def init_distributed_mode()

in src/slurm.py [0:0]

• 80 lines of code
• 16 McCabe index (conditional complexity)

def init_distributed_mode(params):
    """
    Handle single and multi-GPU / multi-node / SLURM jobs.
    Initialize the following variables:
        - n_nodes
        - node_id
        - local_rank
        - global_rank
        - world_size
    """
    params.is_slurm_job = "SLURM_JOB_ID" in os.environ and not params.debug_slurm
    print("SLURM job: %s" % str(params.is_slurm_job))

    # SLURM job
    if params.is_slurm_job:

        assert params.local_rank == -1  # on the cluster, this is handled by SLURM

        SLURM_VARIABLES = [
            "SLURM_JOB_ID",
            "SLURM_JOB_NODELIST",
            "SLURM_JOB_NUM_NODES",
            "SLURM_NTASKS",
            "SLURM_TASKS_PER_NODE",
            "SLURM_MEM_PER_NODE",
            "SLURM_MEM_PER_CPU",
            "SLURM_NODEID",
            "SLURM_PROCID",
            "SLURM_LOCALID",
            "SLURM_TASK_PID",
        ]

        PREFIX = "%i - " % int(os.environ["SLURM_PROCID"])
        for name in SLURM_VARIABLES:
            value = os.environ.get(name, None)
            print(PREFIX + "%s: %s" % (name, str(value)))

        # # job ID
        # params.job_id = os.environ['SLURM_JOB_ID']

        # number of nodes / node ID
        params.n_nodes = int(os.environ["SLURM_JOB_NUM_NODES"])
        params.node_id = int(os.environ["SLURM_NODEID"])

        # local rank on the current node / global rank
        params.local_rank = int(os.environ["SLURM_LOCALID"])
        params.global_rank = int(os.environ["SLURM_PROCID"])

        # number of processes / GPUs per node
        params.world_size = int(os.environ["SLURM_NTASKS"])
        params.n_gpu_per_node = params.world_size // params.n_nodes

        # define master address and master port
        hostnames = subprocess.check_output(
            ["scontrol", "show", "hostnames", os.environ["SLURM_JOB_NODELIST"]]
        )
        params.master_addr = hostnames.split()[0].decode("utf-8")
        assert 10001 <= params.master_port <= 20000 or params.world_size == 1
        print(PREFIX + "Master address: %s" % params.master_addr)
        print(PREFIX + "Master port   : %i" % params.master_port)

        # set environment variables for 'env://'
        os.environ["MASTER_ADDR"] = params.master_addr
        os.environ["MASTER_PORT"] = str(params.master_port)
        os.environ["WORLD_SIZE"] = str(params.world_size)
        os.environ["RANK"] = str(params.global_rank)

    # multi-GPU job (local or multi-node) - jobs started with torch.distributed.launch
    elif params.local_rank != -1:

        assert params.master_port == -1

        # read environment variables
        params.global_rank = int(os.environ["RANK"])
        params.world_size = int(os.environ["WORLD_SIZE"])
        params.n_gpu_per_node = int(os.environ["NGPU"])

        # number of nodes / node ID
        params.n_nodes = params.world_size // params.n_gpu_per_node
        params.node_id = params.global_rank // params.n_gpu_per_node

    # local job (single GPU)
    else:
        assert params.local_rank == -1
        assert params.master_port == -1
        params.n_nodes = 1
        params.node_id = 0
        params.local_rank = 0
        params.global_rank = 0
        params.world_size = 1
        params.n_gpu_per_node = 1

    # sanity checks
    assert params.n_nodes >= 1
    assert 0 <= params.node_id < params.n_nodes
    assert 0 <= params.local_rank <= params.global_rank < params.world_size
    assert params.world_size == params.n_nodes * params.n_gpu_per_node

    # define whether this is the master process / if we are in distributed mode
    params.is_master = params.node_id == 0 and params.local_rank == 0
    params.multi_node = params.n_nodes > 1
    params.multi_gpu = params.world_size > 1

    # summary
    PREFIX = "%i - " % params.global_rank
    print(PREFIX + "Number of nodes: %i" % params.n_nodes)
    print(PREFIX + "Node ID        : %i" % params.node_id)
    print(PREFIX + "Local rank     : %i" % params.local_rank)
    print(PREFIX + "Global rank    : %i" % params.global_rank)
    print(PREFIX + "World size     : %i" % params.world_size)
    print(PREFIX + "GPUs per node  : %i" % params.n_gpu_per_node)
    print(PREFIX + "Master         : %s" % str(params.is_master))
    print(PREFIX + "Multi-node     : %s" % str(params.multi_node))
    print(PREFIX + "Multi-GPU      : %s" % str(params.multi_gpu))
    print(PREFIX + "Hostname       : %s" % socket.gethostname())

    # set GPU device
    if not params.cpu:
        torch.cuda.set_device(params.local_rank)

    # initialize multi-GPU
    if params.multi_gpu:

        # http://pytorch.apachecn.org/en/0.3.0/distributed.html#environment-variable-initialization
        # 'env://' will read these environment variables:
        # MASTER_PORT - required; has to be a free port on machine with rank 0
        # MASTER_ADDR - required (except for rank 0); address of rank 0 node
        # WORLD_SIZE - required; can be set either here, or in a call to init function
        # RANK - required; can be set either here, or in a call to init function

        print("Initializing PyTorch distributed ...")
        torch.distributed.init_process_group(
            init_method="env://", backend="nccl",
        )