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  1. JDK
  2. JDK-8241142

Shenandoah: should not use parallel reference processing with single GC thread

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    • Subcomponent:
      gc
    • Resolved In Build:
      b19

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        Description

        Current code does:

        void ShenandoahHeap::ref_processing_init() {
          assert(_max_workers > 0, "Sanity");

          _ref_processor =
            new ReferenceProcessor(&_subject_to_discovery, // is_subject_to_discovery
                                   ParallelRefProcEnabled, // MT processing
                                   _max_workers, // Degree of MT processing
                                   true, // MT discovery
                                   _max_workers, // Degree of MT discovery
                                   false, // Reference discovery is not atomic
                                   NULL, // No closure, should be installed before use
                                   true); // Scale worker threads

          shenandoah_assert_rp_isalive_not_installed();
        }

        ...and:

          if (FLAG_IS_DEFAULT(ParallelRefProcEnabled)) {
            FLAG_SET_DEFAULT(ParallelRefProcEnabled, true);
          }

        ...so it always runs with parallel reference processing, even when -XX:ParallelGCThreads=1. This probably penalizes the single-threaded containers. Shenandoah should use single-threaded RP when that happens. Look for a relevant block in G1 code.

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                • Assignee:
                  adityam Aditya Mandaleeka
                  Reporter:
                  shade Aleksey Shipilev
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                    Updated:
                    Resolved: