fix async training late-binding bug

docs/conf.py

@@ -21,7 +21,8 @@
 sys.path.insert(0, os.path.abspath('../'))
 
 import mock
-MOCK_MODULES = ['numpy', 'scipy', 'tensorflow', 'scipy.misc', 'h5py', 'nltk', 'cv2']
+MOCK_MODULES = ['numpy', 'scipy', 'tensorflow', 'scipy.misc', 'h5py', 'nltk',
+                'cv2', 'scipy.io']
 for mod_name in MOCK_MODULES:
     sys.modules[mod_name] = mock.Mock()
 

tensorpack/train/trainer.py

@@ -6,6 +6,7 @@
 import threading
 import copy
 import re
+import functools
 from six.moves import zip
 
 from .base import Trainer
@@ -175,7 +176,7 @@ def train(self):
             else:
                 grad_list = [self.process_grads(g) for g in grad_list]
                 # pretend to average the grads, in order to make async and
-                # sync have consistent semantics
+                # sync have consistent effective learning rate
                 def scale(grads):
                     return [(grad / self.config.nr_tower, var) for grad, var in grads]
                 grad_list = map(scale, grad_list)
@@ -192,7 +193,7 @@ def scale(grads):
             self.threads = []
             for k in range(1, self.config.nr_tower):
                 train_op = self.config.optimizer.apply_gradients(grad_list[k])
-                f = lambda : self.sess.run([train_op])
+                f = lambda op=train_op: self.sess.run([op]) # avoid late-binding
                 th = LoopThread(f)
                 th.pause()
                 th.start()