[wmf]

You need to sync twice because Unix is dumb: "According to the standard specification (e.g., POSIX.1-2001), sync() schedules the writes, but may return before the actual writing is done." https://man7.org/linux/man-pages/man2/sync.2.html

[amelius]

Then how do you know the writes are done after the second sync?

[wmf]

AFAIK multiple syncs can't happen at the same time so the second sync implicitly waits for the first one to complete.

[amelius]

If it was that simple, then why doesn't sync just do 2x sync internally?

[wakawaka28]

If I had to guess, it is just extra work to do it twice, and you may not need to wait for it for some use cases. The better way would be to add a flag or alternative function to make the sync a blocking operation in the first place.

[wmf]

Why is creat() missing the e? Why does an FTP server connect back to the client?

[1718627440]

> Unix is dumb

I don't know. Now async I/O is all the rage and that is the same idea.

[wmf]

If they had a sync() system call and a wait_for_sync_to_finish() system call then you'd be right. But they didn't have those.

[1718627440]

https://news.ycombinator.com/item?id=46268127 (To quote yourself :-) )

[marcosdumay]

The syscall is literally called "sync", though.

[1718627440]

I think it is a way of the OS to shoehorn async into a synchronously written application.