GenServer使用指南

1初始化服务器.md

来源：https://raw.githubusercontent.com/benjamintanweihao/elixir-cheatsheets/master/GenServer_CheatSheet.pdf

Client

def start_link(opts \\ []) do
 GenServer.start_link(__MODULE__, :ok, opts)
end

Returns

{:ok, pid}

Callback

def init(:ok) do
 state = init_state()
 {:ok, state}         # 这里的 :ok 对应初始化的 :ok
end

回调可以返回的值

{:ok, state}
{ok, state, 5_000}
{:ok, state, :hibernate}
{:stop, reason*}
RETURN VALUES
:ignore

2同步请求操作.md

Client发送请求

def sync_op(pid, args) do
 GenServer.call(pid, {:sync_op, args})  # :sync_op 是我们指定操作的名称
end

Callback

def handle_call({:sync_op, args}, from, state) do
 new_state = f(state, args)
 {:reply, new_state}
end

回调返回值示例

{:reply, reply, new_state}
{:reply, reply, new_state, 5_000}
{:reply, reply, new_state, :hibernate}
{:noreply, new_state}
{:noreply, new_state, 5_000}
{:noreply, new_state, :hibernate}
{:stop, reason*, reply, new_state}
{:stop, reason*, new_state}

3异步操作.md

handle_cast/2 must be used for asynchronous requests, when you don’t care about a reply. A cast does not even guarantee the server has received the message and, for this reason, should be used sparingly. For example, the create/2 function we have defined in this chapter should have used call/2. We have used cast/2 for didactic purposes.

根据文档，异步操作不保证一定能发送成功，还是尽量少使用

Client发送请求

def async_op(pid, args) do
 GenServer.cast(pid, {:async_op, args})
end

Callback

def handle_cast({:async_op, args}, state) do
 new_state = f(state, args)
 {:noreply, new_state}
end

回调返回值示例

{:noreply, new_state}
{:noreply, new_state, 5_000}
{:noreply, new_state, :hibernate}
RETURN VAL
{:stop, reason*, new_state} 

4Out of band messages.md

def handle_info(msg, state) do
 new_state = f(state, msg)
 {:noreply, new_state}
end

{:noreply, new_state}
{:noreply, new_state, 5_000}
{:noreply, new_state, :hibernate}
RETURN VAL
{:stop, reason*, new_state} 

5Termination.md

def stop(pid, reason \\ :normal, timeout \\ :infinity) do
 GenServer.stop(pid, reason, timeout)
end

回调函数

def terminate(reason, state) do
 # Perform cleanup here
 # …
end

reason参数的示例值

:normal
:shutdown
{:shutdown, term}
term