Functions in jmeter - __threadNum

Add a new Thread group to jmeter.

Add a java req sampler We call a function in jmeter using the syntax 

${__threadNum}
i.e double underscore followed by the function name.

 ${__threadNum}
which we can use in java req name to check the thread number i,e the number of user for which the reqs are executed rigt now if the number of users(or threads) for our thread group are more than 1

We can go to Options Function helper dialog and choose any function from dropdown and click help to see more about this function. We can then click generate and copy the generated function in our script if we are not sure about the syntax.