Dead code in jdk.internal.platform.Metrics?

[Severin Gehwolf]

Hi Bob,

As you probably know, I'm looking at cgroups v2 support[0] in OpenJDK.
When looking at Metrics.java[1] I see that many methods aren't used
anywhere. Neither in tests nor in actual code. It looks like as if the
interface has been modelled along the lines of the cgroups v1
implementation. These methods are:

-    public long getCpuUsage();
-    public long[] getPerCpuUsage();
-    public long getCpuUserUsage();
-    public long getCpuSystemUsage();
-    public double getCpuSetMemoryPressure();
-    public long getMemoryMaxUsage();
-    public long getMemoryUsage();
-    public long getKernelMemoryFailCount();
-    public long getKernelMemoryMaxUsage();
-    public long getKernelMemoryUsage();
-    public long getTcpMemoryFailCount();
-    public long getTcpMemoryMaxUsage();
-    public long getTcpMemoryUsage();
-    public long getBlkIOServiceCount();
-    public long getBlkIOServiced();

They are essentially dead code. Note that not all of them would have an
implementation in cgroups v2. With that in mind, does it actually make
sense for the Metrics interface to define those? We could keep the
implementations for cgroup v1 Metrics, but perhaps remove them from the
interface? It seems the current Metrics interface defines too many
methods for no good reason. Am I missing something? Thoughts?

>From the looks of it it wouldn't even require a CSR as
jdk.internal.platform isn't an exported package.

Here is an example patch removing them, and jdk docker container tests
still pass:
http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8230305/remove_metrics_interface_methods.patch

Thanks,
Severin

[0] https://bugs.openjdk.java.net/browse/JDK-8230305
[1] http://hg.openjdk.java.net/jdk/jdk/file/377f47ccc20b/src/java.base/share/classes/jdk/internal/platform/Metrics.java