Jetbyte Tools Socket Programs
I am trying to construct a server that listens on a single port formultiple clients sending single UDP messages at frequent intervals foruse in a monitoring system.The server runs as a service and has no GUI hence my use ofIOCompletion ports.I am struggling with the use of IoCompletion ports in the workerthreads. Basically I need to get at the received datagrams sourceaddress (from a connectionless socket) such as I would get from therecvfrom function. However I have only had success when usingReadFile within the worker thread after GetQueuedCompletionStatuswhich doesn't of course provide that information. But using recvfromdoesn't seem to generate a completion signal either.I know there is a way to do what I need but I just haven't got my headaround it. Perhaps I can just set the socket non-blocking andinitialise an OVERLAPPED structure somehow so that recvfrom triggers acompletion event? But if so I can't figure out how.Can anybody suggest a solution?Thanks,-Steve.
Quote: which doesn't of course provide that information. But using recvfrom doesn't seem to generate a completion signal either.We have some sample code for a UDP socket server available here:www.jetbyte.com/zips/UDPEchoServer.zip.This uses RecvFrom and SendTo with IOCP.An article about the TCP version of this server can be found here:havent written up the UDP version yet.Hope this helps.-Len Holgateright code, right now.Contract Programming and Consulting Services. Quote: I am trying to construct a server that listens on a single port for multiple clients sending single UDP messages at frequent intervals for use in a monitoring system.
The server runs as a service and has no GUI hence my use of IOCompletion ports. I am struggling with the use of IoCompletion ports in the worker threads. Basically I need to get at the received datagrams source address (from a connectionless socket) such as I would get from the recvfrom function. However I have only had success when using ReadFile within the worker thread after GetQueuedCompletionStatus which doesn't of course provide that information.
But using recvfrom doesn't seem to generate a completion signal either. I know there is a way to do what I need but I just haven't got my head around it. Perhaps I can just set the socket non-blocking and initialise an OVERLAPPED structure somehow so that recvfrom triggers a completion event? But if so I can't figure out how. Can anybody suggest a solution?
Thanks, - Steve. I am trying to construct a server that listens on a single port for multiple clients sending single UDP messages at frequent intervals for use in a monitoring system.
The server runs as a service and has no GUI hence my use of IOCompletion ports. I am struggling with the use of IoCompletion ports in the worker threads. Basically I need to get at the received datagrams source address (from a connectionless socket) such as I would get from the recvfrom function. However I have only had success when using ReadFile within the worker thread after GetQueuedCompletionStatus which doesn't of course provide that information. But using recvfrom doesn't seem to generate a completion signal either. I know there is a way to do what I need but I just haven't got my head around it. Perhaps I can just set the socket non-blocking and initialise an OVERLAPPED structure somehow so that recvfrom triggers a completion event?
But if so I can't figure out how. Can anybody suggest a solution? Thanks, - SteveMany thanks to all those who responded, and I'm sorry I haven'tacknowledged you earlier - Christmas holidays got in the way!My problem stemmed from me remembering incorrectly that I could supplya NULL value for the flags parameter in WSARecvFrom as in RecvFrom andthen I got bitten by a bug in my error handler which ignored thatspecific return value!I now have a working prototype using a single socket (with REUSE) anda slightly better understanding of how the IOCP system works. Onething I'm unclear on though is whether it's better to:-a) initiate a single WSARecvFrom before starting the workerthreads and have them all wait on GetQueuedCompletionStatus. But thenit's slightly trickier for the workers to locate the buffer for theoriginal WSARecvFrom.orb) Get each worker thread to initiate a WSARecvFrom into a localauto buffer and then fall straight through toGetQueuedCompletionStatus.
I suppose this method doesn't need IOCP atall and could just block on a recvfrom.I suppose both methods would work but I'm just trying to get a feelfor what others do.For the final system I need to decide whether to have a single socketINANY, identify the client from the incoming packet, then copy datato client specific structures, or to bind a seperate socket to eachclient so I can pass context information to each thread inGetQueuedCompletionStatus. I suppose I would then initiate a pendingread on each socket before calling GetQueuedCompletionStatus in aworker thread. Just thinking out aloud and grateful for anysuggestions.One more question: By deliberately overloading the server such thatno threads were ready to handle incoming packets, I was surprised byhow many packets were queued by the system and correctly handledlater when a thread became ready again.Where are the packets buffered - in the NDIS layer or somewhere inWinsock? Can I check out what buffer space is available?Thanks again to all,-Steve.
Free Online Tcp Server
I am trying to construct a server that listens on a single port for multiple clients sending single UDP messages at frequent intervals for use in a monitoring system. The server runs as a service and has no GUI hence my use of IOCompletion ports. I am struggling with the use of IoCompletion ports in the worker threads. Basically I need to get at the received datagrams source address (from a connectionless socket) such as I would get from the recvfrom function. However I have only had success when using ReadFile within the worker thread after GetQueuedCompletionStatus which doesn't of course provide that information. But using recvfrom doesn't seem to generate a completion signal either. I know there is a way to do what I need but I just haven't got my head around it.
Perhaps I can just set the socket non-blocking and initialise an OVERLAPPED structure somehow so that recvfrom triggers a completion event? But if so I can't figure out how. Can anybody suggest a solution? Thanks- Steve Many thanks to all those who responded, and I'm sorry I haven't acknowledged you earlier - Christmas holidays got in the way! My problem stemmed from me remembering incorrectly that I could supply a NULL value for the flags parameter in WSARecvFrom as in RecvFrom and then I got bitten by a bug in my error handler which ignored that specific return value! I now have a working prototype using a single socket (with REUSE) and a slightly better understanding of how the IOCP system works. One thing I'm unclear on though is whether it's better to:- a) initiate a single WSARecvFrom before starting the worker threads and have them all wait on GetQueuedCompletionStatus.
But then it's slightly trickier for the workers to locate the buffer for the original WSARecvFrom. or b) Get each worker thread to initiate a WSARecvFrom into a local auto buffer and then fall straight through to GetQueuedCompletionStatus. I suppose this method doesn't need IOCP at all and could just block on a recvfrom. I suppose both methods would work but I'm just trying to get a feel for what others do. For the final system I need to decide whether to have a single socket INANY, identify the client from the incoming packet, then copy data to client specific structures, or to bind a seperate socket to each client so I can pass context information to each thread in GetQueuedCompletionStatus.
I suppose I would then initiate a pending read on each socket before calling GetQueuedCompletionStatus in a worker thread. Just thinking out aloud and grateful for any suggestions. One more question: By deliberately overloading the server such that no threads were ready to handle incoming packets, I was surprised by how many packets were queued by the system and correctly handled later when a thread became ready again.
Where are the packets buffered - in the NDIS layer or somewhere in Winsock? Can I check out what buffer space is available? Thanks again to all, - Steve. Quote: For the final system I need to decide whether to have a single socket INANY, identify the client from the incoming packet, then copy data to client specific structures, or to bind a seperate socket to each client so I can pass context information to each thread in GetQueuedCompletionStatus. I suppose I would then initiate a pending read on each socket before calling GetQueuedCompletionStatus in a worker thread. Just thinking out aloud and grateful for any suggestions.Another time the idea of IOCP is less threads for more clients ( scalabilitymean you grow from 1 to 10 to 100 to 1000 clients but you server live as for1.So first way in your thinking is IOCP way:)Arkady. Just addition to: For the final system I need to decide whether to have a single socket INANY, identify the client from the incoming packet, then copy data to client specific structures, or to bind a seperate socket to each client so I can pass context information to each thread in GetQueuedCompletionStatus.
I suppose I would then initiate a pending read on each socket before calling GetQueuedCompletionStatus in a worker thread. Just thinking out aloud and grateful for any suggestions.Another time the idea of IOCP is less threads for more clients ( scalabilitymean you grow from 1 to 10 to 100 to 1000 clients but you server live as for1.So first way in your thinking is IOCP way:)ArkadyThanks for your comments Arkady,If I choose to implement strategy (b) it still doesn't necessarilymandate a seperate thread for each client.
I think I'm right insaying I could still have lets say just 6 threads doing a blockinglisten on the same socket, set to listen to all clients without usingan I/O completion port. We're onl;y talking UDP and connectionlesssockets. However after looking at the processing load for each clientit looks to be more or less CPU bound, so I might not gain anyperformance benefit from multi-threading in this case after all.Performance wise it's probably a toss up between the time spent usinga single socket and looking up the in-memory client data on eachpacket using the source address, or binding a seperate socket to eachclient, using IOCP, and letting the winsock socket multiplexor & IOCPperform the context lookup for me.Happy new year and still grateful for any further observations andcomments!-Steve. Quote:Thanks for your comments Arkady,If I choose to implement strategy (b) it still doesn't necessarilymandate a seperate thread for each client. I think I'm right insaying I could still have lets say just 6 threads doing a blockinglisten on the same socket, set to listen to all clients without usingan I/O completion port.
We're onl;y talking UDP and connectionlesssockets. Quote:I can either:3) Just listen on a single socket set INADDRANY and in order to providecontext for each received packet identify the sender and look up my localstorage location myself.or4) Create a seperate bound socket for each LPD and start an initialreadfrom on each. Then use IOCP and GetQueuedCompletionStatus to providecontext for each packet.With (3) the server has to lookup the sender in a local table, in (4)winsock has to lookup the sender to identify a bound socket to providecontext for the packet handler.the sender's address is already returned in the pointers you give for the'from' address to WSARecvFrom. There isn't any extra lookup as far as winsockis concerned.
The information is always present. Quote: the sender's address is already returned in the pointers you give for the 'from' address to WSARecvFrom. There isn't any extra lookup as far aswinsock is concerned. The information is always present.Often, a server needs to know more than just the sender's address. Theremay be some state information associated with that client, and the sockethandle nor the sender's address does not provide a way to get at thatinformation directly.There are, of course, many ways to use that information or other informationto easily look up the client information. However, the information requiredcertainly is NOT always present, not in the way you mean.Pete. I can either:3) Just listen on a single socket set INADDRANY and in order to providecontext for each received packet identify the sender and look up my localstorage location myself.or4) Create a seperate bound socket for each LPD and start an initialreadfrom on each.
Online Tcp Client
Then use IOCP and GetQueuedCompletionStatus to providecontext for each packet.With (3) the server has to lookup the sender in a local table, in (4)winsock has to lookup the sender to identify a bound socket to providecontext for the packet handler.the sender's address is already returned in the pointers you give for theOf course - exactly so. Quote:'from' address to WSARecvFrom. There isn't any extra lookup as far as winsockis concerned. The information is always present.The 'extra lookup' is necessary for the server to determine where to storethe supplied data.
The server has to scan it's table for a matchingconnected client to locate a storage address.Alternatively, I could use IOCP and multiple sockets, and then winsockeffectively performs that client lookup for me by providing context infodirectly via GetQueuedCompletionStatus.As I've already said there is unlikely to be any performance differenceeither way - a table lookup is required whoever does it.Therefore I repeat - I don't see a performance benefit for this narrow casein using IOCP. I shall benchmark both approaches and checkout thedifference.Thanks for your comments.-Steve.
the sender's address is already returned in the pointers you give for the 'from' address to WSARecvFrom. There isn't any extra lookup as far aswinsock is concerned.
The information is always present.Often, a server needs to know more than just the sender's address. Theremay be some state information associated with that client, and the sockethandle nor the sender's address does not provide a way to get at thatinformation directly.There are, of course, many ways to use that information or other informationto easily look up the client information. However, the information requiredcertainly is NOT always present, not in the way you mean.PeteThe sender's ADDRESS is always present. That's all I meant. Quote:The 'extra lookup' is necessary for the server to determine where to storethe supplied data. The server has to scan it's table for a matchingconnected client to locate a storage address.Alternatively, I could use IOCP and multiple sockets, and then winsockeffectively performs that client lookup for me by providing context infodirectly via GetQueuedCompletionStatus.As I've already said there is unlikely to be any performance differenceeither way - a table lookup is required whoever does it.Therefore I repeat - I don't see a performance benefit for this narrow casein using IOCP. I shall benchmark both approaches and checkout thedifference.Let me try to explain this again:1.
As far as client addresses go, they're always present in TCP/IP, so there'sno lookup. But I realize that's not what you meant.2. If you have other context information to associate with the I/O, embed thatin the structure containing an OVERLAPPED.
There is NO 'extra lookup' that hasto be done by the OS to return this pointer to you. The overlapped pointer ispermanently associated with the I/O operation.Yes, you may have to have a hashtable or something similar to map a client toyour internal storage. However, there is no 'lookup' overhead in the kernel forGetQueuedCompletion.If you plan to have less than 100 sockets open, I see no reason not to use adifferent socket for each device.
Use connect to filter out the destinationfor each socket and then you don't even have to map anything. 1.I need to program a UDP server, and the server will communicate with manyclients and with a server database. I do not know which communicate model Ishould select: IOCP model or traditional asynchronous socket model. As wellknown, the UDP protocol is unreliable, so I think that I can asynchronouslysend a UDP packet and ignore the operation?s result. If what I thought isright, then I can easily use traditional asynchronous socket model.I would appreciate any comment!Thanks!Dolphin2.3.4.5.6.7.8.9.10.11.12.13.
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