Change the way DownloadManager collects the number of successful downloads

Before a callback was used to increase the number of successful downloads
resulting in multiple worker threads trying to edit the same variable.
Now each worker thread stores the number of successful downloads for itself
and the DownloadManager collects this number after download process
has finished.

youtube_dl_gui/downloadmanager.py

@@ -72,7 +72,9 @@ class DownloadManager(Thread):
         self._successful = 0
         self._running = True
 
-        self._workers = self._init_workers(opt_manager.options['workers_number'])
+        wparams = (opt_manager, self._youtubedl_path(), log_manager)
+        self._workers = [Worker(*wparams) for i in xrange(opt_manager.options['workers_number'])]
+
         self.start()
 
     @property
@@ -86,10 +88,6 @@ class DownloadManager(Thread):
         to complete. """
         return self._time_it_took
 
-    def increase_succ(self):
-        """Increase number of successful downloads. """
-        self._successful += 1
-
     def run(self):
         self._check_youtubedl()
         self._time_it_took = time.time()
@@ -108,6 +106,7 @@ class DownloadManager(Thread):
         for worker in self._workers:
             worker.close()
             worker.join()
+            self._successful += worker.successful
 
         self._time_it_took = time.time() - self._time_it_took
 
@@ -193,16 +192,6 @@ class DownloadManager(Thread):
         path = os.path.join(path, YOUTUBEDL_BIN)
         return path
 
-    def _init_workers(self, workers_number):
-        """Initialize the custom thread pool.
-
-        Returns:
-            Python list that contains the workers.
-
-        """
-        youtubedl = self._youtubedl_path()
-        return [Worker(self.opt_manager, youtubedl, self.increase_succ, self.log_manager) for i in xrange(workers_number)]
-
 
 class Worker(Thread):
 
@@ -218,9 +207,6 @@ class Worker(Thread):
 
         youtubedl (string): Absolute path to youtube-dl binary.
 
-        increase_succ (DownloadManager.increase_succ() method): Callback to
-            increase the number of successful downloads.
-
         log_manager (logmanager.LogManager): Check DownloadManager
             description.
 
@@ -228,9 +214,8 @@ class Worker(Thread):
 
     WAIT_TIME = 0.1
 
-    def __init__(self, opt_manager, youtubedl, increase_succ, log_manager=None):
+    def __init__(self, opt_manager, youtubedl, log_manager=None):
         super(Worker, self).__init__()
-        self.increase_succ = increase_succ
         self.opt_manager = opt_manager
 
         self._downloader = YoutubeDLDownloader(youtubedl, self._data_hook, log_manager)
@@ -238,6 +223,7 @@ class Worker(Thread):
         self._running = True
         self._url = None
         self._index = -1
+        self._successful = 0
 
         self.start()
 
@@ -249,7 +235,7 @@ class Worker(Thread):
 
                 if (ret_code == YoutubeDLDownloader.OK or
                         ret_code == YoutubeDLDownloader.ALREADY):
-                    self.increase_succ()
+                    self._successful += 1
 
                 # Reset url value
                 self._url = None
@@ -282,6 +268,11 @@ class Worker(Thread):
         """Return True if the worker has no job else False. """
         return self._url is None
 
+    @property
+    def successful(self):
+        """Return the number of successful downloads for current worker. """
+        return self._successful
+
     def _data_hook(self, data):
         """Callback method to be used with the YoutubeDLDownloader object.