Use dynamic pool of map instances to reduce waiting times (issue #3)

package.json

@@ -12,11 +12,11 @@
   },
   "dependencies": {
     "async": "1.5.2",
-    "async-lock": "0.3.8",
+    "advanced-pool": "0.3.1",
     "clone": "1.0.2",
     "cors": "2.7.1",
     "express": "4.13.4",
-    "mapbox-gl-native": "3.0.2-earcut",
+    "mapbox-gl-native": "3.0.2",
     "mbtiles": "0.8.2",
     "morgan": "1.7.0",
     "nomnom": "1.8.1",

src/serve_raster.js

@@ -1,7 +1,7 @@
 'use strict';
 
 var async = require('async'),
-    asyncLock = require('async-lock'),
+    advancedPool = require('advanced-pool'),
     crypto = require('crypto'),
     fs = require('fs'),
     path = require('path'),
@@ -32,8 +32,6 @@ mbgl.on('message', function(e) {
 });
 
 module.exports = function(maps, options, prefix) {
-  var lock = new asyncLock();
-
   var app = express().disable('x-powered-by'),
       domains = options.domains,
       tilePath = '/{z}/{x}/{y}.{format}';
@@ -46,9 +44,11 @@ module.exports = function(maps, options, prefix) {
     sources: {},
     tileJSON: {}
   };
-  if (!maps[prefix]) {
-    var createRenderer = function(ratio) {
-      return new mbgl.Map({
+
+  var styleJSON;
+  var createPool = function(ratio, min, max) {
+    var createRenderer = function(ratio, createCallback) {
+      var renderer = new mbgl.Map({
         ratio: ratio,
         request: function(req, callback) {
           var protocol = req.url.split(':')[0];
@@ -115,12 +115,20 @@ module.exports = function(maps, options, prefix) {
           }
         }
       });
+      renderer.load(styleJSON);
+      createCallback(null, renderer);
+    };
+    return new advancedPool.Pool({
+      min: min,
+      max: max,
+      create: createRenderer.bind(null, ratio),
+      destroy: function(renderer) {
+        renderer.release();
+      }
+    });
   };
-    map.renderers[1] = createRenderer(1);
-    map.renderers[2] = createRenderer(2);
-    map.renderers[3] = createRenderer(3);
 
-    var styleJSON = require(path.join(rootPath, styleUrl));
+  styleJSON = require(path.join(rootPath, styleUrl));
 
   map.tileJSON = {
     'tilejson': '2.0.0',
@@ -160,15 +168,13 @@ module.exports = function(maps, options, prefix) {
   });
 
   async.parallel(queue, function(err, results) {
-      map.renderers.forEach(function(renderer) {
-        renderer.load(styleJSON);
-      });
+    // TODO: make pool sizes configurable
+    map.renderers[1] = createPool(1, 2, 8);
+    map.renderers[2] = createPool(2, 2, 4);
+    map.renderers[3] = createPool(3, 2, 4);
   });
 
   maps[prefix] = map;
-  } else {
-    map = maps[prefix];
-  }
 
   var tilePattern = tilePath
     .replace(/\.(?!.*\.)/, ':scale(' + SCALE_PATTERN + ')?.')
@@ -186,17 +192,10 @@ module.exports = function(maps, options, prefix) {
       return res.status(404).send('Invalid format');
     }
 
+    var pool = map.renderers[scale];
+    pool.acquire(function(err, renderer) {
       var mbglZ = Math.max(0, z - 1);
-    var renderer = map.renderers[scale];
       var params = {
-      /*
-      debug: {
-        tileBorders: true,
-        parseStatus: true,
-        timestamps: true,
-        collision: true
-      },
-      */
         zoom: mbglZ,
         center: [lon, lat],
         width: width,
@@ -206,9 +205,8 @@ module.exports = function(maps, options, prefix) {
         params.width *= 2;
         params.height *= 2;
       }
-    lock.acquire(renderer, function(done) {
       renderer.render(params, function(err, data) {
-        done();
+        pool.release(renderer);
         if (err) console.log(err);
 
         var image = sharp(data, {