this post was submitted on 24 Sep 2023
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Rust
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I would likely do it in reverse. Try and find the object and if it doesn't exist create it.
That will always be prune to race conditions, where you check if someting exists (then some other thread creates it) and then you try to create it. You should always try to create first, then if it fails due to it already existing, fetch it. That is a good general rule for anything from hashmaps to databases.
That's true, but also trying to create first has a race condition too. The above code will panic at the unwrap if the record is deleted after the failed insert, and before the select
So, a loop it is....
I'm new to multithreaded programming. How would some other thread create it? Like what's the real-world scenario?
That is all dependent on the program, but the simplest scenario is by an API with two requests at the same time. But it may also be like if you scan for new files, and use inotify, then you may also have a scanning loop as a fallback. Then the scan and inotify may trigger at almost the same time, so if that then results in a db create or insert you can get in to this problem. So, there are multiple ways to get in to trouble, and life always find new ways 😀
Indeed it does haha, thanks