First: Homework Questions
- Memory Game with Server-Side State is due today.
- Project 1: Make a multi-player game.
- You can pick what game you want to make.
- Turn based games should be at least as complex as Connect4.
- Real-time games should be at least as complex as a 2-player
breakout (think Pong with blocks in the middle).
- You'll work with a partner.
- Make sure you've talked to your partner for Project 1 - you want
to be on a team by tomorrow.
- Project 1 is due in 2 weeks.
- If homeworks normally take 8 hours, that means your team has
at least 36 hours to spend on this project.
- For students who claim that homework takes 23 hours...
OTP: Processes & State
# Can compile / recompile from iex
- Stack of integers: push, pop, print
- More than one stack at a time.
- Every five seconds, If the top integer is odd, add 2.
Supervisors and Supervision Trees
- Use the built-in GenServer behavior.
- Add a Registry
- What do we do when we want a bunch of processes?
- We can register by arbitrary term with the Registry module.
- Add a Supervisor
- Supervisor: Start & Monitor processes, potentially restart them when they crash.
- In this case, DynamicSupervisor
- Supervisor module takes a static list of children and keeps them running.
- DynamicSupervisor handles workers spawned at runtime.
- Spin up hangman & show tree in observer.
- iex -S mix phx.server
- install and use kmag to zoom in
If a child is linked to a parent, the parent gets an exit message when the
A process that gets an exit message will exit itself unless it's configured to
trap exits. Trapping exits is what lets supervisors work.
- Current Hangman design:
- User connects to channel.
- Game state is stored in channel and backed up to agent
- When a move comes in, the next state is produced by channel process.
- Two-player Hangman:
- Two users each connect to the same channel.
- They each get their own, seperate, channel process.
- We can't store or update the state in the channels, because then
the game states could get out of sync.
- Solution: Add a process to manage the game state.
- Channel processes sends move messages to game process.
- Game process broadcasts updated state to the channel.
- If the process crashes, the game state will be lost.
- Could keep the backup agent as well.
Let's try building that. We could add turns, but instead we'll just allow either
player to guess whenever they want.
- Write Hangman.Server
- Write Hangman.GameSup
- Add Hangman.GameSup to the application child list.
$ iex -S mix
iex> Hangman.GameServer.guess("foo", "l")
iex> Hangman.GameServer.guess("foo", "z")
iex> Hangman.GameServer.guess("foo", "b")