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Support for handle_continue #234

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7a1ba10
Handle continue on producer init
Apr 10, 2019
67bba00
support continue for consumers
May 16, 2019
299d17e
most tests pass again
May 23, 2019
abb99b2
simplify consumer init subscribe
May 27, 2019
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2 changes: 1 addition & 1 deletion lib/consumer_supervisor.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ defmodule ConsumerSupervisor do
to a producer named `Producer` and starts a new process for each event
received from the producer. Each new process will be started by calling
`Printer.start_link/1`, which simply starts a task that will print the
incoming event to the terminal.
incoming event to the terminal.

defmodule Consumer do
use ConsumerSupervisor
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87 changes: 69 additions & 18 deletions lib/gen_stage.ex
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Expand Up @@ -831,8 +831,8 @@ defmodule GenStage do
end

The returned tuple may also contain 3 or 4 elements. The third
element may be the `:hibernate` atom or a set of options defined
below.
element may be the `:hibernate` atom, the `{:continue, term}` tuple
or a set of options defined below.

Returning `:ignore` will cause `start_link/3` to return `:ignore`
and the process will exit normally without entering the loop or
Expand Down Expand Up @@ -882,11 +882,17 @@ defmodule GenStage do

@callback init(args :: term) ::
{:producer, state}
| {:producer, state, :hibernate | {:continue, term}}
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The current PR doesn't handle hiberrnate, does it? In any case, there are other discussions we need to have regarding hibernate, so probably better to focus on continue for now. :)

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No, but the existing documentation for the init function mentions hibernate, which confused me. I'll remove the hibernate reference from the docs (around lines 833-835) and from this callback.

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I'll remove the hibernate reference from the docs (around lines 833-835) and from this callback.

Fantastic, thank you!

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Hmm, actually, the handle_info callback (and the others) also contains :hibernate. I guess that was a copy paste from the GenServer docs?

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Good catch! Actually we do support hibernate there but not on init. So I guess we crossed this line anyway. So I would go ahead and support it on init too!

| {:producer, state, [producer_option]}
| {:producer, state, :hibernate | {:continue, term}, [producer_option]}
| {:producer_consumer, state}
| {:producer_consumer, state, :hibernate | {:continue, term}}
| {:producer_consumer, state, [producer_consumer_option]}
| {:producer_consumer, state, :hibernate | {:continue, term}, [producer_consumer_option]}
| {:consumer, state}
| {:consumer, state, :hibernate | {:continue, term}}
| {:consumer, state, [consumer_option]}
| {:consumer, state, :hibernate | {:continue, term}, [consumer_option]}
| :ignore
| {:stop, reason :: any}
when state: any
Expand Down Expand Up @@ -1094,6 +1100,25 @@ defmodule GenStage do
| {:stop, reason :: term, new_state}
when new_state: term, event: term

@doc """
Invoked to handle `continue` instructions.

It is useful for performing work after initialization or for splitting the work
in a callback in multiple steps, updating the process state along the way.

Return values are the same as `c:handle_cast/2`.

This callback is optional. If one is not implemented, the server will fail
if a continue instruction is used.

This callback is only supported on Erlang/OTP 21+.
"""
@callback handle_continue(continue :: term, state :: term) ::
{:noreply, [event], new_state}
| {:noreply, [event], new_state, :hibernate}
| {:stop, reason :: term, new_state}
when new_state: term, event: term

@doc """
The same as `c:GenServer.terminate/2`.
"""
Expand Down Expand Up @@ -1127,6 +1152,7 @@ defmodule GenStage do
handle_call: 3,
handle_cast: 2,
handle_info: 2,
handle_continue: 2,
terminate: 2
]

Expand Down Expand Up @@ -1698,22 +1724,40 @@ defmodule GenStage do
def init({mod, args}) do
case mod.init(args) do
{:producer, state} ->
init_producer(mod, [], state)
init_producer(mod, [], state, :no_continue)

{:producer, state, opts} when is_list(opts) ->
init_producer(mod, opts, state)
init_producer(mod, opts, state, :no_continue)

{:producer, state, continue_or_hibernate} ->
init_producer(mod, [], state, continue_or_hibernate)

{:producer, state, continue_or_hibernate, opts} when is_list(opts) ->
init_producer(mod, opts, state, continue_or_hibernate)

{:producer_consumer, state} ->
init_producer_consumer(mod, [], state)
init_producer_consumer(mod, [], state, :no_continue)

{:producer_consumer, state, opts} when is_list(opts) ->
init_producer_consumer(mod, opts, state)
init_producer_consumer(mod, opts, state, :no_continue)

{:producer_consumer, state, continue_or_hibernate} ->
init_producer_consumer(mod, [], state, continue_or_hibernate)

{:producer_consumer, state, continue_or_hibernate, opts} when is_list(opts) ->
init_producer_consumer(mod, opts, state, continue_or_hibernate)

{:consumer, state} ->
init_consumer(mod, [], state)
init_consumer(mod, [], state, :no_continue)

{:consumer, state, opts} when is_list(opts) ->
init_consumer(mod, opts, state)
init_consumer(mod, opts, state, :no_continue)

{:consumer, state, continue_or_hibernate} ->
init_consumer(mod, [], state, continue_or_hibernate)

{:consumer, state, continue_or_hibernate, opts} when is_list(opts) ->
init_consumer(mod, opts, state, continue_or_hibernate)

{:stop, _} = stop ->
stop
Expand All @@ -1726,7 +1770,7 @@ defmodule GenStage do
end
end

defp init_producer(mod, opts, state) do
defp init_producer(mod, opts, state, continue_or_hibernate) do
with {:ok, dispatcher_mod, dispatcher_state, opts} <- init_dispatcher(opts),
{:ok, buffer_size, opts} <-
Utils.validate_integer(opts, :buffer_size, 10000, 0, :infinity, true),
Expand All @@ -1746,7 +1790,10 @@ defmodule GenStage do
dispatcher_state: dispatcher_state
}

{:ok, stage}
case continue_or_hibernate do
:no_continue -> {:ok, stage}
continue_or_hibernate -> {:ok, stage, continue_or_hibernate}
end
else
{:error, message} -> {:stop, {:bad_opts, message}}
end
Expand All @@ -1768,7 +1815,7 @@ defmodule GenStage do
end
end

defp init_producer_consumer(mod, opts, state) do
defp init_producer_consumer(mod, opts, state, continue_or_hibernate) do
with {:ok, dispatcher_mod, dispatcher_state, opts} <- init_dispatcher(opts),
{:ok, subscribe_to, opts} <- Utils.validate_list(opts, :subscribe_to, []),
{:ok, buffer_size, opts} <-
Expand All @@ -1787,17 +1834,17 @@ defmodule GenStage do
dispatcher_state: dispatcher_state
}

consumer_init_subscribe(subscribe_to, stage)
consumer_init_subscribe(subscribe_to, stage, continue_or_hibernate)
else
{:error, message} -> {:stop, {:bad_opts, message}}
end
end

defp init_consumer(mod, opts, state) do
defp init_consumer(mod, opts, state, continue_or_hibernate) do
with {:ok, subscribe_to, opts} <- Utils.validate_list(opts, :subscribe_to, []),
:ok <- Utils.validate_no_opts(opts) do
stage = %GenStage{mod: mod, state: state, type: :consumer}
consumer_init_subscribe(subscribe_to, stage)
consumer_init_subscribe(subscribe_to, stage, continue_or_hibernate)
else
{:error, message} -> {:stop, {:bad_opts, message}}
end
Expand Down Expand Up @@ -2360,11 +2407,11 @@ defmodule GenStage do

## Consumer helpers

defp consumer_init_subscribe(producers, stage) do
defp consumer_init_subscribe(producers, stage, continue_or_hibernate) do
fold_fun = fn
to, {:ok, stage} ->
to, {:ok, stage, continue_or_hibernate} ->
case consumer_subscribe(to, stage) do
{:reply, _, stage} -> {:ok, stage}
{:reply, _, stage} -> {:ok, stage, continue_or_hibernate}
{:stop, reason, _, _} -> {:stop, reason}
{:stop, reason, _} -> {:stop, reason}
end
Expand All @@ -2373,7 +2420,11 @@ defmodule GenStage do
{:stop, reason}
end

:lists.foldl(fold_fun, {:ok, stage}, producers)
:lists.foldl(fold_fun, {:ok, stage, continue_or_hibernate}, producers)
|> case do
{:ok, stage, :no_continue} -> {:ok, stage}
otherwise -> otherwise
end
end

defp consumer_receive({_, ref} = from, {producer_id, cancel, {demand, min, max}}, events, stage) do
Expand Down
2 changes: 1 addition & 1 deletion test/gen_stage_test.exs
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Original file line number Diff line number Diff line change
Expand Up @@ -143,7 +143,7 @@ defmodule GenStageTest do

defmodule Postponer do
@moduledoc """
Discards all events.
Postpones all events.
"""

use GenStage
Expand Down