PID file.
| Interface | IPIDFile | Manages a file that remembers a process ID. |
| Class | PIDFile | Concrete implementation of IPIDFile. |
| Class | NonePIDFile | PID file implementation that does nothing. |
| Variable | nonePIDFile | Undocumented |
| 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. |