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POVNC viewer implementation
 

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    <p>Our team is implementing a VNC viewer (=VNC client) on Windows. The protocol (called RFB) is stateful, meaning that the viewer has to read 1 byte, see what it is, then read either 3 or 10 bytes more, parse them, and so on.</p> <p>We've decided to use asynchronous sockets and a single (UI) thread. Consequently, there are 2 ways to go: </p> <p>1) state machine -- if we get a block on socket reading, just remember the current state and quit. Later on, a socket notification will arrive and the interrupted logic will resume from the proper stage;</p> <p>2) inner message loop -- once we determine that reading from the socket would block, we enter an inner message loop and spin there until all the necessary data is finally received. UI is not thus frozen in case of a block.</p> <p>As experience showed, the second approach is bad, as any message can come while we're in the inner message loop. I cannot tell the full story here, but it simply is not reliable enough. Crashes and kludges.</p> <p>The first option seems to be quite acceptable, but it is not easy to program in such a style. One has to remember the state of an algorithm and values of all the local variables required for further processing.</p> <p>This is quite possible to use multiple threads, but we just thought that the problems in this case would be even much harder: synchronization of frame-buffer access, multi-threading issues, etc. Moreover, even in this variant it seems necessary to use asynchronous sockets as well.</p> <p>So, what way is in your opinion the best ?</p> <p>The problem is quite a general one. This is the problem of organizing asynchronous communication through stateful protocols.</p> <p><strong>Edit 1:</strong> We use C++ and MFC as UI framework.</p>
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    1. COWhich language? Async frameworks usually do a good job of shielding the dirty details of implementing a async IO loop, for e.g. Netty for Java etc.
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      1. USSanjay T. Sharma
    2. COC++ / MFC application.
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