:sig
pid_t task_pid(String key)

:params
key : string uniquely identifying the task
return value : the process ID of the task

:see
>task

:content
Checks whether a process with the given `key` is running and returns its PID if it is.

Returns `0` when no matching task is active.

Related:

- PHP: background-process patterns using `proc_open()`, queues, cron, or worker supervisors
- JavaScript / Node.js: Node `child_process`, worker queues, timers, schedulers, and supervised background jobs