Python Multiprocessing Error with IBM API (Q Experience)

Question

I'm trying to use the IBM Q Experience API and I installed the library and wrote a quick test code. At first, it couldn't find the module. Then, I added the whole sys thing. Admittedly, I just copied that from a stackoverflow post so that may be the problem. Anyways, I got "RunTime Error" which leads to the python multiprocessing lib. The IBM Q doesn't have a big community, so I couldn't find anything after researching a little while. I'm completely unfamiliar with multiprocessing, threading, etc, so I imagine just seeing the code and error will be better than anything I can do to explain. Thanks in advance.

import sys
sys.path.append("../../")

from qiskit import QuantumProgram

#visualization
from tools.visualization import plot_histogram

#set up registers
qp = QuantumProgram()
q = qp.create_quantum_register("q", 3)
c = qp.create_classical_register("c", 3)

#define our circuit
threeQ = qp.create_circuit("threeQ", [q], [c])
threeQ.measure(q[0], c[0])
threeQ.measure(q[1], c[1])
threeQ.measure(q[2], c[2])

#run
result = qp.execute(["threeQ"])

#plot
plot_histogram(result.get_counts("threeQ"))

The error I get (sorry, it's long):

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 106, in spawn_main
    exitcode = _main(fd)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 115, in _main
    prepare(preparation_data)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 226, in prepare
    _fixup_main_from_path(data['init_main_from_path'])
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 278, in _fixup_main_from_path
    run_name="__mp_main__")
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\runpy.py", line 254, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Users\Everybody\firstquantum.py", line 21, in <module>
    print(qp.execute(["threeQ"]))
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_quantumprogram.py", line 1413, in execute
    result = self.run(qobj, wait=wait, timeout=timeout)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_quantumprogram.py", line 1232, in run
    timeout=timeout)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_quantumprogram.py", line 1315, in _run_internal
    job_processor.submit()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_jobprocessor.py", line 118, in submit
    future = executor.submit(run_backend, q_job)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\concurrent\futures\process.py", line 454, in submit
    self._start_queue_management_thread()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\concurrent\futures\process.py", line 415, in _start_queue_management_thread
    self._adjust_process_count()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\concurrent\futures\process.py", line 434, in _adjust_process_count
    p.start()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\context.py", line 212, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\context.py", line 313, in _Popen
    return Popen(process_obj)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\popen_spawn_win32.py", line 34, in __init__
    prep_data = spawn.get_preparation_data(process_obj._name)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 144, in get_preparation_data
    _check_not_importing_main()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 137, in _check_not_importing_main
    is not going to be frozen to produce an executable.''')
RuntimeError:
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 106, in spawn_main
    exitcode = _main(fd)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 115, in _main
    prepare(preparation_data)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 226, in prepare
    _fixup_main_from_path(data['init_main_from_path'])
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 278, in _fixup_main_from_path
    run_name="__mp_main__")
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\runpy.py", line 254, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Users\Everybody\firstquantum.py", line 21, in <module>
    print(qp.execute(["threeQ"]))
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_quantumprogram.py", line 1413, in execute
    result = self.run(qobj, wait=wait, timeout=timeout)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_quantumprogram.py", line 1232, in run
    timeout=timeout)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_quantumprogram.py", line 1315, in _run_internal
    job_processor.submit()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\site-packages\qiskit\_jobprocessor.py", line 118, in submit
    future = executor.submit(run_backend, q_job)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\concurrent\futures\process.py", line 454, in submit
    self._start_queue_management_thread()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\concurrent\futures\process.py", line 415, in _start_queue_management_thread
    self._adjust_process_count()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\concurrent\futures\process.py", line 434, in _adjust_process_count
    p.start()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\context.py", line 212, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\context.py", line 313, in _Popen
    return Popen(process_obj)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\popen_spawn_win32.py", line 34, in __init__
    prep_data = spawn.get_preparation_data(process_obj._name)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 144, in get_preparation_data
    _check_not_importing_main()
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 137, in _check_not_importing_main
    is not going to be frozen to produce an executable.''')
RuntimeError:
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 106, in spawn_main
    exitcode = _main(fd)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 115, in _main
    prepare(preparation_data)
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 226, in prepare
    _fixup_main_from_path(data['init_main_from_path'])
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\multiprocessing\spawn.py", line 278, in _fixup_main_from_path
    run_name="__mp_main__")
  File "C:\Users\Everybody\AppData\Local\Programs\Python\Python35\lib\runpy.py", line 254, in run_path
ERROR

Octameter

Unfortunately, I use Linux and can't reproduce your issue. However, I advise you to try Python3 from Anaconda. You also need to fix one of the imports as from qiskit.tools.visualization import plot_histogram. – Moldy

Thank you, I did have an error with the plot_histogram. So, by python3 w anaconda do you mean installing the newest python using anaconda? Thanks – Octameter

Right, I suggest to use Anaconda as your Python3 environment and install QISKit with pip install qiskit in Anaconda Prompt. – Moldy

Unfortunately, I got a very similar, but not identical error. I assume the difference is just because it is in the python environment. The only main thing I noticed that was different was this last bit: – Octameter

File "C:\Users\Everybody\Anaconda3\envs\py36\lib\concurrent\futures_base.py", line 357, in __get_result raise self._exception concurrent.futures.process.BrokenProcessPool: A process in the process pool was terminated abruptly while the future was running or pending. – Octameter

I've tried Win7: Anaconda3 5.0.1 + pip install qiskit in Anaconda Prompt, and your program worked even without import sys. So, could you, please, elaborate on your environment. What is your OS version? How do you install QISKit? How do you run a program (Jupyter notebook?)? – Moldy

My OS is Windows 10 Home Version 10.0.16299. I'm using Sublime Text Editor and after your advice I reinstalled qiskit using the new python 3.6 environment in anaconda. (made using conda create -n py36 python=3.6 anaconda) I ran the program through the anaconda prompt rather than the command prompt. – Octameter

Sorry, forgot to add that the anaconda version is 4.3.14. If I update anaconda will I need to recreate the environment? – Octameter

Its working now. Thanks Alexander! – Octameter

Answer 1

This is a general issue with multi-threading in Python on Windows. The solution is to put your top-level code in an if __name__ == "__main__" block, as in:

if __name__ == '__main__':
    <your code here>

Hope that helps!

Pale

Thanks a lot! I'm pretty inexperienced with Python, but if you have a minute, I'm curious about what caused the error. Thanks again Doug! – Octameter

I'm not a Python expert either, but you can read more about the issue here among other places. – Pale