defmodule Membrane.Element.Action do
@moduledoc """
This module contains type specifications of actions that can be returned
from element callbacks.
Returning actions is a way of element interaction with
other elements and parts of framework. Each action may be returned by any
callback unless explicitly stated otherwise.
"""
alias Membrane.{Buffer, ChildNotification, Clock, Event, Pad, StreamFormat}
@typedoc """
Sends a message to the parent.
"""
@type notify_parent_t :: {:notify_parent, ChildNotification.t()}
@typedoc """
Sends an event through a pad (input or output).
Allowed only when playback is `playing`.
"""
@type event_t :: {:event, {Pad.ref_t(), Event.t()}}
@typedoc """
Allows to split callback execution into multiple applications of another callback
(called from now sub-callback).
Executions are synchronous in the element process, and each of them passes
subsequent arguments from the args_list, along with the element state (passed
as the last argument each time).
Return value of each execution of sub-callback can be any valid return value
of the original callback (this also means sub-callback can return any action
valid for the original callback, unless explicitly stated). Returned actions
are executed immediately (they are NOT accumulated and executed after all
sub-callback executions are finished).
Useful when a long action is to be undertaken, and partial results need to
be returned before entire process finishes (e.g. default implementation of
`c:Membrane.Filter.handle_process_list/4` uses split action to invoke
`c:Membrane.Filter.handle_process/4` with each buffer)
"""
@type split_t :: {:split, {callback_name :: atom, args_list :: [[any]]}}
@typedoc """
Sends stream format through a pad.
The pad must have output direction. Sent stream format must fit constraints on the pad.
Allowed only when playback is `playing`.
"""
@type stream_format_t :: {:stream_format, {Pad.ref_t(), StreamFormat.t()}}
@typedoc """
Sends buffers through a pad.
The pad must have output direction.
Allowed only when playback is playing.
"""
@type buffer_t :: {:buffer, {Pad.ref_t(), Buffer.t() | [Buffer.t()]}}
@typedoc """
Makes a demand on a pad.
The pad must have input direction and work in pull mode. This action does NOT
entail _sending_ demand through the pad, but just _requesting_ some amount
of data from pad's internal queue, which _sends_ demands automatically when it
runs out of data.
If there is any data available at the pad, the data is passed to
`c:Membrane.Filter.handle_process_list/4`, `c:Membrane.Endpoint.handle_write_list/4`
or `c:Membrane.Sink.handle_write_list/4` callback. Invoked callback is
guaranteed not to receive more data than demanded.
Demand size can be either a non-negative integer, that overrides existing demand,
or a function that is passed current demand, and is to return the new demand.
Allowed only when playback is playing.
"""
@type demand_t :: {:demand, {Pad.ref_t(), demand_size_t}}
@type demand_size_t :: pos_integer | (pos_integer() -> non_neg_integer())
@typedoc """
Executes `c:Membrane.Element.WithOutputPads.handle_demand/5` callback
for the given pad if its demand is greater than 0.
The pad must have output direction and work in pull mode.
## Redemand in Sources and Endpoints
In case of Sources and Endpoints, `:redemand` is just a helper that simplifies element's code.
The element doesn't need to generate the whole demand synchronously at `handle_demand`
or store current demand size in its state, but it can just generate one buffer
and return `:redemand` action.
If there is still one or more buffers to produce, returning `:redemand` triggers
the next invocation of `handle_demand`. In such case, the element is to produce
next buffer and call `:redemand` again.
If there are no more buffers demanded, `handle_demand` is not invoked and
the loop ends.
One more advantage of the approach with `:redemand` action is that produced buffers
are sent one after another in separate messages and this can possibly improve
the latency.
## Redemand in Filters
Redemand in Filters is useful in a situation where not the entire demand of
output pad has been satisfied and there is a need to send a demand for additional
buffers through the input pad.
A typical example of this situation is a parser that has not demanded enough
bytes to parse the whole frame.
## Usage limitations
Allowed only when playback is playing.
"""
@type redemand_t :: {:redemand, Pad.ref_t()}
@typedoc """
Sends buffers/stream format/event to all output pads of element (or to input pads when
event occurs on the output pad).
Used by default implementations of
`c:Membrane.Element.WithInputPads.handle_stream_format/4` and
`c:Membrane.Element.Base.handle_event/4` callbacks in filter.
Allowed only when _all_ below conditions are met:
- element is filter,
- callback is `c:Membrane.Filter.handle_process_list/4`,
`c:Membrane.Element.WithInputPads.handle_stream_format/4`
or `c:Membrane.Element.Base.handle_event/4`,
- playback is `playing`
Keep in mind that `c:Membrane.Filter.handle_process_list/4` can only
forward buffers, `c:Membrane.Element.WithInputPads.handle_stream_format/4` - stream formats
and `c:Membrane.Element.Base.handle_event/4` - events.
"""
@type forward_t ::
{:forward, Buffer.t() | [Buffer.t()] | StreamFormat.t() | Event.t() | :end_of_stream}
@typedoc """
Starts a timer that will invoke `c:Membrane.Element.Base.handle_tick/3` callback
every `interval` according to the given `clock`.
The timer's `id` is passed to the `c:Membrane.Element.Base.handle_tick/3`
callback and can be used for changing its interval via `t:timer_interval_t/0`
or stopping it via `t:stop_timer_t/0`.
If `interval` is set to `:no_interval`, the timer won't issue any ticks until
the interval is set with `t:timer_interval_t/0` action.
If no `clock` is passed, parent's clock is chosen.
Timers use `Process.send_after/3` under the hood.
"""
@type start_timer_t ::
{:start_timer,
{timer_id :: any, interval :: Ratio.t() | Membrane.Time.non_neg_t() | :no_interval}
| {timer_id :: any, interval :: Ratio.t() | Membrane.Time.non_neg_t() | :no_interval,
clock :: Clock.t()}}
@typedoc """
Changes interval of a timer started with `t:start_timer_t/0`.
Permitted only from `c:Membrane.Element.Base.handle_tick/3`, unless the interval
was previously set to `:no_interval`.
If the `interval` is `:no_interval`, the timer won't issue any ticks until
another `t:timer_interval_t/0` action. Otherwise, the timer will issue ticks every
new `interval`. The next tick after interval change is scheduled at
`new_interval + previous_time`, where previous_time is the time of the latest
tick or the time of returning `t:start_timer_t/0` action if no tick has been
sent yet. Note that if `current_time - previous_time > new_interval`, a burst
of `div(current_time - previous_time, new_interval)` ticks is issued immediately.
"""
@type timer_interval_t ::
{:timer_interval,
{timer_id :: any, interval :: Ratio.t() | Membrane.Time.non_neg_t() | :no_interval}}
@typedoc """
Stops a timer started with `t:start_timer_t/0` action.
This action is atomic: stopping timer guarantees that no ticks will arrive from it.
"""
@type stop_timer_t :: {:stop_timer, timer_id :: any}
@typedoc """
This action sets the latency for the element.
This action is not premitted in callback `c:Membrane.Element.Base.handle_init/2`.
"""
@type latency_t :: {:latency, latency :: Membrane.Time.non_neg_t()}
@typedoc """
Marks that processing via a pad (output) has been finished and the pad instance
won't be used anymore.
Triggers `end_of_stream/3` callback at the receiver element.
Allowed only when playback is in playing state.
"""
@type end_of_stream_t :: {:end_of_stream, Pad.ref_t()}
@typedoc """
Terminates element with given reason.
Termination reason follows the OTP semantics:
- Use `:normal` for graceful termination. Allowed only when the parent already requested termination,
i.e. after `c:Membrane.Element.Base.handle_terminate_request/2` is called
- If reason is neither `:normal`, `:shutdown` nor `{:shutdown, term}`, an error is logged
"""
@type terminate_t :: {:terminate, reason :: :normal | :shutdown | {:shutdown, term} | term}
@typedoc """
Type that defines a single action that may be returned from element callbacks.
Depending on element type, callback, current playback and other
circumstances there may be different actions available.
"""
@type t ::
event_t
| notify_parent_t
| split_t
| stream_format_t
| buffer_t
| demand_t
| redemand_t
| forward_t
| start_timer_t
| stop_timer_t
| latency_t
| end_of_stream_t
| terminate_t
end
