Race condition when writing multiple files in the same directory in parallel

[linfaxin]

https://codepen.io/linfaxin/pen/myeXZMv

  import { fs } from "@zenfs/core";

  await Promise.all([
    fs.promises.writeFile("/a1.txt", "a1"),
    fs.promises.writeFile("/a2.txt", "a2"),
  ]);

  const files = await fs.promises.readdir("/");      
  console.log('files', files); // console: ["a2.txt"]

want: ["a1.txt", "a2.txt"]
but get: ["a2.txt"]

[james-pre]

This is almost certainly a time-of-check time-of-use bug. The solution is very complex, and would involve adding synchronization to hundreds of code paths. I'm considering doing this as part of #247, since that would involve the synchronization anyway.

[james-pre]

Hey @linfaxin, I wanted to give you an update on this.

I had some time to work through the problem. It looks like in order to avoid the TOC-TOU issue, most OSes just serialize FS operations using mutexes/locks. #247 will likely involve doing so anyway, meaning running both operations concurrently wouldn't affect performance. The internal serialization will eventually be added, though at the moment the requisite code paths for #247 haven't even been implemented.

I recommend you serialize it in your code, since otherwise it will just be done at a lower level.

[linfaxin]

👌 thank you for your suggestion.