akkoma/lib/pleroma/gun/connection_pool/worker_supervisor.ex
rinpatch ec9d0d146b Connection pool: Fix race conditions in limit enforcement
Fixes race conditions in limit enforcement by putting worker processes
in a DynamicSupervisor
2020-07-15 15:17:27 +03:00

91 lines
2.4 KiB
Elixir

defmodule Pleroma.Gun.ConnectionPool.WorkerSupervisor do
@doc "Supervisor for pool workers. Does not do anything except enforce max connection limit"
use DynamicSupervisor
def start_link(opts) do
DynamicSupervisor.start_link(__MODULE__, opts, name: __MODULE__)
end
def init(_opts) do
DynamicSupervisor.init(
strategy: :one_for_one,
max_children: Pleroma.Config.get([:connections_pool, :max_connections])
)
end
def start_worker(opts) do
case DynamicSupervisor.start_child(__MODULE__, {Pleroma.Gun.ConnectionPool.Worker, opts}) do
{:error, :max_children} ->
case free_pool() do
:ok -> start_worker(opts)
:error -> {:error, :pool_full}
end
res ->
res
end
end
@registry Pleroma.Gun.ConnectionPool
@enforcer_key "enforcer"
defp free_pool do
case Registry.lookup(@registry, @enforcer_key) do
[] ->
pid =
spawn(fn ->
{:ok, _pid} = Registry.register(@registry, @enforcer_key, nil)
max_connections = Pleroma.Config.get([:connections_pool, :max_connections])
reclaim_max =
[:connections_pool, :reclaim_multiplier]
|> Pleroma.Config.get()
|> Kernel.*(max_connections)
|> round
|> max(1)
unused_conns =
Registry.select(
@registry,
[
{{:_, :"$1", {:_, :"$2", :"$3", :"$4"}}, [{:==, :"$2", []}],
[{{:"$1", :"$3", :"$4"}}]}
]
)
case unused_conns do
[] ->
exit(:no_unused_conns)
unused_conns ->
unused_conns
|> Enum.sort(fn {_pid1, crf1, last_reference1}, {_pid2, crf2, last_reference2} ->
crf1 <= crf2 and last_reference1 <= last_reference2
end)
|> Enum.take(reclaim_max)
|> Enum.each(fn {pid, _, _} ->
DynamicSupervisor.terminate_child(__MODULE__, pid)
end)
end
end)
wait_for_enforcer_finish(pid)
[{pid, _}] ->
wait_for_enforcer_finish(pid)
end
end
defp wait_for_enforcer_finish(pid) do
ref = Process.monitor(pid)
receive do
{:DOWN, ^ref, :process, ^pid, :no_unused_conns} ->
:error
{:DOWN, ^ref, :process, ^pid, :normal} ->
:ok
end
end
end