event number tracking Post: 95216

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Top Forums Shell Programming and Scripting event number tracking Post 95216 by matrixmadhan on Monday 9th of January 2006 06:17:46 AM

01-09-2006

Registered User

Quote:

Originally Posted by blowtorch

Use a lock file. Like this:

Code:

while [ -f /logs/lockfile ]; do
   sleep 2
done
touch /logs/lockfile
curevent=`tail -1 /logs/eventnums | cut -f1 -d" "`
eventnum=$(($curevent + 1))
echo "$eventnum event info" >>/logs/central_events.log
echo $eventnum > /logs/eventnums
rm /logs/lockfile

Before we do anything, we can check for existence of the lock file and loop while it exists. Then when we get the all clear, we touch a lock file and then get to work. Once the job is done, we remove the lock file and let other cron jobs get on with it.

--This is not tested--

torch,

if we are using a separate lock file to maintain integrity there is always a problem that it could be corrupted or accidentally deleted during processing.

here is a very similiary approach to yours, to make use of the existing file and work around with the permission bits

Code:

#check whether the file with sequence number is denied of read-access while [ ! -r <file_with_seqno> ] do sleep 1 done curevent=`tail -1 /logs/eventnums | cut -f1 -d" "` #revert the read permission to maintain integrity chmod -r <file_with_seqno> eventnum=$(($curevent + 1)) echo "$eventnum event info" >>/logs/central_events.log echo $eventnum > /logs/eventnums #reset the access permission as before chmod +r <file_with_seqno>

matrixmadhan

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LEARN ABOUT OPENDARWIN

update

update(n)						       Tcl Built-In Commands							 update(n)

__________________________________________________________________________________________________________________________________________________

NAME

       update - Process pending events and idle callbacks

SYNOPSIS

       update ?idletasks?
_________________________________________________________________

DESCRIPTION

       This command is used to bring the application ``up to date'' by entering the event loop repeatedly until all pending events (including idle
       callbacks) have been processed.

       If the idletasks keyword is specified as an argument to the command, then no new events or errors are processed;  only idle  callbacks  are
       invoked.   This causes operations that are normally deferred, such as display updates and window layout calculations, to be performed imme-
       diately.

       The update idletasks command is useful in scripts where changes have been made to the application's state and you  want	those  changes	to
       appear  on  the display immediately, rather than waiting for the script to complete.  Most display updates are performed as idle callbacks,
       so update idletasks will cause them to run.  However, there are some kinds of updates that only happen in response to events, such as those
       triggered by window size changes; these updates will not occur in update idletasks.

       The update command with no options is useful in scripts where you are performing a long-running computation but you still want the applica-
       tion to respond to events such as user interactions;  if you occasionally call update then user input will be  processed  during  the  next
       call to update.

SEE ALSO

       after(n), bgerror(n)

KEYWORDS

       event, flush, handler, idle, update

Tcl									7.5								 update(n)