Track connected user count of workers. (#328)

If a worker (game) is shared, then without tracking players it's impossible to tell when it becomes available for a new game which leads to emulator share and crashes.

pkg/coordinator/handlers.go

@@ -217,7 +217,9 @@ func (o *Server) WS(w http.ResponseWriter, r *http.Request) {
 
 	// Assign available worker to browserClient
 	bc.WorkerID = wc.WorkerID
-	wc.IsAvailable = false
+
+	wc.ChangeUserQuantityBy(1)
+	defer wc.ChangeUserQuantityBy(-1)
 
 	// Everything is cool
 	// Attach to Server instance with sessionID
@@ -237,9 +239,6 @@ func (o *Server) WS(w http.ResponseWriter, r *http.Request) {
 
 	// Notify worker to clean session
 	wc.Send(api.TerminateSessionPacket(sessionID), nil)
-
-	// WorkerClient become available again
-	wc.IsAvailable = true
 }
 
 func (o *Server) getBestWorkerClient(client *BrowserClient, zone string) (*WorkerClient, error) {
@@ -269,7 +268,7 @@ func (o *Server) getBestWorkerClient(client *BrowserClient, zone string) (*Worke
 func (o *Server) getAvailableWorkers() map[string]*WorkerClient {
 	workerClients := map[string]*WorkerClient{}
 	for k, w := range o.workerClients {
-		if w.IsAvailable {
+		if w.HasGameSlot() {
 			workerClients[k] = w
 		}
 	}
@@ -280,7 +279,7 @@ func (o *Server) getAvailableWorkers() map[string]*WorkerClient {
 // getWorkerFromAddress returns the worker has given address
 func (o *Server) getWorkerFromAddress(address string) *WorkerClient {
 	for _, w := range o.workerClients {
-		if w.IsAvailable && w.Address == address {
+		if w.HasGameSlot() && w.Address == address {
 			return w
 		}
 	}

pkg/coordinator/worker.go

@@ -3,6 +3,7 @@ package coordinator
 import (
 	"fmt"
 	"log"
+	"sync"
 
 	"github.com/giongto35/cloud-game/v2/pkg/cws"
 	"github.com/gorilla/websocket"
@@ -16,20 +17,43 @@ type WorkerClient struct {
 	// public server used for ping check (Cannot use worker address because they are not publicly exposed)
 	PingServer     string
 	StunTurnServer string
-	IsAvailable    bool
+	userCount      int // may be atomic
 	Zone           string
+
+	mu sync.Mutex
 }
 
 // NewWorkerClient returns a client connecting to worker.
 // This connection exchanges information between workers and server.
 func NewWorkerClient(c *websocket.Conn, workerID string) *WorkerClient {
 	return &WorkerClient{
-		Client:      cws.NewClient(c),
-		WorkerID:    workerID,
-		IsAvailable: true,
+		Client:   cws.NewClient(c),
+		WorkerID: workerID,
 	}
 }
 
+// ChangeUserQuantityBy increases or decreases the total amount of
+// users connected to the current worker.
+// We count users to determine when the worker becomes new game ready.
+func (wc *WorkerClient) ChangeUserQuantityBy(n int) {
+	wc.mu.Lock()
+	wc.userCount += n
+	// just to be on a safe side
+	if wc.userCount < 0 {
+		wc.userCount = 0
+	}
+	wc.mu.Unlock()
+}
+
+// HasGameSlot tells whether the current worker has a
+// free slot to start a new game.
+// Workers support only one game at a time.
+func (wc *WorkerClient) HasGameSlot() bool {
+	wc.mu.Lock()
+	defer wc.mu.Unlock()
+	return wc.userCount == 0
+}
+
 func (wc *WorkerClient) Printf(format string, args ...interface{}) {
 	log.Printf(fmt.Sprintf("Worker %s] %s", wc.WorkerID, format), args...)
 }