Now on the client side we do have a number of atomic operations.
1) Set - set a resource value to a given value
2) Get - get the current value of a resource
3) Inc - Increment the current resource value and return the reult
4) Dec - Decrement the current resource value and return the result
5) set_limit - set a resource limit
6) get_limit - get a resource limit
7) stop - kills the server
All the calls require 3 parameters:
tag - the name of the resource (Resource_1 .. Resource_4)
opcode - (Set,Get, ... Stop)
value - a numerical value may be zero
For example to increment the 'Resource_1' value by 2 (host hostname timeout 5 seconds)
VAL=$(client.pl -h hostname -t 5 Resource_1 INC 2)
STAT=$?
if [ ${STAT} -eq 0 ]
then
echo "New Value = ${VAL}
fi
To stop the server:
client.pl -h hostname Resource_1 STOP 0
Basically, you can use these calls to loop until a resource reaches a value. Typicallly, the database startup script might SET a value and the co-operating process might loop getting the Resource value until it reaches 1 with a sleep in the loop.
You can start the server manually and the make interactive calls to client.pl to get an idea of how it works. The client and server can be on the same host but the real beauty of this comes into play when you are synchronizing tasks across many hosts.
Typically, I initially do a query of each host
to set the limit value. For example, when you start and you have 2 app servers, you might want to ping each. If you can ping both, the limit is set to 2 otherwise it is set to 1. This would avoid waiting on a resource that would never become available.
I hope I have been somewhat clear in this; it's really easier than it sounds.
Here's client.pl
If it ain't broke, I can fix that.
