1 /*
   2  * Copyright (c) 2001, 2019, 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 "gc/serial/genMarkSweep.hpp"
  35 #include "gc/shared/collectedHeap.inline.hpp"
  36 #include "gc/shared/gcHeapSummary.hpp"
  37 #include "gc/shared/gcTimer.hpp"
  38 #include "gc/shared/gcTrace.hpp"
  39 #include "gc/shared/gcTraceTime.inline.hpp"
  40 #include "gc/shared/genCollectedHeap.hpp"
  41 #include "gc/shared/generation.hpp"
  42 #include "gc/shared/genOopClosures.inline.hpp"
  43 #include "gc/shared/modRefBarrierSet.hpp"
  44 #include "gc/shared/referencePolicy.hpp"
  45 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  46 #include "gc/shared/space.hpp"
  47 #include "gc/shared/strongRootsScope.hpp"
  48 #include "gc/shared/weakProcessor.hpp"
  49 #include "oops/instanceRefKlass.hpp"
  50 #include "oops/oop.inline.hpp"
  51 #include "prims/jvmtiExport.hpp"
  52 #include "runtime/handles.inline.hpp"
  53 #include "runtime/synchronizer.hpp"
  54 #include "runtime/thread.inline.hpp"
  55 #include "runtime/vmThread.hpp"
  56 #include "utilities/copy.hpp"
  57 #include "utilities/events.hpp"
  58 #include "utilities/stack.inline.hpp"
  59 
  60 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
  61   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  62 
  63   GenCollectedHeap* gch = GenCollectedHeap::heap();
  64 #ifdef ASSERT
  65   if (gch->soft_ref_policy()->should_clear_all_soft_refs()) {
  66     assert(clear_all_softrefs, "Policy should have been checked earlier");
  67   }
  68 #endif
  69 
  70   // hook up weak ref data so it can be used during Mark-Sweep
  71   assert(ref_processor() == NULL, "no stomping");
  72   assert(rp != NULL, "should be non-NULL");
  73   set_ref_processor(rp);
  74   rp->setup_policy(clear_all_softrefs);
  75 
  76   gch->trace_heap_before_gc(_gc_tracer);
  77 
  78   // Increment the invocation count
  79   _total_invocations++;
  80 
  81   // Capture used regions for each generation that will be
  82   // subject to collection, so that card table adjustments can
  83   // be made intelligently (see clear / invalidate further below).
  84   gch->save_used_regions();
  85 
  86   allocate_stacks();
  87 
  88   mark_sweep_phase1(clear_all_softrefs);
  89 
  90   mark_sweep_phase2();
  91 
  92   // Don't add any more derived pointers during phase3
  93 #if COMPILER2_OR_JVMCI
  94   assert(DerivedPointerTable::is_active(), "Sanity");
  95   DerivedPointerTable::set_active(false);
  96 #endif
  97 
  98   mark_sweep_phase3();
  99 
 100   mark_sweep_phase4();
 101 
 102   restore_marks();
 103 
 104   // Set saved marks for allocation profiler (and other things? -- dld)
 105   // (Should this be in general part?)
 106   gch->save_marks();
 107 
 108   deallocate_stacks();
 109 
 110   // If compaction completely evacuated the young generation then we
 111   // can clear the card table.  Otherwise, we must invalidate
 112   // it (consider all cards dirty).  In the future, we might consider doing
 113   // compaction within generations only, and doing card-table sliding.
 114   CardTableRS* rs = gch->rem_set();
 115   Generation* old_gen = gch->old_gen();
 116 
 117   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 118   if (gch->young_gen()->used() == 0) {
 119     // We've evacuated the young generation.
 120     rs->clear_into_younger(old_gen);
 121   } else {
 122     // Invalidate the cards corresponding to the currently used
 123     // region and clear those corresponding to the evacuated region.
 124     rs->invalidate_or_clear(old_gen);
 125   }
 126 
 127   gch->prune_nmethods();
 128   JvmtiExport::gc_epilogue();
 129 
 130   // refs processing: clean slate
 131   set_ref_processor(NULL);
 132 
 133   // Update heap occupancy information which is used as
 134   // input to soft ref clearing policy at the next gc.
 135   Universe::update_heap_info_at_gc();
 136 
 137   // Update time of last gc for all generations we collected
 138   // (which currently is all the generations in the heap).
 139   // We need to use a monotonically non-decreasing time in ms
 140   // or we will see time-warp warnings and os::javaTimeMillis()
 141   // does not guarantee monotonicity.
 142   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 143   gch->update_time_of_last_gc(now);
 144 
 145   gch->trace_heap_after_gc(_gc_tracer);
 146 }
 147 
 148 void GenMarkSweep::allocate_stacks() {
 149   GenCollectedHeap* gch = GenCollectedHeap::heap();
 150   // Scratch request on behalf of old generation; will do no allocation.
 151   ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
 152 
 153   // $$$ To cut a corner, we'll only use the first scratch block, and then
 154   // revert to malloc.
 155   if (scratch != NULL) {
 156     _preserved_count_max =
 157       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 158   } else {
 159     _preserved_count_max = 0;
 160   }
 161 
 162   _preserved_marks = (PreservedMark*)scratch;
 163   _preserved_count = 0;
 164 }
 165 
 166 
 167 void GenMarkSweep::deallocate_stacks() {
 168   GenCollectedHeap* gch = GenCollectedHeap::heap();
 169   gch->release_scratch();
 170 
 171   _preserved_mark_stack.clear(true);
 172   _preserved_oop_stack.clear(true);
 173   _marking_stack.clear();
 174   _objarray_stack.clear(true);
 175 }
 176 
 177 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 178   // Recursively traverse all live objects and mark them
 179   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
 180 
 181   GenCollectedHeap* gch = GenCollectedHeap::heap();
 182 
 183   // Because follow_root_closure is created statically, cannot
 184   // use OopsInGenClosure constructor which takes a generation,
 185   // as the Universe has not been created when the static constructors
 186   // are run.
 187   follow_root_closure.set_orig_generation(gch->old_gen());
 188 
 189   // Need new claim bits before marking starts.
 190   ClassLoaderDataGraph::clear_claimed_marks();
 191 
 192   {
 193     StrongRootsScope srs(1);
 194 
 195     gch->full_process_roots(&srs,
 196                             false, // not the adjust phase
 197                             GenCollectedHeap::SO_None,
 198                             ClassUnloading, // only strong roots if ClassUnloading
 199                                             // is enabled
 200                             &follow_root_closure,
 201                             &follow_cld_closure);
 202   }
 203 
 204   // Process reference objects found during marking
 205   {
 206     GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
 207 
 208     ref_processor()->setup_policy(clear_all_softrefs);
 209     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
 210     const ReferenceProcessorStats& stats =
 211       ref_processor()->process_discovered_references(
 212         &is_alive, &keep_alive, &follow_stack_closure, NULL, &pt);
 213     pt.print_all_references();
 214     gc_tracer()->report_gc_reference_stats(stats);
 215   }
 216 
 217   // This is the point where the entire marking should have completed.
 218   assert(_marking_stack.is_empty(), "Marking should have completed");
 219 
 220   {
 221     GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
 222     WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
 223   }
 224 
 225   {
 226     GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
 227 
 228     // Unload classes and purge the SystemDictionary.
 229     bool purged_class = SystemDictionary::do_unloading(gc_timer());
 230 
 231     // Unload nmethods.
 232     CodeCache::do_unloading(&is_alive, purged_class);
 233 
 234     // Prune dead klasses from subklass/sibling/implementor lists.
 235     Klass::clean_weak_klass_links(purged_class);
 236   }
 237 
 238   gc_tracer()->report_object_count_after_gc(&is_alive);
 239 }
 240 
 241 
 242 void GenMarkSweep::mark_sweep_phase2() {
 243   // Now all live objects are marked, compute the new object addresses.
 244 
 245   // It is imperative that we traverse perm_gen LAST. If dead space is
 246   // allowed a range of dead object may get overwritten by a dead int
 247   // array. If perm_gen is not traversed last a Klass* may get
 248   // overwritten. This is fine since it is dead, but if the class has dead
 249   // instances we have to skip them, and in order to find their size we
 250   // need the Klass*!
 251   //
 252   // It is not required that we traverse spaces in the same order in
 253   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 254   // tracking expects us to do so. See comment under phase4.
 255 
 256   GenCollectedHeap* gch = GenCollectedHeap::heap();
 257 
 258   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 259 
 260   gch->prepare_for_compaction();
 261 }
 262 
 263 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 264 public:
 265   void do_generation(Generation* gen) {
 266     gen->adjust_pointers();
 267   }
 268 };
 269 
 270 void GenMarkSweep::mark_sweep_phase3() {
 271   GenCollectedHeap* gch = GenCollectedHeap::heap();
 272 
 273   // Adjust the pointers to reflect the new locations
 274   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
 275 
 276   // Need new claim bits for the pointer adjustment tracing.
 277   ClassLoaderDataGraph::clear_claimed_marks();
 278 
 279   // Because the closure below is created statically, we cannot
 280   // use OopsInGenClosure constructor which takes a generation,
 281   // as the Universe has not been created when the static constructors
 282   // are run.
 283   adjust_pointer_closure.set_orig_generation(gch->old_gen());
 284 
 285   {
 286     StrongRootsScope srs(1);
 287 
 288     gch->full_process_roots(&srs,
 289                             true,  // this is the adjust phase
 290                             GenCollectedHeap::SO_AllCodeCache,
 291                             false, // all roots
 292                             &adjust_pointer_closure,
 293                             &adjust_cld_closure);
 294   }
 295 
 296   gch->gen_process_weak_roots(&adjust_pointer_closure);
 297 
 298   adjust_marks();
 299   GenAdjustPointersClosure blk;
 300   gch->generation_iterate(&blk, true);
 301 }
 302 
 303 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 304 public:
 305   void do_generation(Generation* gen) {
 306     gen->compact();
 307   }
 308 };
 309 
 310 void GenMarkSweep::mark_sweep_phase4() {
 311   // All pointers are now adjusted, move objects accordingly
 312 
 313   // It is imperative that we traverse perm_gen first in phase4. All
 314   // classes must be allocated earlier than their instances, and traversing
 315   // perm_gen first makes sure that all Klass*s have moved to their new
 316   // location before any instance does a dispatch through it's klass!
 317 
 318   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 319   // in the same order in phase2, phase3 and phase4. We don't quite do that
 320   // here (perm_gen first rather than last), so we tell the validate code
 321   // to use a higher index (saved from phase2) when verifying perm_gen.
 322   GenCollectedHeap* gch = GenCollectedHeap::heap();
 323 
 324   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 325 
 326   GenCompactClosure blk;
 327   gch->generation_iterate(&blk, true);
 328 }