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Send data between processes via QSharedMemory

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  • SGaistS Offline
    SGaistS Offline
    SGaist
    Lifetime Qt Champion
    wrote on last edited by
    #6

    What exact error are you getting ?

    Interested in AI ? www.idiap.ch
    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

    MR.SmithM 1 Reply Last reply
    0
    • SGaistS SGaist

      I don't remember if there's a limitation in the characters you can use as key, but i'd start with only ASCII stuff without any special signs.

      MR.SmithM Offline
      MR.SmithM Offline
      MR.Smith
      wrote on last edited by
      #7

      @SGaist I'm changed value of key to simple ASCII: "example".
      Not effect (((
      May be you have an example? I searching it in Google but only one example in qt.io was found.
      No any other(((

      1 Reply Last reply
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      • VRoninV Offline
        VRoninV Offline
        VRonin
        wrote on last edited by
        #8

        Probably off topic, but did you consider using QLocalSocket and WINAPI Named Pipe instead

        "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
        ~Napoleon Bonaparte

        On a crusade to banish setIndexWidget() from the holy land of Qt

        MR.SmithM 1 Reply Last reply
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        • VRoninV VRonin

          Probably off topic, but did you consider using QLocalSocket and WINAPI Named Pipe instead

          MR.SmithM Offline
          MR.SmithM Offline
          MR.Smith
          wrote on last edited by
          #9

          @VRonin Good idea. It's will be my fallback. I need to high speed data transfer (up to 10 MBit/s) and shared memory is a faster method of IPC. It's most suitable for my application.

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          • VRoninV Offline
            VRoninV Offline
            VRonin
            wrote on last edited by VRonin
            #10

            Disclaimer

            what follows is just speculation, not advice.


            The problem with shared memory, as I understand it, is that is no way to signal the reader application that new data is available to consume.

            10 MBit/s is not a lot, named pipe should be able to manage it without a problem, in fact, a TCP socket connected to localhost should also be able to handle that transfer rate without a sweat. Both their typical transfer rates are in the multiple Gbit/sec

            "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
            ~Napoleon Bonaparte

            On a crusade to banish setIndexWidget() from the holy land of Qt

            MR.SmithM 1 Reply Last reply
            2
            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #11

              Check the detailed documentation of QSharedMemory and the setNativeKey. They explain how to achieve communication with non Qt application.

              Interested in AI ? www.idiap.ch
              Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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              • SGaistS SGaist

                What exact error are you getting ?

                MR.SmithM Offline
                MR.SmithM Offline
                MR.Smith
                wrote on last edited by
                #12

                @SGaist When I run two copies of Ot application and write some data to shared memory from one of them and the next trying read data from another I have problem: sharedMemory.isAttached() == FALSE for shared memory with same keys.

                jsulmJ 1 Reply Last reply
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                • MR.SmithM MR.Smith

                  @SGaist When I run two copies of Ot application and write some data to shared memory from one of them and the next trying read data from another I have problem: sharedMemory.isAttached() == FALSE for shared memory with same keys.

                  jsulmJ Offline
                  jsulmJ Offline
                  jsulm
                  Lifetime Qt Champion
                  wrote on last edited by
                  #13

                  @MR.Smith Didn't you say before that it is working when using two Qt apps and doesn't work if one app is not a Qt app?

                  https://forum.qt.io/topic/113070/qt-code-of-conduct

                  MR.SmithM 1 Reply Last reply
                  0
                  • VRoninV VRonin

                    Disclaimer

                    what follows is just speculation, not advice.


                    The problem with shared memory, as I understand it, is that is no way to signal the reader application that new data is available to consume.

                    10 MBit/s is not a lot, named pipe should be able to manage it without a problem, in fact, a TCP socket connected to localhost should also be able to handle that transfer rate without a sweat. Both their typical transfer rates are in the multiple Gbit/sec

                    MR.SmithM Offline
                    MR.SmithM Offline
                    MR.Smith
                    wrote on last edited by
                    #14

                    @VRonin Thank you for recommendation. I will try to use named pipe in my application. It's also good solution for my application.

                    1 Reply Last reply
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                    • jsulmJ jsulm

                      @MR.Smith Didn't you say before that it is working when using two Qt apps and doesn't work if one app is not a Qt app?

                      MR.SmithM Offline
                      MR.SmithM Offline
                      MR.Smith
                      wrote on last edited by
                      #15

                      @jsulm Yes, it's true. I can transfer data from one Qt application to another copy of this Qt application, but I can't transfer data from Qt application to WinAPI application.

                      jsulmJ 1 Reply Last reply
                      0
                      • MR.SmithM MR.Smith

                        @jsulm Yes, it's true. I can transfer data from one Qt application to another copy of this Qt application, but I can't transfer data from Qt application to WinAPI application.

                        jsulmJ Offline
                        jsulmJ Offline
                        jsulm
                        Lifetime Qt Champion
                        wrote on last edited by
                        #16

                        @MR.Smith @SGaist pointed out what you should try

                        https://forum.qt.io/topic/113070/qt-code-of-conduct

                        1 Reply Last reply
                        1
                        • MR.SmithM Offline
                          MR.SmithM Offline
                          MR.Smith
                          wrote on last edited by
                          #17

                          I got successfully transfer data via named pipes. It's good solution and I will use it, not shared memory.
                          Thank you every one for your help and recommendations.

                          1 Reply Last reply
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