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New Relic's Open-Source Elixir Agent
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lib/new_relic/transaction/erlang_trace.ex
defmodule NewRelic.Transaction.ErlangTrace do
use GenServer, restart: :temporary
alias NewRelic.Transaction
# This GenServer watches transaction processes for
# :trace messages signal that a transaction process has
# spwaned another process that we track as a Span
@moduledoc false
def start_link(_) do
GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
end
@overload_queue_len 500
@overload_backoff 60 * 1000
def init(:ok) do
NewRelic.sample_process()
enable_trace_patterns()
overload = %{
queue_len: Application.get_env(:new_relic_agent, :overload_queue_len, @overload_queue_len),
backoff: Application.get_env(:new_relic_agent, :overload_backoff, @overload_backoff)
}
{:ok, %{overload: overload}}
end
# API
def trace() do
GenServer.cast(__MODULE__, {:trace, self()})
end
def disable() do
GenServer.call(__MODULE__, :disable)
end
# Server
def handle_cast({:trace, pid}, state) do
enable_trace_flags(pid)
{:noreply, state}
end
def handle_call(:disable, _from, state) do
{:stop, {:shutdown, :disable}, :ok, state}
end
# Trace messages
def handle_info(
{:trace_ts, source, :return_from, {Task.Supervisor, :async_nolink, _arity},
%Task{pid: pid}, timestamp},
state
) do
overload_protection(state.overload)
enable_trace_flags(pid)
Transaction.Reporter.track_spawn(source, pid, NewRelic.Util.time_to_ms(timestamp))
{:noreply, state}
end
def handle_info(
{:trace_ts, source, :return_from, {:poolboy, :checkout, _}, pid, timestamp},
state
) do
overload_protection(state.overload)
Transaction.Reporter.track_spawn(source, pid, NewRelic.Util.time_to_ms(timestamp))
{:noreply, state}
end
def handle_info(
{:trace_ts, source, :return_from, {:proc_lib, :spawn_link, _}, pid, timestamp},
state
) do
overload_protection(state.overload)
Transaction.Reporter.track_spawn(source, pid, NewRelic.Util.time_to_ms(timestamp))
{:noreply, state}
end
def handle_info(_msg, state) do
{:noreply, state}
end
# Helpers
def enable_trace_flags(pid) do
# Trace function calls so we can install specific trace_patterns
# http://erlang.org/doc/man/erlang.html#trace-3
:erlang.trace(pid, true, [:call, :set_on_spawn, :timestamp])
rescue
# Process is already dead
ArgumentError -> nil
end
def enable_trace_patterns do
# Use function tracers to notice when Async work has been kicked off
# http://erlang.org/doc/man/erlang.html#trace_3_trace_messages_return_from
# http://erlang.org/doc/apps/erts/match_spec.html
trace_proc_lib_spawn_link()
trace_task_async_nolink()
trace_poolboy_checkout()
end
defp trace_proc_lib_spawn_link do
:erlang.trace_pattern({:proc_lib, :spawn_link, :_}, [{:_, [], [{:return_trace}]}], [])
end
defp trace_task_async_nolink do
:erlang.trace_pattern({Task.Supervisor, :async_nolink, :_}, [{:_, [], [{:return_trace}]}], [])
end
defp trace_poolboy_checkout do
:erlang.trace_pattern({:poolboy, :checkout, :_}, [{:_, [], [{:return_trace}]}], [])
end
defp overload_protection(%{backoff: backoff} = overload) do
{:message_queue_len, len} = Process.info(self(), :message_queue_len)
cond do
len >= overload.queue_len ->
NewRelic.log(:error, "ErlangTrace overload: #{len} - shutting down for #{backoff} ms.")
NewRelic.Transaction.ErlangTraceManager.enable_erlang_trace(after: overload.backoff)
exit({:shutdown, :overload})
true ->
:all_good
end
end
end