CODEWITHSUNDEEP
c#multithreadinglistsockets
Amazing User
Amazing User

Reputation: 3563

Multiple access to List<Socket>

I develop the server in C# and have a question:

Let's say I have the List <Socket>, it have 20 objects, from the first object (socket) comes a message that I must:

or

Everything works correctly, if it is currently work one thread with List <Socket>. But if to List <Socket> suddenly turn 20 threads simultaneously (message arrived from everyone), which not only pass on the List and send a message, but also on the basis of the contents of the messages can close the socket and remove it from the List, then I do not know how to create atomic access and not lose productivity.

String targetIp, msg;

lock(socketListMutex)
{
    for(int i = 0; i < listSocket.Count; ++i)
    {
        if(listSocket.elementAt(i).targetIp == targetIp)
        {
            listSocket.sendTo(msg);
            break;
        }
    }
}

Edit 1:

What can happen:

Upvotes: 2

Views: 91

Answers (1)

noseratio
noseratio

Reputation: 61716

The following is based on my understanding of your question, while I'm not quite sure I understood it correctly.

A solution could be as simple as making a copy of the list of sockets, before processing it:

Socket[] sockets;
lock (socketListMutex) 
    sockets = listSocket.ToArray();

foreach (socket in sockets)
{
    // check the state of each socket object
    // and send a message if needed
}

Your requirements don't mention the situation when a new message arrive (possibly on a different socket) before the previous one has been fully processed. In this case, some additional logic would be required to preserve the order of the messages, like queuing.

On a side note, I don't think you need additional threads. Use asynchronous APIs instead:

foreach (socket in sockets)
{
    // send a message to each socket
    await Task.Factory.FromAsync(
        (asyncCallback, state) =>
            socket.BeginSend(buffer, offset, size, socketFlags, asyncCallback, state),
        (asyncResult) =>
            request.EndSend(asyncResult));
}

More on asynchronous socket operations:

Awaiting Socket Operations.

Some thoughts about the threading model of a TCP server app:

https://stackoverflow.com/a/21018042/1768303

Upvotes: 1

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