jenkins

1. View available environment variables in Jenkins Slave machine"
In any jenkins job, click on 'Add Pre-build step' and 
choose either 'Execute Windows Batch Command' or 'Execute Shell'
This will show a text box to enter the batch/shell 
command and beneath this box, there will be link displayed as
See the list of available environment variables

 All multiple triggering of the same job while it is still running

Select check box -Concurrent Job