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8364516: Serial: Move class unloading logic inside SerialFullGC::invoke_at_safepoint #26588

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8364516: Serial: Move class unloading logic inside SerialFullGC::invoke_at_safepoint #26588

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f32132a
sgc-unloading-doc
albertnetymk Aug 1, 2025
f41fb5e
review
albertnetymk Aug 1, 2025
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albertnetymk Aug 1, 2025
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albertnetymk Aug 4, 2025
a912850
Merge branch 'master' into sgc-unloading-doc
albertnetymk Aug 4, 2025
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17 changes: 17 additions & 0 deletions src/hotspot/share/gc/serial/serialFullGC.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -705,6 +705,16 @@ void SerialFullGC::invoke_at_safepoint(bool clear_all_softrefs) {

allocate_stacks();

// Usually, all class unloading work occurs at the end of phase 1, but Serial
// full-gc accesses dead-objs' klass to find out the start of next live-obj
// during phase 2. This requires klasses of dead-objs to be kept loaded.
// Therefore, we declare ClassUnloadingContext at the same level as
// full-gc phases, and purge dead classes (invoking
// ClassLoaderDataGraph::purge) after all phases of full-gc.
ClassUnloadingContext ctx(1 /* num_nmethod_unlink_workers */,
false /* unregister_nmethods_during_purge */,
false /* lock_nmethod_free_separately */);

phase1_mark(clear_all_softrefs);

Compacter compacter{gch};
Expand Down Expand Up @@ -755,6 +765,13 @@ void SerialFullGC::invoke_at_safepoint(bool clear_all_softrefs) {
compacter.phase4_compact();
}

// Delete metaspaces for unloaded class loaders and clean up CLDG.
ClassLoaderDataGraph::purge(true /* at_safepoint */);
DEBUG_ONLY(MetaspaceUtils::verify();)

// Need to clear claim bits for the next full-gc (specifically phase 1 and 3).
ClassLoaderDataGraph::clear_claimed_marks();

restore_marks();

deallocate_stacks();
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10 changes: 0 additions & 10 deletions src/hotspot/share/gc/serial/serialHeap.cpp
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Expand Up @@ -603,9 +603,6 @@ void SerialHeap::do_full_collection(bool clear_all_soft_refs) {
gc_prologue();
COMPILER2_OR_JVMCI_PRESENT(DerivedPointerTable::clear());
CodeCache::on_gc_marking_cycle_start();
ClassUnloadingContext ctx(1 /* num_nmethod_unlink_workers */,
false /* unregister_nmethods_during_purge */,
false /* lock_nmethod_free_separately */);

STWGCTimer* gc_timer = SerialFullGC::gc_timer();
gc_timer->register_gc_start();
Expand All @@ -630,13 +627,6 @@ void SerialHeap::do_full_collection(bool clear_all_soft_refs) {
_old_gen->compute_new_size();
_young_gen->compute_new_size();

// Delete metaspaces for unloaded class loaders and clean up loader_data graph
ClassLoaderDataGraph::purge(/*at_safepoint*/true);
DEBUG_ONLY(MetaspaceUtils::verify();)

// Need to clear claim bits for the next mark.
ClassLoaderDataGraph::clear_claimed_marks();

_old_gen->update_promote_stats();

// Resize the metaspace capacity after full collections
Expand Down