This is a real head scratcher. According to all documentation, file.readAllLines should close the file it's reading from after it completes. But in my app, when I try to write to the file, it throws an IO exception saying "process cannot access the file because it is being used by another process". And this should be really simple - the file in question is only referenced twice - once when it's read into the app on first start, and then when you overwrite it. Here's the code:
Firstly, the code that opens the file (filepath used is c:\Test\cfg.fcs):
Public Function ReadALine(ByVal File_Path As String, ByVal TotalLine As Integer, ByVal Line2Read As Integer) As String
Dim Buffer As Array
Dim Line As String
If TotalLine <= Line2Read Then
Return "No Such Line"
End If
Buffer = File.ReadAllLines(File_Path)
Line = Buffer(Line2Read)
Return Line
End Function
It works perfectly, and should leave the file properly closed, right? but when I run the following a bit later in another module:
file = My.Computer.FileSystem.OpenTextFileWriter("c:\Test\cfg.fcs", False)
file.WriteLine(Form1.GlobalVariables.serialNumber)
it throws an exception saying the file's still in use. Those are the only two times in the whole app that file is even mentioned.
for anyone else running into this problem the solution was simple but still counterintuitive... the problem was only the sequence of the commands. I moved the file.writeline down to the bottom of the suband for some reason that fixed it. strange
Related
I should add a list of files into a ZIP. Procedure code is like this
Sub CreateZip
Dim FileList As New ArrayList 'List of File Paths to be added to the ZIP
For Each path in FileList
Try
AddFileToZip(ZipFilePath, path.ToString)
Catch (ex as New Exception)
....
End Try
Next
End Sub
And this is AddFileToZip
Public Sub AddFileToZip(ByVal zipFilename As String, ByVal fileToAdd As String)
Using zip As Package = System.IO.Packaging.Package.Open(zipFilename, FileMode.OpenOrCreate)
Dim destFilename As String = ".\" & Path.GetFileName(fileToAdd)
Dim uri As Uri = PackUriHelper.CreatePartUri(New Uri(destFilename, UriKind.Relative))
If zip.PartExists(uri) Then
zip.DeletePart(uri)
End If
Dim part As PackagePart = zip.CreatePart(uri, "", CompressionOption.Normal)
Using fileStream As New FileStream(fileToAdd, FileMode.Open, FileAccess.Read)
Using dest As Stream = part.GetStream()
CopyStream(fileStream, dest)
End Using
End Using
End Using
End Sub
At runtime, I get this error message
The process cannot access the file [ZipFilePath] because it is being used by another process
this error is raised randomly, maybe on adding small files into the Zip. If I place breakpoints and run procedure in debug mode, it works.
It seems clear that procedure thread is not synchronized with IO, so that my procedure loop continues even if IO is still adding processed file into Zip (ie VB.NET is faster than IO).
I also tried to place a Thread.Sleep(1000) before AddFileToZip, but this may be not enough to synchronize the two processes. Placing Thread.Sleep(2000) seems to make procedure work, but it may slow down dramaticly performances (I should pack more than 50 files into my Zip).
So, how can I force my loop to "wait" until IO Process has released ZIP file?
I've been trying to set an error trap that will detect if a file is already open. This is no problem when the file is a text file using the following code:
Private Function FILEOPEN(ByVal sFile As String) As Boolean
Dim THISFILEOPEN As Boolean = False
Try
Using f As New IO.FileStream(sFile, IO.FileMode.Open)
THISFILEOPEN = False
End Using
Catch
THISFILEOPEN = True
End Try
Return THISFILEOPEN
End Function
My problem is that when the file is an open JPG file, not a text file, the above function returns False indicating that it is not open? I have tried different variations of the function but still cannot find a function that can tell if a JPG file is open.
You should NOT do this kind of behavior. Simple answer is because after you check, but before you do anything with it, the file may become unavailable. A proper way is to handle an exception as you access the file. You may find this answer helpful:
https://stackoverflow.com/a/11288781/897326
I am making a class that is to help with saving some strings to a local text file (I want to append them to that file and not overwrite so that it is a log file). When I write with the streamwriter to find the end of the previous text, I get an error "the file is not available as it is being used by another process". I looked into this problem on MSDN and I got very little help. I tried to eliminate some variables so I removed the streamreader to check was that the problem and it was. When I tried to write to the file then it worked and I got no error so this made me come to the conclusion that the problem arose in the streamreader. But I could not figure out why?
Here is the code:
Public Sub SaveFile(ByVal Task As String, ByVal Difficulty As Integer, ByVal Time_Taken As String)
Dim SW As String = "C:/Program Files/Business Elements/Dashboard System Files/UserWorkEthic.txt"
Dim i As Integer
Dim aryText(3) As String
aryText(0) = Task
aryText(1) = Difficulty
aryText(2) = Time_Taken
Dim objWriter As System.IO.StreamWriter = New System.IO.StreamWriter(SW, True)
Dim reader As System.IO.StreamReader = New System.IO.StreamReader(SW, True)
reader.ReadToEnd()
reader.EndOfStream.ToString()
For i = 0 To 3
objWriter.WriteLine(aryText(reader.EndOfStream + i))
Next
reader.Close()
objWriter.Close()
End Sub
As Joel has commented on the previous answer it is possible to change the type of locking.
Otherwise building on what Neil has suggested, if to try to write to a file with a new reader it is difficult not to lose the information already within the file.
I would suggest you rename the original file to a temporary name, "UserWorkEthicTEMP.txt" for example. Create a new text file with the original name. Now; read a line, write a line, between the two files, before adding your new data onto the end. Finally Delete the temporary file and you will have the new file with the new details. If you have an error the temporary file will serve as a backup of the original. Some sample code below:
Change file names
Dim Line as string
line=Reader.readline
Do until Line=nothing
objwriter.writeline(line)
line=reader.readline
loop
add new values on the end and remove old file
You are trying to read and write to the same file and this is causing a lock contention. Either store the contents of the file into a variable and then write it back out including your new data to the file.
Psuedo
Reader.Open file
String content = Reader.ReadToEnd()
Reader.Close
Writer.Open file
Loop
Writer.Write newContent
Writer.Close
Is there a method to verify that a file is open? The only thing I can think of is the Try/Catch to see if i can catch the file-open exception but I figured that a method be available to return true/false if file is open.
Currently using System.IO and the following code under class named Wallet.
Private holdPath As String = "defaultLog.txt"
Private _file As New FileStream(holdPath, FileMode.OpenOrCreate, FileAccess.ReadWrite)
Private file As New StreamWriter(_file)
Public Function Check(ByVal CheckNumber As Integer, ByVal CheckAmount As Decimal) As Decimal
Try
file.WriteLine("testing")
file.Close()
Catch e As IOException
'Note sure if this is the proper way.
End Try
Return 0D
End Function
Any pointers will be appreciated! Thank you!!
Private Sub IsFileOpen(ByVal file As FileInfo)
Dim stream As FileStream = Nothing
Try
stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None)
stream.Close()
Catch ex As Exception
If TypeOf ex Is IOException AndAlso IsFileLocked(ex) Then
' do something here, either close the file if you have a handle, show a msgbox, retry or as a last resort terminate the process - which could cause corruption and lose data
End If
End Try
End Sub
Private Shared Function IsFileLocked(exception As Exception) As Boolean
Dim errorCode As Integer = Marshal.GetHRForException(exception) And ((1 << 16) - 1)
Return errorCode = 32 OrElse errorCode = 33
End Function
Call it like this:
Call IsFileOpen(new FileInfo(filePath))
There is really no point using a 'is file in use check' function since you will still need to have try catch to handle the case that the file fails to open. The file open can fail for many more reasons than it just being already open.
Also using a function to do a check is no guarantee of success. The 'is file in use check' might return false only for the file open to fail with a file already open error, because in time between the check and trying to open the file it was opened by someone else.
It looks like the two suggestions from this MSDN forum posting both involve trying to open the file.
The first one is similar to what you are doing now, and the second involves using a Windows API function (CreateFile) and checking for a invalid handle signifying the file is in use. In both cases they are relying on an error condition to determine if the file is open or not. In short, in my opinion the method you are using is correct since there is not a System.IO.File.IsOpen property.
I am using a VB script in SSIS Script Task to add header and Trailer to a flat file. The code was working fine until recently i came across a problem where the rows in the file are more than usual and resulting in a failure on script task with error`Error:
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.
at System.String.GetStringForStringBuilder(String value, Int32 startIndex, Int32 length, Int32 capacity)
at System.Text.StringBuilder.GetNewString(String currentString, Int32 requiredLength)
at System.Text.StringBuilder.Append(Char[] value, Int32 startIndex, Int32 charCount)
at System.IO.StreamReader.ReadToEnd()
at System.IO.File.ReadAllText(String path, Encoding encoding)
at System.IO.File.ReadAllText(String path)`
Can any one help me in fixing the problem please.I think instead of "String Builder" i need to use other string related method. I am getting error at
fileContents.Append(File.ReadAllText(Dts.Connections("DestinationConnection").ConnectionString))
Here is my code:
Public Sub Main()
Dim fileContents As New StringBuilder()
Dim finalfile As String
Dim firstline As String
Dim lastline As String
Dts.VariableDispenser.LockForRead("FirstLine")
Dts.VariableDispenser.LockForRead("LastLine")
Dts.VariableDispenser.LockForRead("FileName")
firstline = CType(Dts.Variables("FirstLine").Value, String)
finalfile = CType(Dts.Variables("FileName").Value, String)
lastline= CType(Dts.Variables("LastLine").Value, String)
'Write header, then append file contents and write back out.
fileContents.AppendLine(String.Format("{0}", firstline))
fileContents.Append(File.ReadAllText(Dts.Connections("DestinationConnection").ConnectionString))
fileContents.AppendLine(String.Format("{0}", lastline))
File.WriteAllText(finalfile, fileContents.ToString())
Dts.TaskResult = ScriptResults.Success
End Sub
Well, one simple way would be to just avoid the StringBuilder: open a TextWriter with File.CreateText, write the first line, then write File.ReadAllText(...), then write the final line.
However, that will only save you some memory - it will roughly halve the memory required, as you won't need it in both the StringBuilder and a string (which is what I think will happen now).
A much better alternative would be to:
Open the writer
Write the header line
Open the other file for reading
Loop over the file, reading a chunk of characters at a time and writing it to the new file, until you're done
Close the other file implicitly (use a Using statement for this)
Write the trailing line
Close the write implicitly (use a Using statement)
That way even if you've got huge files, you only need a small chunk of data in memory at a time.
The problem is File.ReadAllText has limitations when it comes to reading a large file because the entire file is read into memory.
What you will need to do is replace the File.ReadAllText with reading the file line by line and append it accordingly.
EDITED FOR AN EXAMPLE:
Option Explicit
Dim oFSO, sFile, oFile, sText
Set oFSO = CreateObject("Scripting.FileSystemObject")
sFile = "your text file"
If oFSO.FileExists(sFile) Then
Set oFile = oFSO.OpenTextFile(sFile, 1)
Do While Not oFile.AtEndOfStream
sText = oFile.ReadLine
If Trim(sText) <> "" Then
fileContents.AppendLine(sText)
End If
Loop
oFile.Close
Else
WScript.Echo "The file was not there."
End If
It's possible you may still have an issue with the fileContents StringBuilder. The original error shown though was thrown from the File.ReadAllText method. So hopefully, this does the trick.
If not, I would just forget about the fileContents StringBuilder all together and write out the header. Then read from the file line by line and write it out line by line, then finally write the footer.
An alternative (and much more SSIS-like) solution would be to create a Data Flow Task that reads your existing file, pipes it through a Script Component that adds the header and footer, and writes it to the file system. Here's what it might look like in SSIS 2005:
The Script Component will be a Transformation with the SynchronousInputID of its output set to False, so that it can generate header and footer rows:
And the VB source of the transform should look something like this:
Public Class ScriptMain
Inherits UserComponent
Dim headerWritten As Boolean = False
Public Overrides Sub IncomingRows_ProcessInputRow(ByVal Row As IncomingRowsBuffer)
If Not headerWritten Then
WriteHeader()
End If
OutgoingRowsBuffer.AddRow()
OutgoingRowsBuffer.theLine = Row.theLine
End Sub
Public Overrides Sub FinishOutputs()
MyBase.FinishOutputs()
WriteFooter()
End Sub
Private Sub WriteHeader()
OutgoingRowsBuffer.AddRow()
OutgoingRowsBuffer.theLine = "The First Header Line"
headerWritten = True
End Sub
Private Sub WriteFooter()
OutgoingRowsBuffer.AddRow()
OutgoingRowsBuffer.theLine = "Here's a footer line"
OutgoingRowsBuffer.AddRow()
OutgoingRowsBuffer.theLine = "Here's another one"
End Sub
End Class
This lets you use the streaming capabilities of SSIS to your advantage.