8243323: Shenandoah: Recycle immediate garbage before concurrent class unloading

Reviewed-by: shade

src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp

@@ -26,12 +26,13 @@
 
 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
+#include "gc/shenandoah/shenandoahControlThread.hpp"
 #include "gc/shenandoah/shenandoahFreeSet.hpp"
 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 #include "gc/shenandoah/shenandoahHeuristics.hpp"
 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
-#include "gc/shenandoah/shenandoahControlThread.hpp"
+#include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
 #include "gc/shenandoah/shenandoahUtils.hpp"
 #include "gc/shenandoah/shenandoahVMOperations.hpp"
 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
@@ -347,7 +348,9 @@ void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cau
   heap->vmop_entry_final_mark();
 
   // Process weak roots that might still point to regions that would be broken by cleanup
-  heap->entry_weak_roots();
+  if (heap->is_concurrent_weak_root_in_progress()) {
+    heap->entry_weak_roots();
+  }
 
   // Final mark might have reclaimed some immediate garbage, kick cleanup to reclaim
   // the space. This would be the last action if there is nothing to evacuate.
@@ -358,6 +361,11 @@ void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cau
     heap->free_set()->log_status();
   }
 
+  // Perform concurrent class unloading
+  if (heap->is_concurrent_weak_root_in_progress()) {
+    heap->entry_class_unloading();
+  }
+
   // Processing strong roots
   // This may be skipped if there is nothing to update/evacuate.
   // If so, strong_root_in_progress would be unset.

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

@@ -1727,6 +1727,20 @@ void ShenandoahEvacUpdateCleanupOopStorageRootsClosure::reset_dead_counter() {
   _dead_counter = 0;
 }
 
+class ShenandoahIsCLDAliveClosure : public CLDClosure {
+public:
+  void do_cld(ClassLoaderData* cld) {
+    cld->is_alive();
+  }
+};
+
+class ShenandoahIsNMethodAliveClosure: public NMethodClosure {
+public:
+  void do_nmethod(nmethod* n) {
+    n->is_unloading();
+  }
+};
+
 // This task not only evacuates/updates marked weak roots, but also "NULL"
 // dead weak roots.
 class ShenandoahConcurrentWeakRootsEvacUpdateTask : public AbstractGangTask {
@@ -1736,37 +1750,72 @@ private:
   ShenandoahWeakRoot<true /*concurrent*/>  _resolved_method_table_roots;
   ShenandoahWeakRoot<true /*concurrent*/>  _vm_roots;
 
+  // Roots related to concurrent class unloading
+  ShenandoahClassLoaderDataRoots<true /* concurrent */, false /* single thread*/>
+                                           _cld_roots;
+  ShenandoahConcurrentNMethodIterator      _nmethod_itr;
+  bool                                     _concurrent_class_unloading;
+
 public:
   ShenandoahConcurrentWeakRootsEvacUpdateTask() :
     AbstractGangTask("Shenandoah Concurrent Weak Root Task"),
     _jni_roots(OopStorageSet::jni_weak(), ShenandoahPhaseTimings::JNIWeakRoots),
     _string_table_roots(OopStorageSet::string_table_weak(), ShenandoahPhaseTimings::StringTableRoots),
     _resolved_method_table_roots(OopStorageSet::resolved_method_table_weak(), ShenandoahPhaseTimings::ResolvedMethodTableRoots),
-    _vm_roots(OopStorageSet::vm_weak(), ShenandoahPhaseTimings::VMWeakRoots) {
+    _vm_roots(OopStorageSet::vm_weak(), ShenandoahPhaseTimings::VMWeakRoots),
+    _nmethod_itr(ShenandoahCodeRoots::table()),
+    _concurrent_class_unloading(ShenandoahConcurrentRoots::should_do_concurrent_class_unloading()) {
     StringTable::reset_dead_counter();
     ResolvedMethodTable::reset_dead_counter();
+    if (_concurrent_class_unloading) {
+      MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
+      _nmethod_itr.nmethods_do_begin();
+    }
   }
 
   ~ShenandoahConcurrentWeakRootsEvacUpdateTask() {
     StringTable::finish_dead_counter();
     ResolvedMethodTable::finish_dead_counter();
+    if (_concurrent_class_unloading) {
+      MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
+      _nmethod_itr.nmethods_do_end();
+    }
   }
 
   void work(uint worker_id) {
-    ShenandoahEvacOOMScope oom;
-    // jni_roots and weak_roots are OopStorage backed roots, concurrent iteration
-    // may race against OopStorage::release() calls.
-    ShenandoahEvacUpdateCleanupOopStorageRootsClosure cl;
-    _jni_roots.oops_do(&cl, worker_id);
-    _vm_roots.oops_do(&cl, worker_id);
+    {
+      ShenandoahEvacOOMScope oom;
+      // jni_roots and weak_roots are OopStorage backed roots, concurrent iteration
+      // may race against OopStorage::release() calls.
+      ShenandoahEvacUpdateCleanupOopStorageRootsClosure cl;
+      _jni_roots.oops_do(&cl, worker_id);
+      _vm_roots.oops_do(&cl, worker_id);
 
-    cl.reset_dead_counter();
-    _string_table_roots.oops_do(&cl, worker_id);
-    StringTable::inc_dead_counter(cl.dead_counter());
+      cl.reset_dead_counter();
+      _string_table_roots.oops_do(&cl, worker_id);
+      StringTable::inc_dead_counter(cl.dead_counter());
 
-    cl.reset_dead_counter();
-    _resolved_method_table_roots.oops_do(&cl, worker_id);
-    ResolvedMethodTable::inc_dead_counter(cl.dead_counter());
+      cl.reset_dead_counter();
+      _resolved_method_table_roots.oops_do(&cl, worker_id);
+      ResolvedMethodTable::inc_dead_counter(cl.dead_counter());
+    }
+
+    // If we are going to perform concurrent class unloading later on, we need to
+    // cleanup the weak oops in CLD and determinate nmethod's unloading state, so that we
+    // can cleanup immediate garbage sooner.
+    if (_concurrent_class_unloading) {
+      // Applies ShenandoahIsCLDAlive closure to CLDs, native barrier will either NULL the
+      // CLD's holder or evacuate it.
+      ShenandoahIsCLDAliveClosure is_cld_alive;
+      _cld_roots.cld_do(&is_cld_alive);
+
+      // Applies ShenandoahIsNMethodAliveClosure to registered nmethods.
+      // The closure calls nmethod->is_unloading(). The is_unloading
+      // state is cached, therefore, during concurrent class unloading phase,
+      // we will not touch the metadata of unloading nmethods
+      ShenandoahIsNMethodAliveClosure is_nmethod_alive;
+      _nmethod_itr.nmethods_do(&is_nmethod_alive);
+    }
   }
 };
 
@@ -1775,14 +1824,20 @@ void ShenandoahHeap::op_weak_roots() {
     // Concurrent weak root processing
     ShenandoahConcurrentWeakRootsEvacUpdateTask task;
     workers()->run_task(&task);
-
-    if (ShenandoahConcurrentRoots::should_do_concurrent_class_unloading()) {
-      _unloader.unload();
+    if (!ShenandoahConcurrentRoots::should_do_concurrent_class_unloading()) {
+      set_concurrent_weak_root_in_progress(false);
     }
-    set_concurrent_weak_root_in_progress(false);
   }
 }
 
+void ShenandoahHeap::op_class_unloading() {
+  assert (is_concurrent_weak_root_in_progress() &&
+          ShenandoahConcurrentRoots::should_do_concurrent_class_unloading(),
+          "Checked by caller");
+  _unloader.unload();
+  set_concurrent_weak_root_in_progress(false);
+}
+
 void ShenandoahHeap::op_strong_roots() {
   assert(is_concurrent_strong_root_in_progress(), "Checked by caller");
   ShenandoahConcurrentRootsEvacUpdateTask task;
@@ -2851,6 +2906,21 @@ void ShenandoahHeap::entry_weak_roots() {
   op_weak_roots();
 }
 
+void ShenandoahHeap::entry_class_unloading() {
+  static const char* msg = "Concurrent class unloading";
+  ShenandoahConcurrentPhase gc_phase(msg);
+  EventMark em("%s", msg);
+
+  ShenandoahGCPhase phase(ShenandoahPhaseTimings::conc_class_unloading);
+
+  ShenandoahWorkerScope scope(workers(),
+                              ShenandoahWorkerPolicy::calc_workers_for_conc_root_processing(),
+                              "concurrent class unloading");
+
+  try_inject_alloc_failure();
+  op_class_unloading();
+}
+
 void ShenandoahHeap::entry_strong_roots() {
   static const char* msg = "Concurrent strong roots";
   ShenandoahConcurrentPhase gc_phase(msg);

src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp

@@ -398,6 +398,7 @@ public:
   void entry_mark();
   void entry_preclean();
   void entry_weak_roots();
+  void entry_class_unloading();
   void entry_strong_roots();
   void entry_cleanup();
   void entry_evac();
@@ -419,6 +420,7 @@ private:
   void op_mark();
   void op_preclean();
   void op_weak_roots();
+  void op_class_unloading();
   void op_strong_roots();
   void op_cleanup();
   void op_conc_evac();

src/hotspot/share/gc/shenandoah/shenandoahPhaseTimings.hpp

@@ -137,6 +137,7 @@ class outputStream;
   f(conc_mark,                                      "Concurrent Marking")              \
   f(conc_preclean,                                  "Concurrent Precleaning")          \
   f(conc_weak_roots,                                "Concurrent Weak Roots")           \
+  f(conc_class_unloading,                           "Concurrent Class Unloading")      \
   f(conc_strong_roots,                              "Concurrent Strong Roots")         \
   f(conc_evac,                                      "Concurrent Evacuation")           \
   f(conc_update_refs,                               "Concurrent Update Refs")          \