src/hotspot/share/gc/shared/space.cpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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#include "classfile/vmClasses.hpp"
#include "classfile/vmSymbols.hpp"
#include "gc/shared/collectedHeap.inline.hpp"
#include "gc/shared/space.hpp"
#include "gc/shared/spaceDecorator.hpp"
#include "memory/iterator.inline.hpp"
#include "memory/universe.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/java.hpp"
#include "runtime/safepoint.hpp"
#include "utilities/align.hpp"
#include "utilities/copy.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/macros.hpp"

ContiguousSpace::ContiguousSpace():
  _bottom(nullptr),
  _end(nullptr),
  _top(nullptr) {}

void ContiguousSpace::initialize(MemRegion mr,
                                 bool clear_space,
                                 bool mangle_space) {
  HeapWord* bottom = mr.start();
  HeapWord* end    = mr.end();
  assert(Universe::on_page_boundary(bottom) && Universe::on_page_boundary(end),
         "invalid space boundaries");
  set_bottom(bottom);
  set_end(end);
  if (clear_space) {
    clear(mangle_space);
  }
}

void ContiguousSpace::clear(bool mangle_space) {
  set_top(bottom());
  if (ZapUnusedHeapArea && mangle_space) {
    mangle_unused_area();
  }
}

#ifndef PRODUCT

void ContiguousSpace::mangle_unused_area() {
  mangle_unused_area(MemRegion(_top, _end));
}

void ContiguousSpace::mangle_unused_area(MemRegion mr) {
  SpaceMangler::mangle_region(mr);
}

#endif  // NOT_PRODUCT

void ContiguousSpace::print() const { print_on(tty, ""); }

void ContiguousSpace::print_on(outputStream* st, const char* prefix) const {
  st->print_cr("%sspace %zuK, %3d%% used [" PTR_FORMAT ", " PTR_FORMAT ", " PTR_FORMAT ")",
               prefix,
               capacity() / K, (int) ((double) used() * 100 / capacity()),
               p2i(bottom()), p2i(top()), p2i(end()));
}

void ContiguousSpace::verify() const {
  HeapWord* p = bottom();
  HeapWord* t = top();
  while (p < t) {
    oopDesc::verify(cast_to_oop(p));
    p += cast_to_oop(p)->size();
  }
  guarantee(p == top(), "end of last object must match end of space");
}

void ContiguousSpace::object_iterate(ObjectClosure* blk) {
  HeapWord* addr = bottom();
  while (addr < top()) {
    oop obj = cast_to_oop(addr);
    blk->do_object(obj);
    addr += obj->size();
  }
}

// This version requires locking.
inline HeapWord* ContiguousSpace::allocate_impl(size_t size) {
  assert(Heap_lock->owned_by_self() ||
         (SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread()),
         "not locked");
  HeapWord* obj = top();
  if (pointer_delta(end(), obj) >= size) {
    HeapWord* new_top = obj + size;
    set_top(new_top);
    assert(is_object_aligned(obj) && is_object_aligned(new_top), "checking alignment");
    return obj;
  } else {
    return nullptr;
  }
}

// This version is lock-free.
inline HeapWord* ContiguousSpace::par_allocate_impl(size_t size) {
  do {
    HeapWord* obj = top();
    if (pointer_delta(end(), obj) >= size) {
      HeapWord* new_top = obj + size;
      HeapWord* result = Atomic::cmpxchg(top_addr(), obj, new_top);
      // result can be one of two:
      //  the old top value: the exchange succeeded
      //  otherwise: the new value of the top is returned.
      if (result == obj) {
        assert(is_object_aligned(obj) && is_object_aligned(new_top), "checking alignment");
        return obj;
      }
    } else {
      return nullptr;
    }
  } while (true);
}

// Requires locking.
HeapWord* ContiguousSpace::allocate(size_t size) {
  return allocate_impl(size);
}

// Lock-free.
HeapWord* ContiguousSpace::par_allocate(size_t size) {
  return par_allocate_impl(size);
}