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'ServerA PID: <0.146.0>'
iex(3)> GenServer.call(:server_b, :display)
'ServerB PID: <0.147.0>'
iex(4)> GenServer.call(:server_c, :display)
'ServerC PID: <0.148.0>'
# 通过消息 :err 让 serverA 出错
iex(5)> GenServer.cast(:server_a, :err)
:ok
iex(6)>
14:55:16.183 [error] GenServer :server_a terminating
** (stop) "stop ServerA"
Last message: {:"$gen_cast", :err}
State: []
nil
# serverA 出错后，再次查看3个process的PID，发现 supervisor 重启了所有 process，符合策略 :one_for_all
iex(7)> GenServer.call(:server_a, :display)
'ServerA PID: <0.153.0>'
iex(8)> GenServer.call(:server_b, :display)
'ServerB PID: <0.154.0>'
iex(9)> GenServer.call(:server_c, :display)
'ServerC PID: <0.156.0>'
监督树
监督者并不是一维的，监督者也可以监督其它监督者，从而形成树状的监督关系。
修改上面的测试代码如下：（只修改了 Supervisor 的部分）
defmodule PseudoServerA do
use GenServer
def start_link(state, opts \\ []) do
GenServer.start_link(__MODULE__, state, opts)
end
def handle_call(:display, _from, []) do
{:reply, 'ServerA PID: ' ++ :erlang.pid_to_list(self()), []}
end
def handle_cast(:err, []) do
{:stop, "stop ServerA", []}
end
end
defmodule PseudoServerB do
use GenServer
def start_link(state, opts \\ []) do
GenServer.start_link(__MODULE__, state, opts)
end
def handle_call(:display, _from, []) do
{:reply, 'ServerB PID: ' ++ :erlang.pid_to_list(self()), []}
end
def handle_cast(:err, []) do
{:stop, "stop ServerB", []}
end
end
defmodule PseudoServerC do
use GenServer
def start_link(state, opts \\ []) do
GenServer.start_link(__MODULE__, state, opts)
end
def handle_call(:display, _from, []) do
{:reply, 'ServerC PID: ' ++ :erlang.pid_to_list(self()), []}
end
def handle_cast(:err, []) do
{:stop, "stop ServerC", []}
end
end
defmodule SupervisorBranch do
import Supervisor.Spec
def start_link(state) do
children = [
worker(PseudoServerA, [[], [name: :server_a]]),
worker(PseudoServerB, [[], [name: :server_b]]),
]
Supervisor.start_link(children, strategy: :one_for_one)
end
end
defmodule SupervisorRoot do
import Supervisor.Spec
def init() do
children = [
supervisor(SupervisorBranch, [[name: :supervisor_branch]]),
worker(PseudoServerC, [[], [name: :server_c]])
]
# Start the supervisor with children
Supervisor.start_link(children, strategy: :one_for_all)
end
end
测试流程如下：
# 启动 根 监督者
iex(1)> SupervisorRoot.init
{:ok, #PID<0.149.0>}
# 启动后，查看 3 个process 的PID
iex(2)> GenServer.call(:server_a, :display)
'ServerA PID: <0.151.0>'
iex(3)> GenServer.call(:server_b, :display)
'ServerB PID: <0.152.0>'
iex(4)> GenServer.call(:server_c, :display)
'ServerC PID: <0.153.0>'
# 通过消息 :err 让 serverA 出错
iex(5)> GenServer.cast(:server_a, :err)
:ok
iex(6)>
15:31:15.846 [error] GenServer :server_a terminating
** (stop) "stop ServerA"
Last message: {:"$gen_cast", :err}
State: []
nil
# serverA 出错后，因为它的监督者 SupervisorBranch 的策略是 :one_for_one，所以只重启了 serverA
iex(7)> GenServer.call(:server_a, :display)
'ServerA PID: <0.158.0>'
iex(8)> GenServer.call(:server_b, :display)
'ServerB PID: <0.152.0>'
iex(9)> GenServer.call(:server_c, :display)
'ServerC PID: <0.153.0>'
# 通过消息 :err 让 serverC 出错
iex(10)> GenServer.cast
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