Limiting the worker pool to a given size

lib/torque/provider/filterableJson.js

@@ -22,6 +22,11 @@ var Profiler = require('../profiler');
     this._tileQueue = [];
     this.options = options;
     this._filters = {};
+    this._tileProcessingQueue=[]
+    this._workers = [];
+    this._maxWorkerNo = 4;
+
+    this.setupWorkerPool()
     // category mapping for each column
     this.categoryMapping = {}
     this.categoryMappingSize = {}
@@ -52,6 +57,44 @@ var Profiler = require('../profiler');
 
   filterableJson.prototype = {
 
+    setupWorkerPool:function(){
+      for(var i=0; i< this._maxWorkerNo; i++){
+        this._workers.push(this.createProccessTileWorker())
+      }
+    },
+
+    getAvalaibleWorker:function(){
+      return this._workers.pop()
+    },
+    releaseWorker:function(worker){
+      console.log("releasing worker ", worker)
+      this._workers.push(worker)
+      this.processNextTileRequestInQueue()
+    },
+    processNextTileRequestInQueue:function(){
+      console.log("processing next ",this._tileProcessingQueue.length, this._workers.length )
+      if(this._tileProcessingQueue.length>0){
+        job = this._tileProcessingQueue.pop()
+        this.requestWorker(job.rows,job.coord,job.zoom, job.options, job.callback)
+      }
+    },
+    requestWorker:function(rows,coord,zoom,options,callback){
+      worker = this.getAvalaibleWorker()
+      self = this
+      if(worker){
+        worker.onmessage = function(e){
+          callback(e.data)
+          self.releaseWorker(this)
+        }
+        worker.postMessage(JSON.stringify({rows: rows, coord: {x:coord.x,y:coord.y}, zoom:zoom, options: options}))
+      }
+      else{
+        this.addToTileProcessingQueue(rows,coord,zoom,options,callback)
+      }
+    },
+    addToTileProcessingQueue:function(rows,coord,zoom, options, callback){
+      this._tileProcessingQueue.push({rows:rows, coord:coord, zoom:zoom, options: options, callback:callback})
+    },
     /**
      * Creates a worker to process the tile
      */
@@ -70,11 +113,7 @@ var Profiler = require('../profiler');
         callback(this.proccessTileSerial(rows,coord,zoom, this.options))
       }
       else{
-        var worker = this.createProccessTileWorker()
+
-        worker.onmessage = function(e){
-          callback(e.data)
-          worker.terminate()
-        }
 
         var workerSafeOptions= {
           x : new Uint8Array(rows.length),
@@ -82,7 +121,7 @@ var Profiler = require('../profiler');
           resolution: this.options.resolution,
           fields: this.options.fields
         }
-        worker.postMessage(JSON.stringify({rows: rows, coord: {x:coord.x,y:coord.y}, zoom:zoom, options: workerSafeOptions}))
+        this.requestWorker(rows,coord,zoom,workerSafeOptions,callback)
       }
     },
     /**