AkkomaGang/concurrent-limiter
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Remove ETS backend, add max_retries, add options to limit/3.

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Jordan Bracco 2020-05-14 22:38:29 +02:00
parent 9f95ba8f65
commit fb0bcf9e8d
1 changed files with 34 additions and 70 deletions
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104
lib/concurrent_limiter.ex
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@ -6,36 +6,32 @@ defmodule ConcurrentLimiter do
A concurrency limiter. Limits the number of concurrent invocations possible, without using a worker pool or different processes.
It can be useful in cases where you don't need a worker pool but still being able to limit concurrent calls without much overhead. As it internally uses `persistent_term` to store metadata, and can fallback to ETS tables, it is however not made for a large number of limiters and cannot be used for things like a per-user rate limiter.
It supports two storage methods:
* **[atomics](https://erlang.org/doc/man/atomics.html)** recommended and default if your OTP is > 21.2.
* **[ets](https://erlang.org/doc/man/ets.html)** either with a single table per limiter (faster) or a shared table.
You would almost always want to use atomics, ets is mostly there for backwards compatibility.
It can be useful in cases where you don't need a worker pool but still being able to limit concurrent calls without much overhead.
As it internally uses `persistent_term` to store metadata, and can fallback to ETS tables, it is however not made for a large number
of limiters and cannot be used for things like a per-user rate limiter.
"""
@doc """
Initializes a `ConcurrentLimiter`.
"""
@default_wait 150
@default_max_retries 5
@spec new(name, max_running, max_waiting, options) :: :ok | {:error, :existing} when name: atom(),
max_running: non_neg_integer(),
max_waiting: non_neg_integer() | :infinity,
options: [option],
option: {:wait, non_neg_integer()} | backend,
backend: :atomics | ets_backend,
ets_backend: :ets | {:ets, atom()} | {:ets, atom(), ets_options :: []}
option: {:wait, non_neg_integer()} | {:max_retries, non_neg_integer()}
def new(name, max_running, max_waiting, options \\ []) do
name = prefix_name(name)
if defined?(name) do
{:error, :existing}
else
wait = Keyword.get(options, :wait, 150)
backend = Keyword.get(options, :backend, default_backend())
{:ok, backend} = setup_backend(backend)
:persistent_term.put(name, {__MODULE__, max_running, max_waiting, backend, wait})
wait = Keyword.get(options, :wait, @default_wait)
max_retries = Keyword.get(options, :max_retries, @default_max_retries)
atomics = :atomics.new(1, [signed: true])
:persistent_term.put(name, {__MODULE__, max_running, max_waiting, atomics, wait, max_retries})
:ok
end
end
@ -50,8 +46,9 @@ defmodule ConcurrentLimiter do
name = prefix_name(name)
if defined?(name) do
new_wait = Keyword.get(options, :wait)
{__MODULE__, max_running, max_waiting, backend, wait} = :persistent_term.get(name)
new = {__MODULE__, new_max_running || max_running, new_max_waiting || max_waiting, backend, new_wait || wait}
new_max_retries = Keyword.get(options, :max_retries)
{__MODULE__, max_running, max_waiting, ref, wait, max_retries} = :persistent_term.get(name)
new = {__MODULE__, new_max_running || max_running, new_max_waiting || max_waiting, ref, new_wait || wait, new_max_retries || max_retries}
:persistent_term.put(name, new)
:ok
else
@ -59,53 +56,51 @@ defmodule ConcurrentLimiter do
end
end
@spec limit(atom(), function()) :: {:error, :overload} | any()
@spec limit(atom(), function(), opts) :: {:error, :overload} | any() when opts: [option],
option: {:wait, non_neg_integer()} | {:max_retries, non_neg_integer()}
@doc "Limits invocation of `fun`."
def limit(name, fun) do
do_limit(prefix_name(name), fun)
def limit(name, fun, opts \\ []) do
do_limit(prefix_name(name), fun, opts, 0)
end
defp do_limit(name, fun) do
{__MODULE__, max_running, max_waiting, backend, wait} = :persistent_term.get(name)
defp do_limit(name, fun, opts, retries) do
{__MODULE__, max_running, max_waiting, ref, wait, max_retries} = :persistent_term.get(name)
max = max_running + max_waiting
counter = inc(backend, name)
counter = inc(ref, name)
max_retries = Keyword.get(opts, :max_retries) || max_retries
cond do
counter <= max_running ->
try do
fun.()
after
dec(backend, name)
dec(ref, name)
end
counter > max ->
dec(backend, name)
dec(ref, name)
{:error, :overload}
retries + 1 > max_retries ->
{:error, :overload}
counter > max_running ->
wait(backend, name, wait, fun)
wait(ref, name, wait, fun, opts, max_retries, retries + 1)
end
end
defp wait(backend, name, wait, fun) do
defp wait(ref, name, wait, fun, opts, max_retries, retries) do
wait = Keyword.get(opts, :timeout) || wait
Process.sleep(wait)
dec(backend, name)
do_limit(name, fun)
dec(ref, name)
do_limit(name, fun, opts, retries)
end
defp inc({:ets, ets}, name) do
:ets.update_counter(ets, name, {2, 1}, {name, 0})
end
defp inc({:atomics, ref}, _) do
defp inc(ref, _) do
:atomics.add_get(ref, 1, 1)
end
defp dec({:ets, ets}, name) do
:ets.update_counter(ets, name, {2, -1}, {name, 0})
end
defp dec({:atomics, ref}, _) do
defp dec(ref, _) do
:atomics.sub_get(ref, 1, 1)
end
@ -118,35 +113,4 @@ defmodule ConcurrentLimiter do
_ -> false
end
defp default_backend() do
if Code.ensure_loaded?(:atomics) do
:atomics
else
Logger.debug("ConcurrentLimiter: atomics not available, using ETS backend")
:ets
end
end
defp setup_backend(:ets) do
setup_backend({:ets, ETS})
end
defp setup_backend({:ets, name}) do
setup_backend({:ets, name, [{:write_concurrency, true}, {:read_concurrency, true}]})
end
defp setup_backend({:ets, name, options}) do
ets_name = prefix_name(name)
case :ets.whereis(ets_name) do
:undefined -> :ets.new(ets_name, [:public, :named_table] ++ options)
_ -> nil
end
{:ok, {:ets, ets_name}}
end
defp setup_backend(:atomics) do
{:ok, {:atomics, :atomics.new(1, [signed: true])}}
end
end