Cannot build dockerfile

[Arkoprabho]

On trying to build a docker image of pytorch by following the instructions as in README, I reach the following point after which the installation doesn't proceed anymore. The installation was stuck at this point for almost 7 hours after which I interrupted it with a keyboard interrupt.

    running install_egg_info
    running egg_info
    creating torch.egg-info
    writing torch.egg-info/PKG-INFO
    writing dependency_links to torch.egg-info/dependency_links.txt
    writing requirements to torch.egg-info/requires.txt
    writing top-level names to torch.egg-info/top_level.txt
    writing manifest file 'torch.egg-info/SOURCES.txt'
    reading manifest file 'torch.egg-info/SOURCES.txt'
    writing manifest file 'torch.egg-info/SOURCES.txt'
    Copying torch.egg-info to /opt/conda/envs/pytorch-py3.6/lib/python3.6/site-packages/torch-0.4.0a0+9c7ac85-py3.6.egg-info
    running install_scripts
    writing list of installed files to '/tmp/pip-1w4ze9yn-record/install-record.txt'
    Running setup.py install for torch: finished with status 'done'
  Removing source in /tmp/pip-z_6jap1o-build
Successfully installed torch-0.4.0a0+9c7ac85
Cleaning up...
Looking up "https://pypi.python.org/pypi/pip/json" in the cache
No cache entry available
Starting new HTTPS connection (1): pypi.python.org
"GET /pypi/pip/json HTTP/1.1" 200 72983
Updating cache with response from "https://pypi.python.org/pypi/pip/json"
Caching b/c date exists and max-age > 0

My Environment:
OS: Ubuntu 16.04 LTS
Pytorch cloned from repository
Docker version 17.12.0-ce, build c97c6d6
System Information: CPU Ryzen 5 1600, GPU GTX 1060 6GB, RAM 8GB

[Arkoprabho]

A rebuild a day later seemed to fix the problem. Can someone explain why this happened? From what I understood, the issue is more with pip rather than with PyTorch, as can be seen from this link.