System.Metronome

Synchronized execution of sequences of actions, controlled in STM

All data structures are made accessible via Data.Lens abstraction.

Actions to be executed are of type Action = STM (IO ()). At each tick, the scheduled actions are ordered by priority, binded as STM actions ignoring the retrying ones. The results, being IO actions are executed in that order.

Every Track and Metronome lives in its own thread and can be stopped or killed as such, setting a flag in its state.

Track and metronome state are exposed in TVar value to be modified at will. The only closed and inaccessible value is the synchronizing channel, written by the metronome and waited by tracks. The TrackForker returned by a metronome function is closing this channel and it's the only way to fork a track.

See System.Metronome.Practical for an simple wrapper around this module.

Data structures

data Track

State of a track.

Constructors

Track

Fields

_sync :: Ticks

the number of ticks elapsed from the track fork

_frequency :: Frequency

calling frequency relative to metronome ticks frequency

_actions :: [Action]

the actions left to be run

_priority :: Priority

priority of this track among its peers

_muted :: Bool

muted flag, when True, actions are not scheduled, just skipped

data Thread a

supporting values with running and alive flag

Constructors

Thread

Fields

_running :: Bool

stopped or running flag

_alive :: Bool

set to false to require kill thread

_core :: a

core data

data Metronome

State of a metronome

Constructors

Metronome

Fields

_ticks :: [MTime]

next ticking times

_schedule :: [(Priority, Action)]

actions scheduled for the tick to come

Lenses

sync :: Lens Track Ticks

frequency :: Lens Track Frequency

actions :: Lens Track [Action]

priority :: Lens Track Priority

muted :: Lens Track Bool

running :: forall a. Lens (Thread a) Bool

alive :: forall a. Lens (Thread a) Bool

core :: forall a. Lens (Thread a) a

ticks :: Lens Metronome [MTime]

schedule :: Lens Metronome [(Priority, Action)]

Synonyms

type Control a = TVar (Thread a)

A Thread value cell in STM

type Priority = Double

Priority values between tracks under the same metronome.

type Frequency = Integer

Number of metronome ticks between two track ticks

type Ticks = Integer

Number of elapsed ticks

type Action = STM (IO ())

Track effect interface. Write in STM the collective and spit out the IO action to be executed when all STMs for this tick are done or retried

type MTime = Double

Time, in seconds

type TrackForker = Control Track -> IO ()

The action to fork a new track from a track state.

API

metronome

Arguments

:: Control Metronome

initial state

-> IO TrackForker

Fork a metronome from its initial state