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Send data between processes via QSharedMemory

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  • 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(((

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    0
    • 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
      2
      • 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
              0
              • 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
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                • 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.

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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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