fix thread local (#86)

Author: zhreshold

python/decord/bridge/__init__.py

@@ -17,9 +17,12 @@
 
 _CURRENT_BRIDGE = threading.local()
 _CURRENT_BRIDGE.type = 'native'
+_GLOBAL_BRIDGE_TYPE = 'native'  # child threads will derive from the global type but not overwrite
 
 def reset_bridge():
     _CURRENT_BRIDGE.type = 'native'
+    if threading.current_thread().name == 'MainThread':
+        _GLOBAL_BRIDGE_TYPE = 'native'
 
 def set_bridge(new_bridge):
     assert isinstance(new_bridge, str), (
@@ -28,11 +31,17 @@ def set_bridge(new_bridge):
         "valid bridges: {}".format(_BRIDGE_TYPES.keys()))
     global _CURRENT_BRIDGE
     _CURRENT_BRIDGE.type = new_bridge
+    if threading.current_thread().name == 'MainThread':
+        _GLOBAL_BRIDGE_TYPE = new_bridge
 
 def bridge_out(native_arr):
+    if not hasattr(_CURRENT_BRIDGE, 'type'):
+        _CURRENT_BRIDGE.type = _GLOBAL_BRIDGE_TYPE
     return _BRIDGE_TYPES[_CURRENT_BRIDGE.type][0](native_arr)
 
 def bridge_in(arr):
+    if not hasattr(_CURRENT_BRIDGE, 'type'):
+        _CURRENT_BRIDGE.type = _GLOBAL_BRIDGE_TYPE
     return _BRIDGE_TYPES[_CURRENT_BRIDGE.type][1](arr)
 
 class _BridgeScope(object):
@@ -42,6 +51,8 @@ def __init__(self, bridge_type='native'):
 
     def __enter__(self):
         global _CURRENT_BRIDGE
+        if not hasattr(_CURRENT_BRIDGE, 'type'):
+            _CURRENT_BRIDGE.type = _GLOBAL_BRIDGE_TYPE
         try:
             self._prev = _CURRENT_BRIDGE.type
         except AttributeError:

tests/python/unittests/test_bridges.py

@@ -59,6 +59,24 @@ def test_tvm_bridge():
     except ImportError:
         print('Skip test tvm bridge as tvm is not found')
 
+def test_threaded_bridge():
+    # issue #85
+    from decord import cpu, gpu
+    from multiprocessing.dummy import Pool as ThreadPool
+
+    video_paths = [
+      os.path.expanduser('~/Dev/decord/examples/flipping_a_pancake.mkv'), #list of paths to video
+      ]
+
+    def process_path(path):
+        vr = VideoReader(path, ctx=cpu(0))
+
+        for i in range(len(vr)):
+            frame = vr[i]
+
+    pool = ThreadPool(1)
+    pool.map(process_path, video_paths)
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()