parallel.foreach is hanging my application - vb.net

Question

I have a List(of MyCustomObject). This List is the DataSource for TreeView.
Now, all of collected objects must be updated on periodicaly Rising Timer1_Timer event. To update I'm using Parallel.ForEach. This works fine in test app, but final application hangs after adding code for calculations, and random number of relults may absent. Please help to fix it.
Imports System.Threading.Tasks
Imports Telerik.WinControls.UI
Imports System.ComponentModel
Imports System.Threading
Imports Accessibility
Public Class Form1
Dim WithEvents bw As New BackgroundWorker
Private Sub Button6_Click(sender As System.Object, e As System.EventArgs) Handles Button6.Click
Upadte(rt.Nodes.Cast(Of RadTreeNode)())
End Sub
Private Shared Sub Upadte(Of T)(source As IEnumerable(Of T))
Parallel.ForEach(source, New ParallelOptions With {.TaskScheduler = TaskScheduler.FromCurrentSynchronizationContext, .MaxDegreeOfParallelism = 5}, AddressOf zUpdate)
End Sub
' Following fragment is a simple example. Real code is more difficult. It includes Network requests, WQL queries e.t.c.
' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Private Shared Sub zUpdate(Of T)(node As T)
Dim item = TryCast(node, RadTreeNode)
If item Is Nothing Then
Return
End If
Dim n_node As New RadTreeNode("_" & item.Name)
n_node.Nodes.Add("Hardware")
Dim tf As Form = Control.FromHandle(Form1.Handle)
tf.BeginInvoke(New Action(Function() InlineAssignHelper(item, n_node)))
End Sub
' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Private Shared Function InlineAssignHelper(ByRef target As RadTreeNode, ByVal value As RadTreeNode) As RadTreeNode
target.Nodes.Add(value.Clone)
Return target
End Function
End Class
Greate idea! I'll check it. By the way, there's no any secret in full code. It's just much more than 1st example. Here is the copy of complete sub zUpdate without some typical queries, which working fine in STA:
Private Shared Sub zUpdate(Of T)(anode As T)
Dim searcher As New ManagementObjectSearcher
Dim tt_node As RadTreeNode = TryCast(anode, RadTreeNode)
If tt_node Is Nothing Then
Return
End If
Dim t_node As String = tt_node.Name
Dim n_node As New RadTreeNode With {.Name = "_" & t_node, .Text = "_" & t_node}
Dim opt As New ConnectionOptions
opt.Authentication = AuthenticationLevel.PacketPrivacy
opt.EnablePrivileges = True
opt.Impersonation = ImpersonationLevel.Impersonate
opt.Username = CredentialCache.DefaultNetworkCredentials.UserName
opt.Password = CredentialCache.DefaultNetworkCredentials.Password
opt.Authority = "ntlmdomain:" & CredentialCache.DefaultNetworkCredentials.Domain
Dim scope As New ManagementScope("\\" & t_node & "\ROOT\CIMV2", opt)
Dim query As New ObjectQuery
If My.Computer.Network.Ping(t_node, 10) = False Then
Return
GoTo 1
End If
scope.Connect()
If Not scope.IsConnected Then
Return
GoTo 1
End If
'Summary
query.QueryString = "SELECT * FROM Win32_ComputerSystem"
searcher.Scope = scope
searcher.Query = query
n_node.Nodes.Add("Summary")
For Each queryobj As ManagementObject In searcher.Get
With n_node.Nodes("Summary")
.Nodes.Add("Name", "Name:" & queryobj("Name"), 6)
.Nodes.Add("Domain", "Domain:" & queryobj("Domain"), 6)
.Nodes.Add("Manufacturer", "Manufacturer:" & queryobj("Manufacturer"), 6)
.Nodes.Add("Model", "Model:" & queryobj("Model"), 6)
.Nodes.Add("NumberOfLogicalProcessors", "NumberOfLogicalProcessors:" & queryobj("NumberOfLogicalProcessors").ToString, 6)
.Nodes.Add("NumberOfProcessors", "NumberOfProcessors:" & queryobj("NumberOfProcessors").ToString, 6)
.Nodes.Add("TotalPhysicalMemory", "TotalPhysicalMemory:" & queryobj("TotalPhysicalMemory").ToString, 6)
.Nodes.Add("UserName", "UserName:" & queryobj("UserName"), 6)
.Nodes.Add("Workgroup", "Workgroup:" & queryobj("Workgroup"), 6)
End With
Next
'LogicalDisk
query.QueryString = "SELECT * FROM Win32_LogicalDisk"
searcher.Query = query
n_node.Nodes.Add("Hardware")
With n_node.Nodes("Hardware")
.Nodes.Add("LogicalDisks")
With .Nodes("LogicalDisks")
For Each queryobj As ManagementObject In searcher.Get
.Nodes.Add("Name", "Name" & ": " & queryobj("Name"), 6)
With .Nodes("Name")
.Nodes.Add("Description", "Description: " & queryobj("Description"), 6)
.Nodes.Add("DriveType", "DriveType: " & queryobj("DriveType"), 6)
.Nodes.Add("Size", "Size: " & queryobj("Size").ToString, 6)
.Nodes.Add("FreeSpace", "FreeSpace: " & queryobj("FreeSpace"), 6)
.Nodes.Add("VolumeName", "VolumeName: " & queryobj("VolumeName"), 6)
.Nodes.Add("VolumeSerialNumber", "VolumeSerialNumber: " & queryobj("VolumeSerialNumber"), 6)
End With
Next
End With
'network adapters
query.QueryString = "SELECT * FROM Win32_NetworkAdapterConfiguration"
searcher.Query = query
.Nodes.Add("NetworkAdapters")
With .Nodes("NetworkAdapters")
For Each queryobj As ManagementObject In searcher.Get
.Nodes.Add(CStr(queryobj("Description")))
With .Nodes(CStr(queryobj("Description")))
.Nodes.Add("DHCPServer", "DHCPServer: " & queryobj("DHCPServer"), 6)
.Nodes.Add("DNSDomain", "DNSDomain: " & queryobj("DNSDomain"), 6)
.Nodes.Add("DNSHostName", "DNSHostName: " & queryobj("DNSHostName"), 6)
.Nodes.Add("MACAddress", "MACAddress: " & queryobj("MACAddress"), 6)
.Nodes.Add("SettingID", "SettingID: " & queryobj("SettingID"), 6)
End With
Next
End With
End With
'software
query.QueryString = "SELECT * FROM Win32_Product"
searcher.Query = query
n_node.Nodes.Add("Software")
With n_node.Nodes("Software")
For Each queryobj As ManagementObject In searcher.Get
.Nodes.Add(queryobj("Name"))
With .Nodes(queryobj("Name"))
.Nodes.Add("InstallDate", "InstallDate: " & queryobj("InstallDate"), 6)
.Nodes.Add("IdentifyingNumber", "IdentifyingNumber: " & queryobj("IdentifyingNumber"), 6)
End With
Next
End With
Dim tf As Form = Control.FromHandle(Form2.Handle)
tf.BeginInvoke(New Action(Function() InlineAssignHelper(tt_node, n_node)))
1:
If Not searcher Is Nothing Then
searcher.Dispose()
scope = Nothing
End If
End Sub
Private Shared Function InlineAssignHelper(ByRef target As RadTreeNode, ByVal value1 As RadTreeNode) As RadTreeNode
Dim t_str As String = Now.Date.ToString & Now.TimeOfDay.ToString
target.Nodes.Add(t_str)
target.Nodes(t_str).Nodes.Add(value1.Clone)
Return target
End Function

Answer 1

This works fine in test app, but final application hangs after adding
code for calculations, and random number of results may absent.
I suspect this means that your problem may lay in the code that you are not showing us.
The most likely candidate is that the code in your real zupdate method is accessing some sort of shared resource that is deadlocking.