markSweep.cpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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#include "precompiled.hpp"
#include "compiler/compileBroker.hpp"
#include "gc/serial/markSweep.inline.hpp"
#include "gc/shared/collectedHeap.inline.hpp"
#include "gc/shared/gcTimer.hpp"
#include "gc/shared/gcTrace.hpp"
#include "gc/shared/gc_globals.hpp"
#include "memory/iterator.inline.hpp"
#include "memory/universe.hpp"
#include "oops/access.inline.hpp"
#include "oops/compressedOops.inline.hpp"
#include "oops/methodData.hpp"
#include "oops/objArrayKlass.inline.hpp"
#include "oops/oop.inline.hpp"
#include "oops/typeArrayOop.inline.hpp"
#include "utilities/stack.inline.hpp"

uint                    MarkSweep::_total_invocations = 0;

Stack<oop, mtGC>              MarkSweep::_marking_stack;
Stack<ObjArrayTask, mtGC>     MarkSweep::_objarray_stack;

PreservedMarksSet       MarkSweep::_preserved_overflow_stack_set(false /* in_c_heap */);
size_t                  MarkSweep::_preserved_count = 0;
size_t                  MarkSweep::_preserved_count_max = 0;
PreservedMark*          MarkSweep::_preserved_marks = nullptr;
STWGCTimer*             MarkSweep::_gc_timer        = nullptr;
SerialOldTracer*        MarkSweep::_gc_tracer       = nullptr;

AlwaysTrueClosure   MarkSweep::_always_true_closure;
ReferenceProcessor* MarkSweep::_ref_processor;

StringDedup::Requests*  MarkSweep::_string_dedup_requests = nullptr;

MarkSweep::FollowRootClosure  MarkSweep::follow_root_closure;

MarkAndPushClosure MarkSweep::mark_and_push_closure(ClassLoaderData::_claim_stw_fullgc_mark);
CLDToOopClosure    MarkSweep::follow_cld_closure(&mark_and_push_closure, ClassLoaderData::_claim_stw_fullgc_mark);
CLDToOopClosure    MarkSweep::adjust_cld_closure(&adjust_pointer_closure, ClassLoaderData::_claim_stw_fullgc_adjust);

template <class T> void MarkSweep::KeepAliveClosure::do_oop_work(T* p) {
  mark_and_push(p);
}

void MarkSweep::push_objarray(oop obj, size_t index) {
  ObjArrayTask task(obj, index);
  assert(task.is_valid(), "bad ObjArrayTask");
  _objarray_stack.push(task);
}

void MarkSweep::follow_array(objArrayOop array) {
  mark_and_push_closure.do_klass(array->klass());
  // Don't push empty arrays to avoid unnecessary work.
  if (array->length() > 0) {
    MarkSweep::push_objarray(array, 0);
  }
}

void MarkSweep::follow_object(oop obj) {
  assert(obj->is_gc_marked(), "should be marked");
  if (obj->is_objArray()) {
    // Handle object arrays explicitly to allow them to
    // be split into chunks if needed.
    MarkSweep::follow_array((objArrayOop)obj);
  } else {
    obj->oop_iterate(&mark_and_push_closure);
  }
}

void MarkSweep::follow_array_chunk(objArrayOop array, int index) {
  const int len = array->length();
  const int beg_index = index;
  assert(beg_index < len || len == 0, "index too large");

  const int stride = MIN2(len - beg_index, (int) ObjArrayMarkingStride);
  const int end_index = beg_index + stride;

  array->oop_iterate_range(&mark_and_push_closure, beg_index, end_index);

  if (end_index < len) {
    MarkSweep::push_objarray(array, end_index); // Push the continuation.
  }
}

void MarkSweep::follow_stack() {
  do {
    while (!_marking_stack.is_empty()) {
      oop obj = _marking_stack.pop();
      assert (obj->is_gc_marked(), "p must be marked");
      follow_object(obj);
    }
    // Process ObjArrays one at a time to avoid marking stack bloat.
    if (!_objarray_stack.is_empty()) {
      ObjArrayTask task = _objarray_stack.pop();
      follow_array_chunk(objArrayOop(task.obj()), task.index());
    }
  } while (!_marking_stack.is_empty() || !_objarray_stack.is_empty());
}

MarkSweep::FollowStackClosure MarkSweep::follow_stack_closure;

void MarkSweep::FollowStackClosure::do_void() { follow_stack(); }

template <class T> void MarkSweep::follow_root(T* p) {
  assert(!Universe::heap()->is_in(p),
         "roots shouldn't be things within the heap");
  T heap_oop = RawAccess<>::oop_load(p);
  if (!CompressedOops::is_null(heap_oop)) {
    oop obj = CompressedOops::decode_not_null(heap_oop);
    if (!obj->mark().is_marked()) {
      mark_object(obj);
      follow_object(obj);
    }
  }
  follow_stack();
}

void MarkSweep::FollowRootClosure::do_oop(oop* p)       { follow_root(p); }
void MarkSweep::FollowRootClosure::do_oop(narrowOop* p) { follow_root(p); }

// We preserve the mark which should be replaced at the end and the location
// that it will go.  Note that the object that this markWord belongs to isn't
// currently at that address but it will be after phase4
void MarkSweep::preserve_mark(oop obj, markWord mark) {
  // We try to store preserved marks in the to space of the new generation since
  // this is storage which should be available.  Most of the time this should be
  // sufficient space for the marks we need to preserve but if it isn't we fall
  // back to using Stacks to keep track of the overflow.
  if (_preserved_count < _preserved_count_max) {
    _preserved_marks[_preserved_count++] = PreservedMark(obj, mark);
  } else {
    _preserved_overflow_stack_set.get()->push_always(obj, mark);
  }
}

void MarkSweep::mark_object(oop obj) {
  if (StringDedup::is_enabled() &&
      java_lang_String::is_instance(obj) &&
      SerialStringDedup::is_candidate_from_mark(obj)) {
    _string_dedup_requests->add(obj);
  }

  // some marks may contain information we need to preserve so we store them away
  // and overwrite the mark.  We'll restore it at the end of markSweep.
  markWord mark = obj->mark();
  obj->set_mark(markWord::prototype().set_marked());

  ContinuationGCSupport::transform_stack_chunk(obj);

  if (obj->mark_must_be_preserved(mark)) {
    preserve_mark(obj, mark);
  }
}

template <class T> void MarkSweep::mark_and_push(T* p) {
  T heap_oop = RawAccess<>::oop_load(p);
  if (!CompressedOops::is_null(heap_oop)) {
    oop obj = CompressedOops::decode_not_null(heap_oop);
    if (!obj->mark().is_marked()) {
      mark_object(obj);
      _marking_stack.push(obj);
    }
  }
}

template <typename T>
void MarkAndPushClosure::do_oop_work(T* p)            { MarkSweep::mark_and_push(p); }
void MarkAndPushClosure::do_oop(      oop* p)         { do_oop_work(p); }
void MarkAndPushClosure::do_oop(narrowOop* p)         { do_oop_work(p); }

AdjustPointerClosure MarkSweep::adjust_pointer_closure;

void MarkSweep::adjust_marks() {
  // adjust the oops we saved earlier
  for (size_t i = 0; i < _preserved_count; i++) {
    PreservedMarks::adjust_preserved_mark(_preserved_marks + i);
  }

  // deal with the overflow stack
  _preserved_overflow_stack_set.get()->adjust_during_full_gc();
}

void MarkSweep::restore_marks() {
  log_trace(gc)("Restoring " SIZE_FORMAT " marks", _preserved_count + _preserved_overflow_stack_set.get()->size());

  // restore the marks we saved earlier
  for (size_t i = 0; i < _preserved_count; i++) {
    _preserved_marks[i].set_mark();
  }

  // deal with the overflow
  _preserved_overflow_stack_set.restore(nullptr);
}

MarkSweep::IsAliveClosure   MarkSweep::is_alive;

bool MarkSweep::IsAliveClosure::do_object_b(oop p) { return p->is_gc_marked(); }

MarkSweep::KeepAliveClosure MarkSweep::keep_alive;

void MarkSweep::KeepAliveClosure::do_oop(oop* p)       { MarkSweep::KeepAliveClosure::do_oop_work(p); }
void MarkSweep::KeepAliveClosure::do_oop(narrowOop* p) { MarkSweep::KeepAliveClosure::do_oop_work(p); }

void MarkSweep::initialize() {
  MarkSweep::_gc_timer = new STWGCTimer();
  MarkSweep::_gc_tracer = new SerialOldTracer();
  MarkSweep::_string_dedup_requests = new StringDedup::Requests();

  // The Full GC operates on the entire heap so all objects should be subject
  // to discovery, hence the _always_true_closure.
  MarkSweep::_ref_processor = new ReferenceProcessor(&_always_true_closure);
  mark_and_push_closure.set_ref_discoverer(_ref_processor);
}