runtime/vm/zone.cc - sdk - Git at Google

 // 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/leak_sanitizer.h"
 #include "platform/utils.h"
 #include "vm/dart_api_state.h"
 #include "vm/flags.h"
 #include "vm/handles_impl.h"
 #include "vm/heap/heap.h"
 #include "vm/os.h"
 #include "vm/virtual_memory.h"

 namespace dart {

 RelaxedAtomic<intptr_t> Zone::total_size_ = {0};

 // 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 Zone::Segment {
  public:
   Segment* next() const { return next_; }
   intptr_t size() const { return size_; }
   VirtualMemory* memory() const { return memory_; }

   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);
   static void IncrementMemoryCapacity(uintptr_t size);
   static void DecrementMemoryCapacity(uintptr_t size);

  private:
   Segment* next_;
   intptr_t size_;
   VirtualMemory* memory_;
   void* alignment_;

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

   DISALLOW_IMPLICIT_CONSTRUCTORS(Segment);
 };

 // tcmalloc and jemalloc have both been observed to hold onto lots of free'd
 // zone segments (jemalloc to the point of causing OOM), so instead of using
 // malloc to allocate segments, we allocate directly from mmap/zx_vmo_create/
 // VirtualAlloc, and cache a small number of the normal sized segments.
 static constexpr intptr_t kSegmentCacheCapacity = 16;  // 1 MB of Segments
 static Mutex* segment_cache_mutex = nullptr;
 static VirtualMemory* segment_cache[kSegmentCacheCapacity] = {nullptr};
 static intptr_t segment_cache_size = 0;

 void Zone::Init() {
   ASSERT(segment_cache_mutex == nullptr);
   segment_cache_mutex = new Mutex(NOT_IN_PRODUCT("segment_cache_mutex"));
 }

 void Zone::Cleanup() {
   {
     MutexLocker ml(segment_cache_mutex);
     ASSERT(segment_cache_size >= 0);
     ASSERT(segment_cache_size <= kSegmentCacheCapacity);
     while (segment_cache_size > 0) {
       delete segment_cache[--segment_cache_size];
     }
   }
   delete segment_cache_mutex;
   segment_cache_mutex = nullptr;
 }

 Zone::Segment* Zone::Segment::New(intptr_t size, Zone::Segment* next) {
   size = Utils::RoundUp(size, VirtualMemory::PageSize());
   VirtualMemory* memory = nullptr;
   if (size == kSegmentSize) {
     MutexLocker ml(segment_cache_mutex);
     ASSERT(segment_cache_size >= 0);
     ASSERT(segment_cache_size <= kSegmentCacheCapacity);
     if (segment_cache_size > 0) {
       memory = segment_cache[--segment_cache_size];
     }
   }
   if (memory == nullptr) {
     memory = VirtualMemory::Allocate(size, false, "dart-zone");
     total_size_.fetch_add(size);
   }
   if (memory == nullptr) {
     OUT_OF_MEMORY();
   }
   Segment* result = reinterpret_cast<Segment*>(memory->start());
 #ifdef DEBUG
   // Zap the entire allocated segment (including the header).
   memset(reinterpret_cast<void*>(result), kZapUninitializedByte, size);
 #endif
   result->next_ = next;
   result->size_ = size;
   result->memory_ = memory;
   result->alignment_ = nullptr;  // Avoid unused variable warnings.

   LSAN_REGISTER_ROOT_REGION(result, sizeof(*result));

   IncrementMemoryCapacity(size);
   return result;
 }

 void Zone::Segment::DeleteSegmentList(Segment* head) {
   Segment* current = head;
   while (current != NULL) {
     intptr_t size = current->size();
     DecrementMemoryCapacity(size);
     Segment* next = current->next();
     VirtualMemory* memory = current->memory();
 #ifdef DEBUG
     // Zap the entire current segment (including the header).
     memset(reinterpret_cast<void*>(current), kZapDeletedByte, current->size());
 #endif
     LSAN_UNREGISTER_ROOT_REGION(current, sizeof(*current));

     if (size == kSegmentSize) {
       MutexLocker ml(segment_cache_mutex);
       ASSERT(segment_cache_size >= 0);
       ASSERT(segment_cache_size <= kSegmentCacheCapacity);
       if (segment_cache_size < kSegmentCacheCapacity) {
         segment_cache[segment_cache_size++] = memory;
         memory = nullptr;
       }
     }
     if (memory != nullptr) {
       total_size_.fetch_sub(size);
       delete memory;
     }
     current = next;
   }
 }

 void Zone::Segment::IncrementMemoryCapacity(uintptr_t size) {
   ThreadState* current_thread = ThreadState::Current();
   if (current_thread != NULL) {
     current_thread->IncrementMemoryCapacity(size);
   } else if (ApiNativeScope::Current() != NULL) {
     // If there is no current thread, we might be inside of a native scope.
     ApiNativeScope::IncrementNativeScopeMemoryCapacity(size);
   }
 }

 void Zone::Segment::DecrementMemoryCapacity(uintptr_t size) {
   ThreadState* current_thread = ThreadState::Current();
   if (current_thread != NULL) {
     current_thread->DecrementMemoryCapacity(size);
   } else if (ApiNativeScope::Current() != NULL) {
     // If there is no current thread, we might be inside of a native scope.
     ApiNativeScope::DecrementNativeScopeMemoryCapacity(size);
   }
 }

 // TODO(bkonyi): We need to account for the initial chunk size when a new zone
 // is created within a new thread or ApiNativeScope when calculating high
 // watermarks or memory consumption.
 Zone::Zone()
     : initial_buffer_(buffer_, kInitialChunkSize),
       position_(initial_buffer_.start()),
       limit_(initial_buffer_.end()),
       head_(NULL),
       large_segments_(NULL),
       handles_(),
       previous_(NULL) {
   ASSERT(Utils::IsAligned(position_, kAlignment));
   Segment::IncrementMemoryCapacity(kInitialChunkSize);
 #ifdef DEBUG
   // Zap the entire initial buffer.
   memset(initial_buffer_.pointer(), kZapUninitializedByte,
          initial_buffer_.size());
 #endif
 }

 Zone::~Zone() {
   if (FLAG_trace_zones) {
     DumpZoneSizes();
   }
   DeleteAll();
   Segment::DecrementMemoryCapacity(kInitialChunkSize);
 }

 void Zone::DeleteAll() {
   // Traverse the chained list of segments, zapping (in debug mode)
   // and freeing every zone segment.
   if (head_ != NULL) {
     Segment::DeleteSegmentList(head_);
   }
   if (large_segments_ != NULL) {
     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();
   small_segment_capacity_ = 0;
   head_ = NULL;
   large_segments_ = NULL;
   previous_ = NULL;
   handles_.Reset();
 }

 uintptr_t Zone::SizeInBytes() const {
   uintptr_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());
 }

 uintptr_t Zone::CapacityInBytes() const {
   uintptr_t size = 0;
   for (Segment* s = large_segments_; s != NULL; s = s->next()) {
     size += s->size();
   }
   if (head_ == NULL) {
     return size + initial_buffer_.size();
   }
   size += initial_buffer_.size();
   for (Segment* s = head_; s != NULL; s = s->next()) {
     size += s->size();
   }
   return size;
 }

 uword Zone::AllocateExpand(intptr_t size) {
   ASSERT(size >= 0);
   if (FLAG_trace_zones) {
     OS::PrintErr("*** Expanding zone 0x%" Px "\n",
                  reinterpret_cast<intptr_t>(this));
     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);

   // 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);
   }

   const intptr_t kSuperPageSize = 2 * MB;
   intptr_t next_size;
   if (small_segment_capacity_ < kSuperPageSize) {
     // When the Zone is small, grow linearly to reduce size and use the segment
     // cache to avoid expensive mmap calls.
     next_size = kSegmentSize;
   } else {
     // When the Zone is large, grow geometrically to avoid Page Table Entry
     // exhaustion. Using 1.125 ratio.
     next_size = Utils::RoundUp(small_segment_capacity_ >> 3, kSuperPageSize);
   }
   ASSERT(next_size >= kSegmentSize);

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

   // 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 Zone::AllocateLargeSegment(intptr_t size) {
   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);

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

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

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

 char* Zone::MakeCopyOfStringN(const char* str, intptr_t len) {
   ASSERT(len >= 0);
   for (intptr_t i = 0; i < len; i++) {
     if (str[i] == '\0') {
       len = i;
       break;
     }
   }
   char* copy = Alloc<char>(len + 1);  // +1 for '\0'
   strncpy(copy, str, len);
   copy[len] = '\0';
   return copy;
 }

 char* Zone::ConcatStrings(const char* a, const char* b, char join) {
   intptr_t a_len = (a == NULL) ? 0 : strlen(a);
   const intptr_t b_len = strlen(b) + 1;  // '\0'-terminated.
   const intptr_t len = a_len + b_len;
   char* copy = Alloc<char>(len);
   if (a_len > 0) {
     strncpy(copy, a, a_len);
     // Insert join character.
     copy[a_len++] = join;
   }
   strncpy(&copy[a_len], b, b_len);
   return copy;
 }

 void Zone::DumpZoneSizes() {
   intptr_t size = 0;
   for (Segment* s = large_segments_; s != NULL; s = s->next()) {
     size += s->size();
   }
   OS::PrintErr("***   Zone(0x%" Px
                ") size in bytes,"
                " Total = %" Pd " Large Segments = %" Pd "\n",
                reinterpret_cast<intptr_t>(this), SizeInBytes(), size);
 }

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

 char* Zone::PrintToString(const char* format, ...) {
   va_list args;
   va_start(args, format);
   char* buffer = OS::VSCreate(this, format, args);
   va_end(args);
   return buffer;
 }

 char* Zone::VPrint(const char* format, va_list args) {
   return OS::VSCreate(this, format, args);
 }

 StackZone::StackZone(ThreadState* thread)
     : StackResource(thread), zone_(new Zone()) {
   if (FLAG_trace_zones) {
     OS::PrintErr("*** Starting a new Stack zone 0x%" Px "(0x%" Px ")\n",
                  reinterpret_cast<intptr_t>(this),
                  reinterpret_cast<intptr_t>(zone_));
   }

   // This thread must be preventing safepoints or the GC could be visiting the
   // chain of handle blocks we're about the mutate.
   ASSERT(Thread::Current()->MayAllocateHandles());

   zone_->Link(thread->zone());
   thread->set_zone(zone_);
 }

 StackZone::~StackZone() {
   // This thread must be preventing safepoints or the GC could be visiting the
   // chain of handle blocks we're about the mutate.
   ASSERT(Thread::Current()->MayAllocateHandles());

   ASSERT(thread()->zone() == zone_);
   thread()->set_zone(zone_->previous_);
   if (FLAG_trace_zones) {
     OS::PrintErr("*** Deleting Stack zone 0x%" Px "(0x%" Px ")\n",
                  reinterpret_cast<intptr_t>(this),
                  reinterpret_cast<intptr_t>(zone_));
   }

   delete zone_;
 }

 }  // namespace dart
	// 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/leak_sanitizer.h"
	#include "platform/utils.h"
	#include "vm/dart_api_state.h"
	#include "vm/flags.h"
	#include "vm/handles_impl.h"
	#include "vm/heap/heap.h"
	#include "vm/os.h"
	#include "vm/virtual_memory.h"

	namespace dart {

	RelaxedAtomic<intptr_t> Zone::total_size_ = {0};

	// 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 Zone::Segment {
	public:
	Segment* next() const { return next_; }
	intptr_t size() const { return size_; }
	VirtualMemory* memory() const { return memory_; }

	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);
	static void IncrementMemoryCapacity(uintptr_t size);
	static void DecrementMemoryCapacity(uintptr_t size);

	private:
	Segment* next_;
	intptr_t size_;
	VirtualMemory* memory_;
	void* alignment_;

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

	DISALLOW_IMPLICIT_CONSTRUCTORS(Segment);
	};

	// tcmalloc and jemalloc have both been observed to hold onto lots of free'd
	// zone segments (jemalloc to the point of causing OOM), so instead of using
	// malloc to allocate segments, we allocate directly from mmap/zx_vmo_create/
	// VirtualAlloc, and cache a small number of the normal sized segments.
	static constexpr intptr_t kSegmentCacheCapacity = 16; // 1 MB of Segments
	static Mutex* segment_cache_mutex = nullptr;
	static VirtualMemory* segment_cache[kSegmentCacheCapacity] = {nullptr};
	static intptr_t segment_cache_size = 0;

	void Zone::Init() {
	ASSERT(segment_cache_mutex == nullptr);
	segment_cache_mutex = new Mutex(NOT_IN_PRODUCT("segment_cache_mutex"));
	}

	void Zone::Cleanup() {
	{
	MutexLocker ml(segment_cache_mutex);
	ASSERT(segment_cache_size >= 0);
	ASSERT(segment_cache_size <= kSegmentCacheCapacity);
	while (segment_cache_size > 0) {
	delete segment_cache[--segment_cache_size];
	}
	}
	delete segment_cache_mutex;
	segment_cache_mutex = nullptr;
	}

	Zone::Segment* Zone::Segment::New(intptr_t size, Zone::Segment* next) {
	size = Utils::RoundUp(size, VirtualMemory::PageSize());
	VirtualMemory* memory = nullptr;
	if (size == kSegmentSize) {
	MutexLocker ml(segment_cache_mutex);
	ASSERT(segment_cache_size >= 0);
	ASSERT(segment_cache_size <= kSegmentCacheCapacity);
	if (segment_cache_size > 0) {
	memory = segment_cache[--segment_cache_size];
	}
	}
	if (memory == nullptr) {
	memory = VirtualMemory::Allocate(size, false, "dart-zone");
	total_size_.fetch_add(size);
	}
	if (memory == nullptr) {
	OUT_OF_MEMORY();
	}
	Segment* result = reinterpret_cast<Segment*>(memory->start());
	#ifdef DEBUG
	// Zap the entire allocated segment (including the header).
	memset(reinterpret_cast<void*>(result), kZapUninitializedByte, size);
	#endif
	result->next_ = next;
	result->size_ = size;
	result->memory_ = memory;
	result->alignment_ = nullptr; // Avoid unused variable warnings.

	LSAN_REGISTER_ROOT_REGION(result, sizeof(*result));

	IncrementMemoryCapacity(size);
	return result;
	}

	void Zone::Segment::DeleteSegmentList(Segment* head) {
	Segment* current = head;
	while (current != NULL) {
	intptr_t size = current->size();
	DecrementMemoryCapacity(size);
	Segment* next = current->next();
	VirtualMemory* memory = current->memory();
	#ifdef DEBUG
	// Zap the entire current segment (including the header).
	memset(reinterpret_cast<void*>(current), kZapDeletedByte, current->size());
	#endif
	LSAN_UNREGISTER_ROOT_REGION(current, sizeof(*current));

	if (size == kSegmentSize) {
	MutexLocker ml(segment_cache_mutex);
	ASSERT(segment_cache_size >= 0);
	ASSERT(segment_cache_size <= kSegmentCacheCapacity);
	if (segment_cache_size < kSegmentCacheCapacity) {
	segment_cache[segment_cache_size++] = memory;
	memory = nullptr;
	}
	}
	if (memory != nullptr) {
	total_size_.fetch_sub(size);
	delete memory;
	}
	current = next;
	}
	}

	void Zone::Segment::IncrementMemoryCapacity(uintptr_t size) {
	ThreadState* current_thread = ThreadState::Current();
	if (current_thread != NULL) {
	current_thread->IncrementMemoryCapacity(size);
	} else if (ApiNativeScope::Current() != NULL) {
	// If there is no current thread, we might be inside of a native scope.
	ApiNativeScope::IncrementNativeScopeMemoryCapacity(size);
	}
	}

	void Zone::Segment::DecrementMemoryCapacity(uintptr_t size) {
	ThreadState* current_thread = ThreadState::Current();
	if (current_thread != NULL) {
	current_thread->DecrementMemoryCapacity(size);
	} else if (ApiNativeScope::Current() != NULL) {
	// If there is no current thread, we might be inside of a native scope.
	ApiNativeScope::DecrementNativeScopeMemoryCapacity(size);
	}
	}

	// TODO(bkonyi): We need to account for the initial chunk size when a new zone
	// is created within a new thread or ApiNativeScope when calculating high
	// watermarks or memory consumption.
	Zone::Zone()
	: initial_buffer_(buffer_, kInitialChunkSize),
	position_(initial_buffer_.start()),
	limit_(initial_buffer_.end()),
	head_(NULL),
	large_segments_(NULL),
	handles_(),
	previous_(NULL) {
	ASSERT(Utils::IsAligned(position_, kAlignment));
	Segment::IncrementMemoryCapacity(kInitialChunkSize);
	#ifdef DEBUG
	// Zap the entire initial buffer.
	memset(initial_buffer_.pointer(), kZapUninitializedByte,
	initial_buffer_.size());
	#endif
	}

	Zone::~Zone() {
	if (FLAG_trace_zones) {
	DumpZoneSizes();
	}
	DeleteAll();
	Segment::DecrementMemoryCapacity(kInitialChunkSize);
	}

	void Zone::DeleteAll() {
	// Traverse the chained list of segments, zapping (in debug mode)
	// and freeing every zone segment.
	if (head_ != NULL) {
	Segment::DeleteSegmentList(head_);
	}
	if (large_segments_ != NULL) {
	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();
	small_segment_capacity_ = 0;
	head_ = NULL;
	large_segments_ = NULL;
	previous_ = NULL;
	handles_.Reset();
	}

	uintptr_t Zone::SizeInBytes() const {
	uintptr_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());
	}

	uintptr_t Zone::CapacityInBytes() const {
	uintptr_t size = 0;
	for (Segment* s = large_segments_; s != NULL; s = s->next()) {
	size += s->size();
	}
	if (head_ == NULL) {
	return size + initial_buffer_.size();
	}
	size += initial_buffer_.size();
	for (Segment* s = head_; s != NULL; s = s->next()) {
	size += s->size();
	}
	return size;
	}

	uword Zone::AllocateExpand(intptr_t size) {
	ASSERT(size >= 0);
	if (FLAG_trace_zones) {
	OS::PrintErr("*** Expanding zone 0x%" Px "\n",
	reinterpret_cast<intptr_t>(this));
	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);

	// 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);
	}

	const intptr_t kSuperPageSize = 2 * MB;
	intptr_t next_size;
	if (small_segment_capacity_ < kSuperPageSize) {
	// When the Zone is small, grow linearly to reduce size and use the segment
	// cache to avoid expensive mmap calls.
	next_size = kSegmentSize;
	} else {
	// When the Zone is large, grow geometrically to avoid Page Table Entry
	// exhaustion. Using 1.125 ratio.
	next_size = Utils::RoundUp(small_segment_capacity_ >> 3, kSuperPageSize);
	}
	ASSERT(next_size >= kSegmentSize);

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

	// 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 Zone::AllocateLargeSegment(intptr_t size) {
	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);

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

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

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

	char* Zone::MakeCopyOfStringN(const char* str, intptr_t len) {
	ASSERT(len >= 0);
	for (intptr_t i = 0; i < len; i++) {
	if (str[i] == '\0') {
	len = i;
	break;
	}
	}
	char* copy = Alloc<char>(len + 1); // +1 for '\0'
	strncpy(copy, str, len);
	copy[len] = '\0';
	return copy;
	}

	char* Zone::ConcatStrings(const char* a, const char* b, char join) {
	intptr_t a_len = (a == NULL) ? 0 : strlen(a);
	const intptr_t b_len = strlen(b) + 1; // '\0'-terminated.
	const intptr_t len = a_len + b_len;
	char* copy = Alloc<char>(len);
	if (a_len > 0) {
	strncpy(copy, a, a_len);
	// Insert join character.
	copy[a_len++] = join;
	}
	strncpy(&copy[a_len], b, b_len);
	return copy;
	}

	void Zone::DumpZoneSizes() {
	intptr_t size = 0;
	for (Segment* s = large_segments_; s != NULL; s = s->next()) {
	size += s->size();
	}
	OS::PrintErr("*** Zone(0x%" Px
	") size in bytes,"
	" Total = %" Pd " Large Segments = %" Pd "\n",
	reinterpret_cast<intptr_t>(this), SizeInBytes(), size);
	}

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

	char* Zone::PrintToString(const char* format, ...) {
	va_list args;
	va_start(args, format);
	char* buffer = OS::VSCreate(this, format, args);
	va_end(args);
	return buffer;
	}

	char* Zone::VPrint(const char* format, va_list args) {
	return OS::VSCreate(this, format, args);
	}

	StackZone::StackZone(ThreadState* thread)
	: StackResource(thread), zone_(new Zone()) {
	if (FLAG_trace_zones) {
	OS::PrintErr("*** Starting a new Stack zone 0x%" Px "(0x%" Px ")\n",
	reinterpret_cast<intptr_t>(this),
	reinterpret_cast<intptr_t>(zone_));
	}

	// This thread must be preventing safepoints or the GC could be visiting the
	// chain of handle blocks we're about the mutate.
	ASSERT(Thread::Current()->MayAllocateHandles());

	zone_->Link(thread->zone());
	thread->set_zone(zone_);
	}

	StackZone::~StackZone() {
	// This thread must be preventing safepoints or the GC could be visiting the
	// chain of handle blocks we're about the mutate.
	ASSERT(Thread::Current()->MayAllocateHandles());

	ASSERT(thread()->zone() == zone_);
	thread()->set_zone(zone_->previous_);
	if (FLAG_trace_zones) {
	OS::PrintErr("*** Deleting Stack zone 0x%" Px "(0x%" Px ")\n",
	reinterpret_cast<intptr_t>(this),
	reinterpret_cast<intptr_t>(zone_));
	}

	delete zone_;
	}

	} // namespace dart