I have a list of structures that have to be passed as argument to threads; one for each element in the list. The thread will loop until a boolean in the structure become true.
So I made:
For Each ScaleElement In Scales
Dim NewThread As New System.Threading.Thread(Sub() ScaleThread(ScaleElement))
NewThread.Start()
Next
With ScaleElement passed byref. But then, I have a warning: "Wsing the iteration variable in a lambda expression may have unexpected results". And the warning it's right because it seems to run the thread on the same element.
If I try:
For Each ScaleElement In Scales
Dim NewScale = ScaleElement
Dim NewThread As New System.Threading.Thread(Sub() ScaleThread(NewScale))
NewThread.Start()
Next
It works fine but, as the "NewScale" is a different element, when I try to set the condition for breaking the loop in the elements in the list, of course it doesn't work.
ScaleStruct:
Public Structure ScaleStruct
Dim Key As String
Public Scale
Dim Database As String
Dim Table As String
Dim Field As String
Dim Keyname As String
Dim Interval As Integer
Dim Insert As Boolean
Dim Format As String
Public Abort As Boolean
Dim FailCount As Integer
End Structure
The scale variable is set (on the configuration file reading) to a class that reads the scale.
Scales is a "Public Scales As New List(Of ScaleStruct)" so, when I want to stop the threads, I would like to use a boolean (Abort) in the struct.
Then, the thread is a loop:
Private Sub ScaleThread(ByRef Tscale As ScaleStruct)
Do Until Tscale.Abort
...
Loop
End Sub
How can I solve this?
Do you mean that ScaleElement has a Boolean property to determine whether or not to keep going? If so, it sounds like the simplest approach would be to make it a class rather than a structure. (It sounds like it would be a better fit as a class anyway, to be honest.)
Related
I am working on this excellent tutorial, but in the end my first test is not passing, due to the fact that I can clearly see I am creating two different arrays (and pointers), and trying to compare them with one another.
Now the tutorial from what I can see leaves out a few lines of code that I have added, which is also where I see the problem, but without those lines the code does not even run of coarse.
All my other test methods are the same as the example, except for this method that I created the following lines - else nothing happens when you run the test.
Public Sub Run(ByVal dataService As IDataService, ByVal wsService As IWorksheetService)
Dim data As Variant 'Added this line
data = dataService.GetSomeTable 'Added this line
Call wsService.WriteAllData(data) 'Added this line
End Sub
And here is where I can see the code going south...
'#TestMethod
Public Sub WorksheetServiceWorksOffDataFromDataService()
'Arrange
Dim dataServiceStub As MyDataServiceStub
Set dataServiceStub = New MyDataServiceStub
Dim expected As LongLong
expected = VarPtr(dataServiceStub.GetSomeTable) 'expected creates an Array
Dim wsServiceStub As MyWorksheetServiceStub
Set wsServiceStub = New MyWorksheetServiceStub
'Act
With New MyTestableMacro
.Run dataServiceStub, wsServiceStub 'here we create a second array
End With
Dim actual As LongLong
actual = wsServiceStub.WrittenArrayPointer 'here we point to the address of the second array
'Assert
Assert.AreEqual expected, actual ' this test fails cause it points to two different addresses
End Sub
I had to change the type from Long as in the tutorial for the array pointers to LongLong due to the fact that the number on 64 bit is too long for Long. LongPtr also worked
VarPtr is what's artificially complicating that test, introducing frail and flawed pointer logic that doesn't need to be there.
Change your stub data service to return some non-empty data - literally anything will do:
Option Explicit
Implements IDataService
'#Folder "Services.Stubs"
Private Function IDataService_GetSomeTable() As Variant
IDataService_GetSomeTable = GetSomeTable
End Function
Public Function GetSomeTable() As Variant
Dim result(1 To 50, 1 To 10) As Variant
result(1, 1) = "test"
GetSomeTable = result
End Function
Now change the stub worksheet service to keep a copy of the actual data (rather than just a LongPtr):
Option Explicit
Implements IWorksheetService
'#Folder "Services.Stubs"
Private Type TStub
WasWritten As Boolean
WrittenData As Variant
End Type
Private this As TStub
Private Sub IWorksheetService_WriteAllData(ByRef data As Variant)
this.WasWritten = True
this.WrittenData = data
End Sub
Public Property Get DataWasWritten() As Boolean
DataWasWritten = this.WasWritten
End Property
Public Property Get WrittenData() As Variant
WrittenData = this.WrittenData
End Property
Now change the test to assert that IDataService.GetSomeTable is returning the same data that IWorksheetService.WriteAllData works with - you can do that using Assert.SequenceEquals, which compares all elements of two arrays and fails if anything is different:
'#TestMethod
Public Sub WorksheetServiceWorksOffDataFromDataService()
'Arrange
Dim dataServiceStub As StubDataService
Set dataServiceStub = New StubDataService
Dim expected As Variant
expected = dataServiceStub.GetSomeTable
Dim wsServiceStub As StubWorksheetService
Set wsServiceStub = New StubWorksheetService
'Act
With New Macro
.Run dataServiceStub, wsServiceStub
End With
Dim actual As Variant
actual = wsServiceStub.WrittenData
'Assert
Assert.SequenceEquals expected, actual
End Sub
This makes the test much simpler, and it passes:
I will be updating the article with this simpler test later today.
I would like to to copy that values of an array into a Structure.
Example:
' The Array
Dim Columns(2) As String
' The Structure
Private Structure Fields
Public FName As String
Public LName As String
Public Email As String
End Structure
' I would like to map it like so:
Fields.FName = Columns(0)
Fields.LName = Columns(1)
Fields.Email = Columns(2)
Obviously I could write a function if it was so simple, but really there are over 25 columns and it's a pain to write a function that would map it.
Is there some way to do this?
There really is no simple way that will work in all cases. What you are complaining is too much effort is the only way to guarantee that it will work in all cases.
That said, if you can guarantee that the number of elements in the array matches the number of properties/fields in the structure/class and that they are in the same order and of the same types then you could use Reflection in a loop, e.g.
Private Function Map(source As Object()) As SomeType
Dim result As New SomeType
Dim resultType = result.GetType()
Dim fields = resultType.GetFields()
For i = 0 To source.GetUpperBound(0)
fields(i).SetValue(result, source(i))
Next
Return result
End Function
EDIT:
The code I have provided works as is if SomeType is a class but, as I missed the first time around, not for a structure. The reason is that structures are value types and therefore a copy of the original object is being sent to SetValue, so the field value never gets set on that original object. In theory, to prevent a copy being created, you should be able to simply box the value, i.e. wrap it in an Object reference:
Private Function Map(source As Object()) As SomeType
Dim result As Object = New SomeType
Dim resultType = result.GetType()
Dim fields = resultType.GetFields()
For i = 0 To source.GetUpperBound(0)
fields(i).SetValue(result, source(i))
Next
Return DirectCast(result, SomeType)
End Function
As it turns out though, the VB compiler treats that a little differently than the C# compiler treats the equivalent C# code and it still doesn't work. That's because, in VB, the boxed value gets unboxed before being passed to the method, so a copy is still created. In order to make it work in VB, you need to use a ValueType reference instead of Object:
Private Function Map(source As Object()) As SomeType
Dim result As ValueType = New SomeType
Dim resultType = result.GetType()
Dim fields = resultType.GetFields()
For i = 0 To source.GetUpperBound(0)
fields(i).SetValue(result, source(i))
Next
Return DirectCast(result, SomeType)
End Function
OK, that question sounds maybe a little confusing so I'll try to explain it with an example.
Pretend you have an object like this:
Class Something
Private varX As New Integer
Private varY As New String
'[..with the associated property definitions..]
Public Sub New()
End Sub
End Class
And another with:
Class JsonObject
Inherits Dictionary(Of String, String)
Public Function MakeObject() As Object 'or maybe even somethingObject
Dim somethingObject As New Something()
For Each kvp As KeyValuePair(Of String, String) In Me
'Here should happen something to use the Key as varX or varY and the Value as value for the varX or varY
somethingObject.CallByName(Me, kvp.Key, vbGet) = kpv.Value
Next
return somethingObject
End Function
End Class
I've got the 'CallByMe()' function from a previous question of myself
CallByName works different from the way you are trying to use it. Look at the documentation, it will tell you that in this particular case the correct usage would be
CallByName(Me, kvp.Key, vbSet, kpv.Value)
However, the function CallByName is part of a VB library that isn’t supported on all devices (notably it isn’t included in the .NET Mobile framework) and consequently it’s better not to use it.
Using proper reflection is slightly more complicated but guaranteed to work on all platforms.
Dim t = GetType(Something)
Dim field = t.GetField(kvp.Key, BindingFlags.NonPublic Or BindingFlags.Instance)
field.SetValue(Me, kvp.Value)
i have 20,000 items in a queue, and i want to process them using the threadpool.
will this be the best way to do it?
for i as integer = 0 to 19999
ThreadPool.QueueUserWorkItem (PerformTask, ListTask(i))
next
Sub PerformTask(i as string)
' do the work here
end sub
How can i return or set ui control from the PerformTask sub?
You cannot.
However, you can allocate a container (array, list) with a different slot for each result, and write into it. Alternatively, you could pass an object into the worker method that holds both the input and the result. I’d use this method:
Class TaskObject
Dim Input As String
Dim Result As Whatever
End Class
Dim tasks As TaskObject() = New TaskObject(20000) { }
For i as Integer = 0 to tasks.Length - 1
ThreadPool.QueueUserWorkItem(PerformTask, tasks(i))
next
Sub PerformTask(arg As Object)
Dim task As TaskObject = DirectCast(arg, TaskObject)
' do the work here
end sub
Unrelated: you should always enable Option Strict in your projects. No exception. Your code has type errors that the compiler should detect.
I Have a text file that is like the following:
[group1]
value1
value2
value3
[group2]
value1
value2
[group3]
value3
value 4
etc
What I want to be able to do, is load the values into an array (or list?) based on a passed in group value. eg. If i pass in "group2", then it would return a list of "value1" and "value2".
Also these values don't change that often (maybe every 6 months or so), so is there a better way to store them instead of a plain old text file so that it makes it faster to load etc?
Thanks for your help.
Leddo
This is a home work question?
Use the StreamReader class to read the file (you will need to probably use .EndOfStream and ReadLine()) and use the String class for the string manipulation (probably .StartsWith(), .Substring() and .Split().
As for the better way to store them "IT DEPENDS". How many groups will you have, how many values will there be, how often is the data accessed, etc. It's possible that the original wording of the question will give us a better clue about what they were after hear.
Addition:
So, assuming this program/service is up and running all day, and that the file isn't very large, then you probably want to read the file just once into a Dictionary(of String, List(of String)). The ContainsKey method of this will determine if a group exists.
Function GetValueSet(ByVal filename As String) As Dictionary(Of String, List(Of String))
Dim valueSet = New Dictionary(Of String, List(Of String))()
Dim lines = System.IO.File.ReadAllLines(filename)
Dim header As String
Dim values As List(Of String) = Nothing
For Each line As String In lines
If line.StartsWith("[") Then
If Not values Is Nothing Then
valueSet.add(header, values)
End If
header = GetHeader(line)
values = New List(Of String)()
ElseIf Not values Is Nothing Then
Dim value As String = line.Trim()
If value <> "" Then
values.Add(value)
End If
End If
Next
If Not values Is Nothing Then
valueSet.add(header, values)
End If
Return valueSet
End Function
Function GetHeader(ByVal line As String)
Dim index As Integer = line.IndexOf("]")
Return line.Substring(1, index - 1)
End Function
Addition:
Now if your running a multi-threaded solution (that includes all ASP.Net solutions) then you either want to make sure you do this at the application start up (for ASP.Net that's in Global.asax, I think it's ApplicationStart or OnStart or something), or you will need locking. WinForms and Services are by default not multi-threaded.
Also, if the file changes you need to restart the app/service/web-site or you will need to add a file watcher to reload the data (and then multi-threading will need locking because this is not longer confined to application startup).
ok, here is what I edned up coding:
Public Function FillFromFile(ByVal vFileName As String, ByVal vGroupName As String) As List(Of String)
' open the file
' read the entire file into memory
' find the starting group name
Dim blnFoundHeading As Boolean = False
Dim lstValues As New List(Of String)
Dim lines() As String = IO.File.ReadAllLines(vFileName)
For Each line As String In lines
If line.ToLower.Contains("[" & vGroupName.ToLower & "]") Then
' found the heading, now start loading the lines into the list until the next heading
blnFoundHeading = True
ElseIf line.Contains("[") Then
If blnFoundHeading Then
' we are at the end so exit the loop
Exit For
Else
' its another group so keep going
End If
Else
If blnFoundHeading And line.Trim.Length > 0 Then
lstValues.Add(line.Trim)
End If
End If
Next
Return lstValues
End Function
Regarding a possible better way to store the data: you might find XML useful. It is ridiculously easy to read XML data into a DataTable object.
Example:
Dim dtTest As New System.Data.DataTable
dtTest.ReadXml("YourFilePathNameGoesHere.xml")