Dataloader 似乎没有正常关闭，大量调用后报错 | Dataloader may be not closed in some cases, and calling it many times will cause "Resource temporarily unavailable"

[holyseven]

bug描述 Describe the Bug

DataLoader 没有正常关闭thread，如果大量call DataLoader，会导致最后没有资源了。

实例化后的DataLoader，会去申请资源（应该是开了thread），但是没有正常关闭，导致最后申请不到资源，报错RuntimeError: Resource temporarily unavailable。

不确定是否是bug，因为这不是常规操作。但是否有方法避免？

from paddle.io import Dataset, DataLoader
train_loader = DataLoader(train_set, batch_size=2, shuffle=True)
for _ in range(10000):
    for i, e in enumerate(train_loader):
        print(_, i)
        break

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
/tmp/ipykernel_19543/3388343434.py in <module>
      1 for _ in range(1200):
      2     train_loader = DataLoader(train_set, batch_size=2, shuffle=True)
----> 3     for i, e in enumerate(train_loader):
      4         print(_, i)
      5         break

~/miniconda3/envs/pp2/lib/python3.7/site-packages/paddle/fluid/reader.py in __iter__(self)
    424     def __iter__(self):
    425         if self.num_workers == 0:
--> 426             return _DataLoaderIterSingleProcess(self)
    427         elif self._persistent_workers:
    428             if self._iterator is None:

~/miniconda3/envs/pp2/lib/python3.7/site-packages/paddle/fluid/dataloader/dataloader_iter.py in __init__(self, loader)
    168         self._blocking_queue_capacity = 1 * len(self._places)
    169 
--> 170         self._init_thread()
    171         self._shutdown = False
    172 

~/miniconda3/envs/pp2/lib/python3.7/site-packages/paddle/fluid/dataloader/dataloader_iter.py in _init_thread(self)
    188             self._blocking_queue, self._var_names, self._shapes, self._dtypes,
    189             self._need_check_feed, self._places, self._use_buffer_reader, True,
--> 190             self._pin_memory)
    191 
    192         self._thread = threading.Thread(

RuntimeError: Resource temporarily unavailable

其他补充信息 Additional Supplementary Information

和#38371 类似。

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[lyuwenyu]

ps aux能看到相关的进程嘛，直接kill掉试下

[holyseven]

em... it's not a solution at all.

如果出现这个Resource temporarily unavailable问题的话，terminal里面也无法操作。terminal会有弹出bash: fork: retry: 资源暂时不可用。

我现在在jupyter notebook里面运行，只要把jupyter关了或者重启，就可以解决这个问题。但是程序无法继续运行下去。

[heavengate]

dataloader是在一个epoch启动的时候启动线程和子进程，结束的时候释放线程和子进程，如果你代码里中途break出来，挥刀自没法走到结束时释放进程线程的逻辑，你是什么场景需要反复从dataloader for循环里break出来么

[holyseven]

场景：pytorch算法influence function 转paddle，https://github.com/nimarb/pytorch_influence_functions/blob/master/pytorch_influence_functions/influence_function.py#L35-L52。

暂时是按照这样解决的：

iters = train_loader.__iter__()
for _ in range(1200):
    for i, e in enumerate(iters):
        print(_, i)
        break