1 /*
   2  * Copyright (c) 2001, 2012, 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/symbolTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "classfile/vmSymbols.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "code/icBuffer.hpp"
  32 #include "gc_interface/collectedHeap.inline.hpp"
  33 #include "memory/genCollectedHeap.hpp"
  34 #include "memory/genMarkSweep.hpp"
  35 #include "memory/genOopClosures.inline.hpp"
  36 #include "memory/generation.inline.hpp"
  37 #include "memory/modRefBarrierSet.hpp"
  38 #include "memory/referencePolicy.hpp"
  39 #include "memory/space.hpp"
  40 #include "oops/instanceRefKlass.hpp"
  41 #include "oops/oop.inline.hpp"
  42 #include "prims/jvmtiExport.hpp"
  43 #include "runtime/fprofiler.hpp"
  44 #include "runtime/handles.inline.hpp"
  45 #include "runtime/synchronizer.hpp"
  46 #include "runtime/thread.inline.hpp"
  47 #include "runtime/vmThread.hpp"
  48 #include "utilities/copy.hpp"
  49 #include "utilities/events.hpp"
  50 
  51 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
  52   bool clear_all_softrefs) {
  53   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  54 
  55   GenCollectedHeap* gch = GenCollectedHeap::heap();
  56 #ifdef ASSERT
  57   if (gch->collector_policy()->should_clear_all_soft_refs()) {
  58     assert(clear_all_softrefs, "Policy should have been checked earlier");
  59   }
  60 #endif
  61 
  62   // hook up weak ref data so it can be used during Mark-Sweep
  63   assert(ref_processor() == NULL, "no stomping");
  64   assert(rp != NULL, "should be non-NULL");
  65   _ref_processor = rp;
  66   rp->setup_policy(clear_all_softrefs);
  67 
  68   TraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, gclog_or_tty);
  69 
  70   // When collecting the permanent generation Method*s may be moving,
  71   // so we either have to flush all bcp data or convert it into bci.
  72   CodeCache::gc_prologue();
  73   Threads::gc_prologue();
  74 
  75   // Increment the invocation count
  76   _total_invocations++;
  77 
  78   // Capture heap size before collection for printing.
  79   size_t gch_prev_used = gch->used();
  80 
  81   // Some of the card table updates below assume that the perm gen is
  82   // also being collected.
  83   assert(level == gch->n_gens() - 1,
  84          "All generations are being collected, ergo perm gen too.");
  85 
  86   // Capture used regions for each generation that will be
  87   // subject to collection, so that card table adjustments can
  88   // be made intelligently (see clear / invalidate further below).
  89   gch->save_used_regions(level);
  90 
  91   allocate_stacks();
  92 
  93   mark_sweep_phase1(level, clear_all_softrefs);
  94 
  95   mark_sweep_phase2();
  96 
  97   // Don't add any more derived pointers during phase3
  98   COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
  99   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 100 
 101   mark_sweep_phase3(level);
 102 
 103   VALIDATE_MARK_SWEEP_ONLY(
 104     if (ValidateMarkSweep) {
 105       guarantee(_root_refs_stack->length() == 0, "should be empty by now");
 106     }
 107   )
 108 
 109   mark_sweep_phase4();
 110 
 111   VALIDATE_MARK_SWEEP_ONLY(
 112     if (ValidateMarkSweep) {
 113       guarantee(_live_oops->length() == _live_oops_moved_to->length(),
 114                 "should be the same size");
 115     }
 116   )
 117 
 118   restore_marks();
 119 
 120   // Set saved marks for allocation profiler (and other things? -- dld)
 121   // (Should this be in general part?)
 122   gch->save_marks();
 123 
 124   deallocate_stacks();
 125 
 126   // If compaction completely evacuated all generations younger than this
 127   // one, then we can clear the card table.  Otherwise, we must invalidate
 128   // it (consider all cards dirty).  In the future, we might consider doing
 129   // compaction within generations only, and doing card-table sliding.
 130   bool all_empty = true;
 131   for (int i = 0; all_empty && i < level; i++) {
 132     Generation* g = gch->get_gen(i);
 133     all_empty = all_empty && gch->get_gen(i)->used() == 0;
 134   }
 135   GenRemSet* rs = gch->rem_set();
 136   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 137   if (all_empty) {
 138     // We've evacuated all generations below us.
 139     Generation* g = gch->get_gen(level);
 140     rs->clear_into_younger(g);
 141   } else {
 142     // Invalidate the cards corresponding to the currently used
 143     // region and clear those corresponding to the evacuated region
 144     // of all generations just collected (i.e. level and younger).
 145     rs->invalidate_or_clear(gch->get_gen(level),
 146                             true /* younger */);
 147   }
 148 
 149   Threads::gc_epilogue();
 150   CodeCache::gc_epilogue();
 151   JvmtiExport::gc_epilogue();
 152 
 153   if (PrintGC && !PrintGCDetails) {
 154     gch->print_heap_change(gch_prev_used);
 155   }
 156 
 157   // refs processing: clean slate
 158   _ref_processor = NULL;
 159 
 160   // Update heap occupancy information which is used as
 161   // input to soft ref clearing policy at the next gc.
 162   Universe::update_heap_info_at_gc();
 163 
 164   // Update time of last gc for all generations we collected
 165   // (which curently is all the generations in the heap).
 166   // We need to use a monotonically non-deccreasing time in ms
 167   // or we will see time-warp warnings and os::javaTimeMillis()
 168   // does not guarantee monotonicity.
 169   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 170   gch->update_time_of_last_gc(now);
 171 }
 172 
 173 void GenMarkSweep::allocate_stacks() {
 174   GenCollectedHeap* gch = GenCollectedHeap::heap();
 175   // Scratch request on behalf of oldest generation; will do no
 176   // allocation.
 177   ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
 178 
 179   // $$$ To cut a corner, we'll only use the first scratch block, and then
 180   // revert to malloc.
 181   if (scratch != NULL) {
 182     _preserved_count_max =
 183       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 184   } else {
 185     _preserved_count_max = 0;
 186   }
 187 
 188   _preserved_marks = (PreservedMark*)scratch;
 189   _preserved_count = 0;
 190 
 191 #ifdef VALIDATE_MARK_SWEEP
 192   if (ValidateMarkSweep) {
 193     _root_refs_stack    = new (ResourceObj::C_HEAP, mtGC) GrowableArray<void*>(100, true);
 194     _other_refs_stack   = new (ResourceObj::C_HEAP, mtGC) GrowableArray<void*>(100, true);
 195     _adjusted_pointers  = new (ResourceObj::C_HEAP, mtGC) GrowableArray<void*>(100, true);
 196     _live_oops          = new (ResourceObj::C_HEAP, mtGC) GrowableArray<oop>(100, true);
 197     _live_oops_moved_to = new (ResourceObj::C_HEAP, mtGC) GrowableArray<oop>(100, true);
 198     _live_oops_size     = new (ResourceObj::C_HEAP, mtGC) GrowableArray<size_t>(100, true);
 199   }
 200   if (RecordMarkSweepCompaction) {
 201     if (_cur_gc_live_oops == NULL) {
 202       _cur_gc_live_oops           = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true);
 203       _cur_gc_live_oops_moved_to  = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true);
 204       _cur_gc_live_oops_size      = new(ResourceObj::C_HEAP, mtGC) GrowableArray<size_t>(100, true);
 205       _last_gc_live_oops          = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true);
 206       _last_gc_live_oops_moved_to = new(ResourceObj::C_HEAP, mtGC) GrowableArray<HeapWord*>(100, true);
 207       _last_gc_live_oops_size     = new(ResourceObj::C_HEAP, mtGC) GrowableArray<size_t>(100, true);
 208     } else {
 209       _cur_gc_live_oops->clear();
 210       _cur_gc_live_oops_moved_to->clear();
 211       _cur_gc_live_oops_size->clear();
 212     }
 213   }
 214 #endif
 215 }
 216 
 217 
 218 void GenMarkSweep::deallocate_stacks() {
 219   if (!UseG1GC) {
 220     GenCollectedHeap* gch = GenCollectedHeap::heap();
 221     gch->release_scratch();
 222   }
 223 
 224   _preserved_mark_stack.clear(true);
 225   _preserved_oop_stack.clear(true);
 226   _marking_stack.clear();
 227   _objarray_stack.clear(true);
 228 
 229 #ifdef VALIDATE_MARK_SWEEP
 230   if (ValidateMarkSweep) {
 231     delete _root_refs_stack;
 232     delete _other_refs_stack;
 233     delete _adjusted_pointers;
 234     delete _live_oops;
 235     delete _live_oops_size;
 236     delete _live_oops_moved_to;
 237     _live_oops_index = 0;
 238     _live_oops_index_at_perm = 0;
 239   }
 240 #endif
 241 }
 242 
 243 void GenMarkSweep::mark_sweep_phase1(int level,
 244                                   bool clear_all_softrefs) {
 245   // Recursively traverse all live objects and mark them
 246   TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
 247   trace(" 1");
 248 
 249   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking());
 250 
 251   GenCollectedHeap* gch = GenCollectedHeap::heap();
 252 
 253   // Because follow_root_closure is created statically, cannot
 254   // use OopsInGenClosure constructor which takes a generation,
 255   // as the Universe has not been created when the static constructors
 256   // are run.
 257   follow_root_closure.set_orig_generation(gch->get_gen(level));
 258 
 259   // Need new claim bits before marking starts.
 260   ClassLoaderDataGraph::clear_claimed_marks();
 261 
 262   gch->gen_process_strong_roots(level,
 263                                 false, // Younger gens are not roots.
 264                                 true,  // activate StrongRootsScope
 265                                 false, // not scavenging
 266                                 SharedHeap::SO_SystemClasses,
 267                                 &follow_root_closure,
 268                                 true,   // walk code active on stacks
 269                                 &follow_root_closure,
 270                                 &follow_klass_closure);
 271 
 272   // Process reference objects found during marking
 273   {
 274     ref_processor()->setup_policy(clear_all_softrefs);
 275     ref_processor()->process_discovered_references(
 276       &is_alive, &keep_alive, &follow_stack_closure, NULL);
 277   }
 278 
 279   // Follow system dictionary roots and unload classes
 280   bool purged_class = SystemDictionary::do_unloading(&is_alive);
 281 
 282   // Follow code cache roots
 283   CodeCache::do_unloading(&is_alive, purged_class);
 284   follow_stack(); // Flush marking stack
 285 
 286   // Update subklass/sibling/implementor links of live klasses
 287   Klass::clean_weak_klass_links(&is_alive);
 288   assert(_marking_stack.is_empty(), "just drained");
 289 
 290   // Visit interned string tables and delete unmarked oops
 291   StringTable::unlink(&is_alive);
 292   // Clean up unreferenced symbols in symbol table.
 293   SymbolTable::unlink();
 294 
 295   assert(_marking_stack.is_empty(), "stack should be empty by now");
 296 }
 297 
 298 
 299 void GenMarkSweep::mark_sweep_phase2() {
 300   // Now all live objects are marked, compute the new object addresses.
 301 
 302   // It is imperative that we traverse perm_gen LAST. If dead space is
 303   // allowed a range of dead object may get overwritten by a dead int
 304   // array. If perm_gen is not traversed last a Klass* may get
 305   // overwritten. This is fine since it is dead, but if the class has dead
 306   // instances we have to skip them, and in order to find their size we
 307   // need the Klass*!
 308   //
 309   // It is not required that we traverse spaces in the same order in
 310   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 311   // tracking expects us to do so. See comment under phase4.
 312 
 313   GenCollectedHeap* gch = GenCollectedHeap::heap();
 314 
 315   TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
 316   trace("2");
 317 
 318   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking());
 319 
 320   gch->prepare_for_compaction();
 321 }
 322 
 323 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 324 public:
 325   void do_generation(Generation* gen) {
 326     gen->adjust_pointers();
 327   }
 328 };
 329 
 330 void GenMarkSweep::mark_sweep_phase3(int level) {
 331   GenCollectedHeap* gch = GenCollectedHeap::heap();
 332 
 333   // Adjust the pointers to reflect the new locations
 334   TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
 335   trace("3");
 336 
 337   // Need new claim bits for the pointer adjustment tracing.
 338   ClassLoaderDataGraph::clear_claimed_marks();
 339 
 340   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking());
 341 
 342   // Because the two closures below are created statically, cannot
 343   // use OopsInGenClosure constructor which takes a generation,
 344   // as the Universe has not been created when the static constructors
 345   // are run.
 346   adjust_root_pointer_closure.set_orig_generation(gch->get_gen(level));
 347   adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
 348 
 349   gch->gen_process_strong_roots(level,
 350                                 false, // Younger gens are not roots.
 351                                 true,  // activate StrongRootsScope
 352                                 false, // not scavenging
 353                                 SharedHeap::SO_AllClasses,
 354                                 &adjust_root_pointer_closure,
 355                                 false, // do not walk code
 356                                 &adjust_root_pointer_closure,
 357                                 &adjust_klass_closure);
 358 
 359   // Now adjust pointers in remaining weak roots.  (All of which should
 360   // have been cleared if they pointed to non-surviving objects.)
 361   CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,
 362                                                    /*do_marking=*/ false);
 363   gch->gen_process_weak_roots(&adjust_root_pointer_closure,
 364                               &adjust_code_pointer_closure,
 365                               &adjust_pointer_closure);
 366 
 367   adjust_marks();
 368   GenAdjustPointersClosure blk;
 369   gch->generation_iterate(&blk, true);
 370 }
 371 
 372 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 373 public:
 374   void do_generation(Generation* gen) {
 375     gen->compact();
 376   }
 377 };
 378 
 379 void GenMarkSweep::mark_sweep_phase4() {
 380   // All pointers are now adjusted, move objects accordingly
 381 
 382   // It is imperative that we traverse perm_gen first in phase4. All
 383   // classes must be allocated earlier than their instances, and traversing
 384   // perm_gen first makes sure that all Klass*s have moved to their new
 385   // location before any instance does a dispatch through it's klass!
 386 
 387   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 388   // in the same order in phase2, phase3 and phase4. We don't quite do that
 389   // here (perm_gen first rather than last), so we tell the validate code
 390   // to use a higher index (saved from phase2) when verifying perm_gen.
 391   GenCollectedHeap* gch = GenCollectedHeap::heap();
 392 
 393   TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
 394   trace("4");
 395 
 396   VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking());
 397 
 398   GenCompactClosure blk;
 399   gch->generation_iterate(&blk, true);
 400 
 401   VALIDATE_MARK_SWEEP_ONLY(compaction_complete());
 402 }