Fix subtitles race condition

lib/google2vtt.js

@@ -17,6 +17,7 @@ function md5(input) {
 
 var slice = Array.prototype.slice;
 var subtitleDir = path.resolve(__dirname, '..', 'google-drive-subtitles');
+var subtitleLock = {};
 var ONE_HOUR = 60 * 60 * 1000;
 var ONE_DAY = 24 * ONE_HOUR;
 
@@ -86,19 +87,23 @@ function handleGetSubtitles(req, res) {
     var file = [id, lang, md5(name)].join('_') + '.vtt';
     var fileAbsolute = path.join(subtitleDir, file);
 
-    fs.exists(fileAbsolute, function (exists) {
+    takeSubtitleLock(fileAbsolute, function () {
-        if (exists) {
+        fs.exists(fileAbsolute, function (exists) {
-            res.sendFile(file, { root: subtitleDir });
+            if (exists) {
-        } else {
-            fetchSubtitles(id, lang, name, vid, fileAbsolute, function (err) {
-                if (err) {
-                    Logger.errlog.log(err.stack);
-                    return res.sendStatus(500);
-                }
-
                 res.sendFile(file, { root: subtitleDir });
-            });
+                delete subtitleLock[fileAbsolute];
-        }
+            } else {
+                fetchSubtitles(id, lang, name, vid, fileAbsolute, function (err) {
+                    delete subtitleLock[fileAbsolute];
+                    if (err) {
+                        Logger.errlog.log(err.stack);
+                        return res.sendStatus(500);
+                    }
+
+                    res.sendFile(file, { root: subtitleDir });
+                });
+            }
+        });
     });
 }
 
@@ -169,5 +174,22 @@ function clearOldSubtitles() {
     });
 }
 
+function takeSubtitleLock(filename, cb) {
+    if (!subtitleLock.hasOwnProperty(filename)) {
+        subtitleLock[filename] = true;
+        return setImmediate(cb);
+    }
+
+    var tries = 1;
+    var interval = setInterval(function () {
+        tries++;
+        if (!subtitleLock.hasOwnProperty(filename) || tries >= 5) {
+            subtitleLock[filename] = true;
+            clearInterval(interval);
+            return setImmediate(cb);
+        }
+    }, 200);
+}
+
 setInterval(clearOldSubtitles, ONE_HOUR);
 clearOldSubtitles();