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/systemDictionary.hpp"
  29 #include "classfile/vmSymbols.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "code/icBuffer.hpp"
  32 #include "gc/serial/genMarkSweep.hpp"
  33 #include "gc/shared/collectedHeap.inline.hpp"
  34 #include "gc/shared/gcHeapSummary.hpp"
  35 #include "gc/shared/gcTimer.hpp"
  36 #include "gc/shared/gcTrace.hpp"
  37 #include "gc/shared/gcTraceTime.hpp"
  38 #include "gc/shared/genCollectedHeap.hpp"
  39 #include "gc/shared/generation.hpp"
  40 #include "gc/shared/genOopClosures.inline.hpp"
  41 #include "gc/shared/modRefBarrierSet.hpp"
  42 #include "gc/shared/referencePolicy.hpp"
  43 #include "gc/shared/space.hpp"
  44 #include "gc/shared/strongRootsScope.hpp"
  45 #include "oops/instanceRefKlass.hpp"
  46 #include "oops/oop.inline.hpp"
  47 #include "prims/jvmtiExport.hpp"
  48 #include "runtime/fprofiler.hpp"
  49 #include "runtime/handles.inline.hpp"
  50 #include "runtime/synchronizer.hpp"
  51 #include "runtime/thread.inline.hpp"
  52 #include "runtime/vmThread.hpp"
  53 #include "utilities/copy.hpp"
  54 #include "utilities/events.hpp"
  55 #include "utilities/stack.inline.hpp"
  56 
  57 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
  58   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  59 
  60   GenCollectedHeap* gch = GenCollectedHeap::heap();
  61 #ifdef ASSERT
  62   if (gch->collector_policy()->should_clear_all_soft_refs()) {
  63     assert(clear_all_softrefs, "Policy should have been checked earlier");
  64   }
  65 #endif
  66 
  67   // hook up weak ref data so it can be used during Mark-Sweep
  68   assert(ref_processor() == NULL, "no stomping");
  69   assert(rp != NULL, "should be non-NULL");
  70   set_ref_processor(rp);
  71   rp->setup_policy(clear_all_softrefs);
  72 
  73   GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL);
  74 
  75   gch->trace_heap_before_gc(_gc_tracer);
  76 
  77   // When collecting the permanent generation Method*s may be moving,
  78   // so we either have to flush all bcp data or convert it into bci.
  79   CodeCache::gc_prologue();
  80 
  81   // Increment the invocation count
  82   _total_invocations++;
  83 
  84   // Capture heap size before collection for printing.
  85   size_t gch_prev_used = gch->used();
  86 
  87   // Capture used regions for each generation that will be
  88   // subject to collection, so that card table adjustments can
  89   // be made intelligently (see clear / invalidate further below).
  90   gch->save_used_regions();
  91 
  92   allocate_stacks();
  93 
  94   mark_sweep_phase1(clear_all_softrefs);
  95 
  96   mark_sweep_phase2();
  97 
  98   // Don't add any more derived pointers during phase3
  99 #if defined(COMPILER2) || INCLUDE_JVMCI
 100   assert(DerivedPointerTable::is_active(), "Sanity");
 101   DerivedPointerTable::set_active(false);
 102 #endif
 103 
 104   mark_sweep_phase3();
 105 
 106   mark_sweep_phase4();
 107 
 108   restore_marks();
 109 
 110   // Set saved marks for allocation profiler (and other things? -- dld)
 111   // (Should this be in general part?)
 112   gch->save_marks();
 113 
 114   deallocate_stacks();
 115 
 116   // If compaction completely evacuated the young generation then we
 117   // can clear the card table.  Otherwise, we must invalidate
 118   // it (consider all cards dirty).  In the future, we might consider doing
 119   // compaction within generations only, and doing card-table sliding.
 120   CardTableRS* rs = gch->rem_set();
 121   Generation* old_gen = gch->old_gen();
 122 
 123   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 124   if (gch->young_gen()->used() == 0) {
 125     // We've evacuated the young generation.
 126     rs->clear_into_younger(old_gen);
 127   } else {
 128     // Invalidate the cards corresponding to the currently used
 129     // region and clear those corresponding to the evacuated region.
 130     rs->invalidate_or_clear(old_gen);
 131   }
 132 
 133   CodeCache::gc_epilogue();
 134   JvmtiExport::gc_epilogue();
 135 
 136   if (PrintGC && !PrintGCDetails) {
 137     gch->print_heap_change(gch_prev_used);
 138   }
 139 
 140   // refs processing: clean slate
 141   set_ref_processor(NULL);
 142 
 143   // Update heap occupancy information which is used as
 144   // input to soft ref clearing policy at the next gc.
 145   Universe::update_heap_info_at_gc();
 146 
 147   // Update time of last gc for all generations we collected
 148   // (which currently is all the generations in the heap).
 149   // We need to use a monotonically non-decreasing time in ms
 150   // or we will see time-warp warnings and os::javaTimeMillis()
 151   // does not guarantee monotonicity.
 152   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 153   gch->update_time_of_last_gc(now);
 154 
 155   gch->trace_heap_after_gc(_gc_tracer);
 156 }
 157 
 158 void GenMarkSweep::allocate_stacks() {
 159   GenCollectedHeap* gch = GenCollectedHeap::heap();
 160   // Scratch request on behalf of old generation; will do no allocation.
 161   ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
 162 
 163   // $$$ To cut a corner, we'll only use the first scratch block, and then
 164   // revert to malloc.
 165   if (scratch != NULL) {
 166     _preserved_count_max =
 167       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 168   } else {
 169     _preserved_count_max = 0;
 170   }
 171 
 172   _preserved_marks = (PreservedMark*)scratch;
 173   _preserved_count = 0;
 174 }
 175 
 176 
 177 void GenMarkSweep::deallocate_stacks() {
 178   if (!UseG1GC) {
 179     GenCollectedHeap* gch = GenCollectedHeap::heap();
 180     gch->release_scratch();
 181   }
 182 
 183   _preserved_mark_stack.clear(true);
 184   _preserved_oop_stack.clear(true);
 185   _marking_stack.clear();
 186   _objarray_stack.clear(true);
 187 }
 188 
 189 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 190   // Recursively traverse all live objects and mark them
 191   GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer);
 192 
 193   GenCollectedHeap* gch = GenCollectedHeap::heap();
 194 
 195   // Because follow_root_closure is created statically, cannot
 196   // use OopsInGenClosure constructor which takes a generation,
 197   // as the Universe has not been created when the static constructors
 198   // are run.
 199   follow_root_closure.set_generation(gch->old_gen());
 200 
 201   // Need new claim bits before marking starts.
 202   ClassLoaderDataGraph::clear_claimed_marks();
 203 
 204   {
 205     StrongRootsScope srs(1);
 206 
 207     gch->old_process_roots(&srs,
 208                            false, // Younger gens are not roots.
 209                            GenCollectedHeap::SO_None,
 210                            ClassUnloading,
 211                            &follow_root_closure,
 212                            &follow_cld_closure);
 213   }
 214 
 215   // Process reference objects found during marking
 216   {
 217     ref_processor()->setup_policy(clear_all_softrefs);
 218     const ReferenceProcessorStats& stats =
 219       ref_processor()->process_discovered_references(
 220         &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
 221     gc_tracer()->report_gc_reference_stats(stats);
 222   }
 223 
 224   // This is the point where the entire marking should have completed.
 225   assert(_marking_stack.is_empty(), "Marking should have completed");
 226 
 227   // Unload classes and purge the SystemDictionary.
 228   bool purged_class = SystemDictionary::do_unloading(&is_alive);
 229 
 230   // Unload nmethods.
 231   CodeCache::do_unloading(&is_alive, purged_class);
 232 
 233   // Prune dead klasses from subklass/sibling/implementor lists.
 234   Klass::clean_weak_klass_links(&is_alive);
 235 
 236   // Delete entries for dead interned strings.
 237   StringTable::unlink(&is_alive);
 238 
 239   // Clean up unreferenced symbols in symbol table.
 240   SymbolTable::unlink();
 241 
 242   gc_tracer()->report_object_count_after_gc(&is_alive);
 243 }
 244 
 245 
 246 void GenMarkSweep::mark_sweep_phase2() {
 247   // Now all live objects are marked, compute the new object addresses.
 248 
 249   // It is imperative that we traverse perm_gen LAST. If dead space is
 250   // allowed a range of dead object may get overwritten by a dead int
 251   // array. If perm_gen is not traversed last a Klass* may get
 252   // overwritten. This is fine since it is dead, but if the class has dead
 253   // instances we have to skip them, and in order to find their size we
 254   // need the Klass*!
 255   //
 256   // It is not required that we traverse spaces in the same order in
 257   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 258   // tracking expects us to do so. See comment under phase4.
 259 
 260   GenCollectedHeap* gch = GenCollectedHeap::heap();
 261 
 262   GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer);
 263 
 264   gch->prepare_for_compaction();
 265 }
 266 
 267 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 268 public:
 269   void do_generation(Generation* gen) {
 270     gen->adjust_pointers();
 271   }
 272 };
 273 
 274 void GenMarkSweep::mark_sweep_phase3() {
 275   GenCollectedHeap* gch = GenCollectedHeap::heap();
 276 
 277   // Adjust the pointers to reflect the new locations
 278   GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer);
 279 
 280   // Need new claim bits for the pointer adjustment tracing.
 281   ClassLoaderDataGraph::clear_claimed_marks();
 282 
 283   // Because the closure below is created statically, we cannot
 284   // use OopsInGenClosure constructor which takes a generation,
 285   // as the Universe has not been created when the static constructors
 286   // are run.
 287   adjust_pointer_closure.set_generation(gch->old_gen());
 288 
 289   {
 290     StrongRootsScope srs(1);
 291 
 292     gch->old_process_roots(&srs,
 293                            false, // Younger gens are not roots.
 294                            GenCollectedHeap::SO_AllCodeCache,
 295                            false, // Strong and weak roots.
 296                            &adjust_pointer_closure,
 297                            &adjust_cld_closure);
 298   }
 299 
 300   gch->gen_process_weak_roots(&adjust_pointer_closure);
 301 
 302   adjust_marks();
 303   GenAdjustPointersClosure blk;
 304   gch->generation_iterate(&blk, true);
 305 }
 306 
 307 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 308 public:
 309   void do_generation(Generation* gen) {
 310     gen->compact();
 311   }
 312 };
 313 
 314 void GenMarkSweep::mark_sweep_phase4() {
 315   // All pointers are now adjusted, move objects accordingly
 316 
 317   // It is imperative that we traverse perm_gen first in phase4. All
 318   // classes must be allocated earlier than their instances, and traversing
 319   // perm_gen first makes sure that all Klass*s have moved to their new
 320   // location before any instance does a dispatch through it's klass!
 321 
 322   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 323   // in the same order in phase2, phase3 and phase4. We don't quite do that
 324   // here (perm_gen first rather than last), so we tell the validate code
 325   // to use a higher index (saved from phase2) when verifying perm_gen.
 326   GenCollectedHeap* gch = GenCollectedHeap::heap();
 327 
 328   GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer);
 329 
 330   GenCompactClosure blk;
 331   gch->generation_iterate(&blk, true);
 332 }