Start the Same Job Only Once

Vercel's Workflow SDK helps programs run a planned set of steps. The new version stops repeated requests from starting the same job twice. Before, the program checked for an existing job and then started one. Another request could arrive during the gap between those two actions. That gap could let more than one job start by mistake.

The new method accepts a job and claims its token together. A token is a label that identifies the job being requested. It can use an order ID, invoice ID, or request ID. Only one job can own that label at a time. A repeated start returns an error instead of creating another job. The error also identifies the job that already owns the label.

The system can receive messages before the accepted job begins its steps. It keeps these early messages and gives them to the job in order. Inside the job, the program can use the label it already claimed. It does not need to create another place for the messages. A job can also use the label only to block repeated starts.

Teams can keep the label unavailable after the job has ended. The extra setting counts that time from the start of the job. This helps refuse repeated requests that arrive after the work is finished. Developers need to move to workflow 5.4.0 to use the update. The change joins two actions so repeated requests cannot start another job between them.