I am Using same function from many places...
for example below function
Public Sub getUser(ByVal Name as string)
dim myName=Name
.......
insert(myName)
End Sub
I am using this function from so many places...
I have doubt should this function override this myName values with latest function call?
Suppose i called getUser("ABC") so value of myName is now ABC now sudden all call getUser("XYZ") so at insert(myName) will it insert("ABC") or insert("XYZ")??
I need it to be insert("ABC") and then insert("XYZ")
You can use locking to make sure only one thread does something at a time
//declare an object for locking
Dim lockObjcect As New [Object]()
Public Sub getUser(ByVal Name as string)
SyncLock lockObjcect
dim myName=Name
.......
insert(myName)
End SyncLock
End Sub
With the locking, now only one thread will be able to execute the code between SyncLock and End SyncLock this means First ABC will be inserted and then XYZ will be inserted
Related
I'm using .NET Framework 4.0.
I have a function that creates and calls a Task. In some part of its process I need a value stored in the Session, but it returns Nothing because the Task doesn't have the HttpContext.
Here's an example:
Public Class Example
Inherits System.Web.Mvc.Controller
<AcceptVerbs("GET", "POST")>
Public Sub DoSomething()
Dim products As List(Of Product)
Dim something As New Task(Sub()
For Each product In products
product.Name = product.Name.ToUpper
product.Save()
Next
End Sub)
something.Start()
End Sub
End Class
Public Class Product
Public Sub OnProductSave()
Dim session = Web.HttpContext.Current.Session
Dim log As New Log()
log.UserId = session("UserId")
log.Date = DateTime.Now()
log.Save()
End Function
End Class
There is a way that I could use the HttpContext in the Task?
Obs.: In the example I could pass the value of UserId to the function, but in the real case it's more complex than that.
Obs.2: I know that I could create a variable with the value of HttpContext and after set it to the Task's HttpContext, but I think there could be a better way. :)
Using VB.Net (Framework version 4.5.1)
I have a program that sets up a list of (System.Threading.Tasks.Task) tasks that are executed as follows (only relevant code is shown):
po = New System.Threading.Tasks.ParallelOptions()
po.MaxDegreeOfParallelism = 5
Parallel.ForEach( task_list, po, AddressOf do_work )
The program works fine, but I want to add a log file rather than using just Console.WriteLine()
In the do_work() Sub, I want to write to a log file, for example:
Sub do_work( param As String )
Dim thread_id as String = "Thread ID " & System.Threading.Thread.CurrentThread.ManagedThreadId.ToString() & ": "
joblog_append( thread_id & "Beg" )
joblog_append( thread_id & "param = " & param )
joblog_append( thread_id & "End" )
End Sub
Ideally, I would like to create three functions such as:
joblog_open() to open a log file at the start o the program.
joblog_append() to append to the log file; callable from within any task
joblog_close() to close the log file
What is the correct way to implement such logging when the joblog_append() will be called from multiple tasks being executed on separate threads?
All attempts I have tried so far seem to be hit and miss; sometimes the data is written to the output file, sometimes it is not.
Any advice (or better yet, a code example) would be most appreciated.
Thanks in advance.
I think that the issue you have is due to the fact multiple threads are accessing the file at the same time.
A better approach would be to make sure only one thread access the file at a time. You could use a lock (see this SO) or append the messages to be written to a concurrentQueue of string, then process that queue on another thread.
The joblog_append calls _Logger.Log, which in turns enqueue the message and start a new thread to process the queue.
private _Logger as new Logger
Private Sub joblog_append(Message As String)
_Logger.Log(Message)
End Sub
The logger class performs the following.
Append message to to a concurrent queue
Create and start a task (if no one already running) to write queue content to the file.
Set the task to nothing when completed
In the event the task is already created, the message is enqueued and the While condition in the task itself should take care of any messages added while it's running.
'Missing: Idisposable, Fileaccess.Shared,
'TODO: remove debugger.break
Public class Logger
Public Property Messages As new ConcurrentQueue(Of string)
private _WorkerTask as Task
private event WorkerTaskCompleted
private _Stream as FileStream
private _Writer as StreamWriter
Public sub New()
_Stream = io.file.OpenWrite("Mylog.txt")
_Writer = New StreamWriter(_Stream)
End sub
Public sub Log(Message as string)
Messages.Enqueue(Message)
if _WorkerTask Is Nothing
_WorkerTask = New Task(sub()
While Messages.Any
Dim CurrentMessage as string = ""
if Messages.TryDequeue(CurrentMessage)
_Writer.WriteLine(CurrentMessage)
else
debugger.Break
End If
End While
_Writer.Flush
_Stream.Flush
RaiseEvent WorkerTaskCompleted
End Sub)
_WorkerTask.Start
End If
End sub
Private Sub Logger_WorkerTaskCompleted() Handles Me.WorkerTaskCompleted
_WorkerTask = Nothing
End Sub
End Class
Please note. This is my approach to this problem but I do not have anything similar implemented and tested. Therefore, you will have to make your tests to confirm it is working properly.
I have two classes, RecordSet and Record. RecordSet has a Generic List(Of Record).
I can add objects to the list by calling my RecordSet.AddRecord(ObjRecord) function, which returns RecordSet. When the list has a count of 200, some processing occurs and a new RecordSet object is returned, otherwise itself is returned and the application can carry on adding Record objects to the list.
My concern is that there will be 200 objects of RecordSet until garbage collection does it's sweep. Is this a good idea?
Public Class RecordSet
Private lstRecords As New List(Of Record)
Public Function AddRecord(SomeVariable) AS RecordSet
lstRecords.Add(New Record())
If lstRecords.Count = 200 Then
Me.ProcessTheRecords()
Return New RecordSet()
Else
Return Me
End If
End Function
Private Sub ProcessTheRecords()
'Do stuff in here
End Sub
Private Class Record
Public Sub New()
End Sub
End Class
End Class
Then in my application I call:
Dim objRecordSet AS New RecordSet
For Each VariableName In SomeList
objRecordSet = objRecordSet.AddRecord(VariableName)
Next
'Process the remaining objects in objRecordSet here.
First of all, this is really bad pratice, it's hard to follow the code for someone new and is a potential bug source. Instead of returning urself every time, change your design.
Change your function to this:
Public Sub AddRecord(SomeVariable)
lstRecords.Add(New Record()) <--- should't you be doing something with SomeVariable?!
If lstRecords.Count = 200 Then
Me.ProcessTheRecords()
end if
End Function
Private Sub ProcessTheRecords()
'Do stuff in here
Me.lstRecords.clear()
End Sub
Now AddRecord does exactly what it says it does - it adds a new record and modifies the recordSet. ProcessTheRecords does the processing, as its supposed to do, and if u need to clear the list container - oh well, just clear it.
I strongly recommed to read this wiki article about
Cohesion.
Just as a proposiontion, the AddRecord could be a function of return type Boolean, which indicates the success of the operation (maybe an error or exception can be raised by the processing function?).
It's much cleaner now, isn't it?
i have some test code which i run at every load of a page in my asp.net website
this is the code
Sub TryThreads()
Dim t1 = New Thread(AddressOf TryLock)
t1.Priority = ThreadPriority.Lowest
t1.Start()
Dim t2 = New Thread(AddressOf TryLock)
t2.Priority = ThreadPriority.Lowest
t2.Start()
End Sub
Sub TryLock()
Dim LockObject = New Object
SyncLock LockObject
DoTrace("entered locker")
For x = 0 To 10000
Next
DoTrace("exiting locker")
End SyncLock
DoTrace("exited locker")
End Sub
the "dotrace" simply add a record to a log table in the db
now the right result would be that i should have the entries in the db in order "entered","exiting","exited"
but actually when i look in the db i see first 2 "entered" then 2 "exiting" etc.
meaning that the multithreading is working ok, but not the synclock
is that correct?
and how can this be fixed?
the real code will be adding records to the db and might be called from several pages of different sessions, but the same code must not run twice concurrently
i do appreciate anybodys help
thank you very much!!!
EDIT:
in response to Sashas wonderful post i changed my code to a class (it was in a module) and now it looks like this:
Public Class CheckClass
Property LockObject As Object
Get
If HttpRuntime.Cache("CheckSessionsLock") Is Nothing Then HttpRuntime.Cache("CheckSessionsLock") = New Object
Return HttpRuntime.Cache("CheckSessionsLock")
End Get
Set(ByVal value As Object)
If value Is Nothing Then
HttpRuntime.Cache.Remove("CheckSessionsLock")
Else
HttpRuntime.Cache("CheckSessionsLock") = value
End If
End Set
End Property
Sub TryThreads()
Dim t1 = New Thread(AddressOf TryLock)
t1.Priority = ThreadPriority.Lowest
t1.Start()
Dim t2 = New Thread(AddressOf TryLock)
t2.Priority = ThreadPriority.Lowest
t2.Start()
End Sub
Sub TryLock()
SyncLock LockObject
DoTrace("entered locker")
For x = 0 To 10000
Next
DoTrace("exiting locker")
End SyncLock
DoTrace("exited locker")
End Sub
End Class
now it works 80-90% of the time.
on page load i have:
Dim cc = New CheckClass
cc.TryThreads()
if i open multiple pages at once, they still clash some times. but if i'm correct, the issue is now not with the synclock as much as with the httpruntime.cache, because when using a standard property, on one page, the code works 100%.
so how can i make sure that 2 threads, even from totally different sessions never run the trylock simultaneously?
thank you all for helping out
You are creating a new object instance when the TryLock method is called, and use that for locking. If you want mutual exclusion between the two threads, you need to use a common object instance for locking, e.g. a static member of your class or a parameter that you pass to both threads.
I have a DataSet that I have added to my project where I can Insert and Add records using the Add Query function in Visual Studio 2010, however I want to add transactions to this, I have found a few examples but cannot seem to find one that works with these.
I know I need to use the SQLClient.SQLTransaction Class somehow. I used the Add New Data Source Wizard and added the Tables/View/Functions I need, I just need an example using this process such as How to get the DataConnection my DataSet has used. Assuming all options have been set in the wizard and I am only using the pre-defined adapters and options asked for in this wizard, how to I add the Transaction logic to my Database.
For example I have a DataSet called ProductDataSet with the XSD created for this, I have then added my Stock table as a Datasource and Added an AddStock method with a wizard, this also if a new item calls an AddItem method, if either of these fails I want to rollback the AddItem and AddStock in this case.
In this example, I have a dataset called "dsMain" and a few direct queries in a "QueriesTableAdapter". I extend the partial class for the TableAdapter with a function that will create a transaction based on the first (0) connection and then apply it to every connection in the table adapter.
Namespace dsMainTableAdapters
Partial Public Class QueriesTableAdapter
Public Function CreateTransaction() As Data.IDbTransaction
Dim oConnection = Me.CommandCollection(0).Connection
oConnection.Open()
Dim oTrans = oConnection.BeginTransaction()
For Each cmd In Me.CommandCollection
cmd.Connection = oConnection
cmd.Transaction = oTrans
Next
Return oTrans
End Function
End Class
End Namespace
You begin the transaction by calling the new function
Dim qa As New dsMainTableAdapters.QueriesTableAdapter
Dim oTrans = qa.CreateTransaction()
Then you can call TableAdapter queries within your transaction
qa.Query1
qa.Query2
When you are done with your queries you commit the transaction
oTrans.Commit()
You can do the same thing for any TableAdapter that was created for your datasets.
If you have multiple TableAdapters that need to use the same transaction, then in addition to a "CreateTransaction" you should make a "SetTransaction" and have the Transaction be a parameter.
first of all thanks for your answer carter, it helped me very much!
but iam not able to handle the part with the parameters
You can do the same thing for any TableAdapter that was created for your datasets. If you have multiple TableAdapters that need to use the same transaction, then in addition to a "CreateTransaction" you should make a "SetTransaction" and have the Transaction be a parameter.
so iam able to handle 1 transactions with 1 tableadapter, but not 1 transaction with 2 tableadapters:
iam doing this for a school project, and i really need your help!!
here is the code to add a new material and a historical price to it(a changing price, like by fuel; iam saving it in an related table to material in the database):
Namespace DataSetTableAdapters
Partial Public Class MaterialPriceTableAdapter
Public Function SetTransaction() As Data.IDbTransaction
Dim oConnection = Me.CommandCollection(0).Connection
oConnection.Open()
Dim oTrans = oConnection.BeginTransaction()
For Each cmd In Me.CommandCollection
cmd.Connection = oConnection
cmd.Transaction = oTrans
Next
Return oTrans
End Function
End Class
Partial Public Class MaterialTableAdapter
Public Function CreateTransaction(ByVal MaterialPrice As System.Data.Odbc.OdbcTransaction) As Data.IDbTransaction
Dim oConnection = Me.CommandCollection(0).Connection
oConnection.Open()
Dim oTrans = oConnection.BeginTransaction()
For Each cmd In Me.CommandCollection
cmd.Connection = oConnection
cmd.Transaction = oTrans
Next
Return oTrans
End Function
End Namspace
`
and now the code in the form the form:
Public Class AddMaterial
Dim material As New DataSetBATableAdapters.MaterialTableAdapter
Dim materialprice As New DataSetBATableAdapters.MaterialPriceTableAdapter
Dim oTrans = material.CreateTransaction(materialprice.SetTransaction())
Private Sub Save_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Save.Click
Try
material.InsertQuery(NameTextBox.Text, UnitComboBox.SelectedValue)
materialprice.InsertQuery(Date_BeginDateTimePicker.Value, PriceTextBox.Text, Date_EndDateTimePicker.Value, Me.LkwTableAdapter.ScalarQuery())
oTrans.Commit()
Catch ex As Exception
oTrans.Rollback()
MsgBox("Error by Insert")
End Try
Me.Close
End Sub
End Class
if i save a new record the materialprice.insertquery isnt commited by otrans.commit. what am i doing wrong? if you have an idea what it is, please tell me
thanks,
Xeras
This is untested, but this is how I imaging the CreateTransaction/SetTransaction combo should be written (with your OdbcTransaction object).
Public Function CreateTransaction() As System.Data.Odbc.OdbcTransaction
Dim oConnection = Me.CommandCollection(0).Connection
oConnection.Open()
Dim oTrans = oConnection.BeginTransaction()
SetTransaction(oTrans)
Return oTrans
End Function
Public Sub SetTransaction(ByVal oTrans As System.Data.Odbc.OdbcTransaction)
For Each cmd In Me.CommandCollection
cmd.Connection = oTrans.Connection
cmd.Transaction = oTrans
Next
End Sub