: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 anywhere in the runtime instance and returns its PID if it is.

Returns `0` when no matching task is active or task state cannot be read safely. Stale task status files are removed when the recorded PID is no longer alive.

New task status records include the Linux process start tick from `/proc/<pid>/stat`, so `task_pid()` can reject a stale status file if the PID has exited and the numeric PID has since been reused by another process.

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
