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   mark_sweep_phase4();
 104 
 105   restore_marks();
 106 
 107   // Set saved marks for allocation profiler (and other things? -- dld)
 108   // (Should this be in general part?)
 109   gch->save_marks();
 110 
 111   deallocate_stacks();
 112 
 113   // If compaction completely evacuated all generations younger than this
 114   // one, then we can clear the card table.  Otherwise, we must invalidate
 115   // it (consider all cards dirty).  In the future, we might consider doing
 116   // compaction within generations only, and doing card-table sliding.
 117   bool all_empty = true;
 118   for (int i = 0; all_empty && i < level; i++) {
 119     Generation* g = gch->get_gen(i);
 120     all_empty = all_empty && gch->get_gen(i)->used() == 0;
 121   }
 122   GenRemSet* rs = gch->rem_set();
 123   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 124   if (all_empty) {
 125     // We've evacuated all generations below us.
 126     Generation* g = gch->get_gen(level);
 127     rs->clear_into_younger(g);
 128   } else {
 129     // Invalidate the cards corresponding to the currently used
 130     // region and clear those corresponding to the evacuated region
 131     // of all generations just collected (i.e. level and younger).
 132     rs->invalidate_or_clear(gch->get_gen(level),
 133                             true /* younger */);
 134   }
 135 
 136   Threads::gc_epilogue();
 137   CodeCache::gc_epilogue();
 138   JvmtiExport::gc_epilogue();
 139 
 140   if (PrintGC && !PrintGCDetails) {
 141     gch->print_heap_change(gch_prev_used);
 142   }
 143 
 144   // refs processing: clean slate
 145   _ref_processor = NULL;
 146 
 147   // Update heap occupancy information which is used as
 148   // input to soft ref clearing policy at the next gc.
 149   Universe::update_heap_info_at_gc();
 150 
 151   // Update time of last gc for all generations we collected
 152   // (which curently is all the generations in the heap).
 153   // We need to use a monotonically non-deccreasing time in ms
 154   // or we will see time-warp warnings and os::javaTimeMillis()
 155   // does not guarantee monotonicity.
 156   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 157   gch->update_time_of_last_gc(now);
 158 }
 159 
 160 void GenMarkSweep::allocate_stacks() {
 161   GenCollectedHeap* gch = GenCollectedHeap::heap();
 162   // Scratch request on behalf of oldest generation; will do no
 163   // allocation.
 164   ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
 165 
 166   // $$$ To cut a corner, we'll only use the first scratch block, and then
 167   // revert to malloc.
 168   if (scratch != NULL) {
 169     _preserved_count_max =
 170       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 171   } else {
 172     _preserved_count_max = 0;
 173   }
 174 
 175   _preserved_marks = (PreservedMark*)scratch;
 176   _preserved_count = 0;
 177 }
 178 
 179 
 180 void GenMarkSweep::deallocate_stacks() {
 181   if (!UseG1GC) {
 182     GenCollectedHeap* gch = GenCollectedHeap::heap();
 183     gch->release_scratch();
 184   }
 185 
 186   _preserved_mark_stack.clear(true);
 187   _preserved_oop_stack.clear(true);
 188   _marking_stack.clear();
 189   _objarray_stack.clear(true);
 190 }
 191 
 192 void GenMarkSweep::mark_sweep_phase1(int level,
 193                                   bool clear_all_softrefs) {
 194   // Recursively traverse all live objects and mark them
 195   TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
 196   trace(" 1");
 197 
 198   GenCollectedHeap* gch = GenCollectedHeap::heap();
 199 
 200   // Because follow_root_closure is created statically, cannot
 201   // use OopsInGenClosure constructor which takes a generation,
 202   // as the Universe has not been created when the static constructors
 203   // are run.
 204   follow_root_closure.set_orig_generation(gch->get_gen(level));
 205 
 206   // Need new claim bits before marking starts.
 207   ClassLoaderDataGraph::clear_claimed_marks();
 208 
 209   gch->gen_process_strong_roots(level,
 210                                 false, // Younger gens are not roots.
 211                                 true,  // activate StrongRootsScope
 212                                 false, // not scavenging
 213                                 SharedHeap::SO_SystemClasses,
 214                                 &follow_root_closure,
 215                                 true,   // walk code active on stacks
 216                                 &follow_root_closure,
 217                                 &follow_klass_closure);
 218 
 219   // Process reference objects found during marking
 220   {
 221     ref_processor()->setup_policy(clear_all_softrefs);
 222     ref_processor()->process_discovered_references(
 223       &is_alive, &keep_alive, &follow_stack_closure, NULL);
 224   }
 225 
 226   // This is the point where the entire marking should have completed.
 227   assert(_marking_stack.is_empty(), "Marking should have completed");
 228 
 229   // Unload classes and purge the SystemDictionary.
 230   bool purged_class = SystemDictionary::do_unloading(&is_alive);
 231 
 232   // Unload nmethods.
 233   CodeCache::do_unloading(&is_alive, purged_class);
 234 
 235   // Prune dead klasses from subklass/sibling/implementor lists.
 236   Klass::clean_weak_klass_links(&is_alive);
 237 
 238   // Delete entries for dead interned strings.
 239   StringTable::unlink(&is_alive);
 240 
 241   // Clean up unreferenced symbols in symbol table.
 242   SymbolTable::unlink();
 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   TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
 263   trace("2");
 264 
 265   gch->prepare_for_compaction();
 266 }
 267 
 268 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 269 public:
 270   void do_generation(Generation* gen) {
 271     gen->adjust_pointers();
 272   }
 273 };
 274 
 275 void GenMarkSweep::mark_sweep_phase3(int level) {
 276   GenCollectedHeap* gch = GenCollectedHeap::heap();
 277 
 278   // Adjust the pointers to reflect the new locations
 279   TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
 280   trace("3");
 281 
 282   // Need new claim bits for the pointer adjustment tracing.
 283   ClassLoaderDataGraph::clear_claimed_marks();
 284 
 285   // Because the closure below is created statically, we cannot
 286   // use OopsInGenClosure constructor which takes a generation,
 287   // as the Universe has not been created when the static constructors
 288   // are run.
 289   adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
 290 
 291   gch->gen_process_strong_roots(level,
 292                                 false, // Younger gens are not roots.
 293                                 true,  // activate StrongRootsScope
 294                                 false, // not scavenging
 295                                 SharedHeap::SO_AllClasses,
 296                                 &adjust_pointer_closure,
 297                                 false, // do not walk code
 298                                 &adjust_pointer_closure,
 299                                 &adjust_klass_closure);
 300 
 301   // Now adjust pointers in remaining weak roots.  (All of which should
 302   // have been cleared if they pointed to non-surviving objects.)
 303   CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,
 304                                                    /*do_marking=*/ false);
 305   gch->gen_process_weak_roots(&adjust_pointer_closure,
 306                               &adjust_code_pointer_closure);
 307 
 308   adjust_marks();
 309   GenAdjustPointersClosure blk;
 310   gch->generation_iterate(&blk, true);
 311 }
 312 
 313 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 314 public:
 315   void do_generation(Generation* gen) {
 316     gen->compact();
 317   }
 318 };
 319 
 320 void GenMarkSweep::mark_sweep_phase4() {
 321   // All pointers are now adjusted, move objects accordingly
 322 
 323   // It is imperative that we traverse perm_gen first in phase4. All
 324   // classes must be allocated earlier than their instances, and traversing
 325   // perm_gen first makes sure that all Klass*s have moved to their new
 326   // location before any instance does a dispatch through it's klass!
 327 
 328   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 329   // in the same order in phase2, phase3 and phase4. We don't quite do that
 330   // here (perm_gen first rather than last), so we tell the validate code
 331   // to use a higher index (saved from phase2) when verifying perm_gen.
 332   GenCollectedHeap* gch = GenCollectedHeap::heap();
 333 
 334   TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
 335   trace("4");
 336 
 337   GenCompactClosure blk;
 338   gch->generation_iterate(&blk, true);
 339 }