Merge branch 'fix-mp-win-3.0' into 'master'

Fix multiprocessing on Windows

*Related to:*  #184 

I'm still running into #179 with this fix but all processes start now at least.

BTW the current design is pretty bad regarding memory footprint and bootstrap time as you have to pickle the manager object for *every* subprocess. So this does not only fix multiprocessing on Windows. It improves the multiprocessing design on other platforms, too.

See merge request !97

src/flake8/checker.py

@@ -38,6 +38,14 @@
 ])
 
 
+def _run_checks_from_queue(process_queue, results_queue, statistics_queue):
+    LOG.info('Running checks in parallel')
+    for checker in iter(process_queue.get, 'DONE'):
+        LOG.info('Checking "%s"', checker.filename)
+        checker.run_checks(results_queue, statistics_queue)
+    results_queue.put('DONE')
+
+
 class Manager(object):
     """Manage the parallelism and checker instances for each plugin and file.
 
@@ -215,13 +223,6 @@ def _handle_results(self, filename, results):
             )
         return reported_results_count
 
-    def _run_checks_from_queue(self):
-        LOG.info('Running checks in parallel')
-        for checker in iter(self.process_queue.get, 'DONE'):
-            LOG.info('Checking "%s"', checker.filename)
-            checker.run_checks(self.results_queue, self.statistics_queue)
-        self.results_queue.put('DONE')
-
     def is_path_excluded(self, path):
         # type: (str) -> bool
         """Check if a path is excluded.
@@ -309,7 +310,9 @@ def run_parallel(self):
         LOG.info('Starting %d process workers', self.jobs)
         for i in range(self.jobs):
             proc = multiprocessing.Process(
-                target=self._run_checks_from_queue
+                target=_run_checks_from_queue,
+                args=(self.process_queue, self.results_queue,
+                      self.statistics_queue)
             )
             proc.daemon = True
             proc.start()