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Web server problems

Started by OZ8ET, Jul 14 2013 08:29 AM

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8 replies to this topic

#1 OZ8ET

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LocationHundested, Denmark

Posted 14 July 2013 - 08:29 AM

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]Hi[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]I am running a web server on NP2 (previously on NP1) and it seems to run ok.[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]The problem is, when I start pushing it - a little too much processing for each received message combined with hysterical pushing the refresh button on the browser (more than 4 times in Debug mode - a little more en Release mode) - it falls over!.[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]I have tried most of the servers shown in this forum, and they usually works when testing, but when pushing them as above, the same thing happens. [/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]I have not been successful trying to multitask.[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]I have nailed Down the problem to the "socket.Accept" statement.[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]I get this exception: �[/color][color=rgb(30,30,30);]A first chance exception of type 'System.Net.Sockets.SocketException' occurred in Microsoft.SPOT.Net.dll[/color][color=rgb(34,34,34);]�, the first message is received and then everything stops. Other tasks (Onewire and display) are still running.[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]Questions:[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]Is there a limit to how many outstanding messages the socket Accept wil have? And if s� � how many?[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]Is there a way to overcome the problem?[/color][/font]

[font="arial, helvetica, sans-serif;"][color=rgb(34,34,34);]Any help is appreciated.[/color][/font]

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#2 Anthony Glenwright

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Posted 14 July 2013 - 09:48 AM

I believe the limit on sockets for the netduino is 16, and if you are hitting refresh madly then you could hit that limit easily enough. In my web server implementation, I have added a counter for active worker threads and a bit of code that does not create a new worker unless there are less than 4 workers running already. Also I added a setsockoption DontLinger and that seemed to help. With these two enhancements, the web server isn't fast, but it is reliable...

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#3 OZ8ET

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LocationHundested, Denmark

Posted 14 July 2013 - 11:34 AM

Thanks Anthony.

It sounds like a good solution. Could you share some code please?

Erik

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#4 Anthony Glenwright

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Posted 14 July 2013 - 11:25 PM

The SetSocketOption call goes in between your listening socket's bind and listen calls:

mobjListenSocket = New Socket(AddressFamily.InterNetwork,SocketType.Stream, ProtocolType.Tcp)mobjListenSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, True)mobjListenSocket.Bind(New IPEndPoint(IPAddress.Any, Me.Port))mobjListenSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.DontLinger, True)mobjListenSocket.Listen(32)

The worker thread governor code consists of an ArrayList where I add in each worker thread as it is created, and a loop to check that there are less than MAX_WORKERS running:

Public Sub StartNewWorker(ByRef AcceptSocket As Socket)  Dim intWorkerCount As Integer = -1  ' If MAX_WORKERS is reached wait for a worker to complete  Do Until intWorkerCount <> -1 AndAlso intWorkerCount < MAX_WORKERS	        SyncLock mobjWorkerThreads      intWorkerCount = 0      If mobjWorkerThreads.Count <> 0 Then       For intWorkerIndex As Integer = (mobjWorkerThreads.Count - 1) To 0 Step -1			           If DirectCast(mobjWorkerThreads(intWorkerIndex), Thread).IsAlive Then			               ' only count the threads that are active			               intWorkerCount = intWorkerCount + 1			           End If		           Next      End If    End SyncLock	        ' thread limit reached, wait and try again    If intWorkerCount >= MAX_WORKERS Then      Thread.Sleep(100)      ' todo: timeout?  Loop  ' Create new worker thread  Dim objWorker As New HTTPServerWorker(AcceptSocket)  AddHandler objWorker.JSONRequest, AddressOf OnJSONRequest	    AddHandler objWorker.ConnectWebSocket, AddressOf ConnectWebSocket  Dim objWorkerThread As New Thread(New ThreadStart(AddressOf objWorker.ExecuteRequest))	    objWorkerThread.Start()  ' Add to thread pool  SyncLock mobjWorkerThreads	        mobjWorkerThreads.Add(objWorkerThread)	        Debug.Print("New worker thread added.  Worker Thread Count: " & mobjWorkerThreads.Count.ToString)  End SyncLockEnd Sub

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#5 Anthony Glenwright

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Posted 14 July 2013 - 11:34 PM

PS: The web server is a substantially modified version of http://www.microframework.nl

Also if you implement the worker thread governor you will need to add in periodic calls to this function, to remove completed threads from the arraylist.

Private Sub MonitorConnections() ' Endless loop While Thread.CurrentThread.ThreadState <> ThreadState.AbortRequested ' Allow other processes some time. The pause needs to be long enough that this process doesn't have a SyncLock on mobjWorkerThreads ' all of the time, but short enough that completed threads are removed from the thread pool in a timely manner Thread.Sleep(750)

' Lock Thread Pool If mobjWorkerThreads.Count <> 0 Then SyncLock mobjWorkerThreads Me.ActivityLED.SwitchOn()

If mobjWorkerThreads.Count <> 0 Then For intWorkerIndex As Integer = (mobjWorkerThreads.Count - 1) To 0 Step -1 ' If the thread has finished, remove it If Not DirectCast(mobjWorkerThreads(intWorkerIndex), Thread).IsAlive Then ' Remove worker from list mobjWorkerThreads.RemoveAt(intWorkerIndex) Debug.Print("Worker #" & intWorkerIndex.ToString() & " has stopped, removing from pool. New Worker Pool Count: " & mobjWorkerThreads.Count.ToString) Debug.GC(True) End If Next End If End SyncLock Else Me.ActivityLED.SwitchOff() End If End While End Sub

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#6 Anthony Glenwright

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Posted 14 July 2013 - 11:36 PM

By the way, I implemented the thread governor to stop the Netduino from running out of memory rather than running out of sockets - so you might just want to start with the .SetSocketOption call and see how you go.