LastModifiedComparator file comparator is not transitive

[kboyarshinov]

Hello, we are receiving the following error:

java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.TimSort.mergeLo(TimSort.java:743)
at java.util.TimSort.mergeAt(TimSort.java:479)
at java.util.TimSort.mergeCollapse(TimSort.java:406)
at java.util.TimSort.sort(TimSort.java:210)
at java.util.TimSort.sort(TimSort.java:169)
at java.util.Arrays.sort(Arrays.java:2010)
at org.acra.file.ReportLocator.getApprovedReports(ReportLocator.java:55)
at org.acra.util.ApplicationStartupProcessor.sendApprovedReports(ApplicationStartupProcessor.java:70)
at org.acra.ACRA.init(ACRA.java:272)
at org.acra.ACRA.init(ACRA.java:200)

It seems that LastModifiedComparator is not transitive:

final class LastModifiedComparator implements Comparator<File> {
    @Override
    public int compare(@NonNull File lhs, @NonNull File rhs) {
        return (int) (lhs.lastModified() - rhs.lastModified());
    }
}

It should be like this:

final class LastModifiedComparator implements Comparator<File> {
    @Override
    public int compare(@NonNull File lhs, @NonNull File rhs) {
        return Long.compare(lhs.lastModified(), rhs.lastModified());
    }
}

ACRA version: 4.9.0

[william-ferguson-au]

Its only non-transitive if there is more than 1600 years between your 2 outliers.
Do you really have files that are more than 1600 years old?

[kboyarshinov]

I suppose not. Will check and try provide more details. Thanks.

[kboyarshinov]

I have checked the reports on affected device and the earliest report was dated 2010. It can happen after hardware reset or when battery completely ran out, when time is reset to manufacturing time and the application is launcher (starts at boot).

I do not know the reason but changing Comparator to the one I suggested solved the problem and reports were sent.

[F43nd1r]

Long.compare was introduced in API 19. So, we cannot use it.

[kboyarshinov]

Implementation can be used:

public static int compare(long lhs, long rhs) {
        return lhs < rhs ? -1 : (lhs == rhs ? 0 : 1);
}

[william-ferguson-au]

So provide a pull request.

[kboyarshinov]

Thank you. Opened #521

[gregoiredx]

Ran into this bug. I can confirm the comparator fix solved it.
By the way, it's not 1600 years. You can have problems as soon as the cast from long to int is unsafe (so when there is more than Integer.MAX_VALUE milliseconds between two reports, that is less than 25 days)