Investigate java-allocation-instrumenter, ensure it works as expected

[niloc132]

While the server cannot startup without this dependency, we are not setting it up on the bootclasspath as instructed, so it probably doesn't function.

We should disable the allocation.stats.enabled flag by default if it isn't actually functioning, and make the dependency compileOnly if if actually doesn't function.

If it does function, we should force an upgrade from the asm groupId to the modern org.ow2.asm groupId.

[niloc132]

The java-allocation-instrumenter:2.0 that is currently used in DHC does not seem to work as expected (that is, Stats.getGroup("GAllocation") is empty), and is also not the same build that DHE is using (apparently packaged for DHE as allocation:allocation:2.0, I'm not clear exactly where we got this build).

The version 2.0 that can be found in maven central is missing its Premain-Class entry in META-INF/MANIFEST.MF. We could possibly try to repackage this version, or we could update to a newer version.

The latest version found in maven central is 3.3.0 (which is also the latest tag at https://github.com/google/allocation-instrumenter). After updating this dependency, I added -javaagent:/opt/deephaven/server/lib/java-allocation-instrumenter-3.3.0.jar as a JVM arg and confirmed with the groovy call println io.deephaven.base.stats.Stats.getGroup("GAllocation").items to confirm we are getting items.

My plan to close this out is to make the 3.3.0 version a compile-only dependency, disable this feature by default, and add instructions on how to enable this at runtime by adding the jar and referencing it with a -javaagent:/path/to/the/java-allocation-instrumenter.jar jvm arg.

[niloc132]

Here's a minimal set of changes to apply to server/jetty/build.gradle to enable this javaagent at runtime, for future reference:

1. Add a new configuration for the javaagent jar, roughly

configuration {
//...
allocation
}

2. Add a dependency on the jar, using that new configuration (make sure it is the same version that stats is using)

dependencies {
//...
allocation 'com.google.code.java-allocation-instrumenter:java-allocation-instrumenter:3.3.0'
}

3. Add this jar as a javaagent to the jvm args. To do this with JavaExec in its current form, we just append a new string to the extraJvmArgs array. Note that 3.3.0 is a shaded jar, and includes its dependencies, so we only need the very first element in that configuration:

extraJvmArgs += ["-javaagent:${configurations.allocation.iterator().next()}"]

4. Enable allocation stats, by also adding the system property to the extraJvmArgs: -Dallocation.stats.enabled=true

Confirmed by running println io.deephaven.base.stats.Stats.getGroup("GAllocation").items on the jetty server after making this change.