Connection pool: Fix race conditions in limit enforcement

Fixes race conditions in limit enforcement by putting worker processes
in a DynamicSupervisor
This commit is contained in:
rinpatch 2020-05-06 23:14:24 +03:00
parent d08b157699
commit ec9d0d146b
4 changed files with 118 additions and 92 deletions

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@ -243,7 +243,7 @@ defp http_children(Tesla.Adapter.Hackney, _) do
end end
defp http_children(Tesla.Adapter.Gun, _) do defp http_children(Tesla.Adapter.Gun, _) do
[{Registry, keys: :unique, name: Pleroma.Gun.ConnectionPool}] Pleroma.Gun.ConnectionPool.children()
end end
defp http_children(_, _), do: [] defp http_children(_, _), do: []

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@ -1,6 +1,15 @@
defmodule Pleroma.Gun.ConnectionPool do defmodule Pleroma.Gun.ConnectionPool do
@registry __MODULE__ @registry __MODULE__
alias Pleroma.Gun.ConnectionPool.WorkerSupervisor
def children do
[
{Registry, keys: :unique, name: @registry},
Pleroma.Gun.ConnectionPool.WorkerSupervisor
]
end
def get_conn(uri, opts) do def get_conn(uri, opts) do
key = "#{uri.scheme}:#{uri.host}:#{uri.port}" key = "#{uri.scheme}:#{uri.host}:#{uri.port}"
@ -14,96 +23,24 @@ def get_conn(uri, opts) do
{:ok, gun_pid} {:ok, gun_pid}
[] -> [] ->
case enforce_pool_limits() do # :gun.set_owner fails in :connected state for whatevever reason,
:ok -> # so we open the connection in the process directly and send it's pid back
# :gun.set_owner fails in :connected state for whatevever reason, # We trust gun to handle timeouts by itself
# so we open the connection in the process directly and send it's pid back case WorkerSupervisor.start_worker([uri, key, opts, self()]) do
# We trust gun to handle timeouts by itself {:ok, _worker_pid} ->
case GenServer.start(Pleroma.Gun.ConnectionPool.Worker, [uri, key, opts, self()], receive do
timeout: :infinity {:conn_pid, pid} -> {:ok, pid}
) do
{:ok, _worker_pid} ->
receive do
{:conn_pid, pid} -> {:ok, pid}
end
{:error, {:error, {:already_registered, worker_pid}}} ->
get_gun_pid_from_worker(worker_pid)
err ->
err
end end
:error -> {:error, {:error, {:already_registered, worker_pid}}} ->
{:error, :pool_full} get_gun_pid_from_worker(worker_pid)
err ->
err
end end
end end
end end
@enforcer_key "enforcer"
defp enforce_pool_limits() do
max_connections = Pleroma.Config.get([:connections_pool, :max_connections])
if Registry.count(@registry) >= max_connections do
case Registry.lookup(@registry, @enforcer_key) do
[] ->
pid =
spawn(fn ->
{:ok, _pid} = Registry.register(@registry, @enforcer_key, nil)
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(:pool_full)
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, _, _} -> GenServer.call(pid, :idle_close) end)
end
end)
wait_for_enforcer_finish(pid)
[{pid, _}] ->
wait_for_enforcer_finish(pid)
end
else
:ok
end
end
defp wait_for_enforcer_finish(pid) do
ref = Process.monitor(pid)
receive do
{:DOWN, ^ref, :process, ^pid, :pool_full} ->
:error
{:DOWN, ^ref, :process, ^pid, :normal} ->
:ok
end
end
defp get_gun_pid_from_worker(worker_pid) do defp get_gun_pid_from_worker(worker_pid) do
# GenServer.call will block the process for timeout length if # GenServer.call will block the process for timeout length if
# the server crashes on startup (which will happen if gun fails to connect) # the server crashes on startup (which will happen if gun fails to connect)

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@ -1,9 +1,13 @@
defmodule Pleroma.Gun.ConnectionPool.Worker do defmodule Pleroma.Gun.ConnectionPool.Worker do
alias Pleroma.Gun alias Pleroma.Gun
use GenServer use GenServer, restart: :temporary
@registry Pleroma.Gun.ConnectionPool @registry Pleroma.Gun.ConnectionPool
def start_link(opts) do
GenServer.start_link(__MODULE__, opts)
end
@impl true @impl true
def init([uri, key, opts, client_pid]) do def init([uri, key, opts, client_pid]) do
time = :os.system_time(:second) time = :os.system_time(:second)
@ -82,12 +86,6 @@ def handle_info({:gun_down, _pid, _protocol, _reason, _killed_streams} = down_me
{:stop, {:error, down_message}, state} {:stop, {:error, down_message}, state}
end end
@impl true
def handle_call(:idle_close, _, %{key: key} = state) do
Registry.unregister(@registry, key)
{:stop, :normal, state}
end
# LRFU policy: https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.55.1478 # LRFU policy: https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.55.1478
defp crf(time_delta, prev_crf) do defp crf(time_delta, prev_crf) do
1 + :math.pow(0.5, time_delta / 100) * prev_crf 1 + :math.pow(0.5, time_delta / 100) * prev_crf

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@ -0,0 +1,91 @@
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