Sequential state machine: libfprint Reference Manual

## Sequential state machine Sequential state machine — State machine helpers |

## Functions

void | (*FpiSsmCompletedCallback) ()
void | (*FpiSsmHandlerCallback) ()
#define | fpi_ssm_new()
FpiSsm * | fpi_ssm_new_full ()
void | fpi_ssm_free ()
void | fpi_ssm_start ()
void | fpi_ssm_start_subsm ()
void | fpi_ssm_next_state ()
void | fpi_ssm_next_state_delayed ()
void | fpi_ssm_jump_to_state ()
void | fpi_ssm_jump_to_state_delayed ()
void | fpi_ssm_cancel_delayed_state_change ()
void | fpi_ssm_mark_completed ()
void | fpi_ssm_mark_failed ()
void | fpi_ssm_set_data ()
gpointer | fpi_ssm_get_data ()
GError * | fpi_ssm_get_error ()
GError * | fpi_ssm_dup_error ()
int | fpi_ssm_get_cur_state ()
void | fpi_ssm_usb_transfer_cb ()

## Types and Values

| FpiSsm

## Description

Asynchronous driver design encourages some kind of state machine behind it. In most cases, the state machine is entirely linear - you only go to the next state, you never jump or go backwards. The FpiSsm functions help you implement such a machine.

e.g. `S1` ↦ `S2` ↦ `S3` ↦ `S4`

`S1` is the start state There is also an implicit error state and an implicit accepting state (both with implicit edges from every state).

You can also jump to any arbitrary state (while marking completion of the current state) while the machine is running. In other words there are implicit edges linking one state to every other state.

To create an fpi_ssm, you pass a state handler function and the total number of states (4 in the above example) to `fpi_ssm_new()`. Note that the state numbers start at zero, making them match the first value in a C enumeration.

To start a ssm, you pass in a completion callback function to `fpi_ssm_start()` which gets called when the ssm completes (both on error and on failure). Starting a ssm also takes ownership of it.

To iterate to the next state, call `fpi_ssm_next_state()`. It is legal to attempt to iterate beyond the final state - this is equivalent to marking the ssm as successfully completed.

To mark successful completion of a SSM, either iterate beyond the final state or call `fpi_ssm_mark_completed()` from any state. This will also invalidate the machine, freeing it.

To mark failed completion of a SSM, call `fpi_ssm_mark_failed()` from any state. You must pass a non-zero error code.

Your state handling function looks at the return value of `fpi_ssm_get_cur_state()` in order to determine the current state and hence which operations to perform (a switch statement is appropriate).

Typically, the state handling function fires off an asynchronous communication with the device (such as a libsub transfer), and the callback function iterates the machine to the next state upon success (or fails).

Your completion callback should examine the return value of `fpi_ssm_get_error()` in ordater to determine whether the FpiSsm completed or failed. An error code of zero indicates successful completion.

## Functions

### FpiSsmCompletedCallback ()

    void
    (*FpiSsmCompletedCallback) (FpiSsm *ssm,
                                FpDevice *dev,
                                GError *error);

The callback called when a state machine completes successfully, as set when calling `fpi_ssm_start()`.

#### Parameters

ssm | a FpiSsm state machine |
dev | the fp_dev fingerprint device |
error | The GError or `NULL` on successful completion. | [transfer full]

### FpiSsmHandlerCallback ()

    void
    (*FpiSsmHandlerCallback) (FpiSsm *ssm,
                              FpDevice *dev);

The callback called when a state machine transitions from one state to the next, as set when calling `fpi_ssm_new()`.

#### Parameters

ssm | a FpiSsm state machine |
dev | the fp_dev fingerprint device |

### fpi_ssm_new()

    #define             fpi_ssm_new(dev, handler, nr_states)

Allocate a new ssm, with `nr_states` states. The `handler` callback will be called after each state transition. This is a macro that calls `fpi_ssm_new_full()` using the stringified version of `nr_states` , so will work better with named parameters.

#### Parameters

dev | a fp_dev fingerprint device |
handler | the callback function |
nr_states | the number of states |

#### Returns

a new FpiSsm state machine

### fpi_ssm_new_full ()

    FpiSsm *
    fpi_ssm_new_full (FpDevice *dev,
                      FpiSsmHandlerCallback handler,
                      int nr_states,
                      const char *machine_name);

Allocate a new ssm, with `nr_states` states. The `handler` callback will be called after each state transition.

#### Parameters

dev | a fp_dev fingerprint device |
handler | the callback function |
nr_states | the number of states |
machine_name | the name of the state machine (for debug purposes) |

#### Returns

a new FpiSsm state machine

### fpi_ssm_free ()

    void
    fpi_ssm_free (FpiSsm *machine);

Frees a state machine. This does not call any error or success callbacks, so you need to do this yourself.

#### Parameters

machine | an FpiSsm state machine |

### fpi_ssm_start ()

    void
    fpi_ssm_start (FpiSsm *ssm,
                   FpiSsmCompletedCallback callback);

Starts a state machine. You can also use this function to restart a completed or failed state machine. The `callback` will be called on completion.

Note that `ssm` will be stolen when this function is called. So that all associated data will be free'ed automatically, after the `callback` is ran.

#### Parameters

ssm | an FpiSsm state machine. | [transfer full]
callback | the FpiSsmCompletedCallback callback to call on completion |

### fpi_ssm_start_subsm ()

    void
    fpi_ssm_start_subsm (FpiSsm *parent,
                         FpiSsm *child);

Starts a state machine as a child of another. if the child completes successfully, the parent will be advanced to the next state. if the child fails, the parent will be marked as failed with the same error code.

The child will be automatically freed upon completion or failure.

#### Parameters

parent | an FpiSsm state machine |
child | an FpiSsm state machine |

### fpi_ssm_next_state ()

    void
    fpi_ssm_next_state (FpiSsm *machine);

Iterate to next state of a state machine. If the current state is the last state, then the state machine will be marked as completed, as if calling `fpi_ssm_mark_completed()`.

#### Parameters

machine | an FpiSsm state machine |

### fpi_ssm_next_state_delayed ()

    void
    fpi_ssm_next_state_delayed (FpiSsm *machine,
                                int delay,
                                GCancellable *cancellable);

Iterate to next state of a state machine with a delay of `delay` ms. If the current state is the last state, then the state machine will be marked as completed, as if calling `fpi_ssm_mark_completed()`. Passing a valid GCancellable will cause the action to be cancelled when `cancellable` is.

#### Parameters

machine | an FpiSsm state machine |
delay | the milliseconds to wait before switching to the next state |
cancellable | a GCancellable to cancel the delayed operation. | [nullable]

### fpi_ssm_jump_to_state ()

    void
    fpi_ssm_jump_to_state (FpiSsm *machine,
                           int state);

Jump to the `state` state, bypassing intermediary states. If `state` is the last state, the machine won't be completed unless `fpi_ssm_mark_completed()` isn't explicitly called.

#### Parameters

machine | an FpiSsm state machine |
state | the state to jump to |

### fpi_ssm_jump_to_state_delayed ()

    void
    fpi_ssm_jump_to_state_delayed (FpiSsm *machine,
                                   int state,
                                   int delay,
                                   GCancellable *cancellable);

Jump to the `state` state with a delay of `delay` milliseconds, bypassing intermediary states. Passing a valid GCancellable will cause the action to be cancelled when `cancellable` is.

#### Parameters

machine | an FpiSsm state machine |
state | the state to jump to |
delay | the milliseconds to wait before switching to `state` state |
cancellable | a GCancellable to cancel the delayed operation. | [nullable]

### fpi_ssm_cancel_delayed_state_change ()

    void
    fpi_ssm_cancel_delayed_state_change (FpiSsm *machine);

### fpi_ssm_mark_completed ()

    void
    fpi_ssm_mark_completed (FpiSsm *machine);

Mark a ssm as completed successfully. The callback set when creating the state machine with `fpi_ssm_new()` will be called synchronously.

#### Parameters

machine | an FpiSsm state machine |

### fpi_ssm_mark_failed ()

    void
    fpi_ssm_mark_failed (FpiSsm *machine,
                         GError *error);

Mark a state machine as failed with `error` as the error code, completing it.

#### Parameters

machine | an FpiSsm state machine |
error | a GError. | [transfer full]

### fpi_ssm_set_data ()

    void
    fpi_ssm_set_data (FpiSsm *machine,
                      gpointer ssm_data,
                      GDestroyNotify ssm_data_destroy);

Sets `machine` 's data (freeing the existing data, if any).

#### Parameters

machine | an FpiSsm state machine |
ssm_data | a pointer to machine data. | [nullable]
ssm_data_destroy | GDestroyNotify for `ssm_data` . | [nullable]

### fpi_ssm_get_data ()

    gpointer
    fpi_ssm_get_data (FpiSsm *machine);

Retrieve the pointer to SSM data set with `fpi_ssm_set_ssm_data()`

#### Parameters

machine | an FpiSsm state machine |

#### Returns

a pointer

### fpi_ssm_get_error ()

    GError *
    fpi_ssm_get_error (FpiSsm *machine);

Returns the error code set by `fpi_ssm_mark_failed()`.

#### Parameters

machine | an FpiSsm state machine |

#### Returns

a error code.

[transfer none]

### fpi_ssm_dup_error ()

    GError *
    fpi_ssm_dup_error (FpiSsm *machine);

Returns the error code set by `fpi_ssm_mark_failed()`.

#### Parameters

machine | an FpiSsm state machine |

#### Returns

a error code.

[transfer full]

### fpi_ssm_get_cur_state ()

    int
    fpi_ssm_get_cur_state (FpiSsm *machine);

Returns the value of the current state. Note that states are 0-indexed, so a value of 0 means “the first state”.

#### Parameters

machine | an FpiSsm state machine |

#### Returns

the current state.

### fpi_ssm_usb_transfer_cb ()

    void
    fpi_ssm_usb_transfer_cb (FpiUsbTransfer *transfer,
                             FpDevice *device,
                             gpointer unused_data,
                             GError *error);

Can be used in as a FpiUsbTransfer callback handler to automatically advance or fail a statemachine on transfer completion.

Make sure to set the FpiSsm on the transfer.

#### Parameters

transfer | a FpiUsbTransfer |
device | a FpDevice |
unused_data | User data (unused) |
error | The GError or `NULL` |

## Types and Values

### FpiSsm

    typedef struct _FpiSsm FpiSsm;

Sequential state machine that iterates sequentially over a predefined series of states. Can be terminated by either completion or failure error conditions.