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Full Discussion: Semaphore
Top Forums UNIX for Beginners Questions & Answers Semaphore Post 303015705 by uniran on Tuesday 10th of April 2018 01:39:41 PM
Old 04-10-2018
Semaphore
I was asked to add this piece of code to a c program which I will execute through the shell:

Code:
for(long i = 0; i < NITER; i++)
{ sem_wait( &sema);
count++;
sem_post( &sema); }

I didn't get it, which is the critical section ? if it's "count++" how would a thread wake up in order to enter it if the post comes after this critical section ?.
From my understanding post is the action that wakes up the thread in the queue, or increasing the semaphore by 1 if no threads are waiting.
 

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LEARN ABOUT MINIX

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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