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    • Cedric Roux's avatar
      fix issue 227 - UE IP settings disrupts realtime · cff91499
      Cedric Roux authored
      see #227
      
      When the UE connects to the eNodeB and receives its IP address from the
      network, it calls system() to set it in the linux kernel world. This call
      is not done in a realtime thread, but in the NAS, which uses its own thread,
      independent of the realtime processing.
      
      In some situations this totally disrupts realtime processing.
      
      It is difficult to know precisely why that happens, but it seems that calling
      fork(), as system() does, in a multi-threaded program is not a good idea. (So
      say several people on the internet.) It is not clear why the softmodem is
      impacted, but it seems that fork() is really what triggers the disruption.
      Several tests lead to that conclusion.
      
      To fix the problem, we create a child background process very early in main()
      (before anything else basically). Then instead of calling system(), the main
      process sends the string to the background process. The background process
      gets the string, passes it to system() and reports the success/failure back
      to the main process.
      
      This solution involves a lot of system calls, but calling system() in the
      first place is not cheap either. As long as no realtime thread uses this
      mechanism, things should be fine. Time will tell.
      cff91499