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Use Monotonic time for calculating request latency in Plug.Logger #373

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merged 2 commits into from
Mar 30, 2016
Merged

Use Monotonic time for calculating request latency in Plug.Logger #373

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660906b
Switch :os.timestamp to :erlang.monotonic_time for Plug.Logger
Mar 30, 2016
3aac991
Ensure Elixir < 1.2.0 is supported and improve on some names
Mar 30, 2016
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16 changes: 13 additions & 3 deletions lib/plug/logger.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -28,19 +28,29 @@ defmodule Plug.Logger do
[conn.method, ?\s, conn.request_path]
end

before_time = :os.timestamp()
start = current_time()

Conn.register_before_send(conn, fn conn ->
Logger.log level, fn ->
after_time = :os.timestamp()
diff = :timer.now_diff(after_time, before_time)
stop = current_time()
diff = time_diff(start, stop)

[connection_type(conn), ?\s, Integer.to_string(conn.status),
" in ", formatted_diff(diff)]
end
conn
end)
end

# TODO: remove this once Plug supports only Elixir 1.2.
if function_exported?(:erlang, :monotonic_time, 0) do
defp current_time, do: :erlang.monotonic_time
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We should use :erlang.monotonic_time(:micro_seconds) here and remove convert_time_unit call.

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Let's not do that because we lose precision. The ideal is to always convert later.

defp time_diff(start, stop), do: (stop - start) |> :erlang.convert_time_unit(:native, :micro_seconds)
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Can we remove the piping here?

else
defp current_time, do: :os.timestamp()
defp time_diff(start, stop), do: :timer.now_diff(stop, start)
end

defp formatted_diff(diff) when diff > 1000, do: [diff |> div(1000) |> Integer.to_string, "ms"]
defp formatted_diff(diff), do: [diff |> Integer.to_string, "µs"]

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