add small delay to avoid problems on systems with low-resolution mtime

I've seen intermittent failures of the test suite with v6 for a long time,
it seems to have possibly gotten worse with the changes around v7. Or just
being unlucky; all tests failed today.

Seen on amd64 and i386 builders, repeatedly but intermittently:

	unused: FAIL (4.86s)
	Test.hs:928:
	git diff did not show changes to unlocked file

And I think other such failures, all involving v7/v6 mode tests.

I managed to reproduce the unused failure with --keep-failures,
and inside the repo, git diff was indeed not showing any changes for
the modified unlocked file.

The two stats will be the same other than mtime; the old and new files have
the same size and inode, since the test case writes to the file and then
overwrites it.

Indeed, notice the identical timestamps:

	builder@orca:~/gitbuilder/build/.t/tmprepo335$ echo 1 > foo; stat foo; echo 2 > foo; stat foo
	  File: foo
	  Size: 2         	Blocks: 8          IO Block: 4096   regular file
	Device: 801h/2049d	Inode: 3546179     Links: 1
	Access: (0644/-rw-r--r--)  Uid: ( 1000/ builder)   Gid: ( 1000/ builder)
	Access: 2018-10-29 22:14:10.894942036 +0000
	Modify: 2018-10-29 22:14:10.894942036 +0000
	Change: 2018-10-29 22:14:10.894942036 +0000
	 Birth: -
	  File: foo
	  Size: 2         	Blocks: 8          IO Block: 4096   regular file
	Device: 801h/2049d	Inode: 3546179     Links: 1
	Access: (0644/-rw-r--r--)  Uid: ( 1000/ builder)   Gid: ( 1000/ builder)
	Access: 2018-10-29 22:14:10.894942036 +0000
	Modify: 2018-10-29 22:14:10.898942036 +0000
	Change: 2018-10-29 22:14:10.898942036 +0000
	 Birth: -

I'm seeing this in Linux VMs; it doesn't happen on my laptop. I've also
not experienced the intermittent test suite failures on my laptop.

So, I hope that this small delay will avoid the problem.

Update: I didn't, indeed I then reproduced the same failure on my
laptop, so it must be due to something else. But keeping this change anyway
since not needing to worry about lowish-resolution mtime in the test suite seems
worthwhile.
This commit is contained in:
Joey Hess 2018-10-29 18:42:20 -04:00
parent bdeba74d4d
commit 595fb98473
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GPG key ID: DB12DB0FF05F8F38
4 changed files with 95 additions and 46 deletions

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@ -65,7 +65,7 @@ compareStrong (InodeCache x) (InodeCache y) = x == y
- due to some filesystems being remounted.
-
- The weak mtime comparison treats any mtimes that are within 2 seconds
- of one-anther as the same. This is because FAT has only a 2 second
- of one-another as the same. This is because FAT has only a 2 second
- resolution. When a FAT filesystem is used on Linux, higher resolution
- timestamps are cached and used by Linux, but this is lost on unmount,
- so after a remount, the timestamp can appear to have changed.