Parallel.Foreach with hangfire jobs

Suppose my hangfire server is running with 20 worker threads as shown in dashboard. If my code contains Parallel.Foreach - from where will it procure threads for parallelism. From hangfire server pool of 20 threads or from other available threads outside the server pool?

My jobs execute with Parallel.Foreach and I am facing high completion times when multiple jobs containing Parallel.foreach is executed. Time is low when single job is run.