How to periodically execute a function in C ?? Post: 302152459

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Top Forums Programming How to periodically execute a function in C ?? Post 302152459 by Perderabo on Wednesday 19th of December 2007 11:00:25 PM

12-20-2007

Administrator Emeritus

WebKruncher, porter could be more diplomatic, but he does have a point. You are proposing something like:

Code:

trigger=time(NULL)+90;
while (1) {
         if (time(NULL)>trigger) {
                    trigger=time(NULL)+90;
                     do_something();
                     }
         usleep(10);
}

That is not a great way to arrange for something to happen every 90 seconds on any platform. If a process has nothing to do for 90 seconds, then it should do nothing during that 90 seconds. This is true on every platform. The problem is that you are busy looping waiting for 90 seconds to pass. If you replace "usleep(10)" with some code that does useful important work, then you basicly have a technique I would use to display a progress message as a very lengthy program runs. I don't care if the message is several seconds late. But the trigger test is in a main loop that is doing something useful. Take out the time test and my program remains useful. But take out your trigger test and you are left with:
while(1) usleep(10);
That puts quite a load on a system for no good reason.

If there is nothing to do in the loop but wait for 90 seconds to pass, I would simply use:

Code:

while (1) {
        do_something();
        sleep(90);
}

On every system I know, this is a much better solution than spinning in a loop waiting for 90 seconds to pass.

Why do want that loop running during the 90 second delay? Do you realize that the system is doing a lot of work that has no effect? If you are determined that you absolutely must have a loop spinning during the 90 second delay, you could improve the situation quite a bit by simply increasing usleep constant, say to 500000. Or replace it with sleep(1) or even sleep(10). You are still forcing the OS to run your process periodically. But at least not as often.

Perderabo

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LEARN ABOUT DEBIAN

ppmtosixel

ppmtosixel(1)						      General Commands Manual						     ppmtosixel(1)

NAME

       ppmtosixel - convert a portable pixmap into DEC sixel format

SYNOPSIS

       ppmtosixel [-raw] [-margin] [ppmfile]

DESCRIPTION

       Reads  a  portable  pixmap  as input.  Produces sixel commands (SIX) as output.	The output is formatted for color printing, e.g. for a DEC
       LJ250 color inkjet printer.

       If RGB values from the PPM file do not have maxval=100, the RGB values are rescaled.  A printer control header and a color assignment table
       begin the SIX file.  Image data is written in a compressed format by default.  A printer control footer ends the image file.

OPTIONS

       -raw   If  specified,  each  pixel  will  be explicitly described in the image file.  If -raw is not specified, output will default to com-
	      pressed format in which identical adjacent pixels are replaced by "repeat pixel" commands.  A raw file is often an order	of  magni-
	      tude larger than a compressed file and prints much slower.

       -margin
	      If  -margin  is not specified, the image will be start at the left margin (of the window, paper, or whatever).  If -margin is speci-
	      fied, a 1.5 inch left margin will offset the image.

PRINTING

       Generally, sixel files must reach the printer unfiltered.  Use the lpr -x option or cat filename > /dev/tty0?.

BUGS

       Upon rescaling, truncation of the least significant bits of RGB values may result in poor color conversion.  If the original PPM maxval was
       greater	than  100,  rescaling  also reduces the image depth.  While the actual RGB values from the ppm file are more or less retained, the
       color palette of the LJ250 may not match the colors on your screen.  This seems to be a printer limitation.

SEE ALSO

       ppm(5)

AUTHOR

       Copyright (C) 1991 by Rick Vinci.

								   26 April 1991						     ppmtosixel(1)

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