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Connection pool: Fix race conditions in limit enforcement

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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
commit ec9d0d146b
4 changed files with 118 additions and 92 deletions
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105
lib/pleroma/gun/connection_pool.ex
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@ -1,6 +1,15 @@
defmodule Pleroma.Gun.ConnectionPool do
@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
key = "#{uri.scheme}:#{uri.host}:#{uri.port}"
@ -14,96 +23,24 @@ defmodule Pleroma.Gun.ConnectionPool do
{:ok, gun_pid}
[] ->
case enforce_pool_limits() do
:ok ->
# :gun.set_owner fails in :connected state for whatevever reason,
# so we open the connection in the process directly and send it's pid back
# We trust gun to handle timeouts by itself
case GenServer.start(Pleroma.Gun.ConnectionPool.Worker, [uri, key, opts, self()],
timeout: :infinity
) 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
# :gun.set_owner fails in :connected state for whatevever reason,
# so we open the connection in the process directly and send it's pid back
# We trust gun to handle timeouts by itself
case WorkerSupervisor.start_worker([uri, key, opts, self()]) do
{:ok, _worker_pid} ->
receive do
{:conn_pid, pid} -> {:ok, pid}
end
:error ->
{:error, :pool_full}
{:error, {:error, {:already_registered, worker_pid}}} ->
get_gun_pid_from_worker(worker_pid)
err ->
err
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
# GenServer.call will block the process for timeout length if
# the server crashes on startup (which will happen if gun fails to connect)