使用持久状态更正 GenServer 实现
Correct GenServer implementation with persistent state
我对一些 OTP 概念不熟悉。我有 GenServer,它将向 RabbitMQ 发布事件。此 GenServer 的状态为:amqp Chanel
,它在 init() 期间启动一次,并在 cast
次调用之间保持不变。
defmodule Myapp.Events.AmqpTransport do
require Logger
use GenServer
use AMQP
def start_link(_) do
GenServer.start_link(__MODULE__, [], name: __MODULE__)
end
def init(_opts) do
username = get_conf(:username)
password = get_conf(:password)
host = get_conf(:host)
port = get_conf(:port)
vhost = String.replace(get_conf(:vhost), "/", "%2f")
exchange = get_conf(:exchange)
{:ok, conn} = Connection.open("amqp://#{username}:#{password}@#{host}:#{port}/#{vhost}")
{:ok, chan} = Channel.open(conn)
{:ok, chan}
end
def handle_cast({:emit, event}, chan) do
payload = :jiffy.encode(%{event: event})
Basic.publish(
chan,
get_conf(:exchange),
get_conf(:routing_key),
payload
)
{:noreply, :ok, chan}
end
def emit(event) do
GenServer.cast(__MODULE__, {:emit, event})
end
defp get_conf(key) do
conf = Application.get_env(:myapp_events, :rabbit)
conf[key]
end
end
当我使用 Myapp.Events.AmqpTransport.emit(%{"hop": "hej"})
调用它时出现错误:
[error] Supervisor 'Elixir.Myapp.Events.Supervisor' had child
'Elixir.Myapp.Events.AmqpTransport' started with
'Elixir.Myapp.Events.AmqpTransport':start_link([])
at <0.7024.0> exit with reason timeout_value
in gen_server:loop/7 line 437
in context child_terminated
我错过了什么?
您应该 return two-element 元组 {:noreply, chan}
,而不是 three-element 来自 GenDerver.handle_cast/2
.
的元组 {:noreply, :ok, chan}
转换是异步的,因此它们不会 return 任何东西。您的 three-element 元组 {:noreply, _, _}
被视为表单
中的响应
{:noreply, new_state,
timeout() | :hibernate | {:continue, term()}}
和作为第三个元素传递的 state
应该是超时(它不匹配 :hibernate
,也不匹配元组),但它的值不是任何超时意思是
我对一些 OTP 概念不熟悉。我有 GenServer,它将向 RabbitMQ 发布事件。此 GenServer 的状态为:amqp Chanel
,它在 init() 期间启动一次,并在 cast
次调用之间保持不变。
defmodule Myapp.Events.AmqpTransport do
require Logger
use GenServer
use AMQP
def start_link(_) do
GenServer.start_link(__MODULE__, [], name: __MODULE__)
end
def init(_opts) do
username = get_conf(:username)
password = get_conf(:password)
host = get_conf(:host)
port = get_conf(:port)
vhost = String.replace(get_conf(:vhost), "/", "%2f")
exchange = get_conf(:exchange)
{:ok, conn} = Connection.open("amqp://#{username}:#{password}@#{host}:#{port}/#{vhost}")
{:ok, chan} = Channel.open(conn)
{:ok, chan}
end
def handle_cast({:emit, event}, chan) do
payload = :jiffy.encode(%{event: event})
Basic.publish(
chan,
get_conf(:exchange),
get_conf(:routing_key),
payload
)
{:noreply, :ok, chan}
end
def emit(event) do
GenServer.cast(__MODULE__, {:emit, event})
end
defp get_conf(key) do
conf = Application.get_env(:myapp_events, :rabbit)
conf[key]
end
end
当我使用 Myapp.Events.AmqpTransport.emit(%{"hop": "hej"})
调用它时出现错误:
[error] Supervisor 'Elixir.Myapp.Events.Supervisor' had child
'Elixir.Myapp.Events.AmqpTransport' started with
'Elixir.Myapp.Events.AmqpTransport':start_link([])
at <0.7024.0> exit with reason timeout_value
in gen_server:loop/7 line 437
in context child_terminated
我错过了什么?
您应该 return two-element 元组 {:noreply, chan}
,而不是 three-element 来自 GenDerver.handle_cast/2
.
{:noreply, :ok, chan}
转换是异步的,因此它们不会 return 任何东西。您的 three-element 元组 {:noreply, _, _}
被视为表单
{:noreply, new_state,
timeout() | :hibernate | {:continue, term()}}
和作为第三个元素传递的 state
应该是超时(它不匹配 :hibernate
,也不匹配元组),但它的值不是任何超时意思是