stdout buffer problem

[fxiao]

Hi, All,

I am a new member of this forum. I am transferring an C/C++ application from Solaris to Linux. The application use cursor movement to adjust the histogram of the medical images. The application works fine on Solaris for years. But on Linux, after cursor move for a short time, the image will freeze, the histogram won't be changed. I accidentally add a printf("\n") in the callback function of the cursor movement, then problem can be fixed. But there are a lot of blank line will show on the console. I try to use fflush(stdout) to replace printf("\n"). It doesn't work. Any idea and suggestion will be really appreciated. Thank you in advance.

Angela

[JosAH]

Hi, All,

I am a new member of this forum. I am transferring an C/C++ application from Solaris to Linux. The application use cursor movement to adjust the histogram of the medical images. The application works fine on Solaris for years. But on Linux, after cursor move for a short time, the image will freeze, the histogram won't be changed. I accidentally add a printf("\n") in the callback function of the cursor movement, then problem can be fixed. But there are a lot of blank line will show on the console. I try to use fflush(stdout) to replace printf("\n"). It doesn't work. Any idea and suggestion will be really appreciated. Thank you in advance.

Angela

I think that's a curses/ncurses problem. That library takes care of character
display devices and there are many implementations of it. If you have the
sources (I think you have), check the man pages and try to find a 'flush' call
which you can insert at tactical places.

Note that it is not a stdout 'flush' call, it flushes (n)curses' internal buffers.

kind regards,

Jos

[fxiao]

I think that's a curses/ncurses problem. That library takes care of character
display devices and there are many implementations of it. If you have the
sources (I think you have), check the man pages and try to find a 'flush' call
which you can insert at tactical places.

Note that it is not a stdout 'flush' call, it flushes (n)curses' internal buffers.

kind regards,

Jos

Thank you Jos. Do you mean I should add a ncurses flush call in my application code? I am not familiar with ncurses code. If yes, do you have any sample code I can reference? Our Solaris version application didn't use any curses/ncurses code. Is this a Linux problem? --Angela

[JosAH]

Thank you Jos. Do you mean I should add a ncurses flush call in my application code? I am not familiar with ncurses code. If yes, do you have any sample code I can reference? Our Solaris version application didn't use any curses/ncurses code. Is this a Linux problem? --Angela

Before you dig deeper into that (n)curses stuff, can you show some (relevant)
snippets of code? Maybe (n)curses has nothing to do with it; I was just guessing.

Is the output actually character based? Or are you staring at a gui of some sort?

kind regards,

Jos

[fxiao]

Before you dig deeper into that (n)curses stuff, can you show some (relevant)
snippets of code? Maybe (n)curses has nothing to do with it; I was just guessing.

Is the output actually character based? Or are you staring at a gui of some sort?

kind regards,

Jos

Thank you again, Jos. The output is not character based. We actually have the application control panel GUI which is displayed on the computer monitor (display 0), and have two medical viewboxes are installed as display 1 and display 2. The images are displayed on the two viewboxes. We use the control panel to control all image activities. One of the activities is using trackball to adjust the image histogram. We use USB trackball on Linux. It move faster than the PS/2 trackball on Solaris. Please see the following snippets of code.

void cursor_motion_callback(Widget w, XtPointer c, XEvent *event, Boolean *ctd)
{
    // add printf here to fix the image frozen problem, add fflush(stdout) here 
    // doesn't work
    // printf("\n") 
 
    if (!mouse_adjustment)
      return;
    ......
    window = (v_x / MOUSE_SCALE) + WINDOW_MIN;
    level = (v_y/MOUSE_SCALE) + LEVEL_MIN;
    window_level_change();
    ......
}

[JosAH]

Thank you again, Jos. The output is not character based. We actually have the application control panel GUI which is displayed on the computer monitor (display 0), and have two medical viewboxes are installed as display 1 and display 2. The images are displayed on the two viewboxes. We use the control panel to control all image activities. One of the activities is using trackball to adjust the image histogram. We use USB trackball on Linux. It move faster than the PS/2 trackball on Solaris. Please see the following snippets of code.

void cursor_motion_callback(Widget w, XtPointer c, XEvent *event, Boolean *ctd)
{
    // add printf here to fix the image frozen problem, add fflush(stdout) here 
    // doesn't work
    // printf("\n") 
 
    if (!mouse_adjustment)
      return;
    ......
    window = (v_x / MOUSE_SCALE) + WINDOW_MIN;
    level = (v_y/MOUSE_SCALE) + LEVEL_MIN;
    window_level_change();
    ......
}

So (n)curses has nothing to do with this; it's an X (XWindows) thing. It's still
like crystal ball staring to me as far as I can judge from here. The printf() hack
is most certainly a nono. What happens if you remove that little if-test?

OTOH was that method alterted specifically for Linux? Sorry that I can't give you
a more specific answer.

kind regards,

Jos

[fxiao]

So (n)curses has nothing to do with this; it's an X (XWindows) thing. It's still
like crystal ball staring to me as far as I can judge from here. The printf() hack
is most certainly a nono. What happens if you remove that little if-test?

OTOH was that method alterted specifically for Linux? Sorry that I can't give you
a more specific answer.

kind regards,

Jos

Thank you Jos. I can't remove that little if-test. If I do it, I'll get in a dead lock and I can't move the trackball to any where I want. The image frozen problem only happens on Linux. For Solaris, I don't need add printf("\n").

Angela

[JosAH]

Thank you Jos. I can't remove that little if-test. If I do it, I'll get in a dead lock and I can't move the trackball to any where I want. The image frozen problem only happens on Linux. For Solaris, I don't need add printf("\n").

Angela

You can't use that printf("\n") anyway because it would distort the image on your
screen. <thinking out loud> So you have multiple threads running; a printf()
yields control to another thread (or so I understood); if you don't use it the entire
thing locks up; not on Solaris but just on your Linux system. Is there another
way you can yield the current thread? Do you use pthreads?<thinking out loud/>

kind regards,

Jos