After sending pause signal (USR2) SerialWorker performs a job before it actually pauses

[berkcaputcu]

Since the check for paused worker is inside the jobs loop (/lib/qless/worker/serial.rb#L25-L36), SerialWorker needs to perform a job before it knows it's paused.

This check should be done before the reserver reserves a job, so the worker can be paused before it takes a job.