RFR: 8281267: VM HeapDumper dumps array classes several times

[Chris Plummer]

On Tue, 8 Feb 2022 16:49:41 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

> ClassLoaderDataGraph::classes_do description says:
> // Walking classes through the ClassLoaderDataGraph include array classes.
> So do_load_class callback should not dump arrays for the classes and dumper doesn't need to call Universe::basic_type_classes_do (array classes for primitive types are also reported by ClassLoaderDataGraph::classes_do)

test/hotspot/jtreg/serviceability/HeapDump/DuplicateArrayClassesTest.java line 58:

> 56:         String[][][] strArray = new String[0][][];
> 57:         LingeredApp.main(args);
> 58:         System.out.println("" + intArray + strArray);   // to be sure the classes are not unloaded

Use  Reference.reachabilityFence(<array>);

test/hotspot/jtreg/serviceability/HeapDump/DuplicateArrayClassesTest.java line 86:

> 84:             Process p = ProcessTools.startProcess("jcmd", new ProcessBuilder(launcher.getCommand()));
> 85:             // If something goes wrong with heap dumping most likely we'll get crash of the target VM.
> 86:             while (!p.waitFor(5, TimeUnit.SECONDS)) {

5 seconds seems kind of short. Doesn't allow for occasional network hiccups.

test/hotspot/jtreg/serviceability/HeapDump/DuplicateArrayClassesTest.java line 218:

> 216:     }
> 217: 
> 218:     // Reads the whole HPROF_GC_CLASS_DUMP record, returns closs ID.

"class ID"

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PR: https://git.openjdk.java.net/jdk/pull/7384