How To Mutex Across a Network?

Question

I have a desktop application that runs on a network and every instance connects to the same database.

So, in this situation, how can I implement a mutex that works a

Answer 1

In the past I have done the following:

1. Create a table that basically has two fields, function_name and is_running

2. I don't know what RDBMS you are using, but most have a way to lock individual records for update. Here is some pseduocode based on Oracle:

   BEGIN TRANS

   SELECT FOR UPDATE is_running FROM function_table WHERE function_name='foo';

   -- Check here to see if it is running, if not, you can set running to 'true'

   UPDATE function_table set is_running='Y' where function_name='foo';

   COMMIT TRANS

Now I don't have the Oracle PSQL docs with me, but you get the idea. The 'FOR UPDATE' clause locks there record after the read until the commit, so other processes will block on that SELECT statement until the current process commits.