Develop Reference

Data errors with my serial receive method

I'm taking data from a serial instrument for plotting on a chart. The data stream is 230 kbps, and the serial pipeline is less than 50% full, data arrives about 100 kbps and actually doesn't vary really and rate or quantity.
Having used just a serial terminal program, like Teraterm, on the same computer; I can capture data and prove that both the source of the data as well as the test reception method are fine and I see no errors to the captured data.
The Windows Forms application I'm developing loses data. I've reduced it from receiving, capturing (in parallel), parsing, and plotting, to just receiving and capturing. And have found that I still see lost data in the capture.
I'm not a long experienced Windows person, so therefore may not know of better ways to accomplish the same functions. Here are the actions I'm taking to perform receive actions:
I'm using a System.IO.Ports.SerialPort class.
I modify the .DataReceived event via:
+= new SerialDataReceivedEventHandler(comPort_DataReceive);
I then call the open() method.
Note: I may be doing something incorrect here, I never clear the .DataReceived event with a -= at any point, instead each time I open, the event is added yet again. Nevertheless, these problems occur even when I've only talked to the port once.
Here's my code for the data receive function. RxString is a string.
private void comPort_DataReceive(object sender, SerialDataReceivedEventArgs e)
{
RxString = comPort.ReadExisting();
this.Invoke(new EventHandler(ParseData));
}
private void ParseData(object sender, EventArgs e)
{
// Save to capture file, if capture is enabled
if ((WriteToFileEnabled == true) && (WriteToFileName != null))
{
writeFileHandle.Write(RxString);
}
return;
// Previously would parse and plot data
}
So, how would persons execute a receive in this situation to get this data without losing it?
Follow on questions are things like: How big is the buffer for serial receive, or do I need to worry about that if I have a reasonably responsive application? Flow control is irrelevant, the remote device is going to send data no matter what, so it would be up to my computer to take that data and process it or ignore it. But how would I know if I've lost data or experienced framing errors and stuff? (I ask that last one without having searched much on the SerialPort class structure, sorry.)

Lets assume that your device is sending messages that are 85 bytes in length. The DataReceive event handler may or may not fire once to receive those 85 bytes. Since it might fire more than once your code must account for that. The DataReceive event handler should read the bytes available and append them to a buffer that is processed later.
Also, only one of the events raised by the SerialPort class can execute at a time. In the example assume the handler has to fire three times to receive the 85 bytes. While processing the first part the other two can't execute. If while processing the first part one of the other events, PinChanged or ErrorReceived, are needed they can't be executed either.
My first two experiences with the SerialPort class were a 9600 bps terminal and a 1 Mbps bluetooth device. What worked for the slower did not work for the faster, but when I figured out how to get the faster to work the slower could use the same methodology.
My methodology:
Before opening the serial port I start two other background threads that run in a do loop. The first one(Receive) reads all available bytes from the serial port, adds them to a buffer, and signals the second thread on every read. The second one(Protocol) determines if a full message has arrived, does any byte to string conversion, updates the UI, etc. Depending on the application I may start a third thread that handles errors and pin changes. All of these threads are throttled by a Threading AutoResetEvent.
My DataReceive event handler has one line in it, a Set on the AutoResetEvent that is throttling Receive.
A VB example of this can be found here SerialPort Methodology. Since adopting this methodology I have not had any of the problems that seem to plague other SerialPort users and have used it successfully with speeds up to 2Mbps.

C# best way to implement TCP Client Server Application

I want to extend my experience with the .NET framework and want to build a client/server application.
Actually, the client/server is a small Point Of Sale system but first, I want to focus on the communication between server and client.
In the future, I want to make it a WPF application but for now, I simply started with a console application.
2 functionalities:
client(s) receive(s) a dataset and every 15/30min an update with changed prices/new products
(So the code will be in a Async method with a Thread.sleep for 15/30 mins).
when closing the client application, sending a kind of a report (for example, an xml)
On the internet, I found lots of examples but i can't decide which one is the best/safest/performanced manner of working so i need some advice for which techniques i should implement.
CLIENT/SERVER
I want 1 server application that handles max 6 clients. I read that threads use a lot of mb and maybe a better way will be tasks with async/await functionallity.
Example with ASYNC/AWAIT
http://bsmadhu.wordpress.com/2012/09/29/simplify-asynchronous-programming-with-c-5-asyncawait/
Example with THREADS
mikeadev.net/2012/07/multi-threaded-tcp-server-in-csharp/
Example with SOCKETS
codereview.stackexchange.com/questions/5306/tcp-socket-server
This seems to be a great example of sockets, however, the revisioned code isn't working completely because not all the classes are included
msdn.microsoft.com/en-us/library/fx6588te(v=vs.110).aspx
This example of MSDN has a lot more with Buffersize and a signal for the end of a message. I don't know if this just an "old way" to do this because in my previous examples, they just send a string from the client to the server and that's it.
.NET FRAMEWORK REMOTING/ WCF
I found also something about the remoting part of .NET and WCF but don' know if I need to implement this because i think the example with Async/Await isn't bad.
SERIALIZED OBJECTS / DATASET / XML
What is the best way to send data between it? Juse an XML serializer or just binary?
Example with Dataset -> XML
stackoverflow.com/questions/8384014/convert-dataset-to-xml
Example with Remoting
akadia.com/services/dotnet_dataset_remoting.html
If I should use the Async/Await method, is it right to something like this in the serverapplication:
while(true)
{
string input = Console.ReadLine();
if(input == "products")
SendProductToClients(port);
if(input == "rapport")
{
string Example = Console.ReadLine();
}
}

Here are several things anyone writing a client/server application should consider:
Application layer packets may span multiple TCP packets.
Multiple application layer packets may be contained within a single TCP packet.
Encryption.
Authentication.
Lost and unresponsive clients.
Data serialization format.
Thread based or asynchronous socket readers.
Retrieving packets properly requires a wrapper protocol around your data. The protocol can be very simple. For example, it may be as simple as an integer that specifies the payload length. The snippet I have provided below was taken directly from the open source client/server application framework project DotNetOpenServer available on GitHub. Note this code is used by both the client and the server:
private byte[] buffer = new byte[8192];
private int payloadLength;
private int payloadPosition;
private MemoryStream packet = new MemoryStream();
private PacketReadTypes readState;
private Stream stream;
private void ReadCallback(IAsyncResult ar)
{
try
{
int available = stream.EndRead(ar);
int position = 0;
while (available > 0)
{
int lengthToRead;
if (readState == PacketReadTypes.Header)
{
lengthToRead = (int)packet.Position + available >= SessionLayerProtocol.HEADER_LENGTH ?
SessionLayerProtocol.HEADER_LENGTH - (int)packet.Position :
available;
packet.Write(buffer, position, lengthToRead);
position += lengthToRead;
available -= lengthToRead;
if (packet.Position >= SessionLayerProtocol.HEADER_LENGTH)
readState = PacketReadTypes.HeaderComplete;
}
if (readState == PacketReadTypes.HeaderComplete)
{
packet.Seek(0, SeekOrigin.Begin);
BinaryReader br = new BinaryReader(packet, Encoding.UTF8);
ushort protocolId = br.ReadUInt16();
if (protocolId != SessionLayerProtocol.PROTOCAL_IDENTIFIER)
throw new Exception(ErrorTypes.INVALID_PROTOCOL);
payloadLength = br.ReadInt32();
readState = PacketReadTypes.Payload;
}
if (readState == PacketReadTypes.Payload)
{
lengthToRead = available >= payloadLength - payloadPosition ?
payloadLength - payloadPosition :
available;
packet.Write(buffer, position, lengthToRead);
position += lengthToRead;
available -= lengthToRead;
payloadPosition += lengthToRead;
if (packet.Position >= SessionLayerProtocol.HEADER_LENGTH + payloadLength)
{
if (Logger.LogPackets)
Log(Level.Debug, "RECV: " + ToHexString(packet.ToArray(), 0, (int)packet.Length));
MemoryStream handlerMS = new MemoryStream(packet.ToArray());
handlerMS.Seek(SessionLayerProtocol.HEADER_LENGTH, SeekOrigin.Begin);
BinaryReader br = new BinaryReader(handlerMS, Encoding.UTF8);
if (!ThreadPool.QueueUserWorkItem(OnPacketReceivedThreadPoolCallback, br))
throw new Exception(ErrorTypes.NO_MORE_THREADS_AVAILABLE);
Reset();
}
}
}
stream.BeginRead(buffer, 0, buffer.Length, new AsyncCallback(ReadCallback), null);
}
catch (ObjectDisposedException)
{
Close();
}
catch (Exception ex)
{
ConnectionLost(ex);
}
}
private void Reset()
{
readState = PacketReadTypes.Header;
packet = new MemoryStream();
payloadLength = 0;
payloadPosition = 0;
}
If you're transmitting point of sale information, it should be encrypted. I suggest TLS which is easily enabled on through .Net. The code is very simple and there are quite a few samples out there so for brevity I'm not going to show it here. If you are interested, you can find an example implementation in DotNetOpenServer.
All connections should be authenticated. There are many ways to accomplish this. I've use Windows Authentication (NTLM) as well as Basic. Although NTLM is powerful as well as automatic it is limited to specific platforms. Basic authentication simply passes a username and password after the socket has been encrypted. Basic authentication can still, however; authenticate the username/password combination against the local server or domain controller essentially impersonating NTLM. The latter method enables developers to easily create non-Windows client applications that run on iOS, Mac, Unix/Linux flavors as well as Java platforms (although some Java implementations support NTLM). Your server implementation should never allow application data to be transferred until after the session has been authenticated.
There are only a few things we can count on: taxes, networks failing and client applications hanging. It's just the nature of things. Your server should implement a method to clean up both lost and hung client sessions. I've accomplished this in many client/server frameworks through a keep-alive (AKA heartbeat) protocol. On the server side I implement a timer that is reset every time a client sends a packet, any packet. If the server doesn't receive a packet within the timeout, the session is closed. The keep-alive protocol is used to send packets when other application layer protocols are idle. Since your application only sends XML once every 15 minutes sending a keep-alive packet once a minute would able the server side to issue an alert to the administrator when a connection is lost prior to the 15 minute interval possibly enabling the IT department to resolve a network issue in a more timely fashion.
Next, data format. In your case XML is great. XML enables you to change up the payload however you want whenever you want. If you really need speed, then binary will always trump the bloated nature of string represented data.
Finally, as #NSFW already stated, threads or asynchronous doesn't really matter in your case. I've written servers that scale to 10000 connections based on threads as well as asynchronous callbacks. It's all really the same thing when it comes down to it. As #NSFW said, most of us are using asynchronous callbacks now and the latest server implementation I've written follows that model as well.

Threads are not terribly expensive, considering the amount of RAM available on modern systems, so I don't think it's helpful to optimize for a low thread count. Especially if we're talking about a difference between 1 thread and 2-5 threads. (With hundreds or thousands of threads, the cost of a thread starts to matter.)
But you do want to optimize for minimal blocking of whatever threads you do have. So for example instead of using Thread.Sleep to do work on 15 minute intervals, just set a timer, let the thread return, and trust the system to invoke your code 15 minutes later. And instead of blocking operations for reading or writing information over the network, use non-blocking operations.
The async/await pattern is the new hotness for asynchronous programming on .Net, and it is a big improvement over the Begin/End pattern that dates back to .Net 1.0. Code written with async/await is still using threads, it is just using features of C# and .Net to hide a lot of the complexity of threads from you - and for the most part, it hides the stuff that should be hidden, so that you can focus your attention on your application's features rather than the details of multi-threaded programming.
So my advice is to use the async/await approach for all of your IO (network and disk) and use timers for periodic chores like sending those updates you mentioned.
And about serialization...
One of the biggest advantages of XML over binary formats is that you can save your XML transmissions to disk and open them up using readily-available tools to confirm that the payload really contains the data that you thought would be in there. So I tend to avoid binary formats unless bandwidth is scarce - and even then, it's useful to develop most of the app using a text-friendly format like XML, and then switch to binary after the basic mechanism of sending and receiving data have been fleshed out.
So my vote is for XML.
And regarding your code example, well ther's no async/await in it...
But first, note that a typical simple TCP server will have a small loop that listens for incoming connections and starts a thread to hanadle each new connection. The code for the connection thread will then listen for incoming data, process it, and send an appropriate response. So the listen-for-new-connections code and the handle-a-single-connection code are completely separate.
So anyway, the connection thread code might look similar to what you wrote, but instead of just calling ReadLine you'd do something like "string line = await ReadLine();" The await keyword is approximately where your code lets one thread exit (after invoking ReadLine) and then resumes on another thread (when the result of ReadLine is available). Except that awaitable methods should have a name that ends with Async, for example ReadLineAsync. Reading a line of text from the network is not a bad idea, but you'll have to write ReadLineAsync yourself, building upon the existing network API.
I hope this helps.

Is it not possible for two timer_tick events to work in parallel in reading the same data but performing different tasks?

I developed a C# application for reading calls from GSM Modem. I used a timer to read the port regularly and notify me when there is a incoming call.
Now i am trying to use another timer which will write AT+CSQ -To know the signal quality, on the port and read the port for the quality value. In both the timers i used regular expressions to match and separate the data i need. Now the problem is that only my timer2 which is reading the signal quality is only working but not timer reading for incoming calls.
Timer reading signal strength:
private void tmr_sig_quality_Tick(object sender, EventArgs e)
{
if (port.IsOpen)
{
port.WriteLine("AT+CSQ");
string s= port.ReadExisting();
var match= Regex.Match(s,#"\+CSQ: (\d+),(\d+)");
if (match.Success)
{
progressBar1.Value = int.Parse(match.Groups[1].Value);
}
}
}
Timer reading incoming calls:
private void timer1_Tick(object sender, EventArgs e)
{
s = port.ReadExisting();
var match = Regex.Match(s, "RING[^\\+]*\\+CLIP:\\s*\"(?<phone>[^\"]*)\",(\\d+),\"([^\"]*)\",(\\w*),\"(\\w*)\",(\\w*)");
if (match.Success && s.Contains("RING"))
{
incall_status.Text = "Incoming Call...." + match.Groups["phone"].Value;
incall_status.Visible = true;
}
}
Why is this happening and solution please?

Two major problems. First is ReadExisting(), that will always return an empty string. Except when you are debugging and stepping through the code line by line. That gives the modem enough time to send the response. But this won't work when you run at full speed, you'll need to make a blocking call that ensures your program waits long enough to get all the returned characters. Use ReadLine() instead.
Second killer problem is that you are mixing commands. Your tmr_sig_quality_Tick() method is likely to read whatever timer1_Tick() was supposed to read. You'll need to re-think this approach. Something like a queue of commands that doesn't advance until the response to a command is received.

Not an actual answer to your question, but a general advice for communicating with a GSM modem:
Keep in mind that you have only one serial port, thus only one communication channel. A GSM modem can send spontaneous events, such as the RING, FAX, VOICE events, so there is no guarantee that when you write AT+CSQ the first reply is what you expect, i.e. the signal quality.
Having two timers like you're intending is not a good idea since you'll eventually end up with the response of one command in timer A when it was expected in B, because A read one of the spontaneous events...etc.
A much better and robust way is to have a worker thread that reads and interprets the incoming data and then distributes that in you application as needed. It can also handle the outgoing data. Use concurrent queues and some signaling mechanism (i.e. AutoResetEvent) for exchanging data with this thread, that way you get a cleaner interface to your hardware device and don't need to worry about timing and such in your application.

C# Winforms and NetworkStream.BeginRead(), how to open new form based on network event?

I'm having some serious troubles getting communication from one thread to another working between NetworkStream.BeginRead() and a WinForms class (I'm a real newbie when it comes to topics such as threading and Asynchronous calls).
In particular, I'm connected to a remote client via a net socket, simply listening for events. When I receive one, I can correctly collect it into a string using the BeginRead() and EndRead() methods of NetworkStream, no problems. I intend to then open up a new form (using the string as a parameter in the form's constructor) so that the information can be displayed to the user. Effectively, the network event will trigger a form for the user to be opened, and the information However, I'm constantly coming across CrossThreadMessagingExceptions, and I'm not familiar enough with delegates that I'm convinced I'm doing it right. Would someone be able to point me in the right direction?

The rule is: "You can only access controls on the thread on which they created"
You async callbacks are coming back on a different thread, so you need to marshal back to the UI thread if you want to communicate between forms.
Assuming you're NetworkStream code is already in a form, you just need to use Invoke or BeginInvoke. For example:
private void MyAsyncCallback(IAsyncResult ar)
{
var yourString = ...from your socket...;
this.Invoke(new MethodInvoker(() => new Form(yourString)));
}

Socket.SendAsync is not sending in-order on Mono/Linux

There is a a single-threaded server using .NET Socket with TCP protocol, and Socket.Pool(), Socket.Select(), Socket.Receive().
To send, I used:
public void SendPacket(int clientid, byte[] packet)
{
clients[clientid].socket.Send(packet);
}
But it was very slow when sending a lot of data to one client (halting the whole main thread), so I replaced it with this:
public void SendPacket(int clientid, byte[] packet)
{
using (SocketAsyncEventArgs e = new SocketAsyncEventArgs())
{
e.SetBuffer(packet, 0, packet.Length);
clients[clientid].socket.SendAsync(e);
}
}
It works fine on Windows with .NET (I don't know if it's perfect), but on Linux with Mono, packets are either dropped or reordered (I don't know). Reverting to slow version with Socket.Send() works on Linux. Source for whole server.
How to write non-blocking SendPacket() function that works on Linux?

I'm going to take a guess that it has to do with your using statement and your SendAsync call. Perhaps e falls out of scope and is being disposed while SendAsync is still processing the buffer. But then this might throw an exception. I am really just taking a guess. Try removing the using statement and see what happens.

I would say by not abusing the async method. YOu will find nowhere a documentation stating that this acutally is forced to maintain order. it queues iem for a scheuler which get distributed to threads, and by ignoring that the oder is not maintained per documentation you open yourself up to implementation details.
The best possibly is to:
Have a queue per socket.
When you write dasta into this queue, and there is no worker thread, start a work item (ThreadPool) to process the thread.
This way you have separate distinct queues that maintain order. Only one thread will ever process one queue / socket.

I got the same problem; Linux and windows react not in the same way with SendAsync. Sometimes linux truncate the data, but there is a workaround. First of all you need to use a queue. Each time you use SendAsync you have to check the callback.
If e.Offset + e.BytesTransferred < e.Buffer.Length, you just have to e.SetBuffer(e.Offset + e.BytesTransferred, e.Buffer.Length - e.BytesTransferred - e.Offset); and call SendAsync again.
I dont know why mono-linux believe it's completed before sending all the data and it's strange but i'm sure he does.

just like #mathieu, 10y later, I can confirm on Unity Mono+Linux complete callback is called without all bytes being sent in some cases. For me it was large packets only.