Date: Sat, 30 Mar 2024 07:12:06 +0000
Subject: 8149343: assert(rp->num_q() == no_of_gc_workers) failed:
 sanity

---
 .../gc_implementation/g1/g1CollectedHeap.cpp  | 20 +++++++++++--------
 .../share/vm/memory/referenceProcessor.cpp    |  9 +++++++--
 .../share/vm/memory/referenceProcessor.hpp    |  4 +++-
 .../TestDynamicNumberOfGCThreads.java         |  8 ++++++++
 4 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
index 84d5d4d8..5b156f99 100644
--- a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
@@ -5462,7 +5462,7 @@ public:
     _workers(workers),
     _active_workers(n_workers)
   {
-    assert(n_workers > 0, "shouldn't call this otherwise");
+    g1h->ref_processor_stw()->set_active_mt_degree(n_workers);
   }
 
   // Executes the given task using concurrent marking worker threads.
@@ -5595,7 +5595,9 @@ public:
     _queues(task_queues),
     _terminator(workers, _queues),
     _n_workers(workers)
-  { }
+  {
+    g1h->ref_processor_cm()->set_active_mt_degree(workers);
+  }
 
   void work(uint worker_id) {
     ResourceMark rm;
@@ -5760,8 +5762,10 @@ void G1CollectedHeap::process_discovered_references(uint no_of_gc_workers) {
                                               _gc_tracer_stw->gc_id());
   } else {
     // Parallel reference processing
-    assert(rp->num_q() == no_of_gc_workers, "sanity");
-    assert(no_of_gc_workers <= rp->max_num_q(), "sanity");
+    assert(no_of_gc_workers <= rp->max_num_q(),
+          err_msg(
+           "Mismatch between the number of GC workers %u and the maximum number of Reference process queues %u",
+           no_of_gc_workers,  rp->max_num_q()));
 
     G1STWRefProcTaskExecutor par_task_executor(this, workers(), _task_queues, no_of_gc_workers);
     stats = rp->process_discovered_references(&is_alive,
@@ -5796,10 +5800,10 @@ void G1CollectedHeap::enqueue_discovered_references(uint no_of_gc_workers) {
   } else {
     // Parallel reference enqueueing
 
-    assert(no_of_gc_workers == workers()->active_workers(),
-           "Need to reset active workers");
-    assert(rp->num_q() == no_of_gc_workers, "sanity");
-    assert(no_of_gc_workers <= rp->max_num_q(), "sanity");
+    assert(no_of_gc_workers <= rp->max_num_q(),
+          err_msg(
+           "Mismatch between the number of GC workers %u and the maximum number of Reference process queues %u",
+           no_of_gc_workers,  rp->max_num_q()));
 
     G1STWRefProcTaskExecutor par_task_executor(this, workers(), _task_queues, no_of_gc_workers);
     rp->enqueue_discovered_references(&par_task_executor);
diff --git a/hotspot/src/share/vm/memory/referenceProcessor.cpp b/hotspot/src/share/vm/memory/referenceProcessor.cpp
index b916e696..823fd49c 100644
--- a/hotspot/src/share/vm/memory/referenceProcessor.cpp
+++ b/hotspot/src/share/vm/memory/referenceProcessor.cpp
@@ -136,7 +136,7 @@ void ReferenceProcessor::verify_no_references_recorded() {
   guarantee(!_discovering_refs, "Discovering refs?");
   for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
     guarantee(_discovered_refs[i].is_empty(),
-              "Found non-empty discovered list");
+              err_msg("Found non-empty discovered list at %u", i));
   }
 }
 #endif
@@ -780,6 +780,11 @@ private:
   bool _clear_referent;
 };
 
+void ReferenceProcessor::set_active_mt_degree(uint v) {
+  _num_q = v;
+  _next_id = 0;
+}
+
 // Balances reference queues.
 // Move entries from all queues[0, 1, ..., _max_num_q-1] to
 // queues[0, 1, ..., _num_q-1] because only the first _num_q
@@ -862,7 +867,7 @@ void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
   }
 #ifdef ASSERT
   size_t balanced_total_refs = 0;
-  for (uint i = 0; i < _max_num_q; ++i) {
+  for (uint i = 0; i < _num_q; ++i) {
     balanced_total_refs += ref_lists[i].length();
     if (TraceReferenceGC && PrintGCDetails) {
       gclog_or_tty->print("%d ", ref_lists[i].length());
diff --git a/hotspot/src/share/vm/memory/referenceProcessor.hpp b/hotspot/src/share/vm/memory/referenceProcessor.hpp
index 470503ee..da148a6c 100644
--- a/hotspot/src/share/vm/memory/referenceProcessor.hpp
+++ b/hotspot/src/share/vm/memory/referenceProcessor.hpp
@@ -270,7 +270,7 @@ class ReferenceProcessor : public CHeapObj<mtGC> {
 
   uint num_q()                             { return _num_q; }
   uint max_num_q()                         { return _max_num_q; }
-  void set_active_mt_degree(uint v)        { _num_q = v; }
+  void set_active_mt_degree(uint v);
 
   DiscoveredList* discovered_refs()        { return _discovered_refs; }
 
@@ -385,9 +385,11 @@ class ReferenceProcessor : public CHeapObj<mtGC> {
   // round-robin mod _num_q (not: _not_ mode _max_num_q)
   uint next_id() {
     uint id = _next_id;
+    assert(!_discovery_is_mt, "Round robin should only be used in serial discovery");
     if (++_next_id == _num_q) {
       _next_id = 0;
     }
+    assert(_next_id < _num_q, err_msg("_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q));
     return id;
   }
   DiscoveredList* get_discovered_list(ReferenceType rt);
diff --git a/hotspot/test/gc/ergonomics/TestDynamicNumberOfGCThreads.java b/hotspot/test/gc/ergonomics/TestDynamicNumberOfGCThreads.java
index f4a6625a..2005a67e 100644
--- a/hotspot/test/gc/ergonomics/TestDynamicNumberOfGCThreads.java
+++ b/hotspot/test/gc/ergonomics/TestDynamicNumberOfGCThreads.java
@@ -63,6 +63,14 @@ public class TestDynamicNumberOfGCThreads {
     System.arraycopy(baseArgs,  0, finalArgs, extraArgs.length, baseArgs.length);
     pb_enabled = ProcessTools.createJavaProcessBuilder(finalArgs);
     verifyDynamicNumberOfGCThreads(new OutputAnalyzer(pb_enabled.start()));
+
+    // Turn on parallel reference processing
+    String[] parRefProcArg = {"-XX:+ParallelRefProcEnabled", "-XX:-ShowMessageBoxOnError"};
+    String[] parRefArgs = new String[baseArgs.length + parRefProcArg.length];
+    System.arraycopy(parRefProcArg, 0, parRefArgs, 0,                parRefProcArg.length);
+    System.arraycopy(baseArgs,  0, parRefArgs, parRefProcArg.length, baseArgs.length);
+    pb_enabled = ProcessTools.createJavaProcessBuilder(parRefArgs);
+    verifyDynamicNumberOfGCThreads(new OutputAnalyzer(pb_enabled.start()));
   }
 
   static class GCTest {
-- 
2.17.1