I am new to socket programming and the solution at GPS Socket communication (CONCOX) helped me to most of the extent.
I have to track and capture all the data from all these 2500 vehicles. The listener I used from above sends data to database in batches and not continuously.
When I check the status of listener using netstat for port "8888" on which my listener is running, I see a huge list of CLOSE_WAIT and ESTABLISHED status' in the command window.
Can anyone hep me send data from all vehicles continuously to MSSQL Database?
Related
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Seems my question was asked nearly 10 years ago here...
Emulating accept() for UDP (timing-issue in setting up demultiplexed UDP sockets)
...with no clean and scalable solution. I think this could be solved handily by supporting listen() and accept() for UDP, just as connect() is now.
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In a followup to this question...
Can you bind() and connect() both ends of a UDP connection
...is there any mechanism to simultaneously bind() and connect()?
The reason I ask is that a multi-threaded UDP server may wish to move a new "session" to its own descriptor for scalability purposes. The intent is to prevent the listener descriptor from becoming a bottleneck, similar to the rationale behind SO_REUSEPORT.
However, a bind() call with a new descriptor will take over the port from the listener descriptor until the connect() call is made. That provides a window of opportunity, albeit briefly, for ingress datagrams to get delivered to the new descriptor queue.
This window is also a problem for UDP servers wanting to employ DTLS. It's recoverable if the clients retry, but not having to would be preferable.
connect() on UDP does not provide connection demultiplexing.
connect() does two things:
Sets a default address for transmit functions that don't accept a destination address (send(), write(), etc)
Sets a filter on incoming datagrams.
It's important to note that the incoming filter simply discards datagrams that do not match. It does not forward them elsewhere. If there are multiple UDP sockets bound to the same address, some OSes will pick one (maybe random, maybe last created) for each datagram (demultiplexing is totally broken) and some will deliver all datagrams to all of them (demultiplexing succeeds but is incredibly inefficient). Both of these are "the wrong thing". Even an OS that lets you pick between the two behaviors via a socket option is still doing things differently from the way you wanted. The time between bind() and connect() is just the smallest piece of this puzzle of unwanted behavior.
To handle UDP with multiple peers, use a single socket in connectionless mode. To have multiple threads processing received packets in parallel, you can either
call recvfrom on multiple threads which process the data (this works because datagram sockets preserve message boundaries, you'd never do this with a stream socket such as TCP), or
call recvfrom on a single thread, which doesn't do any processing, just queues the message to the thread responsible for processing it.
Even if you had an OS that gave you an option for dispatching incoming UDP based on designated peer addresses (connection emulation), doing that dispatching inside the OS is still not going to be any more efficient than doing it in the server application, and a user-space dispatcher tuned for your traffic patterns is probably going to perform substantially better than a one-size-fits-all dispatcher provided by the OS.
For example, a DNS (DHCP) server is going to transact with a lot of different hosts, nearly all running on port 53 (67-68) at the remote end. So hashing based on the remote port would be useless, you need to hash on the host. Conversely, a cache server supporting a web application server cluster is going to transact with a handful of hosts, and a large number of different ports. Here hashing on remote port will be better.
Do the connection association yourself, don't use socket connection emulation.
The issue you described is the one I encountered some time ago doing TCP-like listen/accept mechanism for UDP.
In my case the solution (which turned out to be bad as I will describe later) was to create one UDP socket to receive any incoming datagrams and when one arrives making this particular socket connected to sender (via recvfrom() with MSG_PEEK and connect()) and returning it to new thread. Moreover, new not connected UDP socket was created for next incoming datagrams. This way the new thread (and dedicated socket) did recv() on the socket and was handling only this particular channel from now on, while the main one was waiting for new datagrams coming from other peers.
Everything had worked well until the incoming datagram rate was higher. The problem was that while the main socket was transitioning to connected state, it was buffering not one but a few more datagrams (coming from many peers) and thus thread created to handle the particular sender was reading in effect a few more datagrams not intended to it.
I could not find solution (e.g. creating new connected socket (instead connecting the main one) and pass the received datagram on main socket to its receive buffer for futher recv()). Eventually, I ended up with N threads, each one having one "listening" socket (with use of SO_REUSEPORT) with datagram scattering done on OS level.
I'm New in Vb.net and I have got stuck with one problem.
I don't know how can I read data from UDP port continuously.
I am getting stream of bytes over my port and i want to read data from port and store it In queue so that I can process the received data accordingly.
help me.
suggest me how to do???
Sample codes are highly appreciated.
What you need to do is read the data from the port on a different (non blocking) thread.
This example on code project is a complete working example on how to do this
I'm trying to make a TCP connection between a server(in this case, my PC) and my telit gl865-dual modem.
I am connecting the modem via serial port(ftdi adaptor) and send or recieve data and commands directly my computer.
The connection can be established and data transmission can be done both ways. But when the modem sends data, there is a delay at least 3-5 seconds, the answer of server can be seen on module in miliseconds.
The commands I use(>> indicates the respond from module):
ad#sd = 1, 0, 4444, "myserversip"
>> CONNECT
Is there a way to arrange send time like server's?
Thanks.
This must be due to slow network.
Check your network speed, if good then you have to see your server side code, why it's delaying.
I have a server that at the minute that creates a new thread for each client connecting securely. If I use a thread pool this will mean that I will have a finite number of clients at once. However this means that I can not be listening on ports for all clients.
My idea is to have the client send a UDP packet with some ID linked to there connection so that they can re-establish the connect rather than lock up a thread for 10-60 seconds (server will keep the SSLsockets in memory). Is that a good way to solve the problem? - I don't see any security security vulnerabilities.
The server is java and the client is C++ not that effects the question.
Your question doesn't make sense. If the client wants to reconnect it should just open a new socket. You are positing at least one extra thread to listen to the UDP port and then ... what? It still has to use the thread pool to handle that client, if that is your self-imposed constraint, or else start a new thread, in which case you may as well not have had the thread pool constraint in the first place.
However this means I cannot be listening on ports for all clients.
No it doesn't. It just means that some clients will get delayed service while the thread pool is full, and a very few clients will get connection failure while the backlog queue is full. It doesn't impair your ability to listen for clients at all.
What if the only port you have say TCP/443 (HTTPS)? What if UDP is firewalled (very much possible)? In other words, you should NOT introduce UDP into this picture.
Even in thread-pool scenario, you can still know the difference between multiple clients who connected to the same server port.
Typical solution for this is to create set of sockets you are going to be watching for at once (in one thread) - in C/C++ it is typically done using select()/poll()/epoll(), and in Java you can use java.nio.
This way, if any client(s) have something to say to you as a server, your select loop will instantly notice that, serve these clients and go back to select(), which consumes very little (effectively 0) CPU usage.
This is an example how to do select loop in C and similar example in Java.
I have situation where I have to handle multiple live UDP streams in the server.
I have two options (as I think)
Single Socket :
1) Listen at single port on the server and receive the data from all clients on the same port and create threads for each client to process the data till the client stop sending.
Here only one port is used to receive the data and number of threads used to process the data.
Multiple Sockets :
2) Client will request open port from the server to send the data and the application will send the open port to the client and opens a new thread listening at the port to receive and process the data.Here for each client will have unique port to send the data.
I already implemented a way to know which packet is coming from which client in UDP.
I have 1000+ clients and 60KB data per second I am receiving.
Is there any performance issues using the above methods
or Is here any efficient way to handle this type of task in C ?
Thanks,
Raghu
With that many clients, having one thread per client is very inefficient since lots and lots of context switches must be performed.
Also, the number of ports you can open per IP is limited (port is a 16 bit number).
Therefore "Single Socket" will be far more efficient. But you can also use "Multipe Sokets" with just a single thread using the asynchronous API. If you can identify the client using the package's payload, then there is no need to have a port per client.