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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Mon, 26 Dec 2011 13:01:20 -0700
Subject: Re: Multithreading
To: Yigit Turgut <y.turgut@gmail.com>
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On Mon, Dec 26, 2011 at 11:31 AM, Yigit Turgut <y.turgut@gmail.com> wrote:
> I have a loop as following ;
>
> start =3D time.time()
> end =3D time.time() - start
> =A0while(end<N):
> =A0 =A0 =A0 =A0 =A0data1 =3D self.chan1.getWaveform()
> =A0 =A0 =A0 =A0 =A0end =3D time.time() - start
> =A0 =A0 =A0 =A0 =A0timer.tick(10) =A0#FPS
> =A0 =A0 =A0 =A0 =A0screen.fill((255,255,255) if white else(0,0,0))
> =A0 =A0 =A0 =A0 =A0white =3D not white
> =A0 =A0 =A0 =A0 =A0pygame.display.update()
> =A0 =A0 =A0 =A0 =A0for i in range(self.size):
> =A0 =A0 =A0 =A0 =A0 =A0 =A0end =3D time.time() - start
> =A0 =A0 =A0 =A0 =A0 =A0 =A0f.write("%3.8f\t%f\n"%(end,data1[i]))
>
> Roughly speaking, this loop displays something at 10 frames per second
> and writes data1 to a file with timestamps.
>
> At first loop data1 is grabbed but to grab the second value (second
> loop) it needs to wait for timer.tick to complete. When I change FPS
> value [timer.tick()], capturing period (time interval between loops)
> of data1 also changes. What I need is to run ;
>
> =A0 =A0 =A0 =A0 =A0timer.tick(10) =A0#FPS
> =A0 =A0 =A0 =A0 =A0screen.fill((255,255,255) if white else(0,0,0))
> =A0 =A0 =A0 =A0 =A0white =3D not white
> =A0 =A0 =A0 =A0 =A0pygame.display.update()
>
> for N seconds but this shouldn't effect the interval between loops
> thus I will be able to continuously grab data while displaying
> something at X fps.
>
> What would be an effective workaround for this situation ?

You essentially have two completely independent loops that need to run
simultaneously with different timings.  Sounds like a good case for
multiple threads (or processes if you prefer, but these aren:

def write_data(self, f, N):
    start =3D time.time()
    while self.has_more_data():
        data1 =3D self.chan1.getWaveform()
        time.sleep(N)
        for i in range(self.size):
            end =3D time.time() - start
            f.write("%3.8f\t%f\n" % (end, data[i]))

def write_data_with_display(self, f, N, X):
    thread =3D threading.Thread(target=3Dself.write_data, args=3D(f, N))
    thread.start()
    white =3D False
    while thread.is_alive():
        timer.tick(X)
        screen.fill((255, 255, 255) if white else (0, 0, 0))
        white =3D not white
        pygame.display.update()