use a worker pool to add concurrency limit on gif renders (#35)

Co-authored-by: Rob ODwyer <rob.odwyer@taplytics.com>

go.mod

@@ -3,6 +3,7 @@ module github.com/BattlesnakeOfficial/exporter
 go 1.17
 
 require (
+	github.com/alitto/pond v1.8.3
 	github.com/disintegration/imaging v1.6.2
 	github.com/ericpauley/go-quantize v0.0.0-20200331213906-ae555eb2afa4
 	github.com/fogleman/gg v1.3.0

go.sum

@@ -1,3 +1,5 @@
+github.com/alitto/pond v1.8.3 h1:ydIqygCLVPqIX/USe5EaV/aSRXTRXDEI9JwuDdu+/xs=
+github.com/alitto/pond v1.8.3/go.mod h1:CmvIIGd5jKLasGI3D87qDkQxjzChdKMmnXMg3fG6M6Q=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -24,37 +26,15 @@ github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
-github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 goji.io/v3 v3.0.0 h1:CXZWGMTie+4tdhKiEpOlrUW9hCc8jF4LHs94sWdfcgQ=
 goji.io/v3 v3.0.0/go.mod h1:c02FFnNiVNCDo+DpR2IhBQpM9r5G1BG/MkHNTPUJ13U=
-golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
-golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/image v0.0.0-20191009234506-e7c1f5e7dbb8/go.mod h1:FeLwcggjj3mMvU+oOTbSwawSJRM1uh48EjtB4UJZlP0=
 golang.org/x/image v0.14.0 h1:tNgSxAFe3jC4uYqvZdTr84SZoM1KfwdC9SKIFrLjFn4=
 golang.org/x/image v0.14.0/go.mod h1:HUYqC05R2ZcZ3ejNQsIHQDQiwWM4JBqmm6MKANTp4LE=
-golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
-golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
-golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
-golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
-golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
-golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
-golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
-golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
-golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
-golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
-golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

http/handlers.go

@@ -354,11 +354,10 @@ func handleGIFGame(w http.ResponseWriter, r *http.Request) {
 }
 
 func handleCommonGIFGame(w http.ResponseWriter, r *http.Request, width, height int) {
-
 	gameID := pat.Param(r, "game")
 	engineURL := r.URL.Query().Get("engine_url")
 
-	log.WithField("game", gameID).WithField("engine_url", engineURL).Info("exporting game")
+	log.WithField("game", gameID).WithField("engine_url", engineURL).Info("rendering gif for game")
 
 	game, err := engine.GetGame(gameID, engineURL)
 	if err != nil {

http/server.go

@@ -12,17 +12,25 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/alitto/pond"
 	log "github.com/sirupsen/logrus"
 	"goji.io/v3"
 	"goji.io/v3/pat"
 )
 
+// How many requests can be queued up for any GIF render before we start rejecting with HTTP 429
+// Half of the current max in-flight requests
+const DEFAULT_RENDER_BACKLOG = 40
+
 type Server struct {
 	router     *goji.Mux
 	httpServer *http.Server
 }
 
 func NewServer() *Server {
+	log.WithField("size", runtime.NumCPU()).Info("Starting GIF render pool")
+	renderPool := pond.New(runtime.NumCPU(), DEFAULT_RENDER_BACKLOG)
+
 	mux := goji.NewMux()
 	mux.Use(Recovery) // captures panics
 
@@ -40,14 +48,13 @@ func NewServer() *Server {
 
 	mux.HandleFunc(pat.Get("/customizations/:type/:name.:ext"), withCaching(handleCustomization))
 
-	mux.HandleFunc(pat.Get("/games/:game/:size.gif"), withCaching(handleGIFGameDimensions))
-	mux.HandleFunc(pat.Get("/games/:game/frames/:frame.txt"), withCaching(handleASCIIFrame))
-	mux.HandleFunc(pat.Get("/games/:game/frames/:frame/:size.gif"), withCaching(handleGIFFrameDimensions))
+	mux.HandleFunc(pat.Get("/games/:game/:size.gif"), withConcurrencyLimit(renderPool, withCaching(handleGIFGameDimensions)))
+	mux.HandleFunc(pat.Get("/games/:game/gif"), withConcurrencyLimit(renderPool, withCaching(handleGIFGame)))
+	mux.HandleFunc(pat.Get("/games/:game/frames/:frame/:size.gif"), withConcurrencyLimit(renderPool, withCaching(handleGIFFrameDimensions)))
+	mux.HandleFunc(pat.Get("/games/:game/frames/:frame/gif"), withConcurrencyLimit(renderPool, withCaching(handleGIFFrame)))
 
-	// Deprecated and undocumented, remove these!
-	mux.HandleFunc(pat.Get("/games/:game/gif"), withCaching(handleGIFGame))
+	mux.HandleFunc(pat.Get("/games/:game/frames/:frame.txt"), withCaching(handleASCIIFrame))
 	mux.HandleFunc(pat.Get("/games/:game/frames/:frame/ascii"), withCaching(handleASCIIFrame))
-	mux.HandleFunc(pat.Get("/games/:game/frames/:frame/gif"), withCaching(handleGIFFrame))
 
 	return &Server{
 		router: mux,
@@ -57,6 +64,28 @@ func NewServer() *Server {
 	}
 }
 
+func withConcurrencyLimit(pool *pond.WorkerPool, wrappedHandler http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		done := make(chan struct{})
+
+		// Try to submit a job to the pool asynchronously, and if it fails, reject the request
+		submitted := pool.TrySubmit(func() {
+			defer close(done)
+			wrappedHandler(w, r)
+		})
+
+		if !submitted {
+			close(done)
+			log.WithField("url", r.URL.String()).Print("No worker available from pool, rejecting request")
+			w.WriteHeader(http.StatusTooManyRequests)
+			return
+		} else {
+			// Block until the job that was submitted to the pool is done
+			<-done
+		}
+	}
+}
+
 func withCaching(wrappedHandler http.HandlerFunc) http.HandlerFunc {
 	appVersion, ok := os.LookupEnv("APP_VERSION")
 	if !ok {