Sampling from episodic loader gives error - "Key image doesn't exist (select from [])!" about pytorch-meta-dataset

[patricks-lab]

Recently, I also found out that the error seems to originate from the utils.py (https://github.com/mboudiaf/pytorch-meta-dataset/blob/master/src/datasets/utils.py) file - sometimes, my program would hang after going into an infinite loop in cycle_ and eventually crashes with the above error.

So basically this is what happens:

First, in https://github.com/mboudiaf/pytorch-meta-dataset/blob/master/src/datasets/pipeline.py the code attempts to fetch a sample from a class, using sample_dic = next(self.class_datasets[class_id]). But then this raises a TypeError: 'TFRecordDataset' object is not an iterator exception, so it attempts to call cycle_() on the class in the except clause.

def get_next(self, class_id):
        try:
            sample_dic = next(self.class_datasets[class_id])
        except (StopIteration, TypeError) as e:
            self.class_datasets[class_id] = cycle_(self.class_datasets[class_id])
            sample_dic = next(self.class_datasets[class_id])
        return sample_dic

But, in the function cycle_ in utils.py the code tries to yield the next sample in the iterator, and if not, it will attempt to reset the iterator. So the code looked like this:

def cycle_(iterable):
    # Creating custom cycle since itertools.cycle attempts to save all outputs in order to
    # re-cycle through them, creating amazing memory leak
    iterator = iter(iterable)
    while True:
        try:
            yield next(iterator)
        except StopIteration:
            iterator = iter(iterable)

The issue I think is happening is that there is some iteration where the class iterable is empty (something like iter([])). I'm wondering if this may be due to a deformed/corrupted tfrecord (since I did specify a fixed 5-way, 10-shot task)? I'm thinking the class is empty since it's telling me that KeyError: "Key image doesn't exist (select from [])!", suggesting that the class we're trying to iterate from might be entirely empty.

As such I am wondering if I need to reinstall the files for meta-dataset? Or is there an issue with the code I'm running?

[brando90]

@mboudiaf I'm also interested in this