simplify matchmaking

lobby/lobby.go

@@ -1,51 +1,87 @@
 package lobby
 
 import (
-	"sync"
+	"context"
+
+	"github.com/google/uuid"
 
-	"git.sunturtle.xyz/studio/shotgun/game"
 	"git.sunturtle.xyz/studio/shotgun/player"
 	"git.sunturtle.xyz/studio/shotgun/serve"
 )
 
 type GameID = serve.GameID
 
-// Lobby is a set of active games.
+type matchMade struct {
+	match chan GameID
+	chall player.ID
+}
+
+type match chan matchMade
+
+// Lobby is a matchmaking service.
 type Lobby struct {
-	mu sync.Mutex
-	// games is the set of all active games in the lobby.
-	games map[GameID]*game.Game
 	// matches is dealers waiting for a match. It MUST be unbuffered.
 	matches chan match
 }
 
 func New() *Lobby {
 	return &Lobby{
-		games:   make(map[GameID]*game.Game),
 		matches: make(chan match),
 	}
 }
 
-// Game returns the game with the given ID.
+// Queue waits for a match and returns a unique ID for it.
-func (l *Lobby) Game(id GameID) *game.Game {
+func (l *Lobby) Queue(ctx context.Context, p player.ID) (id GameID, chall player.ID, deal bool) {
-	l.mu.Lock()
+	select {
-	defer l.mu.Unlock()
+	case m := <-l.matches:
-	return l.games[id]
+		// We found a dealer waiting for a match.
+		r := matchMade{
+			match: make(chan GameID, 1),
+			chall: p,
 		}
-
+		// We don't need to check the context here because the challenger
-// Start begins a new game in the lobby.
+		// channel is buffered and we have exclusive send access on it.
-// The caller must be able to distinguish the dealer's and challenger's conns
+		m <- r
-// in order to provide correct game start DTOs to each.
+		// We do need to check the context here in case they disappeared.
-func (l *Lobby) Start(id GameID, dealer, challenger player.ID) {
+		select {
-	g := game.New(dealer, challenger)
+		case <-ctx.Done():
-	l.mu.Lock()
+			return GameID{}, player.ID{}, false
-	defer l.mu.Unlock()
+		case id := <-r.match:
-	l.games[id] = g
+			return id, p, false
+		}
+	default: // do nothing
+	}
+	// We're a new dealer.
+	m := make(match, 1)
+	select {
+	case <-ctx.Done():
+		return GameID{}, player.ID{}, false
+	case l.matches <- m:
+		// Our match is submitted. Move on.
+	case m := <-l.matches:
+		// We might have become a dealer at the same time someone else did.
+		// We created our match, but we can try to get theirs as well and
+		// never send ours, since l.matches is unbuffered.
+		r := matchMade{
+			match: make(chan GameID, 1),
+			chall: p,
+		}
+		m <- r
+		select {
+		case <-ctx.Done():
+			return GameID{}, player.ID{}, false
+		case id := <-r.match:
+			return id, p, false
+		}
+	}
+	select {
+	case <-ctx.Done():
+		return GameID{}, player.ID{}, false
+	case r := <-m:
+		// Got our challenger. Create the game and send the ID back.
+		id := GameID(uuid.New())
+		// Don't need to check context because the match channel is buffered.
+		r.match <- id
+		return id, r.chall, true
 	}
-
-// Finish removes a game from the lobby.
-func (l *Lobby) Finish(id GameID) {
-	l.mu.Lock()
-	defer l.mu.Unlock()
-	delete(l.games, id)
 }

lobby/lobby_test.go

@@ -2,6 +2,7 @@ package lobby_test
 
 import (
 	"context"
+	"sync/atomic"
 	"testing"
 
 	"git.sunturtle.xyz/studio/shotgun/lobby"
@@ -15,10 +16,17 @@ func TestQueue(t *testing.T) {
 	l := lobby.New()
 	for i := 0; i < 100; i++ {
 		games = games[:0]
+		var dealers, challs atomic.Int32
 		for i := 0; i < N; i++ {
 			i := i
 			go func() {
-				ch <- l.Queue(context.Background(), player.ID{uint8(i), uint8(i >> 8)})
+				id, _, deal := l.Queue(context.Background(), player.ID{uint8(i), uint8(i >> 8)})
+				if deal {
+					dealers.Add(1)
+				} else {
+					challs.Add(1)
+				}
+				ch <- id
 			}()
 		}
 		for i := 0; i < N; i++ {
@@ -34,16 +42,9 @@ func TestQueue(t *testing.T) {
 				t.Errorf("game %v appears %d times", id, c)
 			}
 		}
-		// Every game should have two different players.
+		// The number of dealers must match the number of challengers.
-		for _, id := range games {
+		if dealers.Load() != challs.Load() {
-			g := l.Game(id)
+			t.Errorf("%d dealers != %d challengers", dealers.Load(), challs.Load())
-			if g == nil {
-				t.Errorf("game %v was created but doesn't exist", g)
-				continue
-			}
-			if g.CurrentPlayer().Is(g.Opponent()) {
-				t.Errorf("game %v matched with self", id)
-			}
 		}
 	}
 }

lobby/match.go

@@ -1,70 +0,0 @@
-package lobby
-
-import (
-	"context"
-
-	"git.sunturtle.xyz/studio/shotgun/player"
-	"github.com/google/uuid"
-)
-
-type match struct {
-	dealer player.ID
-	chall  chan player.ID
-	match  chan GameID
-}
-
-// Queue waits for a match.
-// This may cause a new match to be created.
-func (l *Lobby) Queue(ctx context.Context, p player.ID) GameID {
-	select {
-	case <-ctx.Done():
-		return GameID{}
-	case m := <-l.matches:
-		// We found a dealer waiting for a match.
-		// We don't need to check the context here because the challenger
-		// channel is buffered and we have exclusive send access on it.
-		m.chall <- p
-		// We do need to check the context here in case they disappeared.
-		select {
-		case <-ctx.Done():
-			return GameID{}
-		case id := <-m.match:
-			return id
-		}
-	default: // do nothing
-	}
-	// We're a new dealer.
-	m := match{
-		dealer: p,
-		chall:  make(chan player.ID, 1),
-		match:  make(chan GameID, 1),
-	}
-	select {
-	case <-ctx.Done():
-		return GameID{}
-	case l.matches <- m:
-		// Our match is submitted. Move on.
-	case m := <-l.matches:
-		// We might have become a dealer at the same time someone else did.
-		// We created our match, but we can try to get theirs as well and
-		// never send ours, since l.matches is unbuffered.
-		m.chall <- p
-		select {
-		case <-ctx.Done():
-			return GameID{}
-		case id := <-m.match:
-			return id
-		}
-	}
-	select {
-	case <-ctx.Done():
-		return GameID{}
-	case chall := <-m.chall:
-		// Got our challenger. Create the game and send the ID back.
-		id := uuid.New()
-		l.Start(id, p, chall)
-		// Don't need to check context because the match channel is buffered.
-		m.match <- id
-		return id
-	}
-}