twisted.application.runner.

Interface	IPIDFile	Manages a file that remembers a process ID.
Class	PIDFile	Concrete implementation of `IPIDFile` based on `IFilePath`.
Class	NonePIDFile	PID file implementation that does nothing.
Class	AlreadyRunningError	Process is already running.
Class	InvalidPIDFileError	PID file contents are invalid.
Class	StalePIDFileError	PID file contents are valid, but there is no process with the referenced PID.
Class	NoPIDFound	No PID found in PID file.

twisted.application.runner._pidfile module documentation