1 /*
   2  * Copyright (c) 2001, 2018, 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   // When collecting the permanent generation Method*s may be moving,
  79   // so we either have to flush all bcp data or convert it into bci.
  80   CodeCache::gc_prologue();
  81 
  82   // Increment the invocation count
  83   _total_invocations++;
  84 
  85   // Capture used regions for each generation that will be
  86   // subject to collection, so that card table adjustments can
  87   // be made intelligently (see clear / invalidate further below).
  88   gch->save_used_regions();
  89 
  90   allocate_stacks();
  91 
  92   mark_sweep_phase1(clear_all_softrefs);
  93 
  94   mark_sweep_phase2();
  95 
  96   // Don't add any more derived pointers during phase3
  97 #if COMPILER2_OR_JVMCI
  98   assert(DerivedPointerTable::is_active(), "Sanity");
  99   DerivedPointerTable::set_active(false);
 100 #endif
 101 
 102   mark_sweep_phase3();
 103 
 104   mark_sweep_phase4();
 105 
 106   restore_marks();
 107 
 108   // Set saved marks for allocation profiler (and other things? -- dld)
 109   // (Should this be in general part?)
 110   gch->save_marks();
 111 
 112   deallocate_stacks();
 113 
 114   // If compaction completely evacuated the young generation then we
 115   // can clear the card table.  Otherwise, we must invalidate
 116   // it (consider all cards dirty).  In the future, we might consider doing
 117   // compaction within generations only, and doing card-table sliding.
 118   CardTableRS* rs = gch->rem_set();
 119   Generation* old_gen = gch->old_gen();
 120 
 121   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 122   if (gch->young_gen()->used() == 0) {
 123     // We've evacuated the young generation.
 124     rs->clear_into_younger(old_gen);
 125   } else {
 126     // Invalidate the cards corresponding to the currently used
 127     // region and clear those corresponding to the evacuated region.
 128     rs->invalidate_or_clear(old_gen);
 129   }
 130 
 131   CodeCache::gc_epilogue();
 132   JvmtiExport::gc_epilogue();
 133 
 134   // refs processing: clean slate
 135   set_ref_processor(NULL);
 136 
 137   // Update heap occupancy information which is used as
 138   // input to soft ref clearing policy at the next gc.
 139   Universe::update_heap_info_at_gc();
 140 
 141   // Update time of last gc for all generations we collected
 142   // (which currently is all the generations in the heap).
 143   // We need to use a monotonically non-decreasing time in ms
 144   // or we will see time-warp warnings and os::javaTimeMillis()
 145   // does not guarantee monotonicity.
 146   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 147   gch->update_time_of_last_gc(now);
 148 
 149   gch->trace_heap_after_gc(_gc_tracer);
 150 }
 151 
 152 void GenMarkSweep::allocate_stacks() {
 153   GenCollectedHeap* gch = GenCollectedHeap::heap();
 154   // Scratch request on behalf of old generation; will do no allocation.
 155   ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
 156 
 157   // $$$ To cut a corner, we'll only use the first scratch block, and then
 158   // revert to malloc.
 159   if (scratch != NULL) {
 160     _preserved_count_max =
 161       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 162   } else {
 163     _preserved_count_max = 0;
 164   }
 165 
 166   _preserved_marks = (PreservedMark*)scratch;
 167   _preserved_count = 0;
 168 }
 169 
 170 
 171 void GenMarkSweep::deallocate_stacks() {
 172   GenCollectedHeap* gch = GenCollectedHeap::heap();
 173   gch->release_scratch();
 174 
 175   _preserved_mark_stack.clear(true);
 176   _preserved_oop_stack.clear(true);
 177   _marking_stack.clear();
 178   _objarray_stack.clear(true);
 179 }
 180 
 181 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 182   // Recursively traverse all live objects and mark them
 183   GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
 184 
 185   GenCollectedHeap* gch = GenCollectedHeap::heap();
 186 
 187   // Because follow_root_closure is created statically, cannot
 188   // use OopsInGenClosure constructor which takes a generation,
 189   // as the Universe has not been created when the static constructors
 190   // are run.
 191   follow_root_closure.set_orig_generation(gch->old_gen());
 192 
 193   // Need new claim bits before marking starts.
 194   ClassLoaderDataGraph::clear_claimed_marks();
 195 
 196   {
 197     StrongRootsScope srs(1);
 198 
 199     gch->full_process_roots(&srs,
 200                             false, // not the adjust phase
 201                             GenCollectedHeap::SO_None,
 202                             ClassUnloading, // only strong roots if ClassUnloading
 203                                             // is enabled
 204                             &follow_root_closure,
 205                             &follow_cld_closure);
 206   }
 207 
 208   // Process reference objects found during marking
 209   {
 210     GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
 211 
 212     ref_processor()->setup_policy(clear_all_softrefs);
 213     ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
 214     const ReferenceProcessorStats& stats =
 215       ref_processor()->process_discovered_references(
 216         &is_alive, &keep_alive, &follow_stack_closure, NULL, &pt);
 217     pt.print_all_references();
 218     gc_tracer()->report_gc_reference_stats(stats);
 219   }
 220 
 221   // This is the point where the entire marking should have completed.
 222   assert(_marking_stack.is_empty(), "Marking should have completed");
 223 
 224   {
 225     GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
 226     WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
 227   }
 228 
 229   {
 230     GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
 231 
 232     // Unload classes and purge the SystemDictionary.
 233     bool purged_class = SystemDictionary::do_unloading(gc_timer());
 234 
 235     // Unload nmethods.
 236     CodeCache::do_unloading(&is_alive, purged_class);
 237 
 238     // Prune dead klasses from subklass/sibling/implementor lists.
 239     Klass::clean_weak_klass_links(purged_class);
 240   }
 241 
 242   {
 243     GCTraceTime(Debug, gc, phases) t("Scrub String Table", gc_timer());
 244     // Delete entries for dead interned strings.
 245     StringTable::unlink(&is_alive);
 246   }
 247 
 248   {
 249     GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", gc_timer());
 250     // Clean up unreferenced symbols in symbol table.
 251     SymbolTable::unlink();
 252   }
 253 
 254   gc_tracer()->report_object_count_after_gc(&is_alive);
 255 }
 256 
 257 
 258 void GenMarkSweep::mark_sweep_phase2() {
 259   // Now all live objects are marked, compute the new object addresses.
 260 
 261   // It is imperative that we traverse perm_gen LAST. If dead space is
 262   // allowed a range of dead object may get overwritten by a dead int
 263   // array. If perm_gen is not traversed last a Klass* may get
 264   // overwritten. This is fine since it is dead, but if the class has dead
 265   // instances we have to skip them, and in order to find their size we
 266   // need the Klass*!
 267   //
 268   // It is not required that we traverse spaces in the same order in
 269   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 270   // tracking expects us to do so. See comment under phase4.
 271 
 272   GenCollectedHeap* gch = GenCollectedHeap::heap();
 273 
 274   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 275 
 276   gch->prepare_for_compaction();
 277 }
 278 
 279 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 280 public:
 281   void do_generation(Generation* gen) {
 282     gen->adjust_pointers();
 283   }
 284 };
 285 
 286 void GenMarkSweep::mark_sweep_phase3() {
 287   GenCollectedHeap* gch = GenCollectedHeap::heap();
 288 
 289   // Adjust the pointers to reflect the new locations
 290   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
 291 
 292   // Need new claim bits for the pointer adjustment tracing.
 293   ClassLoaderDataGraph::clear_claimed_marks();
 294 
 295   // Because the closure below is created statically, we cannot
 296   // use OopsInGenClosure constructor which takes a generation,
 297   // as the Universe has not been created when the static constructors
 298   // are run.
 299   adjust_pointer_closure.set_orig_generation(gch->old_gen());
 300 
 301   {
 302     StrongRootsScope srs(1);
 303 
 304     gch->full_process_roots(&srs,
 305                             true,  // this is the adjust phase
 306                             GenCollectedHeap::SO_AllCodeCache,
 307                             false, // all roots
 308                             &adjust_pointer_closure,
 309                             &adjust_cld_closure);
 310   }
 311 
 312   gch->gen_process_weak_roots(&adjust_pointer_closure);
 313 
 314   adjust_marks();
 315   GenAdjustPointersClosure blk;
 316   gch->generation_iterate(&blk, true);
 317 }
 318 
 319 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 320 public:
 321   void do_generation(Generation* gen) {
 322     gen->compact();
 323   }
 324 };
 325 
 326 void GenMarkSweep::mark_sweep_phase4() {
 327   // All pointers are now adjusted, move objects accordingly
 328 
 329   // It is imperative that we traverse perm_gen first in phase4. All
 330   // classes must be allocated earlier than their instances, and traversing
 331   // perm_gen first makes sure that all Klass*s have moved to their new
 332   // location before any instance does a dispatch through it's klass!
 333 
 334   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 335   // in the same order in phase2, phase3 and phase4. We don't quite do that
 336   // here (perm_gen first rather than last), so we tell the validate code
 337   // to use a higher index (saved from phase2) when verifying perm_gen.
 338   GenCollectedHeap* gch = GenCollectedHeap::heap();
 339 
 340   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 341 
 342   GenCompactClosure blk;
 343   gch->generation_iterate(&blk, true);
 344 }