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, bool clear_all_softrefs) {
  56   guarantee(level == 1, "We always collect both old and young.");
  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   // 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(level);
  91 
  92   allocate_stacks();
  93 
  94   mark_sweep_phase1(level, clear_all_softrefs);
  95 
  96   mark_sweep_phase2();
  97 
  98   // Don't add any more derived pointers during phase3
  99   COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
 100   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 101 
 102   mark_sweep_phase3(level);
 103 
 104   mark_sweep_phase4();
 105 
 106   restore_marks();
 107 
 108   // Set saved marks for allocation profiler (and other things? -- dld)
 109   // (Should this be in general part?)
 110   gch->save_marks();
 111 
 112   deallocate_stacks();
 113 
 114   // If compaction completely evacuated all generations younger than this
 115   // one, then we can clear the card table.  Otherwise, we must invalidate
 116   // it (consider all cards dirty).  In the future, we might consider doing
 117   // compaction within generations only, and doing card-table sliding.
 118   bool all_empty = true;
 119   for (int i = 0; all_empty && i < level; i++) {
 120     Generation* g = gch->get_gen(i);
 121     all_empty = all_empty && gch->get_gen(i)->used() == 0;
 122   }
 123   GenRemSet* rs = gch->rem_set();
 124   Generation* old_gen = gch->get_gen(level);
 125   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 126   if (all_empty) {
 127     // We've evacuated all generations below us.
 128     rs->clear_into_younger(old_gen);
 129   } else {
 130     // Invalidate the cards corresponding to the currently used
 131     // region and clear those corresponding to the evacuated region.
 132     rs->invalidate_or_clear(old_gen);
 133   }
 134 
 135   Threads::gc_epilogue();
 136   CodeCache::gc_epilogue();
 137   JvmtiExport::gc_epilogue();
 138 
 139   if (PrintGC && !PrintGCDetails) {
 140     gch->print_heap_change(gch_prev_used);
 141   }
 142 
 143   // refs processing: clean slate
 144   _ref_processor = NULL;
 145 
 146   // Update heap occupancy information which is used as
 147   // input to soft ref clearing policy at the next gc.
 148   Universe::update_heap_info_at_gc();
 149 
 150   // Update time of last gc for all generations we collected
 151   // (which currently is all the generations in the heap).
 152   // We need to use a monotonically non-decreasing time in ms
 153   // or we will see time-warp warnings and os::javaTimeMillis()
 154   // does not guarantee monotonicity.
 155   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 156   gch->update_time_of_last_gc(now);
 157 
 158   gch->trace_heap_after_gc(_gc_tracer);
 159 }
 160 
 161 void GenMarkSweep::allocate_stacks() {
 162   GenCollectedHeap* gch = GenCollectedHeap::heap();
 163   // Scratch request on behalf of oldest generation; will do no
 164   // allocation.
 165   ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
 166 
 167   // $$$ To cut a corner, we'll only use the first scratch block, and then
 168   // revert to malloc.
 169   if (scratch != NULL) {
 170     _preserved_count_max =
 171       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 172   } else {
 173     _preserved_count_max = 0;
 174   }
 175 
 176   _preserved_marks = (PreservedMark*)scratch;
 177   _preserved_count = 0;
 178 }
 179 
 180 
 181 void GenMarkSweep::deallocate_stacks() {
 182   if (!UseG1GC) {
 183     GenCollectedHeap* gch = GenCollectedHeap::heap();
 184     gch->release_scratch();
 185   }
 186 
 187   _preserved_mark_stack.clear(true);
 188   _preserved_oop_stack.clear(true);
 189   _marking_stack.clear();
 190   _objarray_stack.clear(true);
 191 }
 192 
 193 void GenMarkSweep::mark_sweep_phase1(int level,
 194                                   bool clear_all_softrefs) {
 195   // Recursively traverse all live objects and mark them
 196   GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer);
 197   trace(" 1");
 198 
 199   GenCollectedHeap* gch = GenCollectedHeap::heap();
 200 
 201   // Because follow_root_closure is created statically, cannot
 202   // use OopsInGenClosure constructor which takes a generation,
 203   // as the Universe has not been created when the static constructors
 204   // are run.
 205   follow_root_closure.set_orig_generation(gch->get_gen(level));
 206 
 207   // Need new claim bits before marking starts.
 208   ClassLoaderDataGraph::clear_claimed_marks();
 209 
 210   gch->gen_process_strong_roots(level,
 211                                 false, // Younger gens are not roots.
 212                                 true,  // activate StrongRootsScope
 213                                 SharedHeap::SO_SystemClasses,
 214                                 &follow_root_closure,
 215                                 &follow_root_closure,
 216                                 &follow_klass_closure);
 217 
 218   // Process reference objects found during marking
 219   {
 220     ref_processor()->setup_policy(clear_all_softrefs);
 221     const ReferenceProcessorStats& stats =
 222       ref_processor()->process_discovered_references(
 223         &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
 224     gc_tracer()->report_gc_reference_stats(stats);
 225   }
 226 
 227   // This is the point where the entire marking should have completed.
 228   assert(_marking_stack.is_empty(), "Marking should have completed");
 229 
 230   // Unload classes and purge the SystemDictionary.
 231   bool purged_class = SystemDictionary::do_unloading(&is_alive);
 232 
 233   // Unload nmethods.
 234   CodeCache::do_unloading(&is_alive, purged_class);
 235 
 236   // Prune dead klasses from subklass/sibling/implementor lists.
 237   Klass::clean_weak_klass_links(&is_alive);
 238 
 239   // Delete entries for dead interned strings.
 240   StringTable::unlink(&is_alive);
 241 
 242   // Clean up unreferenced symbols in symbol table.
 243   SymbolTable::unlink();
 244 
 245   gc_tracer()->report_object_count_after_gc(&is_alive);
 246 }
 247 
 248 
 249 void GenMarkSweep::mark_sweep_phase2() {
 250   // Now all live objects are marked, compute the new object addresses.
 251 
 252   // It is imperative that we traverse perm_gen LAST. If dead space is
 253   // allowed a range of dead object may get overwritten by a dead int
 254   // array. If perm_gen is not traversed last a Klass* may get
 255   // overwritten. This is fine since it is dead, but if the class has dead
 256   // instances we have to skip them, and in order to find their size we
 257   // need the Klass*!
 258   //
 259   // It is not required that we traverse spaces in the same order in
 260   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 261   // tracking expects us to do so. See comment under phase4.
 262 
 263   GenCollectedHeap* gch = GenCollectedHeap::heap();
 264 
 265   GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer);
 266   trace("2");
 267 
 268   gch->prepare_for_compaction();
 269 }
 270 
 271 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 272 public:
 273   void do_generation(Generation* gen) {
 274     gen->adjust_pointers();
 275   }
 276 };
 277 
 278 void GenMarkSweep::mark_sweep_phase3(int level) {
 279   GenCollectedHeap* gch = GenCollectedHeap::heap();
 280 
 281   // Adjust the pointers to reflect the new locations
 282   GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer);
 283   trace("3");
 284 
 285   // Need new claim bits for the pointer adjustment tracing.
 286   ClassLoaderDataGraph::clear_claimed_marks();
 287 
 288   // Because the closure below is created statically, we cannot
 289   // use OopsInGenClosure constructor which takes a generation,
 290   // as the Universe has not been created when the static constructors
 291   // are run.
 292   adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
 293 
 294   gch->gen_process_strong_roots(level,
 295                                 false, // Younger gens are not roots.
 296                                 true,  // activate StrongRootsScope
 297                                 SharedHeap::SO_AllClasses | SharedHeap::SO_AllCodeCache,
 298                                 &adjust_pointer_closure,
 299                                 &adjust_pointer_closure,
 300                                 &adjust_klass_closure);
 301 
 302   gch->gen_process_weak_roots(&adjust_pointer_closure);
 303 
 304   adjust_marks();
 305   GenAdjustPointersClosure blk;
 306   gch->generation_iterate(&blk, true);
 307 }
 308 
 309 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 310 public:
 311   void do_generation(Generation* gen) {
 312     gen->compact();
 313   }
 314 };
 315 
 316 void GenMarkSweep::mark_sweep_phase4() {
 317   // All pointers are now adjusted, move objects accordingly
 318 
 319   // It is imperative that we traverse perm_gen first in phase4. All
 320   // classes must be allocated earlier than their instances, and traversing
 321   // perm_gen first makes sure that all Klass*s have moved to their new
 322   // location before any instance does a dispatch through it's klass!
 323 
 324   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 325   // in the same order in phase2, phase3 and phase4. We don't quite do that
 326   // here (perm_gen first rather than last), so we tell the validate code
 327   // to use a higher index (saved from phase2) when verifying perm_gen.
 328   GenCollectedHeap* gch = GenCollectedHeap::heap();
 329 
 330   GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer);
 331   trace("4");
 332 
 333   GenCompactClosure blk;
 334   gch->generation_iterate(&blk, true);
 335 }