1 /*
   2  * Copyright (c) 2001, 2013, 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_implementation/shared/gcHeapSummary.hpp"
  33 #include "gc_implementation/shared/gcTimer.hpp"
  34 #include "gc_implementation/shared/gcTrace.hpp"
  35 #include "gc_implementation/shared/gcTraceTime.hpp"
  36 #include "gc_interface/collectedHeap.inline.hpp"
  37 #include "memory/genCollectedHeap.hpp"
  38 #include "memory/genMarkSweep.hpp"
  39 #include "memory/genOopClosures.inline.hpp"
  40 #include "memory/generation.inline.hpp"
  41 #include "memory/modRefBarrierSet.hpp"
  42 #include "memory/referencePolicy.hpp"
  43 #include "memory/space.hpp"
  44 #include "oops/instanceRefKlass.hpp"
  45 #include "oops/oop.inline.hpp"
  46 #include "prims/jvmtiExport.hpp"
  47 #include "runtime/fprofiler.hpp"
  48 #include "runtime/handles.inline.hpp"
  49 #include "runtime/synchronizer.hpp"
  50 #include "runtime/thread.inline.hpp"
  51 #include "runtime/vmThread.hpp"
  52 #include "utilities/copy.hpp"
  53 #include "utilities/events.hpp"
  54 
  55 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
  56   bool clear_all_softrefs) {
  57   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  58 
  59   GenCollectedHeap* gch = GenCollectedHeap::heap();
  60 #ifdef ASSERT
  61   if (gch->collector_policy()->should_clear_all_soft_refs()) {
  62     assert(clear_all_softrefs, "Policy should have been checked earlier");
  63   }
  64 #endif
  65 
  66   // hook up weak ref data so it can be used during Mark-Sweep
  67   assert(ref_processor() == NULL, "no stomping");
  68   assert(rp != NULL, "should be non-NULL");
  69   _ref_processor = rp;
  70   rp->setup_policy(clear_all_softrefs);
  71 
  72   GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL);
  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   Threads::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   // Some of the card table updates below assume that the perm gen is
  88   // also being collected.
  89   assert(level == gch->n_gens() - 1,
  90          "All generations are being collected, ergo perm gen too.");
  91 
  92   // Capture used regions for each generation that will be
  93   // subject to collection, so that card table adjustments can
  94   // be made intelligently (see clear / invalidate further below).
  95   gch->save_used_regions(level);
  96 
  97   allocate_stacks();
  98 
  99   mark_sweep_phase1(level, clear_all_softrefs);
 100 
 101   mark_sweep_phase2();
 102 
 103   // Don't add any more derived pointers during phase3
 104   COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
 105   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 106 
 107   mark_sweep_phase3(level);
 108 
 109   mark_sweep_phase4();
 110 
 111   restore_marks();
 112 
 113   // Set saved marks for allocation profiler (and other things? -- dld)
 114   // (Should this be in general part?)
 115   gch->save_marks();
 116 
 117   deallocate_stacks();
 118 
 119   // If compaction completely evacuated all generations younger than this
 120   // one, then we can clear the card table.  Otherwise, we must invalidate
 121   // it (consider all cards dirty).  In the future, we might consider doing
 122   // compaction within generations only, and doing card-table sliding.
 123   bool all_empty = true;
 124   for (int i = 0; all_empty && i < level; i++) {
 125     Generation* g = gch->get_gen(i);
 126     all_empty = all_empty && gch->get_gen(i)->used() == 0;
 127   }
 128   GenRemSet* rs = gch->rem_set();
 129   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 130   if (all_empty) {
 131     // We've evacuated all generations below us.
 132     Generation* g = gch->get_gen(level);
 133     rs->clear_into_younger(g);
 134   } else {
 135     // Invalidate the cards corresponding to the currently used
 136     // region and clear those corresponding to the evacuated region
 137     // of all generations just collected (i.e. level and younger).
 138     rs->invalidate_or_clear(gch->get_gen(level),
 139                             true /* younger */);
 140   }
 141 
 142   Threads::gc_epilogue();
 143   CodeCache::gc_epilogue();
 144   JvmtiExport::gc_epilogue();
 145 
 146   if (PrintGC && !PrintGCDetails) {
 147     gch->print_heap_change(gch_prev_used);
 148   }
 149 
 150   // refs processing: clean slate
 151   _ref_processor = NULL;
 152 
 153   // Update heap occupancy information which is used as
 154   // input to soft ref clearing policy at the next gc.
 155   Universe::update_heap_info_at_gc();
 156 
 157   // Update time of last gc for all generations we collected
 158   // (which curently is all the generations in the heap).
 159   // We need to use a monotonically non-deccreasing time in ms
 160   // or we will see time-warp warnings and os::javaTimeMillis()
 161   // does not guarantee monotonicity.
 162   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 163   gch->update_time_of_last_gc(now);
 164 
 165   gch->trace_heap_after_gc(_gc_tracer);
 166 }
 167 
 168 void GenMarkSweep::allocate_stacks() {
 169   GenCollectedHeap* gch = GenCollectedHeap::heap();
 170   // Scratch request on behalf of oldest generation; will do no
 171   // allocation.
 172   ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
 173 
 174   // $$$ To cut a corner, we'll only use the first scratch block, and then
 175   // revert to malloc.
 176   if (scratch != NULL) {
 177     _preserved_count_max =
 178       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 179   } else {
 180     _preserved_count_max = 0;
 181   }
 182 
 183   _preserved_marks = (PreservedMark*)scratch;
 184   _preserved_count = 0;
 185 }
 186 
 187 
 188 void GenMarkSweep::deallocate_stacks() {
 189   if (!UseG1GC) {
 190     GenCollectedHeap* gch = GenCollectedHeap::heap();
 191     gch->release_scratch();
 192   }
 193 
 194   _preserved_mark_stack.clear(true);
 195   _preserved_oop_stack.clear(true);
 196   _marking_stack.clear();
 197   _objarray_stack.clear(true);
 198 }
 199 
 200 void GenMarkSweep::mark_sweep_phase1(int level,
 201                                   bool clear_all_softrefs) {
 202   // Recursively traverse all live objects and mark them
 203   GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer);
 204   trace(" 1");
 205 
 206   GenCollectedHeap* gch = GenCollectedHeap::heap();
 207 
 208   // Because follow_root_closure is created statically, cannot
 209   // use OopsInGenClosure constructor which takes a generation,
 210   // as the Universe has not been created when the static constructors
 211   // are run.
 212   follow_root_closure.set_orig_generation(gch->get_gen(level));
 213 
 214   // Need new claim bits before marking starts.
 215   ClassLoaderDataGraph::clear_claimed_marks();
 216 
 217   gch->gen_process_strong_roots(level,
 218                                 false, // Younger gens are not roots.
 219                                 true,  // activate StrongRootsScope
 220                                 false, // not scavenging
 221                                 SharedHeap::SO_SystemClasses,
 222                                 &follow_root_closure,
 223                                 true,   // walk code active on stacks
 224                                 &follow_root_closure,
 225                                 &follow_klass_closure);
 226 
 227   // Process reference objects found during marking
 228   {
 229     ref_processor()->setup_policy(clear_all_softrefs);
 230     const ReferenceProcessorStats& stats =
 231       ref_processor()->process_discovered_references(
 232         &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
 233     gc_tracer()->report_gc_reference_stats(stats);
 234   }
 235 
 236   // This is the point where the entire marking should have completed.
 237   assert(_marking_stack.is_empty(), "Marking should have completed");
 238 
 239   // Unload classes and purge the SystemDictionary.
 240   bool purged_class = SystemDictionary::do_unloading(&is_alive);
 241 
 242   // Unload nmethods.
 243   CodeCache::do_unloading(&is_alive, purged_class);
 244 
 245   // Prune dead klasses from subklass/sibling/implementor lists.
 246   Klass::clean_weak_klass_links(&is_alive);
 247 
 248   // Delete entries for dead interned strings.
 249   StringTable::unlink(&is_alive);
 250 
 251   // Clean up unreferenced symbols in symbol table.
 252   SymbolTable::unlink();
 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 tm("phase 2", PrintGC && Verbose, true, _gc_timer);
 275   trace("2");
 276 
 277   gch->prepare_for_compaction();
 278 }
 279 
 280 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 281 public:
 282   void do_generation(Generation* gen) {
 283     gen->adjust_pointers();
 284   }
 285 };
 286 
 287 void GenMarkSweep::mark_sweep_phase3(int level) {
 288   GenCollectedHeap* gch = GenCollectedHeap::heap();
 289 
 290   // Adjust the pointers to reflect the new locations
 291   GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer);
 292   trace("3");
 293 
 294   // Need new claim bits for the pointer adjustment tracing.
 295   ClassLoaderDataGraph::clear_claimed_marks();
 296 
 297   // Because the closure below is created statically, we cannot
 298   // use OopsInGenClosure constructor which takes a generation,
 299   // as the Universe has not been created when the static constructors
 300   // are run.
 301   adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
 302 
 303   gch->gen_process_strong_roots(level,
 304                                 false, // Younger gens are not roots.
 305                                 true,  // activate StrongRootsScope
 306                                 false, // not scavenging
 307                                 SharedHeap::SO_AllClasses,
 308                                 &adjust_pointer_closure,
 309                                 false, // do not walk code
 310                                 &adjust_pointer_closure,
 311                                 &adjust_klass_closure);
 312 
 313   // Now adjust pointers in remaining weak roots.  (All of which should
 314   // have been cleared if they pointed to non-surviving objects.)
 315   CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,
 316                                                    /*do_marking=*/ false);
 317   gch->gen_process_weak_roots(&adjust_pointer_closure,
 318                               &adjust_code_pointer_closure);
 319 
 320   adjust_marks();
 321   GenAdjustPointersClosure blk;
 322   gch->generation_iterate(&blk, true);
 323 }
 324 
 325 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 326 public:
 327   void do_generation(Generation* gen) {
 328     gen->compact();
 329   }
 330 };
 331 
 332 void GenMarkSweep::mark_sweep_phase4() {
 333   // All pointers are now adjusted, move objects accordingly
 334 
 335   // It is imperative that we traverse perm_gen first in phase4. All
 336   // classes must be allocated earlier than their instances, and traversing
 337   // perm_gen first makes sure that all Klass*s have moved to their new
 338   // location before any instance does a dispatch through it's klass!
 339 
 340   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 341   // in the same order in phase2, phase3 and phase4. We don't quite do that
 342   // here (perm_gen first rather than last), so we tell the validate code
 343   // to use a higher index (saved from phase2) when verifying perm_gen.
 344   GenCollectedHeap* gch = GenCollectedHeap::heap();
 345 
 346   GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer);
 347   trace("4");
 348 
 349   GenCompactClosure blk;
 350   gch->generation_iterate(&blk, true);
 351 }