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Postgres sync engine. Sync little subsets of your Postgres data into local apps and services.
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lib/electric/shape_cache/shape_status/shape_db/pool_registry.ex
defmodule Electric.ShapeCache.ShapeStatus.ShapeDb.PoolRegistry do
@moduledoc """
Manages pool registration for a stack. Contains the `exclusive_mode` logic,
so that when enabled, the same write connection is returned for reads and
writes.
In `exclusive_mode` only the writer pool is started by the supervisor.
"""
use GenServer
import Electric, only: [is_stack_id: 1]
def start_link(args) do
GenServer.start_link(__MODULE__, args)
end
@doc """
Used by pool processes for registration. The `exclusive?` boolean is passed
onto the `register_name/2` call and determines whether the connection is
registered for both reads and writes in `exclusive_mode`.
"""
def pool_name(stack_id, role, exclusive?)
when is_stack_id(stack_id) and role in [:read, :write] do
{:via, __MODULE__, {stack_id, role, exclusive?}}
end
@doc """
Used by ShapeDb to retrieve a pool.
"""
def pool_name(stack_id, role) when is_stack_id(stack_id) and role in [:read, :write] do
{:via, __MODULE__, {stack_id, role}}
end
# GenServer name registration callback
def register_name({stack_id, role, exclusive?}, pid) when is_stack_id(stack_id) do
keys = pool_keys(role, exclusive?, pid)
if :ets.insert_new(ets_table(stack_id), keys), do: :yes, else: :no
end
# GenServer name registration callback
def unregister_name({stack_id, role, exclusive?}) do
table = ets_table(stack_id)
pool_keys(role, exclusive?)
|> Enum.each(&:ets.delete(table, &1))
end
# GenServer name registration callback
def whereis_name({stack_id, role}) do
:ets.lookup_element(ets_table(stack_id), role, 2, nil) || :undefined
end
# GenServer name registration callback
def whereis_name({stack_id, :write, true}) do
:ets.lookup_element(ets_table(stack_id), :write, 2, nil) || :undefined
end
def whereis_name({stack_id, role, false}) do
:ets.lookup_element(ets_table(stack_id), role, 2, nil) || :undefined
end
defp pool_keys(:write, true, pid) do
[{:read, pid}, {:write, pid}]
end
defp pool_keys(role, false, pid) do
[{role, pid}]
end
# used by unregister_name/1
defp pool_keys(:write, true) do
[:read, :write]
end
defp pool_keys(role, false) do
[role]
end
@impl GenServer
def init(args) do
stack_id = Keyword.fetch!(args, :stack_id)
Process.set_label({:shape_db_pool_registry, stack_id})
Logger.metadata(stack_id: stack_id)
table =
:ets.new(ets_table(stack_id), [
:public,
:named_table,
read_concurrency: true,
write_concurrency: :auto
])
{:ok, %{table: table, stack_id: stack_id}}
end
defp ets_table(stack_id),
do: :"Electric.ShapeCache.ShapeStatus.ShapeDb.PoolRegistry:#{stack_id}"
end