`File.mtime` doesn't return milliseconds

[AlexWayfer]

truffleruby 21.1.0, like ruby 2.7.2, GraalVM CE Native [x86_64-linux]

Related:

• File.mtime doesn't return milliseconds jruby/jruby#4520
• Add microseconds specs for File.mtime, .atime and .ctime ruby/spec#386

[eregon]

Thank you for the report, I can reproduce:

ruby -e 'p File.mtime("README.md").to_f'   
1619184907.0575614
truffleruby -e 'p File.mtime("README.md").to_f'
1619184907.0

[AlexWayfer]

Yep, sorry for a lack of example, I didn't know how to make it laconically.

[eregon]

We use struct stat.st_mtime and that's a number of seconds, but some platforms have struct stat.st_mtim which is a struct timespec.

truffleruby/src/main/c/truffleposix/truffleposix.c

Line 397 in 1d46891

buffer->mtime = native_stat->st_mtime;

If we store both seconds and nanonseconds into a uint64_t, then it would work until:

> Time.at((2 ** 64) / 1e9)
=> 2554-07-22 01:34:33 186005/262144 +0200

but not after.
So it's probably best to use an extra field for the nanoseconds.

We could store the nanoseconds of atime/mtime/ctime as 3 uint32_t fields at the end of the struct to avoid consuming a full uint64_t just for the nanoseconds.

[bjfish]

This is fixed at: fde89ae.