[GitHub] [incubator-mxnet] cuibuaa opened a new issue #16994: DataLoader: Missing batch_size dim when num_workers > 0

[GitBox <gi...@apache.org>]

cuibuaa opened a new issue #16994: DataLoader: Missing batch_size dim when num_workers > 0
URL: https://github.com/apache/incubator-mxnet/issues/16994
 
 
   ## Description
   When num_workers is not 0, Dataloader misses batch_size dimension for the last batch with one sample.
   
   ### Error Message
   No specific error trace, but this issue will cause a series of errors for the last batch samples
   
   ## To Reproduce
   
   ```
   from mxnet import gluon
   
   class CustomDataSet(gluon.data.Dataset):
       def __init__(self, data):
           self.np_array = np.array(data)
           
       def __len__(self):
           return self.np_array.shape[0]
       
       def __getitem__(self, idx):
           data = self.np_array[idx]
           return data
   
   test_ds = CustomDataSet([[1,1,1,1] for _ in range(5)])
   test_dl = gluon.data.DataLoader(test_ds, 4, last_batch='keep', num_workers=1) # could be any value > 0
   
   cnt = 0
   for x in test_dl:
       if cnt == len(test_dl) - 1:
           print(x)
       cnt += 1
   ```
   
   ### Steps to reproduce
   
   1. if num_workers > 0, the output is :
   [1 1 1 1]
   <NDArray 4 @cpu_shared(0)>
   2. if num_workers = 0, the output is:
   [[1 1 1 1]]
   <NDArray 1x4 @cpu(0)>
   
   ## What have you tried to solve it?
   
   No
   
   ## Environment
   
   We recommend using our script for collecting the diagnositc information. Run the following command and paste the outputs below:
   ```
   curl --retry 10 -s https://raw.githubusercontent.com/dmlc/gluon-nlp/master/tools/diagnose.py | python
   
   # paste outputs here
   ```
   ----------Python Info----------
   Version      : 3.6.6
   Compiler     : GCC 7.2.0
   Build        : ('default', 'Jun 28 2018 17:14:51')
   Arch         : ('64bit', '')
   ------------Pip Info-----------
   Version      : 19.3.1
   Directory    : /home/ubuntu/anaconda3/lib/python3.6/site-packages/pip
   ----------MXNet Info-----------
   No MXNet installed.
   ----------System Info----------
   Platform     : Linux-4.4.0-1096-aws-x86_64-with-debian-stretch-sid
   system       : Linux
   node         : xxxxxxx
   release      : 4.4.0-1096-aws
   version      : #107-Ubuntu SMP Thu Oct 3 01:51:58 UTC 2019
   ----------Hardware Info----------
   machine      : x86_64
   processor    : x86_64
   Architecture:          x86_64
   CPU op-mode(s):        32-bit, 64-bit
   Byte Order:            Little Endian
   CPU(s):                8
   On-line CPU(s) list:   0-7
   Thread(s) per core:    2
   Core(s) per socket:    4
   Socket(s):             1
   NUMA node(s):          1
   Vendor ID:             GenuineIntel
   CPU family:            6
   Model:                 79
   Model name:            Intel(R) Xeon(R) CPU E5-2686 v4 @ 2.30GHz
   Stepping:              1
   CPU MHz:               2700.343
   CPU max MHz:           3000.0000
   CPU min MHz:           1200.0000
   BogoMIPS:              4600.14
   Hypervisor vendor:     Xen
   Virtualization type:   full
   L1d cache:             32K
   L1i cache:             32K
   L2 cache:              256K
   L3 cache:              46080K
   NUMA node0 CPU(s):     0-7
   

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