Atomicity Post: 50813

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Top Forums Programming Atomicity Post 50813 by S.P.Prasad on Monday 3rd of May 2004 09:26:53 AM

05-03-2004

Registered User

First of all I would thank Driver for all the technical support and aid that he has provided.

Driver as you have stated that:

Quote:

lock(resources.semid);
if (data[1].used == 0 && data[2].used == 0) {
data[1].used = 1;
data[2].used = 1;
} else {
unlock(resources.semid);
/* Wait for 1 and 2 to become free */
}
unlock(resources.semid);

We have more than 10 process and in each process it has to LOCK or REL the LOCK for a specific array. One specific process cannot lock or release for more than one resource at a time. As per your pseudo-code then we need to have as many number of SEMAPHORES as there are number of arrays and LOCK / REL piece of code should be injected where locking and releasing of the resource comes into picture within the process. That would include a lot of re-work in the project. Will it be time efficient?

That is what I have posted the same in initial post.

Yes your pseudo-code would work fine if through out the processes we make a check that for a specific array the mapped SEMAPHORE key would lock or unlock the resource.

Thanks Driver, your solution is definitely a valuable one. I will build up a set of test executables implementing your pseudo-code.

Also please let me know if the pseudo-code I posted in my initial post is ok or not?

Thanks in advance.

Last edited by S.P.Prasad; 05-03-2004 at 10:34 AM..

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LEARN ABOUT BSD

shlock

SHLOCK(1)						      General Commands Manual							 SHLOCK(1)

NAME
       shlock - create lock files for use in shell scripts

SYNOPSIS
       shlock -p pid -f name [ -b ] [ -u ] [ -c ]

DESCRIPTION
       Shlock  tries  to  create  a  lock  file named name and write the process ID pid into it.  If the file already exists, shlock will read the
       process ID from the file and test to see if the process is currently running.  If the process exists, then the file will not be created.

       Shlock exits with a zero status if it was able to create the lock file, or non-zero if the file refers to currently-active process.

OPTIONS
       -b     Process IDs are normally read and written in ASCII.  If the ``-b'' flag is used, then they will be written as  a	binary	int.   For
	      compatibility with other systems, the ``-u'' flag is accepted as a synonym for ``-b'' since binary locks are used by many UUCP pack-
	      ages.

       -c     If the ``-c'' flag is used, then shlock will not create a lock file, but will instead use the file to see if the	lock  is  held	by
	      another  program.   If  the  lock  is  valid, the program will exit with a non-zero status; if the lock is not valid (i.e., invoking
	      shlock without the flag would have succeeded), then the program will exit with a zero status.

EXAMPLES
       The following example shows how shlock would be used within a shell script:
	      LOCK=/var/run/innd/LOCK.send
	      trap 'rm -f ${LOCK} ; exit 1' 1 2 3 15
	      if shlock -p $$ -f ${LOCK} ; then
		  # Do appropriate work
	      else
		  echo Locked by `cat ${LOCK}`
	      fi

HISTORY
       Written by Rich $alz <rsalz@uunet.uu.net> after a description of HDB UUCP locking given by Peter Honeyman.  This  is  revision  1.9,  dated
       1996/10/29.

																	 SHLOCK(1)