Pytorch num

出现此现象，一种可能的原因是使用了jupyter执行程序导致，jupyter似乎不支持创建子进程。

代码如下：

import torch,os,math

class MyIterableDataset(torch.utils.data.IterableDataset):
    def __init__(self, start, end):
        super(MyIterableDataset).__init__()
        assert end > start, "this example code only works with end >= start"
        self.start = start
        self.end = end
    def __iter__(self):
        worker_info = torch.utils.data.get_worker_info()
        if worker_info is None:  # single-process data loading, return the full iterator
            iter_start = self.start
            iter_end = self.end
        else:  # in a worker process
            # split workload
            per_worker = int(math.ceil((self.end - self.start) / float(worker_info.num_workers)))
            worker_id = worker_info.id
            iter_start = self.start + worker_id * per_worker
            iter_end = min(iter_start + per_worker, self.end)
        return iter(range(iter_start, iter_end))
# should give same set of data as range(3, 7), i.e., [3, 4, 5, 6].
ds = MyIterableDataset(start=3, end=7)

print('Single-process loading 1')
print(list(torch.utils.data.DataLoader(ds, num_workers=0)))

# Mult-process loading with two worker processes
# Worker 0 fetched [3, 4].  Worker 1 fetched [5, 6].
print('Mult-process loading 2')
print(list(torch.utils.data.DataLoader(ds, num_workers=1)))

# With even more workers
print('Mult-process loading 3')
print(list(torch.utils.data.DataLoader(ds, num_workers=20)))

# time.sleep(5)
exit()

jupyter执行结果：

shell执行结果：

其它程序shell执行结果:

 可见问题得到解决。