with python 3.6.7 + pytorch 1.0.0, init_process_group() sometimes hangs and never returns. Any idea of how to fix it? I need to run some projects under 1.0 version. Here are details.
Code scripts
a.py
import torch
import torch.distributed as dist
import os

def get_mpi_rank():
    return int(os.environ['RANK'])

def get_mpi_size():
    return int(os.environ.get('WORLD_SIZE', '1'))

rank = get_mpi_rank()
world_size = get_mpi_size()

init_param={'backend': 'nccl',
        'init_method': 'env://',
        'rank': rank,
        'world_size': world_size}

from pprint import pformat
print('before {} - {}\n'.format(rank,
    pformat(init_param)))
dist.init_process_group(**init_param)
print('after {}'.format(rank))

When it works
python 2.7.12 + pytorch 0.4.1
$ python --version
Python 2.7.12
$ python -c 'import torch; print torch.__version__'
0.4.1
$ python -m torch.distributed.launch --nproc_per_node 2 a.py
before 1 - {'backend': 'nccl', 'init_method': 'env://', 'rank': 1, 'world_size': 2}

before 0 - {'backend': 'nccl', 'init_method': 'env://', 'rank': 0, 'world_size': 2}

after 0
after 1

If i run the scripts multiple times, it always succeeds.
When it does not work
$ python --version
Python 3.6.7 :: Anaconda, Inc.
$ python -c 'import torch; print(torch.__version__)'
1.0.0
$ python -m torch.distributed.launch --nproc_per_node 2 a.py
before 1 - {'backend': 'nccl', 'init_method': 'env://', 'rank': 1, 'world_size': 2}

before 0 - {'backend': 'nccl', 'init_method': 'env://', 'rank': 0, 'world_size': 2}

after 0

The rank 0 is able to finish the function call of init_process_group, but the rank 1 never returns. Then, I use the gdb to attach the hanged process.
$ sudo gdb -p 40855
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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For help, type "help".
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Attaching to process 40855
Reading symbols from /raid/jianfw/anaconda3/bin/python3.6...done.
Reading symbols from /lib/x86_64-linux-gnu/libpthread.so.0...Reading symbols from /usr/lib/debug/.build-id/ce/17e023542265fc11d9bc8f534bb4f070493d30.debug...done.
done.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.23.so...done.
done.
Reading symbols from /lib/x86_64-linux-gnu/libdl.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libdl-2.23.so...done.
done.
(gdb) where
#0  0x00007f0ce5586c00 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1  0x00007f0cde561e88 in c10d::tcputil::connect(std::string const&, unsigned short, bool, std::chrono::duration<long, std::ratio<1l, 1000l> > const&) ()
   from /raid/jianfw/anaconda3/lib/python3.6/site-packages/torch/lib/libtorch_python.so
#2  0x00007f0cde55cef5 in c10d::TCPStore::TCPStore(std::string const&, unsigned short, bool) () from /raid/jianfw/anaconda3/lib/python3.6/site-packages/torch/lib/libtorch_python.so
#3  0x00007f0cde4f09f6 in void pybind11::cpp_function::initialize<void pybind11::detail::initimpl::constructor<std::string const&, int, bool>::execute<pybind11::class_<c10d::TCPStore, std::shared_ptr<c10d::TCPStore> >, , 0>(pybind11::class_<c10d::TCPStore, std::shared_ptr<c10d::TCPStore> >&)::{lambda(pybind11::detail::value_and_holder&, std::string const&, int, bool)#1}, void, pybind11::detail::value_and_holder&, std::string const&, int, bool, pybind11::name, pybind11::is_method, pybind11::sibling, pybind11::detail::is_new_style_constructor>(void pybind11::detail::initimpl::constructor<std::string const&, int, bool>::execute<pybind11::class_<c10d::TCPStore, std::shared_ptr<c10d::TCPStore> >, , 0>(pybind11::class_<c10d::TCPStore, std::shared_ptr<c10d::TCPStore> >&)::{lambda(pybind11::detail::value_and_holder&, std::string const&, int, bool)#1}&&, void (*)(pybind11::detail::value_and_holder&, std::string const&, int, bool), pybind11::name const&, pybind11::is_method const&, pybind11::sibling const&, pybind11::detail::is_new_style_constructor const&)::{lambda(pybind11::detail::function_call&)#3}::_FUN(pybind11::detail::function_call) () from /raid/jianfw/anaconda3/lib/python3.6/site-packages/torch/lib/libtorch_python.so
#4  0x00007f0cddff0e36 in pybind11::cpp_function::dispatcher(_object*, _object*, _object*) () from /raid/jianfw/anaconda3/lib/python3.6/site-packages/torch/lib/libtorch_python.so
#5  0x000055b391cbe3d4 in _PyCFunction_FastCallDict () at /tmp/build/80754af9/python_1540319457073/work/Objects/methodobject.c:231
#6  0x000055b391cbe7ef in _PyObject_FastCallDict () at /tmp/build/80754af9/python_1540319457073/work/Objects/abstract.c:2313
#7  0x000055b391cc3303 in _PyObject_Call_Prepend () at /tmp/build/80754af9/python_1540319457073/work/Objects/abstract.c:2373
#8  0x000055b391cbe1de in PyObject_Call () at /tmp/build/80754af9/python_1540319457073/work/Objects/abstract.c:2261
#9  0x000055b391d1b78b in slot_tp_init () at /tmp/build/80754af9/python_1540319457073/work/Objects/typeobject.c:6420
#10 0x000055b391d47f57 in type_call () at /tmp/build/80754af9/python_1540319457073/work/Objects/typeobject.c:915
#11 0x000055b391cbe5bb in _PyObject_FastCallDict () at /tmp/build/80754af9/python_1540319457073/work/Objects/abstract.c:2331
#12 0x000055b391d47d6e in call_function () at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:4861
#13 0x000055b391d6a71a in _PyEval_EvalFrameDefault () at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:3335
#14 0x000055b391d4a860 in gen_send_ex (closing=0, exc=0, arg=0x0, gen=0x7f0ca53fed58) at /tmp/build/80754af9/python_1540319457073/work/Objects/genobject.c:189
#15 gen_iternext (gen=0x7f0ca53fed58) at /tmp/build/80754af9/python_1540319457073/work/Objects/genobject.c:563
#16 builtin_next () at /tmp/build/80754af9/python_1540319457073/work/Python/bltinmodule.c:1330
#17 0x000055b391cbe311 in _PyCFunction_FastCallDict () at /tmp/build/80754af9/python_1540319457073/work/Objects/methodobject.c:234
#18 0x000055b391d47c1c in call_function () at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:4837
#19 0x000055b391d6a71a in _PyEval_EvalFrameDefault () at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:3335
#20 0x000055b391d42ad9 in _PyEval_EvalCodeWithName (qualname=0x0, name=0x0, closure=0x0, kwdefs=0x0, defcount=2, defs=0x7f0ca578dd60, kwstep=2, kwcount=<optimized out>,
    kwargs=0x7f0ce447eae8, kwnames=0x7f0ce447eae0, argcount=<optimized out>, args=0x55b393457df0, locals=0x0, globals=<optimized out>, _co=0x7f0ca54e8270)
    at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:4166
#21 PyEval_EvalCodeEx () at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:4187
#22 0x000055b391d43a06 in function_call () at /tmp/build/80754af9/python_1540319457073/work/Objects/funcobject.c:604
#23 0x000055b391cbe1de in PyObject_Call () at /tmp/build/80754af9/python_1540319457073/work/Objects/abstract.c:2261
#24 0x000055b391d6bd9a in do_call_core (kwdict=0x7f0ce58c0678, callargs=0x7f0ce594b048, func=0x7f0ca54f0a60) at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:5106
#25 _PyEval_EvalFrameDefault () at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:3404
#26 0x000055b391d42ad9 in _PyEval_EvalCodeWithName (qualname=0x0, name=0x0, closure=0x0, kwdefs=0x0, defcount=0, defs=0x0, kwstep=2, kwcount=<optimized out>, kwargs=0x0, kwnames=0x0,
    argcount=0, args=0x0, locals=0x7f0ce5901360, globals=0x7f0ce5901360, _co=0x7f0ce448e5d0) at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:4166
#27 PyEval_EvalCodeEx () at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:4187
#28 0x000055b391d4387c in PyEval_EvalCode (co=co@entry=0x7f0ce448e5d0, globals=globals@entry=0x7f0ce5901360, locals=locals@entry=0x7f0ce5901360)
    at /tmp/build/80754af9/python_1540319457073/work/Python/ceval.c:731
#29 0x000055b391dc4074 in run_mod () at /tmp/build/80754af9/python_1540319457073/work/Python/pythonrun.c:1025
#30 0x000055b391dc4471 in PyRun_FileExFlags () at /tmp/build/80754af9/python_1540319457073/work/Python/pythonrun.c:978
#31 0x000055b391dc4673 in PyRun_SimpleFileExFlags () at /tmp/build/80754af9/python_1540319457073/work/Python/pythonrun.c:419
#32 0x000055b391dc477d in PyRun_AnyFileExFlags () at /tmp/build/80754af9/python_1540319457073/work/Python/pythonrun.c:81
#33 0x000055b391dc81b0 in run_file (p_cf=0x7ffc8471a94c, filename=0x55b3933a6300 L"a.py", fp=0x55b393433e20) at /tmp/build/80754af9/python_1540319457073/work/Modules/main.c:340
#34 Py_Main () at /tmp/build/80754af9/python_1540319457073/work/Modules/main.c:811
#35 0x000055b391c8fb4e in main () at /tmp/build/80754af9/python_1540319457073/work/Programs/python.c:69
#36 0x00007f0ce51cc830 in __libc_start_main (main=0x55b391c8fa60 <main>, argc=4, argv=0x7ffc8471ab58, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>,
    stack_end=0x7ffc8471ab48) at ../csu/libc-start.c:291
#37 0x000055b391d711a8 in _start () at ../sysdeps/x86_64/elf/start.S:103

Looks like it hangs at the function call of c10d::TCPStore::TCPStore(std::string const&, unsigned short, bool) (), c10d::tcputil::connect(std::string const&, unsigned short, bool, std::chrono::duration<long, std::ratio<1l, 1000l> > const&) ()
Any idea to fix it?
Thanks