8381115: [lworld] There are a number of SA tests failing with --enable-preview due partial FlatArrayKlass support

[plummercj]

Although SA has some FlatArrayKlass support, it is mostly incomplete. This is causing heap walking to abort when a flattened array of value objects is encountered. 4 SA tests are failing in non-obvious ways because of this.

JDK-8380769 [lworld] resourcehogs/serviceability/sa/TestHeapDumpForLargeArray.java fails with 'truncating to' missing from stdout/stderr with --enable-preview
JDK-8380851 [lworld] serviceability/sa/ClhsdbJstackWithConcurrentLock.java fails with "', (a java/util/concurrent/locks/ReentrantLock$NonfairSync)' not found in jstack output" when using --enable-preview
JDK-8380852 [lworld] serviceability/sa/CDSJMapClstats.java fails with "'BootClassLoader' missing from stdout/stderr" with "-XX:-UseCompressedOops --enable-preview"
JDK-8380853 [lworld] serviceability/sa/ClhsdbJhisto.java fails with "'java.nio.HeapByteBuffer' missing from stdout/stderr" with "-XX:-UseCompressedOops --enable-preview"

The main shortcoming is that there is no FlatArray type in SA yet, and also the code to instantiate it is missing in the following:

  public Oop newOop(OopHandle handle) {
...
    Klass klass = Oop.getKlassForOopHandle(handle);
    if (klass != null) {
      if (klass instanceof TypeArrayKlass) return new TypeArray(handle, this);
 + if (klass instanceof FlatArrayKlass) return new FlatArray(handle, this);
      if (klass instanceof ObjArrayKlass) return new ObjArray(handle, this);
      if (klass instanceof InstanceKlass) return new Instance(handle, this);
    }
    throw new UnknownOopException(handle.toString());
  }

Without the added code, this method throws UnknownOopException when it encounters a flattened array. That in turn causes the heap walking to stop scanning the region it is in, thinking that it has reached the top of the used part of the region. See ObjectHeap.iterateLiveRegions().

Tested tier1, tier2 svc, and tier5 svc CI testing with and w/o --enable-preview. Did tier5, tier6, and tier7 with --enable-preview on linux-x64-debug only.

---

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Issue

• JDK-8381115: [lworld] There are a number of SA tests failing with --enable-preview due partial FlatArrayKlass support (Bug - P4)

Reviewers

• Alex Menkov (@alexmenkov - Committer) ⚠️ Review applies to 9cb99259

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8381115: [lworld] There are a number of SA tests failing with --enable-preview due partial FlatArrayKlass support

Reviewed-by: amenkov

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At the time when this comment was updated there had been 224 new commits pushed to the lworld branch:

• 35b7ee2: 8381211: [lworld] ProblemList compiler/c2/irTests/TestFloat16ScalarOperations.java on linux-aarch64
• 4bdc262: Merge
• 69deec2: 8378985: serviceability/sa/TestJhsdbJstackMixedWithXComp.java failed if sender frame is return barrier of Continuation
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[alexmenkov]

Looks good.
I added a note about comment for the class, also Array class has
// Array is an abstract superclass for TypeArray and ObjArray
FlatArray can be added there, or the comment can be generalized, smth like 'super class for different array classes'

[alexmenkov]

Suggested change

	// A FlatArray is an array containing flattened value types.
	// A FlatArray is an array containing flattened value objects.