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• How to port signal() to sigaction() ?

  28 septembre 2016, par Shark

  due to recent problems discovered with NDK12 and NDK13b2, i’m thinking of ’porting’ libx264’s use of signal() (and missing bsd_signal() in ndk12) to use sigaction() instead.

  The problem is, I’m not quite sure what’s the simple&fastest way to replace signal() calls with sigaction() ones.

  For all i see, it’s mainly used in x264-snapshot/common/cpu.c in the following manner :

  using the following signal handler :

  static void sigill_handler( int sig )
  
  {
  
      if( !canjump )
  
      {
  
          signal( sig, SIG_DFL );
  
          raise( sig );
  
      }
  
  
  
      canjump = 0;
  
      siglongjmp( jmpbuf, 1 );
  
  }

  This is the problematic x264_cpu_detect function... currently, i’m guessing i only need to tackle the ARM version, but i’ ; ; still have to replace all occurances of signal() with sigaction() so i might just cover both of them to get the thing building...

  FYI - the NDK13 beta2 still has "unstable" libc and the build doesn’t fail on this part, but rather the first invocation of the rand() function somewhere else... So i’m out of luck and replacing the signal() calls might be better than just waiting for the official NDK13 release. I’m doing this to get rid of text-relocations so i can run the library (and doubango) on API 24 (Android N)

  the problematic part of function that invokes signal() :

  #elif SYS_LINUX
  
  
  
  uint32_t x264_cpu_detect( void )
  
  {
  
      static void (*oldsig)( int );
  
  
  
      oldsig = signal( SIGILL, sigill_handler );
  
      if( sigsetjmp( jmpbuf, 1 ) )
  
      {
  
          signal( SIGILL, oldsig );
  
          return 0;
  
      }
  
  
  
      canjump = 1;
  
      asm volatile( "mtspr 256, %0\n\t"
  
                    "vand 0, 0, 0\n\t"
  
                    :
  
                    : "r"(-1) );
  
      canjump = 0;
  
  
  
      signal( SIGILL, oldsig );
  
  
  
      return X264_CPU_ALTIVEC;
  
  }
  
  #endif
  
  
  
  #elif ARCH_ARM
  
  
  
  void x264_cpu_neon_test( void );
  
  int x264_cpu_fast_neon_mrc_test( void );
  
  
  
  uint32_t x264_cpu_detect( void )
  
  {
  
      int flags = 0;
  
  #if HAVE_ARMV6
  
      flags |= X264_CPU_ARMV6;
  
  
  
      // don't do this hack if compiled with -mfpu=neon
  
  #if !HAVE_NEON
  
      static void (* oldsig)( int );
  
      oldsig = signal( SIGILL, sigill_handler );
  
      if( sigsetjmp( jmpbuf, 1 ) )
  
      {
  
          signal( SIGILL, oldsig );
  
          return flags;
  
      }
  
  
  
      canjump = 1;
  
      x264_cpu_neon_test();
  
      canjump = 0;
  
      signal( SIGILL, oldsig );
  
  #endif
  
  
  
      flags |= X264_CPU_NEON;
  
  
  
      // fast neon -> arm (Cortex-A9) detection relies on user access to the
  
      // cycle counter; this assumes ARMv7 performance counters.
  
      // NEON requires at least ARMv7, ARMv8 may require changes here, but
  
      // hopefully this hacky detection method will have been replaced by then.
  
      // Note that there is potential for a race condition if another program or
  
      // x264 instance disables or reinits the counters while x264 is using them,
  
      // which may result in incorrect detection and the counters stuck enabled.
  
      // right now Apple does not seem to support performance counters for this test
  
  #ifndef __MACH__
  
      flags |= x264_cpu_fast_neon_mrc_test() ? X264_CPU_FAST_NEON_MRC : 0;
  
  #endif
  
      // TODO: write dual issue test? currently it's A8 (dual issue) vs. A9 (fast      mrc)
  
  #endif
  
      return flags;
  
  }
  
  
  
  #else
  
  
  
  uint32_t x264_cpu_detect( void )
  
  {
  
      return 0;
  
  }

  So the question is really this : what would be the quickest/easiest//fastest way to replace the signal() calls with sigaction() ones while preserving the current functionality ?

  EDIT :
  The reason i’m trying to get rid of signal() are these build errors :

  /home/devshark/SCRATCH/doubango/thirdparties/android/armv5te/lib/dist/libx264.a(cpu.o):cpu.c:function sigill_handler: error: undefined reference to 'bsd_signal'
  
  
  
  /home/devshark/SCRATCH/doubango/thirdparties/android/armv5te/lib/dist/libx264.a(cpu.o):cpu.c:function x264_cpu_detect: error: undefined reference to 'bsd_signal'
  
  /home/devshark/SCRATCH/doubango/thirdparties/android/armv5te/lib/dist/libx264.a(cpu.o):cpu.c:function x264_cpu_detect: error: undefined reference to 'bsd_signal'
  
  
  
  /home/devshark/SCRATCH/doubango/thirdparties/android/armv5te/lib/dist/libx264.a(cpu.o):cpu.c:function x264_cpu_detect: error: undefined reference to 'bsd_signal'

  I already know that this is a known NDK12 problem, that might be solved by bringing bsd_signal back to the libc in NDK13. However, in it’ beta state with it’s unstable libc - it’s currently missing the rand() function and simply waiting for it might not do the trick. But in the worst-case scenario, i guess i’ll just have to wait for it and retry after it’s release.

  But as it currently is, the prebuilt version of the library i want to use has text-relocations and is being rejected by phones running newer API / version of the android OS.

  EDIT2 :
  I also know that signal() usually works by using sigaction() under the hood, but maybe i won’t get bsd_signal related build-errors... since i’m suspecting that this one isn’t using it. It’s obviously using bsd_signal, which may or may not be the same underlying thing :/

• How do I run two indefinite loops simultaneously, while also changing variables within them ?

  11 octobre 2016, par Nyalmo

  I’m trying to write a script in Python that records a stream of an IP camera in realtime. It only keeps about a minute worth of recording, constantly overwriting the same files. Whenever an external sensor is triggered I want a variable to be set (event variable) which merges the recording with an extra 30 seconds it records after the sensor is triggered. The combined 90 seconds are then saved as the date and time for later review.

  The idea was to have 2 indefinite while loops, the first containing both the real time recording and the event. The second one would constantly read input and activate the ’event’ function. Initially I though I could just have a software version of the hardware interrupt I’ve learned before, though after some research it seems that’s only for exceptions. I’m currently using TkInter, simulating the external input with keypresses.

  When I tried it out the input wouldn’t cause the event to be triggered. So my question is : How do I run the two indefinite loops simultaneously, while also having the input loop change variables in the main loop so that the ’event’ can actually occur in real-time ?

  Since I’m using ffmpeg to record the stream, once the command is called to record it can’t be stopped, but I want the event variable to be changed as soon as possible.

  I’ve looked at several similar questions regarding multiple loops, and have tried multiprocessing(though this only seems to be used for performance, which is not that important here), making two separate files(not sure how to have them work together) and lastly, threads. None of these seem to work in my situation as I can’t get them running in the way that I want.

  Here is my latest attempt, using threads :

  i = 0
  
  event = False
  
  aboutToQuit = False
  
  someVar = 'Event Deactivated'
  
  lastVar = False
  
  
  
  def process(frame):
  
      print "Thread"
  
      i = 0    
  
      frame = frame 
  
      frame.bind("<space>", switch)
  
      frame.bind("<escape>", exit) 
  
      frame.pack()
  
      frame.focus_set()
  
  
  
  def switch(eventl):
  
      print(['Activating','Deactivating'][event])
  
      event = eventl
  
      event = not(event)
  
  
  
  def exit(eventl):
  
      print'Exiting Application'
  
      global aboutToQuit
  
      #aboutToQuit = True
  
      root.destroy()
  
  
  
  print("the imported file is", tkinter.__file__)
  
  def GetTime(): #function opens a script which saves the final merged file as date and time.
  
      time = datetime.datetime.now()
  
      subprocess.call("./GetTime.sh", shell = True)
  
      return (time)
  
  
  
  def main(root):
  
      global event, aboutToQuit, someVar,lastVar      
  
      while (not aboutToQuit):
  
          root.update() # always process new events
  
  
  
          if event == False:
  
              someVar = 'Event Deactivated'
  
              subprocess.call(Last30S_Command) #records last 30 seconds overwriting itself.
  
              print "Merge now"
  
              subprocess.call(Merge_Command) #merges last 30 seconds with the old 30 seconds       
  
              print "Shift now"
  
              subprocess.call(Shift_Command) #copies the last30s recording to the old 30 seconds, overwriting it.
  
              if lastVar == True: #Triggers only when lastVar state changes
  
                  print someVar
  
                  lastVar = False
  
              time.sleep(.1)
  
  
  
          if event == True: 
  
               someVar = 'Event Activated'
  
              print"Record Event"
  
              subprocess.call(EventRecord_Command) #records 30 seconds after event is triggered.
  
              print"EventMerge Now"
  
              subprocess.call(EventMerge_Command) # merges the 1 minute recording of Merge_Command with 30 seconds of EventRecord_Command
  
              if lastVar == False:
  
                  print someVar
  
                  lastVar = True
  
              time.sleep(.1)
  
              GetTime() #Saves 90 seconds of EventMerge_Command as date and time.
  
              subprocess.call(EventShift_Command) #Copies EventRecord file to the old 30 second recording, overwriting it
  
  
  
          if aboutToQuit:
  
             break
  
  
  
  
  
  if __name__ == "__main__":
  
      root = Tk() 
  
      frame = Frame(root, width=100, height=100)   
  
  #   maintthread = threading.Thread(target=main(root))
  
  #   inputthread = threading.Thread(target=process(frame))
  
  #   inputthread.daemon = True
  
  #   inputthread.start()
  
  #   maintthread.daemon = True
  
  #   maintthread.start()
  
  #   maintthread.join()
  
      Process(target=process(frame)).start()
  
      Process(target=main(root)).start()
  
      print "MainLoop"
  
  </escape></space>

• configure : Place all temporary files in one separate directory

  21 septembre 2014, par Michał Górny

  configure : Place all temporary files in one separate directory
  Place all temporary files within a single, quasi-atomically created
  
  temporary directory rather than relying on unsafe ’mktemp -u’. This
  
  prevents possible race conditions in case two parallel ’mktemp -u’ calls
  
  returned the same path. Additionally, it reduces TMPDIR pollution by
  
  keeping all test files in a single subdirectory.
  Signed-off-by : Diego Biurrun <diego@biurrun.de>
  

  • [DBH] configure