GrpcConnectionPool.Strategy behaviour (grpc_connection_pool v0.3.5)

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Behaviour for connection selection strategies.

A strategy determines which channel index to select when get_channel/1 is called. Built-in strategies:

  • :round_robin — Lock-free atomics-based round-robin (default)
  • :random — Random selection, good for avoiding hot-spotting
  • :power_of_two — Power-of-two-choices with least-recently-used tiebreak

Custom Strategies

Implement this behaviour to create a custom strategy:

defmodule MyApp.WeightedStrategy do
  @behaviour GrpcConnectionPool.Strategy

  @impl true
  def init(_pool_name, _pool_size), do: %{}

  @impl true
  def select(_state, channel_count, _ets_table) do
    # Custom selection logic
    {:ok, :rand.uniform(channel_count) - 1}
  end
end

Then configure it:

config = GrpcConnectionPool.Config.new(
  pool: [strategy: MyApp.WeightedStrategy]
)

Summary

Types

state()

Callbacks

init(pool_name, pool_size)

Initialize strategy state for a pool.

select(state, channel_count, ets_table)

Select a channel index from the pool.

Types

state()

@type state() :: term()

Callbacks

init(pool_name, pool_size)

@callback init(pool_name :: atom(), pool_size :: pos_integer()) :: state()

Initialize strategy state for a pool.

Called once during pool startup. The returned state is stored in :persistent_term and passed to select/3 on each call.

select(state, channel_count, ets_table)

@callback select(state(), channel_count :: pos_integer(), ets_table :: atom()) ::
  {:ok, non_neg_integer()}

Select a channel index from the pool.

Must return an index in the range 0..channel_count-1. Called on every get_channel invocation — must be fast.