Generate PNG files on worker pool

resources/asciinema/system.edn

@@ -4,14 +4,15 @@
   :db   #var asciinema.component.db/hikaricp
   :ragtime #var duct.component.ragtime/ragtime
   :file-store #var asciinema.component.s3-file-store/s3-file-store
-  :exp-set #var asciinema.component.redis-client/redis-client}
+  :exp-set #var asciinema.component.redis-client/redis-client
+  :executor #var asciinema.component.fixed-thread-executor/fixed-thread-executor}
  :endpoints
  {:asciicasts #var asciinema.endpoint.asciicasts/asciicasts-endpoint}
  :dependencies
  {:http [:app]
   :app  [:asciicasts]
   :ragtime [:db]
-  :asciicasts [:db :file-store :exp-set]}
+  :asciicasts [:db :file-store :exp-set :executor]}
  :config
  {:app
   {:middleware
@@ -64,4 +65,7 @@
    :path-prefix "uploads/"}
   :exp-set
   {:host redis-host
-   :port redis-port}}}
+   :port redis-port}
+  :executor
+  {:threads 1
+   :queue-length 1}}}

src/asciinema/boundary/executor.clj

@@ -0,0 +1,4 @@
+(ns asciinema.boundary.executor)
+
+(defprotocol Executor
+  (execute [this f]))

src/asciinema/component/fixed_thread_executor.clj

@@ -0,0 +1,39 @@
+(ns asciinema.component.fixed-thread-executor
+  (:require [aleph.flow :as flow]
+            [asciinema.boundary.executor :as executor]
+            [com.stuartsierra.component :as component]
+            [manifold.deferred :as d])
+  (:import [java.util.concurrent
+            ExecutorService
+            RejectedExecutionException
+            TimeUnit]))
+
+(defrecord FixedThreadExecutor [threads queue-length]
+  executor/Executor
+  (execute [{:keys [^ExecutorService executor]} f]
+    (try
+      (let [result (d/deferred)
+            f (fn []
+                (try
+                  (d/success! result (f))
+                  (catch Exception e
+                    (d/error! result e))))]
+        (.execute executor f)
+        result)
+      (catch RejectedExecutionException _
+        {:status 503 :headers {"Retry-After" "5"} :body "<h1>503</h1>"})))
+
+  component/Lifecycle
+  (start [{:keys [threads queue-length] :as component}]
+    (let [executor (flow/fixed-thread-executor threads {:onto? false
+                                                        :initial-thread-count threads
+                                                        :queue-length queue-length})]
+      (assoc component :executor executor)))
+  (stop [{:keys [^ExecutorService executor] :as component}]
+    (.shutdown executor)
+    (when-not (.awaitTermination executor 1000 TimeUnit/MILLISECONDS)
+      (.shutdownNow executor))
+    (assoc component :executor nil)))
+
+(defn fixed-thread-executor [{:keys [threads queue-length]}]
+  (->FixedThreadExecutor threads queue-length))

src/asciinema/endpoint/asciicasts.clj

@@ -3,6 +3,7 @@
              [asciicast-database :as adb]
              [expiring-set :as exp-set]
              [file-store :as fstore]
+             [executor :as executor]
              [user-database :as udb]]
             [asciinema.model.asciicast :as asciicast]
             [asciinema.util.io :refer [with-tmp-dir]]
@@ -37,7 +38,7 @@
 
 (def png-ttl-days 7)
 
-(defn asciicasts-endpoint [{:keys [db file-store exp-set]}]
+(defn asciicasts-endpoint [{:keys [db file-store exp-set executor]}]
   (api
    {:exceptions {:handlers {:compojure.api.exception/default exception-handler}}}
    (context
@@ -63,7 +64,9 @@
                               theme (assoc :theme theme)
                               scale (assoc :scale (Integer/parseInt scale)))
                  png-store-path (asciicast/png-store-path asciicast png-params)]
-             (when-not (exp-set/contains? exp-set png-store-path)
+             (if (exp-set/contains? exp-set png-store-path)
+               (fstore/serve-file file-store png-store-path {})
+               (executor/execute executor (fn []
                                             (with-tmp-dir [dir "asciinema-png-"]
                                               (let [json-store-path (asciicast/json-store-path asciicast)
                                                     json-local-path (str dir "/asciicast.json")
@@ -74,6 +77,6 @@
                                                     (io/copy in out)))
                                                 (a2png json-local-path png-local-path png-params)
                                                 (fstore/put-file file-store (io/file png-local-path) png-store-path)
-                   (exp-set/conj! exp-set png-store-path expires))))
+                                                (exp-set/conj! exp-set png-store-path expires)))
-             (fstore/serve-file file-store png-store-path {}))
+                                            (fstore/serve-file file-store png-store-path {})))))
            (response/not-found))))))