1 /*
  2  * Copyright (c) 2001, 2023, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "precompiled.hpp"
 26 #include "classfile/classLoaderDataGraph.hpp"
 27 #include "classfile/javaClasses.hpp"
 28 #include "classfile/stringTable.hpp"
 29 #include "classfile/symbolTable.hpp"
 30 #include "classfile/systemDictionary.hpp"
 31 #include "classfile/vmSymbols.hpp"
 32 #include "code/codeCache.hpp"
 33 #include "code/icBuffer.hpp"
 34 #include "compiler/oopMap.hpp"
 35 #include "gc/serial/cardTableRS.hpp"
 36 #include "gc/serial/genMarkSweep.hpp"
 37 #include "gc/serial/serialGcRefProcProxyTask.hpp"
 38 #include "gc/shared/collectedHeap.inline.hpp"
 39 #include "gc/shared/gcHeapSummary.hpp"
 40 #include "gc/shared/gcTimer.hpp"
 41 #include "gc/shared/gcTrace.hpp"
 42 #include "gc/shared/gcTraceTime.inline.hpp"
 43 #include "gc/shared/genCollectedHeap.hpp"
 44 #include "gc/shared/generation.hpp"
 45 #include "gc/shared/modRefBarrierSet.hpp"
 46 #include "gc/shared/referencePolicy.hpp"
 47 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
 48 #include "gc/shared/slidingForwarding.hpp"
 49 #include "gc/shared/space.hpp"
 50 #include "gc/shared/strongRootsScope.hpp"
 51 #include "gc/shared/weakProcessor.hpp"
 52 #include "memory/universe.hpp"
 53 #include "oops/instanceRefKlass.hpp"
 54 #include "oops/oop.inline.hpp"
 55 #include "prims/jvmtiExport.hpp"
 56 #include "runtime/handles.inline.hpp"
 57 #include "runtime/javaThread.hpp"
 58 #include "runtime/synchronizer.hpp"
 59 #include "runtime/vmThread.hpp"
 60 #include "utilities/copy.hpp"
 61 #include "utilities/events.hpp"
 62 #include "utilities/stack.inline.hpp"
 63 #if INCLUDE_JVMCI
 64 #include "jvmci/jvmci.hpp"
 65 #endif
 66 
 67 void GenMarkSweep::invoke_at_safepoint(bool clear_all_softrefs) {
 68   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
 69 
 70   GenCollectedHeap* gch = GenCollectedHeap::heap();
 71 #ifdef ASSERT
 72   if (gch->soft_ref_policy()->should_clear_all_soft_refs()) {
 73     assert(clear_all_softrefs, "Policy should have been checked earlier");
 74   }
 75 #endif
 76 
 77   gch->trace_heap_before_gc(_gc_tracer);
 78 
 79   // Increment the invocation count
 80   _total_invocations++;
 81 
 82   // Capture used regions for each generation that will be
 83   // subject to collection, so that card table adjustments can
 84   // be made intelligently (see clear / invalidate further below).
 85   gch->save_used_regions();
 86 
 87   allocate_stacks();
 88 
 89   mark_sweep_phase1(clear_all_softrefs);
 90 
 91   SlidingForwarding::begin();
 92 
 93   mark_sweep_phase2();
 94 
 95   // Don't add any more derived pointers during phase3
 96 #if COMPILER2_OR_JVMCI
 97   assert(DerivedPointerTable::is_active(), "Sanity");
 98   DerivedPointerTable::set_active(false);
 99 #endif
100 
101   mark_sweep_phase3();
102 
103   mark_sweep_phase4();
104 
105   restore_marks();
106 
107   // Set saved marks for allocation profiler (and other things? -- dld)
108   // (Should this be in general part?)
109   gch->save_marks();
110 
111   SlidingForwarding::end();
112 
113   deallocate_stacks();
114 
115   MarkSweep::_string_dedup_requests->flush();
116 
117   bool is_young_gen_empty = (gch->young_gen()->used() == 0);
118   gch->rem_set()->maintain_old_to_young_invariant(gch->old_gen(), is_young_gen_empty);
119 
120   gch->prune_scavengable_nmethods();
121 
122   // Update heap occupancy information which is used as
123   // input to soft ref clearing policy at the next gc.
124   Universe::heap()->update_capacity_and_used_at_gc();
125 
126   // Signal that we have completed a visit to all live objects.
127   Universe::heap()->record_whole_heap_examined_timestamp();
128 
129   gch->trace_heap_after_gc(_gc_tracer);
130 }
131 
132 void GenMarkSweep::allocate_stacks() {
133   GenCollectedHeap* gch = GenCollectedHeap::heap();
134   // Scratch request on behalf of old generation; will do no allocation.
135   ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
136 
137   // $$$ To cut a corner, we'll only use the first scratch block, and then
138   // revert to malloc.
139   if (scratch != nullptr) {
140     _preserved_count_max =
141       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
142   } else {
143     _preserved_count_max = 0;
144   }
145 
146   _preserved_marks = (PreservedMark*)scratch;
147   _preserved_count = 0;
148 }
149 
150 
151 void GenMarkSweep::deallocate_stacks() {
152   GenCollectedHeap* gch = GenCollectedHeap::heap();
153   gch->release_scratch();
154 
155   _preserved_overflow_stack.clear(true);
156   _marking_stack.clear();
157   _objarray_stack.clear(true);
158 }
159 
160 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
161   // Recursively traverse all live objects and mark them
162   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
163 
164   GenCollectedHeap* gch = GenCollectedHeap::heap();
165 
166   ClassLoaderDataGraph::verify_claimed_marks_cleared(ClassLoaderData::_claim_stw_fullgc_mark);
167 
168   ref_processor()->start_discovery(clear_all_softrefs);
169 
170   {
171     StrongRootsScope srs(0);
172 
173     CLDClosure* weak_cld_closure = ClassUnloading ? nullptr : &follow_cld_closure;
174     MarkingCodeBlobClosure mark_code_closure(&follow_root_closure, !CodeBlobToOopClosure::FixRelocations, true);
175     gch->process_roots(GenCollectedHeap::SO_None,
176                        &follow_root_closure,
177                        &follow_cld_closure,
178                        weak_cld_closure,
179                        &mark_code_closure);
180   }
181 
182   // Process reference objects found during marking
183   {
184     GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
185 
186     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
187     SerialGCRefProcProxyTask task(is_alive, keep_alive, follow_stack_closure);
188     const ReferenceProcessorStats& stats = ref_processor()->process_discovered_references(task, pt);
189     pt.print_all_references();
190     gc_tracer()->report_gc_reference_stats(stats);
191   }
192 
193   // This is the point where the entire marking should have completed.
194   assert(_marking_stack.is_empty(), "Marking should have completed");
195 
196   {
197     GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
198     WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
199   }
200 
201   {
202     GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
203     CodeCache::UnloadingScope scope(&is_alive);
204 
205     // Unload classes and purge the SystemDictionary.
206     bool purged_class = SystemDictionary::do_unloading(gc_timer());
207 
208     // Unload nmethods.
209     CodeCache::do_unloading(purged_class);
210 
211     // Prune dead klasses from subklass/sibling/implementor lists.
212     Klass::clean_weak_klass_links(purged_class);
213 
214     // Clean JVMCI metadata handles.
215     JVMCI_ONLY(JVMCI::do_unloading(purged_class));
216   }
217 
218   {
219     GCTraceTime(Debug, gc, phases) tm_m("Report Object Count", gc_timer());
220     gc_tracer()->report_object_count_after_gc(&is_alive, nullptr);
221   }
222 }
223 
224 
225 void GenMarkSweep::mark_sweep_phase2() {
226   // Now all live objects are marked, compute the new object addresses.
227   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
228 
229   GenCollectedHeap::heap()->prepare_for_compaction();
230 }
231 
232 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
233 public:
234   void do_generation(Generation* gen) {
235     gen->adjust_pointers();
236   }
237 };
238 
239 void GenMarkSweep::mark_sweep_phase3() {
240   GenCollectedHeap* gch = GenCollectedHeap::heap();
241 
242   // Adjust the pointers to reflect the new locations
243   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
244 
245   ClassLoaderDataGraph::verify_claimed_marks_cleared(ClassLoaderData::_claim_stw_fullgc_adjust);
246 
247   if (UseAltGCForwarding) {
248     AdjustPointerClosure<true> adjust_pointer_closure;
249     CLDToOopClosure adjust_cld_closure(&adjust_pointer_closure, ClassLoaderData::_claim_stw_fullgc_adjust);
250     CodeBlobToOopClosure code_closure(&adjust_pointer_closure, CodeBlobToOopClosure::FixRelocations);
251     gch->process_roots(GenCollectedHeap::SO_AllCodeCache,
252                        &adjust_pointer_closure,
253                        &adjust_cld_closure,
254                        &adjust_cld_closure,
255                        &code_closure);
256     gch->gen_process_weak_roots(&adjust_pointer_closure);
257   } else {
258     AdjustPointerClosure<false> adjust_pointer_closure;
259     CLDToOopClosure adjust_cld_closure(&adjust_pointer_closure, ClassLoaderData::_claim_stw_fullgc_adjust);
260     CodeBlobToOopClosure code_closure(&adjust_pointer_closure, CodeBlobToOopClosure::FixRelocations);
261     gch->process_roots(GenCollectedHeap::SO_AllCodeCache,
262                        &adjust_pointer_closure,
263                        &adjust_cld_closure,
264                        &adjust_cld_closure,
265                        &code_closure);
266     gch->gen_process_weak_roots(&adjust_pointer_closure);
267   }
268   adjust_marks();
269   GenAdjustPointersClosure blk;
270   gch->generation_iterate(&blk, true);
271 }
272 
273 class GenCompactClosure: public GenCollectedHeap::GenClosure {
274 public:
275   void do_generation(Generation* gen) {
276     gen->compact();
277   }
278 };
279 
280 void GenMarkSweep::mark_sweep_phase4() {
281   // All pointers are now adjusted, move objects accordingly
282   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
283 
284   GenCompactClosure blk;
285   GenCollectedHeap::heap()->generation_iterate(&blk, true);
286 }
--- EOF ---