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
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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.
I have just learned that you can use a Thread pool for multi client TCP-connections, I have an C# application today that I like to implement this to. I have read some, for example the first answer to this question ( Best way to accept multiple tcp clients? ), but I dont really get how to make the last adjustments to work with my "needs". I have a messagehandeling function for each connection (each connection is 2 threads, one for recieving/sending messages (connection open for a long duration moste of the time) and one for doing Tasks depending on the messages (also creates answers to send back). I would now like to use the recieving method in the link below, but how can I do this with a thread pool in my example?
If anything is unclear, just ask questions!
/Nick
Just avoid having one thread per connection. It generate lot of overhead on the OS and doesn't scale well.
Today we use NIO : non blocking I/O. One thread can handle 10k+ connections. There are very easy way to use them, like NodeJs for example. NIO libraries are available for most platform/languages (Netty for Java, NodeJs with javascript,...).
You should specify wich language/environement you are using.
My question is to settle an argument with my co-workers on C++ vs C#.
We have implemented a server that receives a large amount of UDP streams. This server was developed in C++ using asynchronous sockets and overlapped I/O using completion ports. We use 5 completion ports with 5 threads. This server can easily handle a 500 Mbps throughput on a gigabit network without any lost of packets / error (we didn't push our tests farther than 500 Mbps).
We have tried to re-implement the same kind of server in C# and we have not been able to reach the same incoming throughput. We are using asynchronous receive using ReceiveAsync method and a pool of SocketAsyncEventArgs to avoid the overhead of creating new object for every receive call. Each SAEventArgs has a buffer set to it so we do not need to allocate memory for every receive. The pool is very, very large so we can queue more than 100 receive requests. This server is unable to handle an incoming throughput of more than 240 Mbps. Over that limit, we lose some packets in our UDP streams.
My question is this: should I expect the same performance using C++ sockets and C# sockets? My opinion is that it should be the same performance if memory is managed correctly in .NET.
Side question: would anybody know a good article/reference explaining how .NET sockets use I/O completion ports under the hood?
would anybody know a good article/reference explaining how .NET sockets use I/O completion ports under the hood?
I suspect the only reference would be the implementation (ie. Reflector or other assembly de-compiler). With that you will find that all asynchronous IO goes through an IO Completion Port with call backs being processed in the IO-thread pool (which is separate to the normal thread pool).
use 5 completion ports
I would expect to use a single completion port processing all the IO into a single pool of threads with one thread per pool servicing completions (assuming you are doing any other IO, including disk, asynchronously as well).
Multiple completion ports would make sense if you have some form of prioritisation going on.
My question is this: should I expect the same performance using C++ sockets and C# sockets?
Yes or no, depending on how narrowly you define the "using ... sockets" part. In terms of the operations from the start of the asynchronous operation until the completion is posted to the completion port I would expect no significant difference (all the processing is in the Win32 API or Windows kernel).
However the safety that the .NET runtime provides will add some overhead. Eg. buffer lengths will be checked, delegates validated etc. If the limit on the application is CPU then this is likely to make a difference, and at the extreme a small difference can easily add up.
Also the .NET version will occasionally pause for GC (.NET 4.5 does asynchronous collection, so this will get better in the future). There are techniques to minimise garbage accumulating (eg. reuse objects rather than creating them, make use of structures while avoiding boxing).
In the end, if the C++ version works and is meeting your performance needs, why port?
You can't do a straight port of the code from C++ to C# and expect the same performance. .NET does a lot more than C++ when it comes to memory management (GC) and making sure that your code is safe (boundary checks etc).
I would allocate one large buffer for all IO operations (for instance 65535 x 500 = 32767500 bytes) and then assign a chunk to each SocketAsyncEventArgs (and for send operations). Memory is cheaper than CPU. Use a buffer manager / factory to provide chunks for all connections and IO operations (Flyweight pattern). Microsoft does this in their Async example.
Both Begin/End and Async methods uses IO completion ports in the background. The latter doesn't need to allocate objects for each operation which boosts performance.
My guess is that you're not seeing the same performance because .NET and C++ are actually doing different things. Your C++ code may not be as safe, or check boundaries. Also, are you simply measuring the ability to receive the packets without any processing? Or does your throughput include packet processing time? If so, then the code you may have written to process the packets may not be as efficient.
I'd suggest using a profiler to check where the most time is being spent and trying to optimize that. The actual socket code should be quite performant.
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