I'm doing an application in C#, with a server and some clients (not more than 60), and I would like to be able to deal with each client independently. The communication between server and client is simple but I have to wait for some ack's and I don't want to block any query.
So far, I've done two versions of the server side, one it's based on this:
http://aviadezra.blogspot.com.es/2008/07/code-sample-net-sockets-multiple.html
and in the other one, I basically create a new thread for each client. Both versions work fine...but I would like to know pros and cons of the two methods.
Any programming pattern to follow in this sort of situation?
To answer your question it's both. You have threads and classes running in those threads. Whether you use WCF, async, sockets, or whatever, you will be running some object in a thread (or shuffled around a threadpool like with async). With WCF you can configure the concurrency model, and if you have to wait for ack's or other acknowledgement you'd be best to set it to multiple threads so you don't block other requests.
In the example you linked to the author is using AsyncCallback as the mechanism for telling you that a socket has data. But, from the MSDN you can see:
Use an AsyncCallback delegate to process the results of an asynchronous operation in a separate thread
So it's really no different for small scale apps. Using async like this can help you avoid allocating stack space for each thread, if you were to do a large application this would matter. But for a small app I think it just adds complexity. C# 4.5+ and F# do a cleaner job with async, so if you can use something like that then maybe go for it.
Doing it the way you have, you have a single thread that is responsible for socket management. It'll sit and accept new connections. When it gets a request it hands that socket to a new dedicated thread that will then sit on that socket and read from it. This thread is your client connection. I like to encapsulate the socket client reading into a base class that can do the low level io required and then act as a router for requests. I.e. when I get request XYZ I'll do request ABC. You can even have it dispatch events and subscribe to those events elsewhere (like in the async example). Now you've decoupled your client logic from your socket reading logic.
If you do things with WCF you don't need sockets and all that extra handling, but you should still be aware that calls are multi-threaded and properly synchronize your application when applicable.
For 60 clients I think you should choose whatever works best for you. WCF is easy to set up and easy to work with, I'd use that, but sockets are fine too. If you are concerned about the number of threads running, don't be. While it's bad to have too many threads running, most of your threads will actually be blocked while they are waiting on IO. Threads that are in a wait state aren't scheduled by the OS and don't really matter. Not to mention the waiting is most likely is using io completion ports under the hood so the wait overhead is pretty much negligible for a small application like yours.
In the end, I'd go with whatever is easiest to write, maintain, and extend.
Related
I'm trying to build this server that receives connections on a socket, authenticates the user and then "sends" the socket to the class of the user that matches it(with the info given in the authentication), to be added to a thread pool (of the multiple devices of that client) to be processed (exchanging information, updating things elsewhere, etc..).
I chose to do it this way because I don't want to be sending requests to the server 24/7, just keep a lightweight thread open for each device, communicating with it in real time.
Now, all I've seen so far that might do something like this is Socket.DuplicateAndClose, but that works for processes, not threads.
So is anyone aware of any way to do this, or should I take a different approach?
Thank you.
EDIT:
It seemed that there was some confusion, what I meant was, move it to another Socket inside another class, then the threads open on that class will process it. If I accept the connection to authenticate it, that socket then is having that connection, beforehand I couldn't have known to accept it with the specific socket in the specific class because I didn't know where it came from, and now, I have a thread I can't do anything with because I can't tell that class to use this thread, because if I do and use it in a thread of that class, the next socket I use to accept the connection will be the one that's occupied by that same class. I could use a huge array to store accepted sockets and tell classes that that socket number was theirs, but that would not only be limited but a bunch of loose sockets as well, which would work but would be neither optimized or organized.
There is no restriction on which threads access a given socket.
Any thread can perform operations on any socket (providing the thread's process has an open handle to that thread).
Performing multiple IO operations of the same type (eg. two reads) concurrently on one socket is likely to lead to confusion – you cannot control which will get the next data, and it could then complete second. But any form of explicit or implicit concurrence control can be used to avoid that.
(The same applies to other kernel objects like files, named pipes, shared memory sections, semaphores, …. The only thing that is restricted is only the thread holding a mutex or critical section can release it.)
I have a C# application which listens for incoming TCP connections and receive data from previously accepted connections. Please help me whether i use Threadpool or Async methods to write the program?? Note that, once a connection is accepted, it doesn't close it and continuously receive data from the connection, at the same time it accept more connections
A threadpool thread works best when the code takes less than half a second and does not a lot of I/O that will block the thread. Which is exactly the opposite scenario you describe.
Using Socket.BeginReceive() is strongly indicated here. Highly optimized at both the operating level and the framework, your program uses a single thread to wait for all pending reads to complete. Scaling to handle thousands of active connections is quite feasible.
Writing asynchronous code cleanly can be quite difficult, variables that you'd normally make local variables in a method that runs on the threadpool thread turn into fields of a class. You need a state machine to keep track of the connection state. You'll greatly benefit from the async/await support available in C# version 5 which allows you to turn those state variables back into local variables. The little wrappers you find in this answer or this blog post will help a great deal.
It mainly depends on what do you want to do with your connections. If you have unknown number of connections which you don't know how long they will be open, I think it's better to do it with async calls.
But if you at least know the avg. number of connection and the connections are short-term connections like a web server's connections, then it's better to do it with threadpool since you won't waste time creating threads for each socket.
First off, if you possibly can, don't use TCP/IP. I recommend you self-host WebAPI and/or SignalR instead. But if you do decide to use TCP/IP...
You should always use asynchronous APIs for sockets. Ideally, you want to be constantly reading from the socket and periodically writing (keepalive messages, if nothing else). What you don't want to do is to have time where you're only reading (e.g., waiting for the next message), or time where you're only writing (e.g., sending a message). When you're reading, you should be periodically writing; and when you're writing, you should be continuously reading.
This helps you detect half-open connections, and also avoids deadlocks.
You may find my TCP/IP .NET Sockets FAQ helpful.
Definately use asynchronous sockets... It's never a good idea to block a thread waiting for IO.
If you decide you have high performance needs, you should consider using the EAP design pattern for your sockets.
This will allow you to create an asynchronous solution with a lower memory profile. However, some find that using events with sockets is awkard and a bit clunky... if you fall into this category, you could take a look at this blog post to use .NET 4.5's async/await keywords with it: http://blogs.msdn.com/b/pfxteam/archive/2011/12/15/10248293.aspx#comments
I was trying to think if I would get any scalability benefits from using BeginAccept vs just blocking in a dedicated thread waiting for connections. Obviously, the individual clients are going to use BeginXXX/EndXXX pairs to utilize IOCP for network IO, but I'm thinking waiting on a client connection should have very low latency. I plan on creating a Task to process incoming connections so my follow up code after the Accept is completed won't block the main accept thread for very long (long enough to create a Task object pretty much) and I can go right back to blocking on new connections. This is pretty much what I would do with BeginAccept/EndAccept only without the complexities of managing the asynchronous call.
So, my question is what, if any, scaleability benefits do I get by using IOCP for accept? Please note, this is not for sending / receiving on individual client sockets, but just for accepting connections on the server listening socket.
If you only have a single port you're listening on, it probably isn't worth it - just like if you only need to deal with a few connections at a time, you may not bother using asynchronous operations to handle those.
The server-side benefit of asynchrony is usually when you scale up - for handling connections, it's when you get a lot of connections; for BeginAccept it's when you're listening on a lot of different ports. That's probably rarer, but if you ever do want to listen to 100 different ports (e.g. if you host lots of web sites on one server and for some reason want to just listen on different ports instead of using Host headers) then you don't want 100 threads sitting around just consuming stack space.
I am writing a server that needs to serve a large number of clients. I am considering what is the best thread strategy to use: I read that the ThreadPool class on the .NET Framework allocates threads after taking into account parameters like the number of cores the machine is running on, which is great. However, if there is no thread available, it waits for one to become available.
The connections on my sockets may be fairly long, i.e. a thread may run for quite some time before it is done serving its client and terminating. Therefore, if I start a new thread for every socket, it is possible in theory for a large number of threads to be idle (waiting for data on the socket), yet still considered to be running, and thus preventing the ThreadPool from allocating new threads, and serving other clients. On the other hand, using a predefined number of threads to serve all sockets does not make an optimal use of the machine's multiple cores.
I am assuming there is a better way to do this... Any suggestions?
Thank you.
You want to be using asynchronous sockets. They utilize the thread pool but do not use up threads while waiting for data on the socket (i.e. they are non-blocking).
Don't allocate threads yourself. Use IIS, or Windows Process Activation Service: http://msdn.microsoft.com/en-us/library/ms733109.aspx
The .NET ThreadPool is much smarter than that. I'd recommend using either the Task/TaskScheduler framework or the APM model of the related FCL classes. That'll almost certainly be superior to any manual thread spawning strategy - unless you come up with one which beats'em all...
I highly recommend this video, Jeffrey Richter gives a talk about general multithreading and thread pooling. He also mentions the best strategies for server multithreading
I am trying to make an app that will pass data between two servers Connection1 and Conenction2 using sockets.What i would like to do is receive data from Connection1 and pass it to Connection2 and vice-versa.Connection1 and Conenction2 are on different threads. What is the best way to call methods on different threads in order to pass data back and forth between them.Both threads will use the same message object type to communicate in both directions between them.
Thanks
You should use immutable data transfer objects.
As long as a simple object is deeply immutable (meaning that neither it nor any of it's properties can change), there is nothing wrong with using it on multiple threads.
To pass the instances between threads, you might want to use a pseudo-mutable thread-safe stack. (This depends on your design)
If .NET 4 is an option, I'd strongly recommend having a look at the ConcurrentQueue<T> and possibly even wrapping it with a BlockingCollection<T> if that suits your needs.
That depends on what those threads are doing. While passing data between threads is relatively straight forward, waking the threads to process the data can be more tricky. When you design communication with a thread per/connection paradigm, your thread is almost all the time stuck in a Read method, like Socket.Receive. While in this state, other threads cannot actually wake this thread to have him send the data they want it sent. One solution is to have the Receive time out every second and check if it has data to transmit, but that just plain sucks.
Another idea is to have 2 threads per socket, one to Send one to Receive. But then all the advantages of having a thread per socket are gone: you are no longer able to have a simple state management of the 'session' in the thread code, you have a state shared between two threads and it's just a mess.
You can consider using async Receive instead: the socket thread posts a BeginReceive then waits on an event. The event is signaled by either the Receive completion or by the send queue having something 'dropped' in (or you can wait on multiple events, same thing basically). Now this would work, but at this moment you have a half-breed, part async part one-thread -per-socket. If you go down this path, I'd go the whole 9 yards: make the server fully async.
Going fully async would be the best solution. Instead of exchanging data between threads, completion routines operate on locked data. The Connection1 BeginReceive completes when it receives data, you parse the received data and analyze the content, then decide to send it on Connection2. So you invoke BeginSend on Connection2's socket, meaning the thread that received the data also send the data. This is much more efficient ans scales better than the thread-per-socket model, but the big disadvantage is that is just plain complicated if you're mot familiar with async and multithreaded programming.
See Asynchronous Server Socket Example and Asynchronous Client Socket Example for a primer.
What you are describing as asynchronous messaging. Microsoft has already written an app for this called MSMQ
I would use WCF on .NET 3.5 for this task, it will be more scalable. I'm using WCF for a lot of my works and its flawless. The good thing about it is you can share your data across any platform.
http://msdn.microsoft.com/en-us/netframework/aa663324.aspx