Thread: Shared memory between Apps

  1. #1
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    Shared memory between Apps

    Im working on a project that has two parts to it that need to communicate. One of the parts is a service that runs in the background that "dispatches" messages and one or more apps that "recieve" the messages. Im wondering how one can set up a shared memory space for all these programs to access. the information being passed back and forth is too big to stuff into a custom windows message.

    can someone provice any insight on this? any links or tutorials would be greatly appreciated

    EDIT: I believe, froma previous post, this type of system is called custom marshalling.
    Last edited by Mastadex; 05-09-2006 at 11:34 AM.

  2. #2
    Yes, my avatar is stolen anonytmouse's Avatar
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    You can use memory mapping.

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    Thanks alot. This is exactly what i need.

    The problem is that memory mapped files are not dynamically resizable, but i can always create new "pages" or even new mapped files to store this data. this is easy stuff.

    My question now is: will continuous shared memory calls slow down the system or fragment the PAGEFILE.SYS file? Is this the most efficient way of moving lots of continuous data between processes??
    Last edited by Mastadex; 05-10-2006 at 08:08 AM.
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  4. #4
    Yes, my avatar is stolen anonytmouse's Avatar
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    No, if you need to stream data between processes, you should use a pipe (see example 2, you can use BugMeNot to get a password). Communication between processes is known as interprocess communications.

  5. #5
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    Alright ill change my code to use pipes now. Since im going to have many processes communicating with one main process (a service), is it possible to have many processes connected to one pipe????
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  6. #6
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    You'll need a seperate pipe for each connecting process. You should google for Beej's Guide, it will show you how to set up a simple multi-client server.

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    Hmm, I opted out for WM_COPYDATA instead. The problem is now, how does one communicate with a service if services dont have a WndProc. Does this mean that the only optional route is to use pipes instead?

    EDIT: Apperently u can register a window using the bare bones. nothing but the WndProc filled into WinClassEx struct.

    Code:
    // Register class
    WinClass.cbSize			= sizeof(WNDCLASSEX); 
    WinClass.style			= NULL;//CS_OWNDC | CS_HREDRAW | CS_VREDRAW;
    WinClass.lpfnWndProc	= (WNDPROC) WndProc;
    WinClass.cbClsExtra		= 0;
    WinClass.cbWndExtra		= 0;
    WinClass.hInstance		= NULL;//hInstance;
    WinClass.hIcon			= NULL;//LoadIcon(hInstance, (LPCTSTR) "APP_ICON");
    WinClass.hCursor		= NULL;//LoadCursor(NULL, IDC_ARROW);
    WinClass.hbrBackground	= NULL;
    WinClass.lpszMenuName	= 0;
    WinClass.lpszClassName	= "bar";
    WinClass.hIconSm		= NULL;//LoadIcon(hInstance, (LPCTSTR) "APP_ICON");
    
    // Register the window
    RegisterClassEx(&WinClass);
    HWND me = CreateWindowEx(WS_EX_APPWINDOW, "bar", "bar", WS_POPUP | WS_CLIPSIBLINGS | WS_CLIPCHILDREN, 0, 0, 0, 0, NULL, NULL, NULL, NULL);

    I have all the essential stuff commented out that would make a window usable. The fact that its 0 by 0 pixels big and doesnt even have a pointer to the instance of itself.

    So if i put this in my service code, It should register the class and ill be able to send the messages into the WndProc of the service????
    Last edited by Mastadex; 05-11-2006 at 03:35 PM.
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