defmodule Membrane.ParentSpec do
@moduledoc """
Structure representing the topology of a pipeline/bin.
It can be incorporated into a pipeline or a bin by returning
`t:Membrane.Pipeline.Action.spec_t/0` or `t:Membrane.Bin.Action.spec_t/0`
action, respectively. This commonly happens within `c:Membrane.Pipeline.handle_init/1`
and `c:Membrane.Bin.handle_init/1`, but can be done in any other callback also.
## Children
Children that should be spawned when the pipeline/bin starts can be defined
with the `:children` field.
You have to set it to a map, where keys are valid children names (`t:Membrane.Child.name_t/0`)
that are unique within this pipeline/bin and values are either child's module or
struct of that module.
Sample definitions:
%{
first_element: %Element.With.Options.Struct{option_a: 42},
some_element: Element.Without.Options,
some_bin: Bin.Using.Default.Options
}
## Links
Links that should be made when the children are spawned can be defined with the
`:links` field. Links can be defined with the use of `link/1` and `to/2` functions
that allow specifying elements linked, and `via_in/2` and `via_out/2` that allow
specifying pads' names and parameters. If pads are not specified, name `:input`
is assumed for inputs and `:output` for outputs.
Sample definition:
[
link(:source_a)
|> to(:converter)
|> via_in(:input_a, target_queue_size: 20)
|> to(:mixer),
link(:source_b)
|> via_out(:custom_output)
|> via_in(:input_b, options: [mute: true])
|> to(:mixer)
|> via_in(:input, toilet_capacity: 500)
|> to(:sink)
]
See the docs for `via_in/3` and `via_out/3` for details on pad properties that can be set.
Links can also contain children definitions, for example:
[
link(:first_element, %Element.With.Options.Struct{option_a: 42})
|> to(:some_element, Element.Without.Options)
|> to(:element_specified_in_children)
]
Which is particularly convenient for creating links conditionally:
maybe_link = &to(&1, :some_element, Some.Element)
[
link(:first_element)
|> then(if condition?, do: maybe_link, else: & &1)
|> to(:another_element)
]
You can also use `link_linear/1` in order to link subsequent children using default pads
(linking `:input` to `:output` of previous element). That might be especially helpful when creating
testing pipelines.
children = [source: Some.Source, filter: Some.Filter, sink: Some.Sink]
links = link_linear(children)
### Bins
For bins boundaries, there are special links allowed. The user should define links
between the bin's input and the first child's input (input-input type) and last
child's output and bin output (output-output type). In this case, `link_bin_input/1`
and `to_bin_output/2` should be used.
Sample definition:
[
link_bin_input() |> to(:filter1) |> to(:filter2) |> to_bin_output(:custom_output)
]
### Dynamic pads
In most cases, dynamic pads can be linked the same way as static ones, although
in the following situations, exact pad reference must be passed instead of a name:
- When that reference is needed later, for example, to handle a notification related
to that particular pad instance
pad = Pad.ref(:output, make_ref())
[
link(:tee) |> via_out(pad) |> to(:sink)
]
- When linking dynamic pads of a bin with its children, for example in
`c:Membrane.Bin.handle_pad_added/3`
@impl true
def handle_pad_added(Pad.ref(:input, _) = pad, _ctx, state) do
links = [link_bin_input(pad) |> to(:mixer)]
{{:ok, spec: %ParentSpec{links: links}}, state}
end
## Stream sync
`:stream_sync` field can be used for specifying elements that should start playing
at the same moment. An example can be audio and video player sinks. This option
accepts either `:sinks` atom or a list of groups (lists) of elements. Passing `:sinks`
results in synchronizing all sinks in the pipeline, while passing a list of groups
of elements synchronizes all elements in each group. It is worth mentioning
that to keep the stream synchronized all involved elements need to rely on
the same clock.
By default, no elements are synchronized.
Sample definitions:
```
%ParentSpec{stream_sync: [[:element1, :element2], [:element3, :element4]]}
%ParentSpec{stream_sync: :sinks}
```
## Clock provider
A clock provider is an element that exports a clock that should be used as the pipeline
clock. The pipeline clock is the default clock used by elements' timers.
For more information see `Membrane.Element.Base.def_clock/1`.
## Crash groups
A crash group is a logical entity that prevents the whole pipeline from crashing when one of
its children crash.
### Adding children to a crash group
```elixir
children = %{
:some_element_1 => %SomeElement{
# ...
},
:some_element_2 => %SomeElement{
# ...
}
}
spec = %ParentSpec{children: children, crash_group: {group_id, :temporary}}
```
The crash group is defined by a two-element tuple, first element is an ID which is of type
`Membrane.CrashGroup.name_t()`, and the second is a mode. Currently, we support only
`:temporary` mode which means that Membrane will not make any attempts to restart crashed child.
In the above snippet, we create new children - `:some_element_1` and `:some_element_2`, we add it
to the crash group with id `group_id`. Crash of `:some_element_1` or `:some_element_2` propagates
only to the rest of the members of the crash group and the pipeline stays alive.
Currently, crash group covers all children within one or more `ParentSpec`s.
### Handling crash of a crash group
When any of the members of the crash group goes down, the callback:
[`handle_crash_group_down/3`](https://hexdocs.pm/membrane_core/Membrane.Pipeline.html#c:handle_crash_group_down/3)
is called.
```elixir
@impl true
def handle_crash_group_down(crash_group_id, ctx, state) do
# do some stuff in reaction to crash of group with id crash_group_id
end
```
### Limitations
At this moment crash groups are only useful for elements with dynamic pads.
Crash groups work only in pipelines and are not supported in bins.
## Log metadata
`:log_metadata` field can be used to set the `Membrane.Logger` metadata for all children from that
`Membrane.ParentSpec`
"""
alias Membrane.{Child, Pad}
alias Membrane.ParentError
require Membrane.Pad
defmodule LinkBuilder do
@moduledoc false
use Bunch.Access
defstruct children: [], links: [], status: nil
@type t :: %__MODULE__{
children: [{Child.name_t(), module | struct}],
links: [map],
status: status_t
}
@type status_t :: :from | :from_pad | :to_pad | :done
@spec update(t, status_t, Keyword.t()) :: t
def update(
%__MODULE__{links: [%{to: to} | _] = links, status: :done} = builder,
status,
entries
) do
%__MODULE__{builder | links: [Map.new([from: to] ++ entries) | links], status: status}
end
def update(%__MODULE__{links: [link | links]} = builder, status, entries) do
%__MODULE__{builder | links: [Map.merge(link, Map.new(entries)) | links], status: status}
end
end
@opaque link_builder_t :: LinkBuilder.t()
@type child_spec_t :: module | struct
@type children_spec_t ::
[{Child.name_t(), child_spec_t}]
| %{Child.name_t() => child_spec_t}
@type pad_options_t :: Keyword.t()
@type links_spec_t :: [link_builder_t() | links_spec_t]
@type crash_group_spec_t :: {any(), :temporary} | nil
@typedoc """
Struct used when starting and linking children within a pipeline or a bin.
"""
@type t :: %__MODULE__{
children: children_spec_t,
links: links_spec_t,
crash_group: crash_group_spec_t() | nil,
stream_sync: :sinks | [[Child.name_t()]],
clock_provider: Child.name_t() | nil,
node: node() | nil,
log_metadata: Keyword.t()
}
defstruct children: %{},
links: [],
crash_group: nil,
stream_sync: [],
clock_provider: nil,
node: nil,
log_metadata: []
@doc """
Begins a link.
See the _links_ section of the moduledoc for more information.
"""
@spec link(Child.name_t()) :: link_builder_t()
def link(child_name) do
%LinkBuilder{links: [%{from: child_name}], status: :from}
end
@doc """
Defines a child and begins a link with it.
See the _links_ section of the moduledoc for more information.
"""
@spec link(Child.name_t(), child_spec_t()) :: link_builder_t()
def link(child_name, child_spec) do
link(child_name) |> Map.update!(:children, &[{child_name, child_spec} | &1])
end
@doc """
Begins a link with a bin's pad.
See the _links_ section of the moduledoc for more information.
"""
@spec link_bin_input(Pad.name_t() | Pad.ref_t()) :: link_builder_t() | no_return
def link_bin_input(pad \\ :input) do
:ok = validate_pad_name(pad)
link({Membrane.Bin, :itself})
|> LinkBuilder.update(:from_pad, from_pad: pad, from_pad_props: %{})
end
@doc """
Specifies output pad name and properties of the preceding child.
The possible properties are:
- `options` - If a pad defines options, they can be passed here as a keyword list. Pad options are documented
in moduledoc of each element. See `Membrane.Element.WithOutputPads.def_output_pad/2` and `Membrane.Bin.def_output_pad/2`
for information about defining pad options.
See the _links_ section of the moduledoc for more information.
"""
@spec via_out(link_builder_t(), Pad.name_t() | Pad.ref_t(), options: pad_options_t()) ::
link_builder_t() | no_return
def via_out(builder, pad, props \\ [])
def via_out(%LinkBuilder{status: :from_pad}, pad, _props) do
raise ParentError,
"Invalid link specification: output #{inspect(pad)} placed after another output or bin's input"
end
def via_out(%LinkBuilder{status: :to_pad}, pad, _props) do
raise ParentError, "Invalid link specification: output #{inspect(pad)} placed after an input"
end
def via_out(%LinkBuilder{links: [%{to: {Membrane.Bin, :itself}} | _]}, pad, _props) do
raise ParentError,
"Invalid link specification: output #{inspect(pad)} placed after bin's output"
end
def via_out(%LinkBuilder{} = builder, pad, props) do
:ok = validate_pad_name(pad)
props =
case Bunch.Config.parse(props, options: [default: []]) do
{:ok, props} ->
props
{:error, reason} ->
raise ParentError, "Invalid link specification: invalid pad props: #{inspect(reason)}"
end
LinkBuilder.update(builder, :from_pad,
from_pad: pad,
from_pad_props: props
)
end
@doc """
Specifies input pad name and properties of the subsequent child.
The possible properties are:
- `options` - If a pad defines options, they can be passed here as a keyword list. Pad options are documented
in moduledoc of each element. See `Membrane.Element.WithInputPads.def_input_pad/2` and `Membrane.Bin.def_input_pad/2`
for information about defining pad options.
Additionally, the following properties can be used to adjust the flow control parameters. If set within a bin
on an input that connects to the bin input, they will be overridden if set when linking to the bin in its parent.
- `toilet_capacity` - Used when a toilet is created, that is for pull input pads that have push output pads
linked to them. When a push output produces more buffers than the pull input can consume, the buffers are accumulated
in a queue called toilet. If the toilet size grows above its capacity, it overflows by raising an error.
- `target_queue_size` - The size of the queue of the input pad that Membrane will try to maintain. That allows for fulfilling
the demands of the element by taking data from the queue while the actual sending of demands is done asynchronously,
smoothing the processing. Used only for pads working in pull mode with manual demands. See `t:Membrane.Pad.mode_t/0`
and `t:Membrane.Pad.demand_mode_t/0` for more info.
- `min_demand_factor` - A factor used to calculate `minimal demand` (`minimal_demand = target_queue_size * min_demand_factor`).
Membrane won't send smaller demand that `minimal demand`, to reduce demands' overhead. However, user will always receive
as many buffers as they actually demanded, all excess buffers will be queued internally.
Used only for pads working in pull mode with manual demands. See `t:Membrane.Pad.mode_t/0` and `t:Membrane.Pad.demand_mode_t/0`
for more info. Defaults to `#{Membrane.Core.Element.InputQueue.default_min_demand_factor()}` (the default may change in the future).
- `auto_demand_size` - Size of automatically generated demands. Used only for pads working in pull mode with automatic demands.
See `t:Membrane.Pad.mode_t/0` and `t:Membrane.Pad.demand_mode_t/0` for more info.
- `throttling_factor` - an integer specifying how frequently should a sender update the number of buffers in the `Toilet`. Defaults to 1,
meaning, that the sender will update the toilet with each buffer being sent. Setting that factor for elements,
which are running on the same node, does not have an impact of performance. However, once the sending element and the receiving element are put on different nodes,
the sender updates the toilet with interprocess messages and setting a bigger `throttling_factor` can reduce the number of messages
in the system.
At the same time, setting a greater `throttling_factor` can result in a toilet overflow being detected later.
See the _links_ section of the moduledoc for more information.
"""
@spec via_in(link_builder_t(), Pad.name_t() | Pad.ref_t(),
options: pad_options_t(),
toilet_capacity: number | nil,
target_queue_size: number | nil,
min_demand_factor: number | nil,
auto_demand_size: number | nil,
throttling_factor: number | nil
) ::
link_builder_t() | no_return
def via_in(builder, pad, props \\ [])
def via_in(%LinkBuilder{status: :to_pad}, pad, _props) do
raise ParentError,
"Invalid link specification: input #{inspect(pad)} placed after another input"
end
def via_in(%LinkBuilder{links: [%{to: {Membrane.Bin, :itself}} | _]}, pad, _props) do
raise ParentError,
"Invalid link specification: input #{inspect(pad)} placed after bin's output"
end
def via_in(%LinkBuilder{} = builder, pad, props) do
:ok = validate_pad_name(pad)
props =
props
|> Bunch.Config.parse(
options: [default: []],
target_queue_size: [default: nil],
min_demand_factor: [default: nil],
auto_demand_size: [default: nil],
toilet_capacity: [default: nil],
throttling_factor: [default: 1]
)
|> case do
{:ok, props} ->
props
{:error, reason} ->
raise ParentError, "Invalid link specification: invalid pad props: #{inspect(reason)}"
end
if builder.status == :from_pad do
builder
else
via_out(builder, :output)
end
|> LinkBuilder.update(:to_pad,
to_pad: pad,
to_pad_props: props
)
end
@doc """
Continues or ends a link.
See the _links_ section of the moduledoc for more information.
"""
@spec to(link_builder_t(), Child.name_t()) :: link_builder_t() | no_return
def to(%LinkBuilder{links: [%{to: {Membrane.Bin, :itself}} | _]}, child_name) do
raise ParentError,
"Invalid link specification: child #{inspect(child_name)} placed after bin's output"
end
def to(%LinkBuilder{} = builder, child_name) do
if builder.status == :to_pad do
builder
else
via_in(builder, :input)
end
|> LinkBuilder.update(:done, to: child_name)
end
@doc """
Defines a child and continues or ends a link with it.
See the _links_ section of the moduledoc for more information.
"""
@spec to(link_builder_t(), Child.name_t(), child_spec_t()) :: link_builder_t() | no_return
def to(%LinkBuilder{} = builder, child_name, child_spec) do
builder |> to(child_name) |> Map.update!(:children, &[{child_name, child_spec} | &1])
end
@doc """
Ends a link with a bin's output.
See the _links_ section of the moduledoc for more information.
"""
@spec to_bin_output(link_builder_t(), Pad.name_t() | Pad.ref_t()) ::
link_builder_t() | no_return
def to_bin_output(builder, pad \\ :output)
def to_bin_output(%LinkBuilder{status: :to_pad}, pad) do
raise ParentError, "Invalid link specification: bin's output #{pad} placed after an input"
end
def to_bin_output(builder, pad) do
:ok = validate_pad_name(pad)
if builder.status == :from_pad do
builder
else
via_out(builder, :output)
end
|> LinkBuilder.update(:to_pad, to_pad: pad, to_pad_props: %{})
|> to({Membrane.Bin, :itself})
end
@doc """
Links subsequent children using default pads (linking `:input` to `:output` of
previous element). The list of children must consist at least of 2 elements.
## Example
Membrane.ParentSpec.link_linear([el1: MembraneElement1, el2: MembraneElement2])
"""
@spec link_linear(children :: [child_spec_t()]) :: links_spec_t()
def link_linear(children) when is_list(children) and length(children) > 1 do
[{first_child_name, first_child_spec} | other_children] = children
links =
other_children
|> Enum.reduce(link(first_child_name, first_child_spec), fn {child_name, child_spec},
builder ->
to(builder, child_name, child_spec)
end)
[links]
end
defp validate_pad_name(pad) when Pad.is_pad_name(pad) or Pad.is_pad_ref(pad) do
:ok
end
defp validate_pad_name(pad) do
raise ParentError, "Invalid link specification: invalid pad name: #{inspect(pad)}"
end
end
