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process_router.ex
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process_router.ex
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defmodule Commanded.ProcessManagers.ProcessRouter do
@moduledoc false
use GenServer
use Commanded.Registration
require Logger
alias Commanded.Event.Upcast
alias Commanded.EventStore
alias Commanded.EventStore.RecordedEvent
alias Commanded.ProcessManagers.FailureContext
alias Commanded.ProcessManagers.ProcessManagerInstance
alias Commanded.ProcessManagers.ProcessRouter
alias Commanded.ProcessManagers.Supervisor
alias Commanded.Subscriptions
defmodule State do
@moduledoc false
defstruct [
:command_dispatcher,
:consistency,
:event_timeout,
:idle_timeout,
:process_manager_name,
:process_manager_module,
:subscribe_from,
:supervisor,
:subscription,
:subscription_ref,
:last_seen_event,
:process_event_timer,
process_managers: %{},
pending_acks: %{},
pending_events: []
]
end
def start_link(process_manager_name, process_manager_module, command_dispatcher, opts \\ []) do
name = {ProcessRouter, process_manager_name}
state = %State{
process_manager_name: process_manager_name,
process_manager_module: process_manager_module,
command_dispatcher: command_dispatcher,
consistency: opts[:consistency] || :eventual,
subscribe_from: opts[:start_from] || :origin,
event_timeout: opts[:event_timeout],
idle_timeout: opts[:idle_timeout] || :infinity
}
Registration.start_link(name, __MODULE__, state)
end
@impl GenServer
def init(%State{} = state) do
:ok = register_subscription(state)
{:ok, state, {:continue, :subscribe_to_events}}
end
@doc """
Acknowledge successful handling of the given event by a process manager instance
"""
def ack_event(process_router, %RecordedEvent{} = event, instance) do
GenServer.cast(process_router, {:ack_event, event, instance})
end
@doc false
def process_instance(process_router, process_uuid) do
GenServer.call(process_router, {:process_instance, process_uuid})
end
@doc false
def process_instances(process_router) do
GenServer.call(process_router, :process_instances)
end
@doc false
@impl GenServer
def handle_continue(:subscribe_to_events, %State{} = state) do
{:noreply, subscribe_to_events(state)}
end
@doc false
@impl GenServer
def handle_call(:process_instances, _from, %State{} = state) do
%State{process_managers: process_managers} = state
reply = Enum.map(process_managers, fn {process_uuid, pid} -> {process_uuid, pid} end)
{:reply, reply, state}
end
@doc false
@impl GenServer
def handle_call({:process_instance, process_uuid}, _from, %State{} = state) do
%State{process_managers: process_managers} = state
reply =
case Map.get(process_managers, process_uuid) do
nil -> {:error, :process_manager_not_found}
process_manager -> process_manager
end
{:reply, reply, state}
end
@doc false
@impl GenServer
def handle_cast({:ack_event, event, instance}, %State{} = state) do
%State{pending_acks: pending_acks} = state
%RecordedEvent{event_number: event_number} = event
state =
case pending_acks |> Map.get(event_number, []) |> List.delete(instance) do
[] ->
# Enqueue a message to continue processing any pending events
GenServer.cast(self(), :process_pending_events)
state = %State{state | pending_acks: Map.delete(pending_acks, event_number)}
# no pending acks so confirm receipt of event
confirm_receipt(event, state)
pending ->
# pending acks, don't ack event but wait for outstanding instances
%State{state | pending_acks: Map.put(pending_acks, event_number, pending)}
end
{:noreply, state}
end
@doc false
@impl GenServer
def handle_cast(:process_pending_events, %State{pending_events: []} = state),
do: {:noreply, state}
@doc false
@impl GenServer
def handle_cast(:process_pending_events, %State{} = state) do
%State{pending_events: [event | pending_events]} = state
case length(pending_events) do
0 ->
:ok
1 ->
Logger.debug(fn -> describe(state) <> " has 1 pending event to process" end)
count ->
Logger.debug(fn -> describe(state) <> " has #{count} pending events to process" end)
end
case handle_event(event, state) do
%State{} = state -> {:noreply, %State{state | pending_events: pending_events}}
reply -> reply
end
end
@doc false
# Subscription to event store has successfully subscribed, init process router
@impl GenServer
def handle_info({:subscribed, subscription}, %State{subscription: subscription} = state) do
Logger.debug(fn -> describe(state) <> " has successfully subscribed to event store" end)
{:ok, supervisor} = Supervisor.start_link()
{:noreply, %State{state | supervisor: supervisor}}
end
@doc false
@impl GenServer
def handle_info({:events, events}, %State{} = state) do
Logger.debug(fn -> describe(state) <> " received #{length(events)} event(s)" end)
%State{pending_events: pending_events} = state
unseen_events =
events
|> Enum.reject(&event_already_seen?(&1, state))
|> Upcast.upcast_event_stream()
state =
case {pending_events, unseen_events} do
{[], []} ->
# no pending or unseen events, so state is unmodified
state
{[], _} ->
# no pending events, but some unseen events so start processing them
GenServer.cast(self(), :process_pending_events)
%State{state | pending_events: unseen_events}
{_, _} ->
# already processing pending events, append the unseen events so they are processed afterwards
%State{state | pending_events: pending_events ++ unseen_events}
end
{:noreply, state}
end
@doc false
# Shutdown process manager when processing an event has taken too long.
@impl GenServer
def handle_info({:event_timeout, event_number}, %State{} = state) do
%State{pending_acks: pending_acks, event_timeout: event_timeout} = state
case Map.get(pending_acks, event_number, []) do
[] ->
{:noreply, state}
_pending ->
Logger.error(fn ->
describe(state) <>
" has taken longer than " <>
inspect(event_timeout) <>
"ms to process event #" <> inspect(event_number) <> " and is now stopping"
end)
{:stop, :event_timeout, state}
end
end
@doc false
# Stop process manager when event store subscription process terminates.
@impl GenServer
def handle_info(
{:DOWN, ref, :process, pid, reason},
%State{subscription_ref: ref, subscription: pid} = state
) do
Logger.debug(fn -> describe(state) <> " subscription DOWN due to: #{inspect(reason)}" end)
{:stop, reason, state}
end
@doc false
# Remove a process manager instance that has stopped with a normal exit reason.
@impl GenServer
def handle_info({:DOWN, _ref, :process, pid, :normal}, %State{} = state) do
%State{process_managers: process_managers} = state
state = %State{state | process_managers: remove_process_manager(process_managers, pid)}
{:noreply, state}
end
@doc false
# Stop process router when a process manager instance terminates abnormally.
@impl GenServer
def handle_info({:DOWN, _ref, :process, _pid, reason}, %State{} = state) do
Logger.warn(fn -> describe(state) <> " is stopping due to: #{inspect(reason)}" end)
{:stop, reason, state}
end
# Register this process manager as a subscription with the given consistency
defp register_subscription(%State{} = state) do
%State{consistency: consistency, process_manager_name: name} = state
Subscriptions.register(name, consistency)
end
defp subscribe_to_events(%State{} = state) do
%State{process_manager_name: process_manager_name, subscribe_from: subscribe_from} = state
{:ok, subscription} =
EventStore.subscribe_to(:all, process_manager_name, self(), subscribe_from)
subscription_ref = Process.monitor(subscription)
%State{state | subscription: subscription, subscription_ref: subscription_ref}
end
# Ignore already seen event
defp event_already_seen?(
%RecordedEvent{event_number: event_number},
%State{last_seen_event: last_seen_event}
) do
not is_nil(last_seen_event) and event_number <= last_seen_event
end
defp handle_event(%RecordedEvent{} = event, %State{} = state) do
%RecordedEvent{data: data} = event
%State{process_manager_module: process_manager_module} = state
try do
case process_manager_module.interested?(data) do
{:start, process_uuid} ->
Logger.debug(fn -> describe(state) <> " is interested in event " <> describe(event) end)
process_uuid
|> List.wrap()
|> Enum.reduce(state, fn process_uuid, state ->
{process_instance, state} = start_or_continue_process_manager(process_uuid, state)
delegate_event(process_instance, event, state)
end)
{:start!, process_uuid} ->
Logger.debug(fn -> describe(state) <> " is interested in event " <> describe(event) end)
{state, process_instances} =
process_uuid
|> List.wrap()
|> Enum.reduce({state, []}, fn process_uuid, {state, process_instances} ->
{process_instance, state} = start_or_continue_process_manager(process_uuid, state)
if ProcessManagerInstance.new?(process_instance) do
{state, [process_instance | process_instances]}
else
throw(
handle_routing_error(
{:error, {:start!, :process_already_started}},
event,
state
)
)
end
end)
process_instances
|> Enum.reverse()
|> Enum.reduce(state, &delegate_event(&1, event, &2))
{:continue, process_uuid} ->
Logger.debug(fn -> describe(state) <> " is interested in event " <> describe(event) end)
process_uuid
|> List.wrap()
|> Enum.reduce(state, fn process_uuid, state ->
{process_instance, state} = start_or_continue_process_manager(process_uuid, state)
delegate_event(process_instance, event, state)
end)
{:continue!, process_uuid} ->
Logger.debug(fn -> describe(state) <> " is interested in event " <> describe(event) end)
{state, process_instances} =
process_uuid
|> List.wrap()
|> Enum.reduce({state, []}, fn process_uuid, {state, process_instances} ->
{process_instance, state} = start_or_continue_process_manager(process_uuid, state)
if ProcessManagerInstance.new?(process_instance) do
throw(
handle_routing_error(
{:error, {:continue!, :process_not_started}},
event,
state
)
)
else
{state, [process_instance | process_instances]}
end
end)
process_instances
|> Enum.reverse()
|> Enum.reduce(state, &delegate_event(&1, event, &2))
{:stop, process_uuid} ->
Logger.debug(fn ->
describe(state) <> " has been stopped by event " <> describe(event)
end)
state =
process_uuid
|> List.wrap()
|> Enum.reduce(state, &stop_process_manager/2)
ack_and_continue(event, state)
false ->
Logger.debug(fn ->
describe(state) <> " is not interested in event " <> describe(event)
end)
ack_and_continue(event, state)
end
rescue
e -> handle_routing_error({:error, e}, event, state)
catch
reply -> reply
end
end
defp handle_routing_error(error, %RecordedEvent{} = failed_event, %State{} = state) do
%RecordedEvent{data: data} = failed_event
%State{process_manager_module: process_manager_module} = state
failure_context = %FailureContext{last_event: failed_event}
case process_manager_module.error(error, data, failure_context) do
:skip ->
# Skip the problematic event by confirming receipt
Logger.info(fn -> describe(state) <> " is skipping event" end)
ack_and_continue(failed_event, state)
{:stop, reason} ->
Logger.warn(fn -> describe(state) <> " has requested to stop: #{inspect(error)}" end)
{:stop, reason, state}
invalid ->
Logger.warn(fn ->
describe(state) <> " returned an invalid error response: #{inspect(invalid)}"
end)
{:stop, error, state}
end
end
# Continue processing any pending events and confirm receipt of the given event id
defp ack_and_continue(%RecordedEvent{} = event, %State{} = state) do
GenServer.cast(self(), :process_pending_events)
confirm_receipt(event, state)
end
# Confirm receipt of given event
defp confirm_receipt(%RecordedEvent{event_number: event_number} = event, %State{} = state) do
Logger.debug(fn ->
describe(state) <> " confirming receipt of event: #{inspect(event_number)}"
end)
do_ack_event(event, state)
%State{state | last_seen_event: event_number}
end
defp start_or_continue_process_manager(process_uuid, %State{} = state) do
%State{process_managers: process_managers} = state
case Map.get(process_managers, process_uuid) do
process_manager when is_pid(process_manager) ->
{process_manager, state}
nil ->
start_process_manager(process_uuid, state)
end
end
defp start_process_manager(process_uuid, %State{} = state) do
%State{
command_dispatcher: command_dispatcher,
idle_timeout: idle_timeout,
process_managers: process_managers,
process_manager_name: process_manager_name,
process_manager_module: process_manager_module,
supervisor: supervisor
} = state
opts = [
command_dispatcher: command_dispatcher,
idle_timeout: idle_timeout,
process_manager_name: process_manager_name,
process_manager_module: process_manager_module,
process_router: self(),
process_uuid: process_uuid
]
{:ok, process_manager} = Supervisor.start_process_manager(supervisor, opts)
Process.monitor(process_manager)
state = %State{
state
| process_managers: Map.put(process_managers, process_uuid, process_manager)
}
{process_manager, state}
end
defp stop_process_manager(process_uuid, %State{} = state) do
%State{process_managers: process_managers} = state
case Map.get(process_managers, process_uuid) do
nil ->
state
process_manager ->
:ok = ProcessManagerInstance.stop(process_manager)
%State{state | process_managers: Map.delete(process_managers, process_uuid)}
end
end
defp remove_process_manager(process_managers, pid) do
Enum.reduce(process_managers, process_managers, fn
{process_uuid, process_manager_pid}, acc when process_manager_pid == pid ->
Map.delete(acc, process_uuid)
_, acc ->
acc
end)
end
defp do_ack_event(event, %State{} = state) do
%State{consistency: consistency, process_manager_name: name, subscription: subscription} =
state
:ok = EventStore.ack_event(subscription, event)
:ok = Subscriptions.ack_event(name, consistency, event)
end
# Delegate event to process instance who will ack event processing on success
defp delegate_event(process_instance, %RecordedEvent{} = event, %State{} = state) do
%State{pending_acks: pending_acks} = state
%RecordedEvent{event_number: event_number} = event
:ok = ProcessManagerInstance.process_event(process_instance, event)
pending_acks =
Map.update(pending_acks, event_number, [process_instance], fn
pending -> [process_instance | pending]
end)
state = %State{state | pending_acks: pending_acks}
start_event_timer(event_number, state)
end
# Event timeout not configured
defp start_event_timer(_event_number, %State{event_timeout: nil} = state), do: state
defp start_event_timer(event_number, %State{process_event_timer: process_event_timer} = state)
when is_reference(process_event_timer) do
Process.cancel_timer(process_event_timer)
state = %State{state | process_event_timer: nil}
start_event_timer(event_number, state)
end
defp start_event_timer(event_number, %State{event_timeout: event_timeout} = state)
when is_integer(event_timeout) do
%State{event_timeout: event_timeout} = state
process_event_timer =
Process.send_after(self(), {:event_timeout, event_number}, event_timeout)
%State{state | process_event_timer: process_event_timer}
end
defp describe(%State{process_manager_module: process_manager_module}),
do: inspect(process_manager_module)
defp describe(%RecordedEvent{} = event) do
%RecordedEvent{
event_number: event_number,
stream_id: stream_id,
stream_version: stream_version
} = event
"#{inspect(event_number)} (#{inspect(stream_id)}@#{inspect(stream_version)})"
end
end