Split Function Freezing UI - Some Backgroundworker Help Please

[SeanVb]

Hi,

I'm currently running multiple For Each loops which are time consuming loops. They started to cause issues so I added them to a backgroundworker, not only for the threading advantages but also the progress bar updating. However the below Split function is still causing the UI to freeze as it takes about 10 seconds to perform the split and the progress bar in the For Each loop that follows does not show the user that something is happening. Is there a way to stop the function from causing the freeze or making it update the progress bar?

lines = Split(My.Computer.FileSystem.ReadAllText(OpenFileDialog1.FileName), vbNewLine)
For Each line In lines
    'More code
next

I know I can use a string as apposed to the lines array, update the backgroundworkers and loop the file line by line like this...

        processLength = File.ReadAllLines(OpenFileDialog1.FileName).Length
        For Each SplitLine As String In File.ReadAllLines(OpenFileDialog1.FileName)
            progressbarLabelText = "Processing data..."
            loopProcessCount += 1
            bwAMC.ReportProgress(((loopProcessCount / processLength) Mod 100) * 100)
            tempLine = tempLine & SplitLine & vbNewLine
        Next

But doing so means I would have to change all my code that uses the lines array. Something I hope to avoid.

Any suggestions would be greatly appreciated.

Regards,

S

[Shaggy Hiker]

Consider this function rather than ReadAlltext plus a split:

https://msdn.microsoft.com/en-us/lib...v=vs.110).aspx

That may do the same job faster. Split would tend to be slower.

However, I think you already have a problem because you are accessing the OpenFileDialog, which I believe will tie you to the UI process. OpenFileDialog doesn't do all that much other than give you a friendly means to choose what amounts to a string (a full path, but still just a string). So, get that string from OpenFileDialog in the UI and put it in a form level variable. Then, in the background process, use that string rather than OpenFileDialog.

[Sitten Spynne]

(Consider what Shaggy Hiker posted also, I got caught up in a different thing that might be there.)

Well, I don't really see enough code here to definitively say what's happening. But if the "more code" comment looks like your 2nd code sample, that's a hint.

The UI thread freezes when you ask it to do more than 1 second of work within 1 second. It unfreezes once it's able to do less than 1 second of work per second. So it's obvious why the code needs to go on a background thread.

But think about how often a loop that goes over each line of the file will execute. It'll probably happen many hundreds of times per second. Now think about how long it takes to update the UI in response, probably 2-3ms. That means if you're reading only about 300-500 lines per second, you start asking for more than 1s of UI updates per second. That's when the UI freezes. Even if you're close, more like 900ms per 1s, that doesn't leave a lot of time for user interaction and it's likely to look frozen anyway.

So when you're updating the UI from a background thread, it's often worth writing code to try and 'throttle' updates to happen less frequently. I feel like once per second is adequate, other people get excited about 4-5 times per second. A simple way to do that would look something like this:

Dim lastUpdate As DateTime = DateTime.Now
For Each line in lines
    ' the code to do whatever

    Dim timeDelta As TimeSpan = DateTime.Now - lastUpdate
    If timeDelta > TimeSpan.FromSeconds(1) Then
        ' Update the UI
    End If
Next

' Remember to do one last progress update for 100%, since it might not have happened
' in the loop.

This could be the solution, but I need to see more code to be sure.

[jmcilhinney]

Why would you have to change all your code that uses the 'lines' array? Why wouldn't you simply change this:

lines = Split(My.Computer.FileSystem.ReadAllText(OpenFileDialog1.FileName), vbNewLine)

to this:

lines = IO.File.ReadAllLines(OpenFileDialog1.FileName)

Any code that uses 'lines' doesn't care how it's populated.

That said, if you have a large file then it's still going to take time to read it all in and split it into lines, whether you do it yourself or you let the Framework do it for you.