The ironic.common.fsm Module

State machine modelling, copied from TaskFlow project.

This work will be turned into a library. See https://github.com/harlowja/automaton

This is being used in the implementation of: http://specs.openstack.org/openstack/ironic-specs/specs/kilo/new-ironic-state-machine.html

class ironic.common.fsm.FSM(start_state=None)

Bases: object

A finite state machine.

This class models a state machine, and expects an outside caller to manually trigger the state changes one at a time by invoking process_event

add_state(state, on_enter=None, on_exit=None, target=None, terminal=None, stable=False)

Adds a given state to the state machine.

The on_enter and on_exit callbacks, if provided will be expected to take two positional parameters, these being the state being exited (for on_exit) or the state being entered (for on_enter) and a second parameter which is the event that is being processed that caused the state transition.

Parameters:

• stable – Use this to specify that this state is a stable/passive state. A state must have been previously defined as ‘stable’ before it can be used as a ‘target’
• target – The target state for ‘state’ to go to. Before a state can be used as a target it must have been previously added and specified as ‘stable’

add_transition(start, end, event)

Adds an allowed transition from start -> end for the given event.

copy(shallow=False)

Copies the current state machine (shallow or deep).

NOTE(harlowja): the copy will be left in an uninitialized state.

NOTE(harlowja): when a shallow copy is requested the copy will share

the same transition table and state table as the source; this can be advantageous if you have a machine and transitions + states that is defined somewhere and want to use copies to run with (the copies have the current state that is different between machines).

initialize(state=None)

Sets up the state machine.

sets the current state to the specified state, or start_state if no state was specified..

is_valid_event(event)

Check whether the event is actionable in the current state.

process_event(event)

Trigger a state change in response to the provided event.