Regenerating s3fs-refresh-cache & _read_cache recursion

Looking at your patch to the _read_cache() function, it looks like it actually breaks the anti-stampede code for every future cache read after 10 failed attempts to acquire the lock for a single file. Probably not the best solution.

In the attached patch, I've re-coded the recursive call into a goto. Could you try that out to see if it works? I've never actually used a goto before, since it's considered such a bad practice. But it seems like this is exactly the kind of situation it would actually be useful for.

Though as I look further into this, I'm really not sure why you'd be having this recursion problem at all. The lock that _read_cache() acquires applies only to a single file, so I'm not really sure what circumstances would even be able to repeatedly trigger the !lock_acquire($cid, 1) condition. Could you please describe what you (or some script) were doing when this recursion problem occurred?

For the cache refresh patch, I'm not really sure what it's doing. What "integrity constraint issues" are you testing for, and how is your code dealing with them?

Did you ever solve your problem with this issue? Please let me know yes, or no, so I can either close this issue or continue to work toward a solution.

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