sdk/runtime/vm/zone.cc

// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

#include "vm/zone.h"

#include "platform/assert.h"
#include "platform/utils.h"
#include "vm/flags.h"
#include "vm/isolate.h"
#include "vm/os.h"

namespace dart {

DEFINE_DEBUG_FLAG(bool, trace_zone_sizes,
                  false, "Traces allocation sizes in the zone.");


// Zone segments represent chunks of memory: They have starting
// address encoded in the this pointer and a size in bytes. They are
// chained together to form the backing storage for an expanding zone.
class BaseZone::Segment {
 public:
  Segment* next() const { return next_; }
  intptr_t size() const { return size_; }

  uword start() { return address(sizeof(Segment)); }
  uword end() { return address(size_); }

  // Allocate or delete individual segments.
  static Segment* New(intptr_t size, Segment* next);
  static void DeleteSegmentList(Segment* segment);

 private:
  Segment* next_;
  intptr_t size_;

  // Computes the address of the nth byte in this segment.
  uword address(int n) { return reinterpret_cast<uword>(this) + n; }

  static void Delete(Segment* segment) { delete[] segment; }

  DISALLOW_IMPLICIT_CONSTRUCTORS(Segment);
};


void BaseZone::Segment::DeleteSegmentList(Segment* head) {
  Segment* current = head;
  while (current != NULL) {
    Segment* next = current->next();
#ifdef DEBUG
    // Zap the entire current segment (including the header).
    memset(current, kZapDeletedByte, current->size());
#endif
    Segment::Delete(current);
    current = next;
  }
}


BaseZone::Segment* BaseZone::Segment::New(intptr_t size,
                                          BaseZone::Segment* next) {
  ASSERT(size >= 0);
  Segment* result = reinterpret_cast<Segment*>(new uint8_t[size]);
  if (result != NULL) {
#ifdef DEBUG
    // Zap the entire allocated segment (including the header).
    memset(result, kZapUninitializedByte, size);
#endif
    result->next_ = next;
    result->size_ = size;
  }
  return result;
}


BaseZone::BaseZone()
    : initial_buffer_(buffer_, kInitialChunkSize),
      position_(initial_buffer_.start()),
      limit_(initial_buffer_.end()),
      head_(NULL),
      large_segments_(NULL) {
#ifdef DEBUG
    // Zap the entire initial buffer.
  memset(initial_buffer_.pointer(), kZapUninitializedByte,
         initial_buffer_.size());
#endif
}


BaseZone::~BaseZone() {
  DeleteAll();
#if defined(DEBUG)
  if (FLAG_trace_zone_sizes) {
    DumpZoneSizes();
  }
#endif
}


void BaseZone::DeleteAll() {
  // Traverse the chained list of segments, zapping (in debug mode)
  // and freeing every zone segment.
  Segment::DeleteSegmentList(head_);
  Segment::DeleteSegmentList(large_segments_);

  // Reset zone state.
#ifdef DEBUG
  memset(initial_buffer_.pointer(), kZapDeletedByte, initial_buffer_.size());
#endif
  position_ = initial_buffer_.start();
  limit_ = initial_buffer_.end();
  head_ = NULL;
  large_segments_ = NULL;
}


intptr_t BaseZone::SizeInBytes() const {
  intptr_t size = 0;
  for (Segment* s = large_segments_; s != NULL; s = s->next()) {
    size += s->size();
  }
  if (head_ == NULL) {
    return size + (position_ - initial_buffer_.start());
  }
  size += initial_buffer_.size();
  for (Segment* s = head_->next(); s != NULL; s = s->next()) {
    size += s->size();
  }
  return size + (position_ - head_->start());
}


uword BaseZone::AllocateExpand(intptr_t size) {
#if defined(DEBUG)
  ASSERT(size >= 0);
  if (FLAG_trace_zone_sizes) {
    DumpZoneSizes();
  }
  // Make sure the requested size is already properly aligned and that
  // there isn't enough room in the Zone to satisfy the request.
  ASSERT(Utils::IsAligned(size, kAlignment));
  intptr_t free_size = (limit_ - position_);
  ASSERT(free_size <  size);
#endif

  // First check to see if we should just chain it as a large segment.
  intptr_t max_size = Utils::RoundDown(kSegmentSize - sizeof(Segment),
                                       kAlignment);
  ASSERT(max_size > 0);
  if (size > max_size) {
    return AllocateLargeSegment(size);
  }

  // Allocate another segment and chain it up.
  head_ = Segment::New(kSegmentSize, head_);

  // Recompute 'position' and 'limit' based on the new head segment.
  uword result = Utils::RoundUp(head_->start(), kAlignment);
  position_ = result + size;
  limit_ = head_->end();
  ASSERT(position_ <= limit_);
  return result;
}


uword BaseZone::AllocateLargeSegment(intptr_t size) {
#if defined(DEBUG)
  ASSERT(size >= 0);
  // Make sure the requested size is already properly aligned and that
  // there isn't enough room in the Zone to satisfy the request.
  ASSERT(Utils::IsAligned(size, kAlignment));
  intptr_t free_size = (limit_ - position_);
  ASSERT(free_size <  size);
#endif

  // Create a new large segment and chain it up.
  ASSERT(Utils::IsAligned(sizeof(Segment), kAlignment));
  size += sizeof(Segment);  // Account for book keeping fields in size.
  large_segments_ = Segment::New(size, large_segments_);

  uword result = Utils::RoundUp(large_segments_->start(), kAlignment);
  return result;
}


char* BaseZone::MakeCopyOfString(const char* str) {
  intptr_t len = strlen(str) + 1;  // '\0'-terminated.
  char* copy = reinterpret_cast<char*>(Allocate(len));
  strncpy(copy, str, len);
  return copy;
}


uword BaseZone::Reallocate(uword data, intptr_t old_size, intptr_t new_size) {
  ASSERT(new_size >= 0);
  uword new_data = Allocate(new_size);
  if (data != 0) {
    memmove(reinterpret_cast<void*>(new_data),
            reinterpret_cast<void*>(data),
            Utils::Minimum(old_size, new_size));
  }
  return new_data;
}


#if defined(DEBUG)
void BaseZone::DumpZoneSizes() {
  intptr_t size = 0;
  for (Segment* s = large_segments_; s != NULL; s = s->next()) {
    size += s->size();
  }
  OS::Print("Size in bytes allocated, Total = %d Large Segments = %d\n",
            SizeInBytes(), size);
}
#endif


Zone::Zone(Isolate* isolate)
    : StackResource(isolate),
      zone_(),
      handles_(),
      previous_(NULL) {
  // Assert that there is no current zone as we only want to scope
  // zones when transitioning from generated dart code to dart VM
  // runtime code.
  previous_ = isolate->current_zone();
  isolate->set_current_zone(this);
}


Zone::~Zone() {
  ASSERT(isolate()->current_zone() == this);
  isolate()->set_current_zone(previous_);
}


void Zone::VisitObjectPointers(ObjectPointerVisitor* visitor) {
  Zone* zone = this;
  while (zone != NULL) {
    zone->handles()->VisitObjectPointers(visitor);
    zone = zone->previous_;
  }
}

}  // namespace dart