Fix issues related to 'concurrent.futures' on Python 3.7 and 3.8 (close

#32)

.gitignore

@@ -22,3 +22,4 @@ __env__
 /images/
 /misc/
 __misc__
+python/

README.rst

@@ -214,6 +214,7 @@ Changelog
     thumbnails from the cache instead of generating them from original images
   * Update the code to not use deprecated constants on newer Pillow versions
   * Various typo fixed (@kianmeng, #31)
+  * Fix issues related to ``concurrent.futures`` on Python 3.7 and 3.8 (#32)
 
 * **v1.1.2:**
 

yoga_image_optimizer/stoppable_process_pool_executor.py

@@ -1,3 +1,4 @@
+import sys
 import functools
 import multiprocessing
 from concurrent.futures import ProcessPoolExecutor
@@ -28,9 +29,15 @@ def __init__(self, *args, **kwargs):
 
     def shutdown(self, *args, **kwargs):
         processes = self._processes
-        ProcessPoolExecutor.shutdown(self, *args, **kwargs)
+
+        # Python < 3.9: We should wait else we got an OSError:
+        # https://bugs.python.org/issue36281
+        if sys.version_info.major >= 3 and sys.version_info.minor < 9:
+            kwargs["wait"] = True
+
         for pid, process in processes.items():
             process.kill()
+        ProcessPoolExecutor.shutdown(self, *args, **kwargs)
         self._state_manager.shutdown()
 
     shutdown.__doc__ = ProcessPoolExecutor.shutdown.__doc__

yoga_image_optimizer/thumbnailer.py

@@ -1,4 +1,5 @@
 import os
+import sys
 from concurrent.futures import ThreadPoolExecutor
 from concurrent.futures import CancelledError
 
@@ -152,6 +153,12 @@ def cancel(self, uuid):
         del self._pending[uuid]
 
     def cancel_all(self):
+        # Python < 3.9: futures must be cancelled manually
+        if sys.version_info.major >= 3 and sys.version_info.minor < 9:
+            for future in [p["future"] for p in self._pending.values()]:
+                future.cancel()
+            self._executor.shutdown(wait=False)
+        else:
+            self._executor.shutdown(wait=False, cancel_futures=True)
         self._pending = {}
-        self._executor.shutdown(wait=False, cancel_futures=True)
         self._executor = ThreadPoolExecutor(max_workers=self._MAX_WORKERS)