import os
import sys
import py3nvml


# GPU picking
# http://stackoverflow.com/a/41638727/419116

# credit to Yaroslavv Bulatav for the general idea, the error checking and CUDA_DEVICE_ORDER workaround
# https://github.com/yaroslavvb/stuff/blob/252668efe602da30a34948bfb8b4f89f1ef9d60a/notebook_util.py
# This uses py3nvml to avoid issues parsing the output of nvidia-smi on different platforms

_already_initialised = False

def setup_gpus(num_gpus, memory_fraction=0.8):
    global _already_initialised

    if not _already_initialised:
        assert 'tensorflow' not in sys.modules, 'GPU setup must happen before importing TensorFlow'
        os.environ["CUDA_DEVICE_ORDER"] = "PCI_BUS_ID"  # see tensorflow issue #152
        num_grabbed = py3nvml.grab_gpus(num_gpus, gpu_fraction=memory_fraction)
        assert num_grabbed == num_gpus, 'Could not grab {} GPU devices with {}% memory available'.format(num_gpus,
                                                                                                         memory_fraction * 100)
        if os.environ['CUDA_VISIBLE_DEVICES'] == "":
            os.environ['CUDA_VISIBLE_DEVICES'] = "-1"  # see tensorflow issues: #16824, #2175
        _already_initialised = True