profile.eprof.ex

defmodule Mix.Tasks.Profile.Eprof do
  use Mix.Task

  @shortdoc "Profiles the given file or expression with eprof"

  @moduledoc """
  Profiles the given file or expression using Erlang's `eprof` tool.

  [`:eprof`](`:eprof`) provides time information of each function call and can be useful
  when you want to discover the bottlenecks related to this.

  Before running the code, it invokes the `app.start` task which compiles
  and loads your project. After that, the target expression is profiled together
  with all matching function calls using the Erlang trace BIFs. The tracing of
  the function calls for that is enabled when the profiling is begun, and
  disabled when profiling is stopped.

  To profile the code, you can use syntax similar to the `mix run` task:

      $ mix profile.eprof -e Hello.world
      $ mix profile.eprof -e "[1, 2, 3] |> Enum.reverse |> Enum.map(&Integer.to_string/1)"
      $ mix profile.eprof my_script.exs arg1 arg2 arg3

  This task is automatically re-enabled, so you can profile multiple times
  in the same Mix invocation.

  ## Command line options

    * `--matching` - only profile calls matching the given `Module.function/arity` pattern
    * `--calls` - filters out any results with a call count lower than this
    * `--time` - filters out any results that took lower than specified (in µs)
    * `--sort` - sorts the results by `time` or `calls` (default: `time`)
    * `--eval`, `-e` - evaluates the given code
    * `--require`, `-r` - requires pattern before running the command
    * `--parallel`, `-p` - makes all requires parallel
    * `--no-warmup` - skips the warmup step before profiling
    * `--no-compile` - does not compile even if files require compilation
    * `--no-deps-check` - does not check dependencies
    * `--no-archives-check` - does not check archives
    * `--no-halt` - does not halt the system after running the command
    * `--no-start` - does not start applications after compilation
    * `--no-elixir-version-check` - does not check the Elixir version from mix.exs

  ## Profile output

  Example output:

      #                                               CALLS     % TIME µS/CALL
      Total                                              24 100.0   26    1.08
      Enum.reduce_range_inc/4                             5  3.85    1    0.20
      :erlang.make_fun/3                                  1  7.69    2    2.00
      Enum.each/2                                         1  7.69    2    2.00
      anonymous fn/0 in :elixir_compiler_0.__FILE__/1     1  7.69    2    2.00
      :erlang.integer_to_binary/1                         5 15.39    4    0.80
      :erlang.apply/2                                     1 15.39    4    4.00
      anonymous fn/3 in Enum.each/2                       5 19.23    5    1.00
      String.Chars.Integer.to_string/1                    5 23.08    6    1.20

      Profile done over 8 matching functions

  The default output contains data gathered from all matching functions. The first
  row after the header contains the sums of the partial results and the average time
  for all the function calls listed. The following rows contain the function call,
  followed by the number of times that the function was called, then by the percentage
  of time that the call uses, then the total time for that function in microseconds,
  and, finally, the average time per call in microseconds.

  When `--matching` option is specified, call count tracing will be started only for
  the functions matching the given pattern:

      #                                               CALLS     % TIME µS/CALL
      Total                                               5 100.0    6    1.20
      String.Chars.Integer.to_string/1                    5 100.0    6    1.20

      Profile done over 1 matching functions

  The pattern can be a module name, such as `String` to count all calls to that module,
  a call without arity, such as `String.split`, to count all calls to that function
  regardless of arity, or a call with arity, such as `String.split/3`, to count all
  calls to that exact module, function and arity.

  ## Caveats

  You should be aware that the code being profiled is running in an anonymous
  function which is invoked by [`:eprof` module](https://www.erlang.org/doc/man/eprof.html).
  Thus, you'll see some additional entries in your profile output. It is also
  important to note that the profiler is stopped as soon as the code has finished running,
  and this may need special attention, when: running asynchronous code as function calls which were
  called before the profiler stopped will not be counted; running synchronous code as long
  running computations and a profiler without a proper MFA trace pattern or filter may
  lead to a result set which is difficult to comprehend.

  You should expect a slowdown in your code execution using this tool since `:eprof` has
  some performance impact on the execution, but the impact is considerably lower than
  `Mix.Tasks.Profile.Fprof`. If you have a large system try to profile a limited
  scenario or focus on the main modules or processes. Another alternative is to use
  `Mix.Tasks.Profile.Cprof` that uses [`:cprof`](`:cprof`) and has a low performance degradation effect.
  """

  @switches [
    parallel: :boolean,
    require: :keep,
    eval: :keep,
    config: :keep,
    matching: :string,
    halt: :boolean,
    compile: :boolean,
    deps_check: :boolean,
    calls: :integer,
    time: :integer,
    sort: :string,
    start: :boolean,
    archives_check: :boolean,
    warmup: :boolean,
    elixir_version_check: :boolean,
    parallel_require: :keep
  ]

  @aliases [
    r: :require,
    p: :parallel,
    e: :eval,
    c: :config
  ]

  @impl true
  def run(args) do
    {opts, head} = OptionParser.parse_head!(args, aliases: @aliases, strict: @switches)
    Mix.Task.reenable("profile.eprof")

    Mix.Tasks.Run.run(
      ["--no-mix-exs" | args],
      opts,
      head,
      &profile_code(&1, opts),
      &profile_code(File.read!(&1), opts)
    )
  end

  defp profile_code(code_string, opts) do
    opts = Enum.map(opts, &parse_opt/1)

    content =
      quote do
        unquote(__MODULE__).profile(
          fn ->
            unquote(Code.string_to_quoted!(code_string))
          end,
          unquote(Macro.escape(opts))
        )
      end

    # Use compile_quoted since it leaves less noise than eval_quoted
    Code.compile_quoted(content)
  end

  defp parse_opt({:matching, matching}) do
    case Mix.Utils.parse_mfa(matching) do
      {:ok, [m, f, a]} -> {:matching, {m, f, a}}
      {:ok, [m, f]} -> {:matching, {m, f, :_}}
      {:ok, [m]} -> {:matching, {m, :_, :_}}
      :error -> Mix.raise("Invalid matching pattern: #{matching}")
    end
  end

  defp parse_opt({:sort, "time"}), do: {:sort, :time}
  defp parse_opt({:sort, "calls"}), do: {:sort, :calls}
  defp parse_opt({:sort, other}), do: Mix.raise("Invalid sort option: #{other}")
  defp parse_opt(other), do: other

  @doc """
  Allows to programmatically run the `eprof` profiler on expression in `fun`.

  Returns the return value of `fun`.

  ## Options

    * `:matching` - only profile calls matching the given pattern in form of
      `{module, function, arity}`, where each element may be replaced by `:_`
      to allow any value
    * `:calls` - filters out any results with a call count lower than this
    * `:time` - filters out any results that took lower than specified (in µs)
    * `:sort` - sort the results by `:time` or `:calls` (default: `:time`)
    * `:warmup` - if the code should be warmed up before profiling (default: `true`)
    * `:set_on_spawn` - if newly spawned processes should be measured (default: `true`)

  """
  @spec profile((-> result), keyword()) :: result when result: any()
  def profile(fun, opts \\ []) when is_function(fun, 0) do
    Mix.ensure_application!(:tools)
    {return_value, results} = profile_and_analyse(fun, opts)
    print_output(results)
    return_value
  end

  defp profile_and_analyse(fun, opts) do
    if Keyword.get(opts, :warmup, true) do
      IO.puts("Warmup...\n")
      fun.()
    end

    :eprof.start()
    matching = Keyword.get(opts, :matching, {:_, :_, :_})
    set_on_spawn = Keyword.get(opts, :set_on_spawn, true)
    {:ok, return_value} = :eprof.profile([], fun, matching, set_on_spawn: set_on_spawn)

    results =
      Enum.map(:eprof.dump(), fn {pid, call_results} ->
        parsed_calls =
          call_results
          |> filter_results(opts)
          |> sort_results(opts)
          |> add_totals()

        {pid, parsed_calls}
      end)

    :eprof.stop()

    {return_value, results}
  end

  defp filter_results(call_results, opts) do
    calls_opt = Keyword.get(opts, :calls, 0)
    time_opt = Keyword.get(opts, :time, 0)

    call_results
    |> Stream.filter(fn {_mfa, {count, _time}} -> count >= calls_opt end)
    |> Stream.filter(fn {_mfa, {_count, time}} -> time >= time_opt end)
  end

  defp sort_results(call_results, opts) do
    Enum.sort_by(call_results, sort_function(Keyword.get(opts, :sort, :time)))
  end

  defp sort_function(:time), do: fn {_mfa, {_count, time}} -> time end
  defp sort_function(:calls), do: fn {_mfa, {count, _time}} -> count end

  defp add_totals(call_results) do
    {function_count, call_count, total_time} =
      Enum.reduce(call_results, {0, 0, 0}, fn {_, {count, time}}, acc ->
        {function_count, call_count, total_time} = acc
        {function_count + 1, call_count + count, total_time + time}
      end)

    {function_count, call_results, call_count, total_time}
  end

  @header ["#", "CALLS", "%", "TIME", "µS/CALL"]

  defp print_output([]) do
    print_function_count(0)
  end

  defp print_output(results) do
    Enum.each(results, &print_result/1)
  end

  defp print_result({pid, {function_count, call_results, call_count, total_time}}) do
    formatted_rows = Enum.map(call_results, &format_row(&1, total_time))
    formatted_total = format_total(total_time, call_count)

    column_lengths = column_lengths(@header, formatted_rows)

    IO.puts("")

    print_pid_row(pid)
    print_row(@header, column_lengths)
    print_row(formatted_total, column_lengths)
    Enum.each(formatted_rows, &print_row(&1, column_lengths))

    IO.puts("")

    print_function_count(function_count)
  end

  defp print_pid_row(pid) do
    IO.puts("Profile results of #{inspect(pid)}")
  end

  defp format_row({{module, function, arity}, {count, time}}, total_time) do
    mfa = Exception.format_mfa(module, function, arity)
    time_percentage = :erlang.float_to_binary(100 * divide(time, total_time), [{:decimals, 2}])
    time_per_call = :erlang.float_to_binary(divide(time, count), [{:decimals, 2}])
    count = Integer.to_string(count)
    time = Integer.to_string(time)

    [mfa, count, time_percentage, time, time_per_call]
  end

  defp format_total(total_time, total_count) do
    time_per_call = :erlang.float_to_binary(divide(total_time, total_count), [{:decimals, 2}])

    [
      "Total",
      Integer.to_string(total_count),
      "100.00",
      Integer.to_string(total_time),
      time_per_call
    ]
  end

  defp divide(_, 0), do: 0.0
  defp divide(t, n), do: t / n

  defp column_lengths(header, rows) do
    max_lengths = Enum.map(header, &String.length/1)

    Enum.reduce(rows, max_lengths, fn row, max_lengths ->
      Stream.map(row, &String.length/1)
      |> Stream.zip(max_lengths)
      |> Enum.map(&max/1)
    end)
  end

  defp max({a, b}) when a >= b, do: a
  defp max({_, b}), do: b

  @format "~-*s ~*s ~*s ~*s ~*s~n"

  defp print_row(row, column_lengths) do
    to_print =
      column_lengths
      |> Stream.zip(Stream.map(row, &String.to_charlist/1))
      |> Enum.flat_map(&Tuple.to_list/1)

    :io.format(@format, to_print)
  end

  defp print_function_count(count) do
    IO.puts("Profile done over #{count} matching functions")
  end
end