GenServer Intro
A GenServer process manages state and loops indefinitely until stopped. Elixir provides a module for implementing a GenServer process. To use the GenServer module, you need to implement its behavior. The main functions that a GenServer needs to implement are
init(init_arg)
The init function sets off the initial state for your process.
init should return {:ok, state} to start the GenServer process loop.
handle_call
handle_call is used when you want to grab values from the GenServer state.
handle_call should return {:reply, reply, new_state} when you want to send a reply back to the user.
handle_cast
handle_cast is used when you want to update the state inside the GenServer.
handle_cast should return {:noreply, new_state} to continue the GenServer process loop.
handle_info
handle_info is used when you want to send messages to the GenServer process that aren’t handled by handle_call or handle_cast. handle_info can be used to send messages from within the GenServer callbacks.
handle_info should return {:noreply, new_state} to continue the GenServer process loop.
GenServer Practice
To further grasp usage of GenServers, implement the following modules
Counter
defmodule Counter do
use GenServer
@impl true
def init(init_arg) do
end
@impl true
def handle_cast(:increment, state) do
end
@impl true
def handle_cast(:decrement, state) do
end
@impl true
def handle_call(:get, _from, state) do
end
endKey Value Store
defmodule KeyValue do
use GenServer
@impl true
def init(init_arg) do # consider adding a guard here
end
@impl true
def handle_call({:get, ...}, _from, state) do
end
@impl true
def handle_cast({:set, key, value}, state) do
end
def handle_cast({:delete, key}, state) do
end
endCache
defmodule Cache do
use GenServer
def init(_init_arg) do
end
def handle_call({:get, key}, _from, state) do
end
def handle_cast({:put, key, value, ttl}, state) do
end
def handle_info({:ttl_delete, key}, state) do
end
end