Atomicity Post: 50847

Sponsored Content

Top Forums Programming Atomicity Post 50847 by S.P.Prasad on Tuesday 4th of May 2004 07:53:17 AM

05-04-2004

Registered User

Thanks for the information, Driver.

Quote:

Process 2 now gets to execute, finds the shared variable zero too and writes its PID to it. Then process 1 gets to execute again and overwrites the PID of the other process.

The second if takes care such that only one process has the right to execute code:

Quote:

if (shared_variable_One = = getpid ( ) )
{
if ( ++ shared_variable_two > 1 ) /* Variable Shared Across Processes Initially initialized as 0*/
goto RERUN:
/* Set the bit value */
shared_variable_One = 0 ;
shared_variable_two = 0 ;
}

I hope that I am clear.

Quote:

I'm now sure why shared libraries come into play now ...

Shared libraries (also called dynamic libraries) are linked into the program in two stages. First, during compile time, the linker verifies that all the symbols (again, functions, variables and the like) required by the program, are either linked into the program, or in one of its shared libraries. However, the object files from the dynamic library are not inserted into the executable file. Instead, when the program is started, a program in the system (called a dynamic loader) checks out which shared libraries were linked with the program, loads them to memory, and attaches them to the copy of the program in memory.

The complex phase of dynamic loading makes launching the program slightly slower, but this is a very insignificant drawback, that is out-weighted by a great advantage - if a second program linked with the same shared library is executed, it can use the same copy of the shared library, thus saving a lot of memory. Only one copy of the library is stored in memory at any given time. This means we can use far less memory to run our programs, and the executable files are much smaller, thus saving a lot of disk space as well.

Hence if I write LOCK() and REL() subroutines as a part of Shared Library and link it to the executable, will not aid me to make the operations atomic. I can easily validate in the subroutines which address is requested for locking and which for release.

Thanks in advance.

I personally thank Driver and Perderabo for their interest shown to solve the issue. Please continue aiding me till we conclude to a unanimous decision.

S.P.Prasad

View Public Profile for S.P.Prasad

Find all posts by S.P.Prasad

LEARN ABOUT LINUX

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)