1 /*
   2  * Copyright (c) 2001, 2015, 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/javaClasses.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "classfile/vmSymbols.hpp"
  31 #include "code/codeCache.hpp"
  32 #include "code/icBuffer.hpp"
  33 #include "gc/serial/genMarkSweep.hpp"
  34 #include "gc/shared/collectedHeap.inline.hpp"
  35 #include "gc/shared/gcHeapSummary.hpp"
  36 #include "gc/shared/gcTimer.hpp"
  37 #include "gc/shared/gcTrace.hpp"
  38 #include "gc/shared/gcTraceTime.inline.hpp"
  39 #include "gc/shared/genCollectedHeap.hpp"
  40 #include "gc/shared/generation.hpp"
  41 #include "gc/shared/genOopClosures.inline.hpp"
  42 #include "gc/shared/modRefBarrierSet.hpp"
  43 #include "gc/shared/referencePolicy.hpp"
  44 #include "gc/shared/space.hpp"
  45 #include "gc/shared/strongRootsScope.hpp"
  46 #include "oops/instanceRefKlass.hpp"
  47 #include "oops/oop.inline.hpp"
  48 #include "prims/jvmtiExport.hpp"
  49 #include "runtime/fprofiler.hpp"
  50 #include "runtime/handles.inline.hpp"
  51 #include "runtime/synchronizer.hpp"
  52 #include "runtime/thread.inline.hpp"
  53 #include "runtime/vmThread.hpp"
  54 #include "utilities/copy.hpp"
  55 #include "utilities/events.hpp"
  56 #include "utilities/stack.inline.hpp"
  57 
  58 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
  59   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  60 
  61   GenCollectedHeap* gch = GenCollectedHeap::heap();
  62 #ifdef ASSERT
  63   if (gch->collector_policy()->should_clear_all_soft_refs()) {
  64     assert(clear_all_softrefs, "Policy should have been checked earlier");
  65   }
  66 #endif
  67 
  68   // hook up weak ref data so it can be used during Mark-Sweep
  69   assert(ref_processor() == NULL, "no stomping");
  70   assert(rp != NULL, "should be non-NULL");
  71   set_ref_processor(rp);
  72   rp->setup_policy(clear_all_softrefs);
  73 
  74   gch->trace_heap_before_gc(_gc_tracer);
  75 
  76   // When collecting the permanent generation Method*s may be moving,
  77   // so we either have to flush all bcp data or convert it into bci.
  78   CodeCache::gc_prologue();
  79 
  80   // Increment the invocation count
  81   _total_invocations++;
  82 
  83   // Capture used regions for each generation that will be
  84   // subject to collection, so that card table adjustments can
  85   // be made intelligently (see clear / invalidate further below).
  86   gch->save_used_regions();
  87 
  88   allocate_stacks();
  89 
  90   mark_sweep_phase1(clear_all_softrefs);
  91 
  92   mark_sweep_phase2();
  93 
  94   // Don't add any more derived pointers during phase3
  95 #if defined(COMPILER2) || INCLUDE_JVMCI
  96   assert(DerivedPointerTable::is_active(), "Sanity");
  97   DerivedPointerTable::set_active(false);
  98 #endif
  99 
 100   mark_sweep_phase3();
 101 
 102   mark_sweep_phase4();
 103 
 104   restore_marks();
 105 
 106   // Set saved marks for allocation profiler (and other things? -- dld)
 107   // (Should this be in general part?)
 108   gch->save_marks();
 109 
 110   deallocate_stacks();
 111 
 112   // If compaction completely evacuated the young generation then we
 113   // can clear the card table.  Otherwise, we must invalidate
 114   // it (consider all cards dirty).  In the future, we might consider doing
 115   // compaction within generations only, and doing card-table sliding.
 116   CardTableRS* rs = gch->rem_set();
 117   Generation* old_gen = gch->old_gen();
 118 
 119   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 120   if (gch->young_gen()->used() == 0) {
 121     // We've evacuated the young generation.
 122     rs->clear_into_younger(old_gen);
 123   } else {
 124     // Invalidate the cards corresponding to the currently used
 125     // region and clear those corresponding to the evacuated region.
 126     rs->invalidate_or_clear(old_gen);
 127   }
 128 
 129   CodeCache::gc_epilogue();
 130   JvmtiExport::gc_epilogue();
 131 
 132   // refs processing: clean slate
 133   set_ref_processor(NULL);
 134 
 135   // Update heap occupancy information which is used as
 136   // input to soft ref clearing policy at the next gc.
 137   Universe::update_heap_info_at_gc();
 138 
 139   // Update time of last gc for all generations we collected
 140   // (which currently is all the generations in the heap).
 141   // We need to use a monotonically non-decreasing time in ms
 142   // or we will see time-warp warnings and os::javaTimeMillis()
 143   // does not guarantee monotonicity.
 144   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 145   gch->update_time_of_last_gc(now);
 146 
 147   gch->trace_heap_after_gc(_gc_tracer);
 148 }
 149 
 150 void GenMarkSweep::allocate_stacks() {
 151   GenCollectedHeap* gch = GenCollectedHeap::heap();
 152   // Scratch request on behalf of old generation; will do no allocation.
 153   ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
 154 
 155   // $$$ To cut a corner, we'll only use the first scratch block, and then
 156   // revert to malloc.
 157   if (scratch != NULL) {
 158     _preserved_count_max =
 159       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 160   } else {
 161     _preserved_count_max = 0;
 162   }
 163 
 164   _preserved_marks = (PreservedMark*)scratch;
 165   _preserved_count = 0;
 166 }
 167 
 168 
 169 void GenMarkSweep::deallocate_stacks() {
 170   if (!UseG1GC) {
 171     GenCollectedHeap* gch = GenCollectedHeap::heap();
 172     gch->release_scratch();
 173   }
 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->gen_process_roots(&srs,
 200                            GenCollectedHeap::OldGen,
 201                            false, // Younger gens are not roots.
 202                            GenCollectedHeap::SO_None,
 203                            ClassUnloading,
 204                            &follow_root_closure,
 205                            &follow_root_closure,
 206                            &follow_cld_closure);
 207   }
 208 
 209   // Process reference objects found during marking
 210   {
 211     GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
 212 
 213     ref_processor()->setup_policy(clear_all_softrefs);
 214     const ReferenceProcessorStats& stats =
 215       ref_processor()->process_discovered_references(
 216         &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
 217     gc_tracer()->report_gc_reference_stats(stats);
 218   }
 219 
 220   // This is the point where the entire marking should have completed.
 221   assert(_marking_stack.is_empty(), "Marking should have completed");
 222 
 223   {
 224     GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
 225 
 226     // Unload classes and purge the SystemDictionary.
 227     bool purged_class = SystemDictionary::do_unloading(&is_alive);
 228 
 229     // Unload nmethods.
 230     CodeCache::do_unloading(&is_alive, purged_class);
 231 
 232     // Prune dead klasses from subklass/sibling/implementor lists.
 233     Klass::clean_weak_klass_links(&is_alive);
 234   }
 235 
 236   {
 237     GCTraceTime(Debug, gc, phases) t("Scrub String Table", gc_timer());
 238     // Delete entries for dead interned strings.
 239     StringTable::unlink(&is_alive);
 240   }
 241 
 242   {
 243     GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", gc_timer());
 244     // Clean up unreferenced symbols in symbol table.
 245     SymbolTable::unlink();
 246   }
 247 
 248   gc_tracer()->report_object_count_after_gc(&is_alive);
 249 }
 250 
 251 
 252 void GenMarkSweep::mark_sweep_phase2() {
 253   // Now all live objects are marked, compute the new object addresses.
 254 
 255   // It is imperative that we traverse perm_gen LAST. If dead space is
 256   // allowed a range of dead object may get overwritten by a dead int
 257   // array. If perm_gen is not traversed last a Klass* may get
 258   // overwritten. This is fine since it is dead, but if the class has dead
 259   // instances we have to skip them, and in order to find their size we
 260   // need the Klass*!
 261   //
 262   // It is not required that we traverse spaces in the same order in
 263   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 264   // tracking expects us to do so. See comment under phase4.
 265 
 266   GenCollectedHeap* gch = GenCollectedHeap::heap();
 267 
 268   GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
 269 
 270   gch->prepare_for_compaction();
 271 }
 272 
 273 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 274 public:
 275   void do_generation(Generation* gen) {
 276     gen->adjust_pointers();
 277   }
 278 };
 279 
 280 void GenMarkSweep::mark_sweep_phase3() {
 281   GenCollectedHeap* gch = GenCollectedHeap::heap();
 282 
 283   // Adjust the pointers to reflect the new locations
 284   GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
 285 
 286   // Need new claim bits for the pointer adjustment tracing.
 287   ClassLoaderDataGraph::clear_claimed_marks();
 288 
 289   // Because the closure below is created statically, we cannot
 290   // use OopsInGenClosure constructor which takes a generation,
 291   // as the Universe has not been created when the static constructors
 292   // are run.
 293   adjust_pointer_closure.set_orig_generation(gch->old_gen());
 294 
 295   {
 296     StrongRootsScope srs(1);
 297 
 298     gch->gen_process_roots(&srs,
 299                            GenCollectedHeap::OldGen,
 300                            false, // Younger gens are not roots.
 301                            GenCollectedHeap::SO_AllCodeCache,
 302                            GenCollectedHeap::StrongAndWeakRoots,
 303                            &adjust_pointer_closure,
 304                            &adjust_pointer_closure,
 305                            &adjust_cld_closure);
 306   }
 307 
 308   gch->gen_process_weak_roots(&adjust_pointer_closure);
 309 
 310   adjust_marks();
 311   GenAdjustPointersClosure blk;
 312   gch->generation_iterate(&blk, true);
 313 }
 314 
 315 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 316 public:
 317   void do_generation(Generation* gen) {
 318     gen->compact();
 319   }
 320 };
 321 
 322 void GenMarkSweep::mark_sweep_phase4() {
 323   // All pointers are now adjusted, move objects accordingly
 324 
 325   // It is imperative that we traverse perm_gen first in phase4. All
 326   // classes must be allocated earlier than their instances, and traversing
 327   // perm_gen first makes sure that all Klass*s have moved to their new
 328   // location before any instance does a dispatch through it's klass!
 329 
 330   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 331   // in the same order in phase2, phase3 and phase4. We don't quite do that
 332   // here (perm_gen first rather than last), so we tell the validate code
 333   // to use a higher index (saved from phase2) when verifying perm_gen.
 334   GenCollectedHeap* gch = GenCollectedHeap::heap();
 335 
 336   GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
 337 
 338   GenCompactClosure blk;
 339   gch->generation_iterate(&blk, true);
 340 }