commit 2fde7e3de639ad40fa6a46a3839495b68d702443
author Daniele Di Proietto <ddiproietto@google.com> Wed Oct 04 07:35:02 2023 +0000
committer Daniele Di Proietto <ddiproietto@google.com> Thu Oct 05 13:25:04 2023 +0000
tree a2f3f7f2081bbcde289208c26d0c3234cb7887ed
parent 588afc706ccc44c15d33fcb4e644652a2fbbf782

heap_graph_tracker: Fix strong fields for non strong references

When building a flamegraph, once we find an object whose type has a
reference kind (WEAK, SOFT, FINALIZER or PHANTOM), we ignore all its
children. It turns out that this is not accurate, only the reference
through the `java.lang.ref.Reference.referent` field should be ignored.

This prevents correct accounting for types that extend Reference, such
as `java.util.WeakHashMap$Entry<K,V>`. Here's the code for that:

```
class java.lang.ref.Reference<T> {
  volatile T referent;
}

class java.lang.ref.WeakReference<T> extends Reference<T> {
  //...
}

class java.util.WeakHashMap$Entry<K,V> extends WeakReference<K> {
  //...
  V value;
}
```

The type `java.util.WeakHashMap$Entry<K,V>` is marked as
KIND_WEAK_REFERENCE by the runtime.

When getting children of an object of type
`java.util.WeakHashMap$Entry<K,V>`, we should ignore its
`java.lang.ref.Reference.referent` field, but we should consider its
`java.util.WeakHashMap$Entry<K,V>.value` field.

ahat has [similar logic](https://cs.android.com/android/platform/superproject/main/+/main:art/tools/ahat/src/main/com/android/ahat/heapdump/AhatClassInstance.java;drc=3bc7238ded3e123ff7f7211d92c88b2731fec3d7;l=440)
where the "referent" field is treated specially.

This commit adds a new test that correctly checks the new behavior for
weak references and removes weak reference from another test (it was
checking the wrong behavior, added in 4771c5d("Ignore weak references
for flamegraph."))

Bug: 302662734
Change-Id: I820df2c824217cca8a81f1eaffd4f63be87ee606