Source code for dgl.multiprocessing.pytorch

"""PyTorch multiprocessing wrapper."""
from functools import wraps
import random
import traceback
from _thread import start_new_thread
import torch
import torch.multiprocessing as mp

from ..utils import create_shared_mem_array, get_shared_mem_array

def thread_wrapped_func(func):
    Wraps a process entry point to make it work with OpenMP.
    def decorated_function(*args, **kwargs):
        queue = mp.Queue()
        def _queue_result():
            exception, trace, res = None, None, None
                res = func(*args, **kwargs)
            except Exception as e:  # pylint: disable=broad-except
                exception = e
                trace = traceback.format_exc()
            queue.put((res, exception, trace))

        start_new_thread(_queue_result, ())
        result, exception, trace = queue.get()
        if exception is None:
            return result
            assert isinstance(exception, Exception)
            raise exception.__class__(trace)
    return decorated_function

# pylint: disable=missing-docstring
class Process(mp.Process):
    # pylint: disable=dangerous-default-value
    def __init__(self, group=None, target=None, name=None, args=(), kwargs={}, *, daemon=None):
        target = thread_wrapped_func(target)
        super().__init__(group, target, name, args, kwargs, daemon=daemon)

def _get_shared_mem_name(id_):
    return "shared" + str(id_)

[docs]def call_once_and_share(func, shape, dtype, rank=0): """Invoke the function in a single process of the PyTorch distributed process group, and share the result with other processes. Parameters ---------- func : callable Any callable that accepts no arguments and returns an arbitrary object. shape : tuple[int] The shape of the shared tensor. Must match the output of :attr:`func`. dtype : torch.dtype The data type of the shared tensor. Must match the output of :attr:`func`. rank : int, optional The process ID to actually execute the function. """ current_rank = torch.distributed.get_rank() dist_buf = torch.LongTensor([1]) if torch.distributed.get_backend() == 'nccl': # Use .cuda() to transfer it to the correct device. Should be OK since # PyTorch recommends the users to call set_device() after getting inside # torch.multiprocessing.spawn() dist_buf = dist_buf.cuda() # Process with the given rank creates and populates the shared memory array. if current_rank == rank: id_ = random.getrandbits(32) name = _get_shared_mem_name(id_) result = create_shared_mem_array(name, shape, dtype) result[:] = func() dist_buf[0] = id_ # Broadcasts the name of the shared array to other processes. torch.distributed.broadcast(dist_buf, rank) # If no exceptions, other processes open the same shared memory object. if current_rank != rank: id_ = dist_buf.item() name = _get_shared_mem_name(id_) result = get_shared_mem_array(name, shape, dtype) return result
[docs]def shared_tensor(shape, dtype=torch.float32): """Create a tensor in shared memory accessible by all processes within the same ``torch.distributed`` process group. The content is uninitialized. Parameters ---------- shape : tuple[int] The shape of the tensor. dtype : torch.dtype, optional The dtype of the tensor. Returns ------- Tensor The shared tensor. """ return call_once_and_share(lambda: torch.empty(*shape, dtype=dtype), shape, dtype)