I have two separate vb.net applications. One is a GUI frontend WinForm and the other is a console application which handles file transfers and runs in the background. The file transfer application monitors a directory and when new files are found, it transfers the files to a destination. It checks that the remote destination is accessible. I would like to have a flag which indicates the file transfer task can connect to remote destination and display this status on the GUI.
Example of how the GUI application starts the File Transfer console application:
Public FileXferProcess As Process
Dim startInfo As New ProcessStartInfo("FileXfer.exe")
startInfo.CreateNoWindow = True
startInfo.UseShellExecute = False
FileXferProcess = Process.Start(startInfo)
I know there are many different types of interprocess communication techniques but I am looking for the simplest solution for sharing a boolean state.
I ended up using a mutex to pass a flag between the separate processes. That does not require any overhead and handles if the process if abruptly closed (since the mutex will be destroyed with the task that created it).
Below are code snippets:
In File Transfer task
Public hMutex_Connected As Mutex
...
' If connected, set mutex
hMutex_Connected = New Mutex(True, "FileXfer_Connected")
...
' If disconnected, destroy mutex
hMutex_Connected.Close()
In Main application GUI
Public Function IsConnected() As Boolean
Dim bConnected As Boolean = False
Try
Mutex.OpenExisting("FileXfer_Connected")
bConnected = True
Catch ex As WaitHandleCannotBeOpenedException
' "Mutex does not exist."
Catch ex As UnauthorizedAccessException
' "Unauthorized access: " & ex.Message
Catch ex As Exception
' ex.ToString
End Try
Return bConnected
End Function
Related
I have a system that backs up data to a network with certain parameters in place such as:
'If x process is running, do not run the backup'
Because it's connected to a network, users will constantly be on it. The problem I have is that I don't want the data to get moved onto the network if it's in use, plus, the data is unable to move across if someone is using file explorer on the same computer as the program is on.
I would use 'If explorer is running, do not run the backup' but explorer is linked to windows and is always running
If program.Count > 0 Or program2.Count > 0 Then
Try
Msgbox("Process Running")
Catch ex As Exception
End Try
Else
'backup data
End If
Is there a way to try get the program to transfer files, but if fails because the file directory is already open, then do x?
Try this. It should generate an error if you can't lock the file.
Public Function IsFileLocked(file As FileInfo) As Boolean
Dim stream = DirectCast(Nothing, FileStream)
Try
stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None)
Catch generatedExceptionName As IOException
'handle the exception your way
Return True
Finally
If stream IsNot Nothing Then
stream.Close()
End If
End Try
Return False
End Function
I'm trying to read the Windows update log on remote PCs on my LAN. Most of the time I can successfully read the file but at times the program locks up. Likely due to one issue or another - doesn't really matter. What I do need is a way to recover when the Filestream/Streamreader locks up - I'm not sure which is causing the lock. Some streams can set a timeout but the filestream below returns False on a .CanTimeout call.
How can I break out if the stream locks up? (Sometimes the lock is so tight a power off is needed to recover.)
Is there a way to test if the stream will fail before I actually attempt the read?
Is there an alternate way to read a remote log file that another program has open? (I'm using the stream method because the regular File.IO was blocked because the file is open on the remote PC.)
I'm getting closer (I think) with this code. I browed the pathExists code from the referenced post but it was the OP and not an answer.
Imports System.IO
Import System.Threading
...
Function GetAULog(PCName As String) As String
Try
Dim sLogPath As String = String.Format("\\{0}\c$\Windows\SoftwareDistribution\ReportingEvents.log", PCName)
If PCName = My.Computer.Name Then
sLogPath = String.Format("C:\Windows\SoftwareDistribution\ReportingEvents.log", PCName)
End If
' read file open by another process
If Not pathExists(sLogPath) Then
MsgBox("AU log file not found - PC on?")
Return "NA"
End If
Using fs As New FileStream(sLogPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)
Using sr As New StreamReader(fs)
Dim s As String = sr.ReadToEnd
Return s
End Using
End Using
Catch ex As Exception
MsgBox(ex.Message)
Return ""
End Try
End Function
Public Function pathExists(path As String) As Boolean
Dim exists As Boolean = True
Dim t As New Thread(New ThreadStart(Sub() exists = System.IO.File.Exists(path)))
t.Start()
Dim completed As Boolean = t.Join(500)
'half a sec of timeout
If Not completed Then
exists = False
t.Abort()
End If
t = Nothing
Return exists
End Function
At least when the PC is off the pathExists() code returns False in short order.
My problem now is the process does not end when the program exits - at least in the IDE, didn't check runtime.
I added t = Nothing but that didn't help. I couldn't figure out the proper Using syntax to test that. How do I properly cleanup after a thread timeout?
I've had the situation with this locking until restart problem. It seems to be caused by the tcpip auto tuning feature. You can cure this issue by running
netsh interface tcp set global autotuninglevel=disable
Run this on both machines if you have access. I tried a few workarounds for this issue with checking locks etc but the only way I could solve it was to disable this. The issue is not really with locking but with something at a lower level in the file sharing protocol.
See this article for more detail
"Final" code shown below. The exceptions are not firing when the timeout occurs so the .Abort was evidently OK.
When the timeout does occur, because the remote PC did not respond, there is a process left hanging which goes away after 30 seconds or so. I notice this when using the IDE, I run the program and test a PC that is off. If I then exit the program the form closes but the IDE hangs for ~30 seconds - I can click Stop-Debugging at this point and it works, but the IDE continues on its own after the ~30 second timeout.
I guess the t = Nothing in the Finally block does not dispose of the thread. t.Dispose does not exists.
So, things are working OK with the exception of the dangling thread that eventually clears itself up. The program is no longer hanging to the point where it cannot not be stopped.
'Imports System.IO
'Imports System.Threading
Public Function pathExists(path As String) As Boolean
' check for file exists on remote PC
Dim exists As Boolean = False
Dim t As New Thread(New ThreadStart(Sub() exists = System.IO.File.Exists(path)))
Try
t.Start()
Dim completed As Boolean = t.Join(500)
'half a sec of timeout
If Not completed Then
exists = False
t.Abort()
End If
Catch ex2 As ThreadInterruptedException
MsgBox("timeout on AU log exists test" & vbNewLine & ex2.Message,, "ThreadInterruptedException")
Catch exAbort As ThreadAbortException
MsgBox("timeout on AU log exists test" & vbNewLine & exAbort.Message,, "ThreadAbortException")
Catch ex As Exception
MsgBox("exception on AU log exists test" & vbNewLine & ex.Message)
Finally
t = Nothing
End Try
Return exists
End Function
I have sent a file by SFTP to another server using WinSCP in VB.NET.
I would like to see if the connection was successful or not.
I also need to know if the file already exists in the directory beforehand.
There are a couple of things you can do. You can create a session log that tells you (in a LOT of detail) what happened during your file transfer. You can also put a try-catch block around mySession.Open(mySessionOptions) to catch an error.
Finally, use mySession.FileExists(remotepath) to check to see if the file is already on the server.
Dim mySessionOptions As New SessionOptions
With mySessionOptions
.Protocol = Protocol.Sftp
.HostName = "999.999.999.999"
.UserName = "login"
.Password = "mypassword"
.SshHostKeyFingerprint = "ssh-dss 1024 99:87:99:4d:99:a3:99:b9:99:15:99:f2:99:87:88:b2"
End With
Using mySession As Session = New Session
' Will continuously report progress of synchronization
AddHandler mySession.FileTransferred, AddressOf FileTransferred
' Connect
mySession.SessionLogPath = "C:\Users\yourName\yourFolder\Sessionlog.log"
'Use Try-Catch to check for error in connection
Try
mySession.Open(mySessionOptions)
Catch ex As Exception
MessageBox.show(ex.Message)
mySession.Close()
Exit Sub
End Try
'Check to see if file exist already on server
If mySession.FileExists(remotePath) Then
MessageBox.Show("File Exists on Server")
mySession.Close()
Exit Sub
End If
mySession.PutFiles("C:\Users\yourName\yourFolder\yourfile.dat", remotePath)
mySession.Close()
End Using
Remember to check the log you created to see exactly what happened.
I've wrote a program which on startup loads the computer list from Active Directory. This takes about 10 seconds. If the user has started the program with a specific host as parameter, it should be usable immediately.
So to don't interrupt the user I want to load the computer list in a different thread. The problem is that it writes to a variable (the computer list) which is also used in the main thread.
You may think, I could simply use a temporary variable and when its done overwrite the main variable. But I have to keep existing data of the main variable.
'hosts list
Private Shared hosts As New SortedDictionary(Of String, HostEntry)
'Get all computers in Active Directory
'Will run in a extra thread
Private Delegate Sub GetADcomputersDelegate()
Private Sub GetADcomputers()
If Me.InvokeRequired Then
Me.Invoke(New GetADcomputersDelegate(AddressOf GetADcomputers), Nothing)
Else
lblStatusAD.Text = "Getting Computers..."
Try
Dim search As New DirectorySearcher(ActiveDirectory.Domain.GetCurrentDomain().GetDirectoryEntry(), "(objectClass=computer)")
For Each host As SearchResult In search.FindAll()
'AddHost creates a new HostEntry object and adds it to my "global" hosts variable
'It also checks if a host is already present in the list and only updates it.
AddHost(host.GetDirectoryEntry().Properties("cn").Value.ToLower(), host.GetDirectoryEntry().Properties("description").Value)
Next
Catch ex As Exception
Debug.WriteLine("GetADcomputers() Exception: " & ex.Message)
End Try
ThreadPool.SetMaxThreads(hosts.Count, hosts.Count)
Dim ah As String = activehost
'Fill my ListBox with the computers
lstHosts.DataSource = New BindingSource(hosts, Nothing)
'Select the computer that was selected before
UseHost(ah)
lblStatusAD.Text = ""
End If
End Sub
So when GetADcomputers() runs in its own thread, the main thread is also blocked. I guess because auf the hosts variable.
So what could I change to make the thread do it's work and after that apply the updated computer list without losing data of entries in old hosts list? And all this in a fast and efficient way.
That code is very wrong. If you call that method on a secondary thread then it immediately marshals a call back to the UI thread and does EVERYTHING on the UI thread. What you should be doing is executing all the background work on the secondary thread and then marshalling to the UI thread ONLY to update the UI.
Get rid of that If...Else block and just make the entire body of the method what's current ly in the Else block. Next, identify all the lines that specifically interact with the UI and remove each of those to their own method. You then add If...Else blocks to each of those methods so that only the code that actually touches the UI is executed on the UI thread.
Here's a start:
Private Sub GetADcomputers()
UpdateStatusADLabel("Getting Computers...")
Try
Dim search As New DirectorySearcher(ActiveDirectory.Domain.GetCurrentDomain().GetDirectoryEntry(), "(objectClass=computer)")
For Each host As SearchResult In search.FindAll()
'AddHost creates a new HostEntry object and adds it to my "global" hosts variable
'It also checks if a host is already present in the list and only updates it.
AddHost(host.GetDirectoryEntry().Properties("cn").Value.ToLower(), host.GetDirectoryEntry().Properties("description").Value)
Next
Catch ex As Exception
Debug.WriteLine("GetADcomputers() Exception: " & ex.Message)
End Try
ThreadPool.SetMaxThreads(hosts.Count, hosts.Count)
Dim ah As String = activehost
'Fill my ListBox with the computers
lstHosts.DataSource = New BindingSource(hosts, Nothing)
'Select the computer that was selected before
UseHost(ah)
lblStatusAD.Text = ""
End Sub
Private Sub UpdateStatusADLabel(text As String)
If lblStatusAD.InvokeRequired Then
lblStatusAD.Invoke(New Action(Of String)(AddressOf UpdateStatusADLabel), text)
Else
lblStatusAD.Text = text
End If
End Sub
I am creating an application which on startup (MainWindow loaded) starts a BackgroundWorker, which on DoWork checks whether there is a newer version of the file (DatasSource for an Autocompletebox) available. If so, I download and merge this with the existing file and create a new file.
Now I want to do this on startup and also periodically (like 30 minutes). So I created a threading.Timer [it's a private member in MainWindow class] and initialize it in RunWorkerCompleted of the backgroundWorker (as mentioned above). The timer goes to the callback successfully but at the file download code (just a fyi, a different namespace and different class) it just terminates and I can't figure out why?
I have tried using Windows.Timers.Timer, ThreadPool.RegisterWaitForSingleObject() but no luck...
Can anyone point me to the right direction? I am open to any solution.
Download code:
Public Sub MergeHistoryFile()
/*Check the directory if there are any downloaded files(.tmp);if there are;just delete them*/
/*some code which checks if file on web is modified;if yes download file*/
Try
Dim waiter As Threading.AutoResetEvent = New AutoResetEvent(False)
_downloader = New WebClient()
AddHandler _downloader.DownloadDataCompleted, AddressOf Me.DownloaderFileCompleted
_downloader.DownloadDataAsync(New Uri(path_file), waiter)
waiter.WaitOne()
Catch ex As Exception
Throw ex
End Try
/*some more code which checks if there something new in the downloaded file;if yes merge the local and the downloaded file reinitialize the autocomplebox*/
End Sub
Private _downloadCancelled As Boolean = False
Private Sub DownloaderFileCompleted(ByVal sender As Object, ByVal e As System.Net.DownloadDataCompletedEventArgs)
If IsNothing(e.Error) Then
If Not (IsNothing(e.Result)) Then
Using fs As New FileStream(Path.Combine(HistoryPath, "_tempDownladedFile.tmp"), FileMode.CreateNew)
fs.Write(e.Result, 0, e.Result.Count)
End Using
CType(e.UserState, Threading.AutoResetEvent).Set()
End If
Else
_downloadCancelled = True
_downloader.CancelAsync()
End If
End Sub
There are several problems with this code, as I pointed out in my comment.
I think your primary problem is that when you create the file, you're passing FileMode.CreateNew, which is going to fail if the file already exists. As the documentation says:
CreateNew Specifies that the operating system should create a new file. This requires FileIOPermissionAccess.Write permission. If the file already exists, an IOException exception is thrown.
You probably want FileMode.Create.
So what happens is that the FileStream constructor throws an exception, which causes your DownloadFileCompleted method to exit without ever setting the event that tells the caller to stop waiting.