C++ GenCollectedHeap::old_gen方法代码示例

void GenMarkSweep::mark_sweep_phase3() {
  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // Adjust the pointers to reflect the new locations
  GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());

  // Need new claim bits for the pointer adjustment tracing.
  ClassLoaderDataGraph::clear_claimed_marks();

  // Because the closure below is created statically, we cannot
  // use OopsInGenClosure constructor which takes a generation,
  // as the Universe has not been created when the static constructors
  // are run.
  adjust_pointer_closure.set_orig_generation(gch->old_gen());

  {
    StrongRootsScope srs(1);

    gch->gen_process_roots(&srs,
                           GenCollectedHeap::OldGen,
                           false, // Younger gens are not roots.
                           GenCollectedHeap::SO_AllCodeCache,
                           GenCollectedHeap::StrongAndWeakRoots,
                           &adjust_pointer_closure,
                           &adjust_pointer_closure,
                           &adjust_cld_closure);
  }

  gch->gen_process_weak_roots(&adjust_pointer_closure);

  adjust_marks();
  GenAdjustPointersClosure blk;
  gch->generation_iterate(&blk, true);
}

void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
  // Recursively traverse all live objects and mark them
  GCTraceTime(Trace, gc) tm("Phase 1: Mark live objects", _gc_timer);

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // Because follow_root_closure is created statically, cannot
  // use OopsInGenClosure constructor which takes a generation,
  // as the Universe has not been created when the static constructors
  // are run.
  follow_root_closure.set_orig_generation(gch->old_gen());

  // Need new claim bits before marking starts.
  ClassLoaderDataGraph::clear_claimed_marks();

  {
    StrongRootsScope srs(1);

    gch->gen_process_roots(&srs,
                           GenCollectedHeap::OldGen,
                           false, // Younger gens are not roots.
                           GenCollectedHeap::SO_None,
                           ClassUnloading,
                           &follow_root_closure,
                           &follow_root_closure,
                           &follow_cld_closure);
  }

  // Process reference objects found during marking
  {
    ref_processor()->setup_policy(clear_all_softrefs);
    const ReferenceProcessorStats& stats =
      ref_processor()->process_discovered_references(
        &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
    gc_tracer()->report_gc_reference_stats(stats);
  }

  // This is the point where the entire marking should have completed.
  assert(_marking_stack.is_empty(), "Marking should have completed");

  // Unload classes and purge the SystemDictionary.
  bool purged_class = SystemDictionary::do_unloading(&is_alive);

  // Unload nmethods.
  CodeCache::do_unloading(&is_alive, purged_class);

  // Prune dead klasses from subklass/sibling/implementor lists.
  Klass::clean_weak_klass_links(&is_alive);

  // Delete entries for dead interned strings.
  StringTable::unlink(&is_alive);

  // Clean up unreferenced symbols in symbol table.
  SymbolTable::unlink();

  gc_tracer()->report_object_count_after_gc(&is_alive);
}

bool DefNewGeneration::collection_attempt_is_safe() {
  if (!to()->is_empty()) {
    log_trace(gc)(":: to is not empty ::");
    return false;
  }
  if (_old_gen == NULL) {
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    _old_gen = gch->old_gen();
  }
  return _old_gen->promotion_attempt_is_safe(used());
}

void GenMarkSweep::allocate_stacks() {
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  // Scratch request on behalf of old generation; will do no allocation.
  ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);

  // $$$ To cut a corner, we'll only use the first scratch block, and then
  // revert to malloc.
  if (scratch != NULL) {
    _preserved_count_max =
      scratch->num_words * HeapWordSize / sizeof(PreservedMark);
  } else {
    _preserved_count_max = 0;
  }

  _preserved_marks = (PreservedMark*)scratch;
  _preserved_count = 0;
}

HeapWord* GenCollectorPolicy::expand_heap_and_allocate(size_t size,
                                                       bool   is_tlab) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();
  HeapWord* result = NULL;
  Generation *old = gch->old_gen();
  if (old->should_allocate(size, is_tlab)) {
    result = old->expand_and_allocate(size, is_tlab);
  }
  if (result == NULL) {
    Generation *young = gch->young_gen();
    if (young->should_allocate(size, is_tlab)) {
      result = young->expand_and_allocate(size, is_tlab);
    }
  }
  assert(result == NULL || gch->is_in_reserved(result), "result not in heap");
  return result;
}

void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
  assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");

  GenCollectedHeap* gch = GenCollectedHeap::heap();
#ifdef ASSERT
  if (gch->collector_policy()->should_clear_all_soft_refs()) {
    assert(clear_all_softrefs, "Policy should have been checked earlier");
  }
#endif

  // hook up weak ref data so it can be used during Mark-Sweep
  assert(ref_processor() == NULL, "no stomping");
  assert(rp != NULL, "should be non-NULL");
  set_ref_processor(rp);
  rp->setup_policy(clear_all_softrefs);

  gch->trace_heap_before_gc(_gc_tracer);

  // When collecting the permanent generation Method*s may be moving,
  // so we either have to flush all bcp data or convert it into bci.
  CodeCache::gc_prologue();

  // Increment the invocation count
  _total_invocations++;

  // Capture used regions for each generation that will be
  // subject to collection, so that card table adjustments can
  // be made intelligently (see clear / invalidate further below).
  gch->save_used_regions();

  allocate_stacks();

  mark_sweep_phase1(clear_all_softrefs);

  mark_sweep_phase2();

  // Don't add any more derived pointers during phase3
#if defined(COMPILER2) || INCLUDE_JVMCI
  assert(DerivedPointerTable::is_active(), "Sanity");
  DerivedPointerTable::set_active(false);
#endif

  mark_sweep_phase3();

  mark_sweep_phase4();

  restore_marks();

  // Set saved marks for allocation profiler (and other things? -- dld)
  // (Should this be in general part?)
  gch->save_marks();

  deallocate_stacks();

  // If compaction completely evacuated the young generation then we
  // can clear the card table.  Otherwise, we must invalidate
  // it (consider all cards dirty).  In the future, we might consider doing
  // compaction within generations only, and doing card-table sliding.
  CardTableRS* rs = gch->rem_set();
  Generation* old_gen = gch->old_gen();

  // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
  if (gch->young_gen()->used() == 0) {
    // We've evacuated the young generation.
    rs->clear_into_younger(old_gen);
  } else {
    // Invalidate the cards corresponding to the currently used
    // region and clear those corresponding to the evacuated region.
    rs->invalidate_or_clear(old_gen);
  }

  CodeCache::gc_epilogue();
  JvmtiExport::gc_epilogue();

  // refs processing: clean slate
  set_ref_processor(NULL);

  // Update heap occupancy information which is used as
  // input to soft ref clearing policy at the next gc.
  Universe::update_heap_info_at_gc();

  // Update time of last gc for all generations we collected
  // (which currently is all the generations in the heap).
  // We need to use a monotonically non-decreasing time in ms
  // or we will see time-warp warnings and os::javaTimeMillis()
  // does not guarantee monotonicity.
  jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
  gch->update_time_of_last_gc(now);

  gch->trace_heap_after_gc(_gc_tracer);
}

void DefNewGeneration::collect(bool   full,
                               bool   clear_all_soft_refs,
                               size_t size,
                               bool   is_tlab) {
  assert(full || size > 0, "otherwise we don't want to collect");

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  _gc_timer->register_gc_start();
  DefNewTracer gc_tracer;
  gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());

  _old_gen = gch->old_gen();

  // If the next generation is too full to accommodate promotion
  // from this generation, pass on collection; let the next generation
  // do it.
  if (!collection_attempt_is_safe()) {
    log_trace(gc)(":: Collection attempt not safe ::");
    gch->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
    return;
  }
  assert(to()->is_empty(), "Else not collection_attempt_is_safe");

  init_assuming_no_promotion_failure();

  GCTraceTime(Trace, gc) tm("DefNew", NULL, gch->gc_cause());

  gch->trace_heap_before_gc(&gc_tracer);

  // These can be shared for all code paths
  IsAliveClosure is_alive(this);
  ScanWeakRefClosure scan_weak_ref(this);

  age_table()->clear();
  to()->clear(SpaceDecorator::Mangle);

  gch->rem_set()->prepare_for_younger_refs_iterate(false);

  assert(gch->no_allocs_since_save_marks(),
         "save marks have not been newly set.");

  // Not very pretty.
  CollectorPolicy* cp = gch->collector_policy();

  FastScanClosure fsc_with_no_gc_barrier(this, false);
  FastScanClosure fsc_with_gc_barrier(this, true);

  KlassScanClosure klass_scan_closure(&fsc_with_no_gc_barrier,
                                      gch->rem_set()->klass_rem_set());
  CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure,
                                           &fsc_with_no_gc_barrier,
                                           false);

  set_promo_failure_scan_stack_closure(&fsc_with_no_gc_barrier);
  FastEvacuateFollowersClosure evacuate_followers(gch,
                                                  &fsc_with_no_gc_barrier,
                                                  &fsc_with_gc_barrier);

  assert(gch->no_allocs_since_save_marks(),
         "save marks have not been newly set.");

  {
    // DefNew needs to run with n_threads == 0, to make sure the serial
    // version of the card table scanning code is used.
    // See: CardTableModRefBSForCTRS::non_clean_card_iterate_possibly_parallel.
    StrongRootsScope srs(0);

    gch->gen_process_roots(&srs,
                           GenCollectedHeap::YoungGen,
                           true,  // Process younger gens, if any,
                                  // as strong roots.
                           GenCollectedHeap::SO_ScavengeCodeCache,
                           GenCollectedHeap::StrongAndWeakRoots,
                           &fsc_with_no_gc_barrier,
                           &fsc_with_gc_barrier,
                           &cld_scan_closure);
  }

  // "evacuate followers".
  evacuate_followers.do_void();

  FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
  ReferenceProcessor* rp = ref_processor();
  rp->setup_policy(clear_all_soft_refs);
  const ReferenceProcessorStats& stats =
  rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers,
                                    NULL, _gc_timer);
  gc_tracer.report_gc_reference_stats(stats);
  gc_tracer.report_tenuring_threshold(tenuring_threshold());

  if (!_promotion_failed) {
    // Swap the survivor spaces.
    eden()->clear(SpaceDecorator::Mangle);
    from()->clear(SpaceDecorator::Mangle);
    if (ZapUnusedHeapArea) {
      // This is now done here because of the piece-meal mangling which
      // can check for valid mangling at intermediate points in the
      // collection(s).  When a young collection fails to collect
      // sufficient space resizing of the young generation can occur
//.........这里部分代码省略.........

void DefNewGeneration::compute_new_size() {
  // This is called after a GC that includes the old generation, so from-space
  // will normally be empty.
  // Note that we check both spaces, since if scavenge failed they revert roles.
  // If not we bail out (otherwise we would have to relocate the objects).
  if (!from()->is_empty() || !to()->is_empty()) {
    return;
  }

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  size_t old_size = gch->old_gen()->capacity();
  size_t new_size_before = _virtual_space.committed_size();
  size_t min_new_size = initial_size();
  size_t max_new_size = reserved().byte_size();
  assert(min_new_size <= new_size_before &&
         new_size_before <= max_new_size,
         "just checking");
  // All space sizes must be multiples of Generation::GenGrain.
  size_t alignment = Generation::GenGrain;

  // Compute desired new generation size based on NewRatio and
  // NewSizeThreadIncrease
  size_t desired_new_size = old_size/NewRatio;
  int threads_count = Threads::number_of_non_daemon_threads();
  size_t thread_increase_size = threads_count * NewSizeThreadIncrease;
  desired_new_size = align_size_up(desired_new_size + thread_increase_size, alignment);

  // Adjust new generation size
  desired_new_size = MAX2(MIN2(desired_new_size, max_new_size), min_new_size);
  assert(desired_new_size <= max_new_size, "just checking");

  bool changed = false;
  if (desired_new_size > new_size_before) {
    size_t change = desired_new_size - new_size_before;
    assert(change % alignment == 0, "just checking");
    if (expand(change)) {
       changed = true;
    }
    // If the heap failed to expand to the desired size,
    // "changed" will be false.  If the expansion failed
    // (and at this point it was expected to succeed),
    // ignore the failure (leaving "changed" as false).
  }
  if (desired_new_size < new_size_before && eden()->is_empty()) {
    // bail out of shrinking if objects in eden
    size_t change = new_size_before - desired_new_size;
    assert(change % alignment == 0, "just checking");
    _virtual_space.shrink_by(change);
    changed = true;
  }
  if (changed) {
    // The spaces have already been mangled at this point but
    // may not have been cleared (set top = bottom) and should be.
    // Mangling was done when the heap was being expanded.
    compute_space_boundaries(eden()->used(),
                             SpaceDecorator::Clear,
                             SpaceDecorator::DontMangle);
    MemRegion cmr((HeapWord*)_virtual_space.low(),
                  (HeapWord*)_virtual_space.high());
    gch->barrier_set()->resize_covered_region(cmr);

    log_debug(gc, heap, ergo)(
        "New generation size " SIZE_FORMAT "K->" SIZE_FORMAT "K [eden=" SIZE_FORMAT "K,survivor=" SIZE_FORMAT "K]",
        new_size_before/K, _virtual_space.committed_size()/K,
        eden()->capacity()/K, from()->capacity()/K);
    log_trace(gc, heap, ergo)(
        "  [allowed " SIZE_FORMAT "K extra for %d threads]",
          thread_increase_size/K, threads_count);
      }
}