WIP: clean up request coordinator with functionality and docs

apps/ethereum_jsonrpc/config/config.exs

@@ -6,6 +6,14 @@ config :logger, :ethereum_jsonrpc,
   metadata: [:application, :request_id],
   metadata_filter: [application: :ethereum_jsonrpc]
 
+config :ethereum_jsonrpc, EthereumJSONRPC.RequestCoordinator,
+  rolling_window_opts: [
+    window_count: 6,
+    window_length: :timer.seconds(10),
+    bucket: EthereumJSONRPC.RequestCoordinator.TimeoutCounter
+  ],
+  wait_per_timeout: :timer.seconds(10)
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{Mix.env()}.exs"

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc.ex

@@ -17,7 +17,16 @@ defmodule EthereumJSONRPC do
   """
 
   alias Explorer.Chain.Block
-  alias EthereumJSONRPC.{Blocks, Receipts, Subscription, Transactions, Transport, Uncles, Variant}
+  alias EthereumJSONRPC.{
+    Blocks,
+    Receipts,
+    RequestCoordinator,
+    Subscription,
+    Transactions,
+    Transport,
+    Uncles,
+    Variant
+  }
 
   @typedoc """
   Truncated 20-byte [KECCAK-256](https://en.wikipedia.org/wiki/SHA-3) hash encoded as a hexadecimal number in a
@@ -49,7 +58,7 @@ defmodule EthereumJSONRPC do
 
   """
   @type json_rpc_named_arguments :: [
-          {:transport, Transport.t()} | {:transport_options, Transport.options()} | {:variant, Variant.t()}
+          {:transport, Transport.t()} | {:transport_options, Transport.options()} | {:variant, Variant.t()} | {:throttle_timeout, non_neg_integer()}
         ]
 
   @typedoc """
@@ -310,8 +319,9 @@ defmodule EthereumJSONRPC do
   def json_rpc(request, named_arguments) when (is_map(request) or is_list(request)) and is_list(named_arguments) do
     transport = Keyword.fetch!(named_arguments, :transport)
     transport_options = Keyword.fetch!(named_arguments, :transport_options)
+    throttle_timeout = Keyword.get(named_arguments, :throttle_timeout, 60_000)
 
-    transport.json_rpc(request, transport_options)
+    RequestCoordinator.perform(request, transport, transport_options, throttle_timeout)
   end
 
   @doc """

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/application.ex

@@ -9,9 +9,14 @@ defmodule EthereumJSONRPC.Application do
 
   @impl Application
   def start(_type, _args) do
+    rolling_window_opts =
+      :ethereum_jsonrpc,
+      |> Application.fetch_env!(RequestCoordinator)
+      |> Keyword.fetch!(:rolling_window_opts)
+
     children = [
       :hackney_pool.child_spec(:ethereum_jsonrpc, recv_timeout: 60_000, timeout: 60_000, max_connections: 1000),
-      {RollingWindow, [RequestCoordinator.rolling_window_opts(), [name: TimeoutCounter]]}
+      {RollingWindow, [rolling_window_opts]}
     ]
 
     Supervisor.start_link(children, strategy: :one_for_one, name: EthereumJSONRPC.Supervisor)

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/request_coordinator.ex

@@ -1,14 +1,38 @@
 defmodule EthereumJSONRPC.RequestCoordinator do
   @moduledoc """
-  Retries JSONRPC requests according to the provided retry_options
+  Coordinates requests with a backoff strategy.
 
-  Leverages `EthereumJSONRPC.RollingWindow` to keep track of the count
-  of recent timeouts, and waits a small amount of time per timeout.
+  This module leverages `EthereumJSONRPC.RollingWindow` to track request timeout
+  that have occurred recently. Options for this functionality can be changed at
+  the application configuration level.
 
-  To see the rolling window options, see `EthereumJSONRPC.Application`
+  ## Configuration
+
+  The following are the expected and supported options for this module:
+
+  * `:rolling_window_opts` - Options for the process tracking timeouts
+    * `:window_count` - Number of windows
+    * `:window_length` - Length of each window in milliseconds
+    * `:bucket` - name of the bucket to uniquely identify the dataset
+  * `:wait_per_timeout` - Milliseconds to wait for each recent timeout within the tracked window
+
+  ### Example Configuration
+
+      config :ethereum_jsonrpc, EthereumJSONRPC.RequestCoordinator,
+        rolling_window_opts: [
+          window_count: 6,
+          window_length: :timer.seconds(10),
+          bucket: EthereumJSONRPC.RequestCoordinator.TimeoutCounter
+        ],
+        wait_per_timeout: :timer.seconds(10)
+
+  With this configuration, timeouts are tracked for 6 windows of 10 seconds for a total of 1 minute.
   """
-  alias EthereumJSONRPC.{RollingWindow, TimeoutCounter}
 
+  alias EthereumJSONRPC.{RollingWindow, Transport}
+  alias EthereumJSONRPC.RequestCoordinator.TimeoutCounter
+
+  @timeout_key :timeout
   @wait_per_timeout :timer.seconds(5)
   @rolling_window_opts [
     bucket: :ethereum_jsonrpc_bucket,
@@ -23,67 +47,53 @@ defmodule EthereumJSONRPC.RequestCoordinator do
   end
 
   @doc """
-  Retries the request according to the provided retry_options
+  Performs a JSON RPC request and adds necessary backoff.
 
-  If none were provided, the request is not retried. In all cases, the request
-  waits an amount of time before proceeding based on the count of recent
-  failures.
+  In the event that too many requests have timed out recently and the current
+  request were to exceed someout threshold, the request isn't performed and
+  `{:error, :timeout}` is returned.
   """
-  def perform(request, named_arguments) do
-    transport = Keyword.fetch!(named_arguments, :transport)
-    transport_options = Keyword.fetch!(named_arguments, :transport_options)
-    retry_options = Keyword.get(named_arguments, :retry_options)
-
-    if retry_options do
-      retry_timeout = Keyword.get(retry_options, :retry_timeout, 5_000)
-
-      fn ->
-        request(transport, request, transport_options, true)
-      end
-      |> Task.async()
-      |> Task.await(retry_timeout)
+  @spec perform(Transport.request(), Transport.t(), Transport.options(), non_neg_integer()) :: {:ok, Transport.result()} | {:error, term()}
+  @spec perform(Transport.batch_request(), Transport.t(), Transport.options(), non_neg_integer()) :: {:ok, Transport.batch_result()} | {:error, term()}
+  def perform(request, transport, transport_options, throttle_timeout) do
+    sleep_time = sleep_time()
+
+    if sleep_time <= throttle_timeout do
+      :timer.sleep(sleep_time)
+
+      request
+      |> transport.json_rpc(transport_options)
+      |> handle_transport_response()
     else
-      request(transport, request, transport_options, false)
+      {:error, :timeout}
     end
   end
 
-  defp request(transport, request, transport_options, retry?) do
-    key = something_that_uniquely_identifies_this_transport(transport, transport_options)
+  defp handle_transport_response({:error, :timeout} = error) do
+    increment_recent_timeouts()
+    error
+  end
 
-    sleep_if_too_many_recent_timeouts(key)
+  defp handle_transport_response(response), do: response
 
-    case transport.json_rpc(request, transport_options) do
-      {:error, :timeout} = error ->
-        increment_recent_timeouts(key)
+  defp sleep_time do
+    wait_coefficient = RollingWindow.count(bucket(), @timeout_key)
 
-        if retry? do
-          request(transport, request, transport_options, true)
-        else
-          error
-        end
+    wait_per_timeout =
+      :ethereum_jsonrpc
+      |> Application.get_env(__MODULE__)
+      |> Keyword.fetch!(:wait_per_timeout)
 
-      response ->
-        response
-    end
+    wait_coefficient * @wait_per_timeout
   end
 
-  defp increment_recent_timeouts(key) do
-    RollingWindow.inc(TimeoutCounter, key)
+  defp increment_recent_timeouts do
+    RollingWindow.inc(bucket(), @timeout_key)
 
     :ok
   end
 
-  defp sleep_if_too_many_recent_timeouts(key) do
-    wait_coefficient = count_of_recent_timeouts(key)
-
-    :timer.sleep(wait_coefficient * @wait_per_timeout)
-  end
-
-  defp something_that_uniquely_identifies_this_transport(transport, transport_options) do
-    to_string(transport) <> "." <> transport_options[:url]
-  end
-
-  defp count_of_recent_timeouts(key) do
-    RollingWindow.count(TimeoutCounter, key)
+  defp bucket do
+    Application.get_env(:ethereum_jsonrpc, __MODULE__)[:rolling_window_opts]
   end
 end

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/rolling_window.ex

@@ -71,6 +71,7 @@ defmodule EthereumJSONRPC.RollingWindow do
     default = List.to_tuple([key | windows])
 
     :ets.update_counter(table, key, {2, 1}, default)
+    # TODO consider broadcasting to indexers than some threshold has been met with result of updating the counter
 
     {:noreply, state}
   end