo(path)
Dim data(fi.Length) As Byte
Dim fs As FileStream = New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' Task(Of Integer) returns the number of bytes read
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
' It is possible to do other work here while waiting
' for the antecedent task to complete.
' ...
' Add the continuation, which returns a Task<string>.
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
If (antecedent.Result < 100) Then
Return "Data is too small to bother with."
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
' Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet03>
Public Sub ShowCallingFromAsync()
Dim path As String = "\\docbuild2\public\Main\Logs\DllDiffReport\DllDiffReport_BetweenInBuildAndInPublicShare.html"
'<snippet04>
Dim myTask As Task(Of String) = GetFileStringAsync(path)
' Do some other work
' ...
Try
Console.WriteLine(myTask.Result.Substring(0, 500))
Catch ex As AggregateException
Console.WriteLine(ex.InnerException.Message)
End Try
'</snippet04>
Console.WriteLine("Press Enter to exit.")
Console.ReadLine()
End Sub
'<snippet05>
Public Function GetFileStringAsync2(ByVal path As String) As Task(Of String)
Dim fi = New FileInfo(path)
Dim data(fi.Length) As Byte
Dim state As New MyCustomState()
Dim fs As New FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, data.Length, True)
' We still pass null for the last parameter because
' the state variable is visible to the continuation delegate.
Dim myTask As Task(Of Integer) = Task(Of Integer).Factory.FromAsync(
AddressOf fs.BeginRead, AddressOf fs.EndRead, data, 0, data.Length, Nothing)
Return myTask.ContinueWith(Function(antecedent)
fs.Close()
' Capture custom state data directly in the user delegate.
' No need to pass it through the FromAsync method.
If (state.StateData.Contains("New York, New York")) Then
Return "Start spreading the news!"
End If
' If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < data.Length) Then
Array.Resize(data, antecedent.Result)
End If
'/ Will be returned in the Result property of the Task<string>
'/ at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(data)
End Function)
End Function
'</snippet05>
'<snippet06>
Public Function GetMultiFileData(ByVal filesToRead As String()) As Task(Of String)
Dim fs As FileStream
Dim tasks(filesToRead.Length) As Task(Of String)
Dim fileData() As Byte = Nothing
For i As Integer = 0 To filesToRead.Length
fileData(&H1000) = New Byte()
fs = New FileStream(filesToRead(i), FileMode.Open, FileAccess.Read, FileShare.Read, fileData.Length, True)
' By adding the continuation here, the
' Result of each task will be a string.
tasks(i) = Task(Of Integer).Factory.FromAsync(AddressOf fs.BeginRead,
AddressOf fs.EndRead,
fileData,
0,
fileData.Length,
Nothing).
ContinueWith(Function(antecedent)
fs.Close()
'If we did not receive the entire file, the end of the
' data buffer will contain garbage.
If (antecedent.Result < fileData.Length) Then
ReDim Preserve fileData(antecedent.Result)
End If
'Will be returned in the Result property of the Task<string>
' at some future point after the asynchronous file I/O operation completes.
Return New UTF8Encoding().GetString(fileData)
End Function)
Next
Return Task(Of String).Factory.ContinueWhenAll(tasks, Function(data)
' Propagate all exceptions and mark all faulted tasks as observed.
Task.WaitAll(data)
' Combine the results from all tasks.
Dim sb As New StringBuilder()
For Each t As Task(Of String) In data
sb.Append(t.Result)
Next
' Final result to be returned eventually on the calling thread.
Return sb.ToString()
End Function)
End Function
'</snippet06>
Class MyCustomState
Public StateData As String
Public Sub New()
StateData = "Hello"
End Sub
End Class
End Class
End Module