DiskSpaceMetrics returns NaN when garbage collected

When using standard DiskSpaceMetrics, metrics returned are always NaN Jon said that it is a known issue:

there is an issue with that binder where we should have used a strong reference gauge

Jon also has given a workaround:

Iterable<Tag> tagsWithPath = Tags.concat(tags, "path", absolutePath);
        Gauge.builder("disk.free", path, File::getUsableSpace)
                .strongReference(true)
                .tags(tagsWithPath)
                .description("Usable space for path")
                .baseUnit("bytes")
                .register(registry);
        Gauge.builder("disk.total", path, File::getTotalSpace)
                .strongReference(true)
                .tags(tagsWithPath)
                .description("Total space for path")
                .baseUnit("bytes")
                .register(registry);

[shakuzen]

I think that that would work if a reference to DiskSpaceMetrics was retained in using code. However, I assume some (or most?) users do the following: new DiskSpaceMetrics(new File("/"), tags).bindTo(compositeRegistry); in which case the path as well as the DiskSpaceMetrics object won’t be retained.

@roded thank you for having the patience to explain how this could be reproduced. I have now reproduced this and we’ll get it fixed.

[roded]

I’m experiencing the same issue with micrometer 1.1.4. Setting the Gauge’s strongReference to true has resolved the issue as suggested.

@shakuzen, regarding the path reference: I think that that would work if a reference to DiskSpaceMetrics was retained in using code. However, I assume some (or most?) users do the following: new DiskSpaceMetrics(new File("/"), tags).bindTo(compositeRegistry); in which case the path as well as the DiskSpaceMetrics object won’t be retained.

I believe that this issue should be reopened.