gin/v8_platform.cc - chromium/src - Git at Google

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "gin/public/v8_platform.h"

 #include <algorithm>

 #include "base/allocator/partition_allocator/address_space_randomization.h"
 #include "base/allocator/partition_allocator/page_allocator.h"
 #include "base/allocator/partition_allocator/random.h"
 #include "base/bind.h"
 #include "base/bit_cast.h"
 #include "base/bits.h"
 #include "base/debug/stack_trace.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/system/sys_info.h"
 #include "base/task/post_task.h"
 #include "base/task/task_traits.h"
 #include "base/task/thread_pool/thread_pool_instance.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
 #include "gin/per_isolate_data.h"

 namespace gin {

 namespace {

 base::LazyInstance<V8Platform>::Leaky g_v8_platform = LAZY_INSTANCE_INITIALIZER;

 constexpr base::TaskTraits kLowPriorityTaskTraits = {
     base::ThreadPool(), base::TaskPriority::BEST_EFFORT};

 constexpr base::TaskTraits kDefaultTaskTraits = {
     base::ThreadPool(), base::TaskPriority::USER_VISIBLE};

 constexpr base::TaskTraits kBlockingTaskTraits = {
     base::ThreadPool(), base::TaskPriority::USER_BLOCKING};

 void PrintStackTrace() {
   base::debug::StackTrace trace;
   trace.Print();
 }

 class ConvertableToTraceFormatWrapper final
     : public base::trace_event::ConvertableToTraceFormat {
  public:
   explicit ConvertableToTraceFormatWrapper(
       std::unique_ptr<v8::ConvertableToTraceFormat> inner)
       : inner_(std::move(inner)) {}
   ~ConvertableToTraceFormatWrapper() override = default;
   void AppendAsTraceFormat(std::string* out) const final {
     inner_->AppendAsTraceFormat(out);
   }

  private:
   std::unique_ptr<v8::ConvertableToTraceFormat> inner_;

   DISALLOW_COPY_AND_ASSIGN(ConvertableToTraceFormatWrapper);
 };

 class EnabledStateObserverImpl final
     : public base::trace_event::TraceLog::EnabledStateObserver {
  public:
   EnabledStateObserverImpl() {
     base::trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(this);
   }

   ~EnabledStateObserverImpl() override {
     base::trace_event::TraceLog::GetInstance()->RemoveEnabledStateObserver(
         this);
   }

   void OnTraceLogEnabled() final {
     base::AutoLock lock(mutex_);
     for (auto* o : observers_) {
       o->OnTraceEnabled();
     }
   }

   void OnTraceLogDisabled() final {
     base::AutoLock lock(mutex_);
     for (auto* o : observers_) {
       o->OnTraceDisabled();
     }
   }

   void AddObserver(v8::TracingController::TraceStateObserver* observer) {
     {
       base::AutoLock lock(mutex_);
       DCHECK(!observers_.count(observer));
       observers_.insert(observer);
     }

     // Fire the observer if recording is already in progress.
     if (base::trace_event::TraceLog::GetInstance()->IsEnabled())
       observer->OnTraceEnabled();
   }

   void RemoveObserver(v8::TracingController::TraceStateObserver* observer) {
     base::AutoLock lock(mutex_);
     DCHECK(observers_.count(observer) == 1);
     observers_.erase(observer);
   }

  private:
   base::Lock mutex_;
   std::unordered_set<v8::TracingController::TraceStateObserver*> observers_;

   DISALLOW_COPY_AND_ASSIGN(EnabledStateObserverImpl);
 };

 base::LazyInstance<EnabledStateObserverImpl>::Leaky g_trace_state_dispatcher =
     LAZY_INSTANCE_INITIALIZER;

 // TODO(skyostil): Deduplicate this with the clamper in Blink.
 class TimeClamper {
  public:
 // As site isolation is enabled on desktop platforms, we can safely provide
 // more timing resolution. Jittering is still enabled everywhere.
 #if defined(OS_ANDROID)
   static constexpr double kResolutionSeconds = 100e-6;
 #else
   static constexpr double kResolutionSeconds = 5e-6;
 #endif

   TimeClamper() : secret_(base::RandUint64()) {}

   double ClampTimeResolution(double time_seconds) const {
     bool was_negative = false;
     if (time_seconds < 0) {
       was_negative = true;
       time_seconds = -time_seconds;
     }
     // For each clamped time interval, compute a pseudorandom transition
     // threshold. The reported time will either be the start of that interval or
     // the next one depending on which side of the threshold |time_seconds| is.
     double interval = floor(time_seconds / kResolutionSeconds);
     double clamped_time = interval * kResolutionSeconds;
     double tick_threshold = ThresholdFor(clamped_time);

     if (time_seconds >= tick_threshold)
       clamped_time = (interval + 1) * kResolutionSeconds;
     if (was_negative)
       clamped_time = -clamped_time;
     return clamped_time;
   }

  private:
   inline double ThresholdFor(double clamped_time) const {
     uint64_t time_hash = MurmurHash3(bit_cast<int64_t>(clamped_time) ^ secret_);
     return clamped_time + kResolutionSeconds * ToDouble(time_hash);
   }

   static inline double ToDouble(uint64_t value) {
     // Exponent for double values for [1.0 .. 2.0]
     static const uint64_t kExponentBits = uint64_t{0x3FF0000000000000};
     static const uint64_t kMantissaMask = uint64_t{0x000FFFFFFFFFFFFF};
     uint64_t random = (value & kMantissaMask) | kExponentBits;
     return bit_cast<double>(random) - 1;
   }

   static inline uint64_t MurmurHash3(uint64_t value) {
     value ^= value >> 33;
     value *= uint64_t{0xFF51AFD7ED558CCD};
     value ^= value >> 33;
     value *= uint64_t{0xC4CEB9FE1A85EC53};
     value ^= value >> 33;
     return value;
   }

   const uint64_t secret_;
   DISALLOW_COPY_AND_ASSIGN(TimeClamper);
 };

 base::LazyInstance<TimeClamper>::Leaky g_time_clamper =
     LAZY_INSTANCE_INITIALIZER;

 #if BUILDFLAG(USE_PARTITION_ALLOC)
 base::PageAccessibilityConfiguration GetPageConfig(
     v8::PageAllocator::Permission permission) {
   switch (permission) {
     case v8::PageAllocator::Permission::kRead:
       return base::PageRead;
     case v8::PageAllocator::Permission::kReadWrite:
       return base::PageReadWrite;
     case v8::PageAllocator::Permission::kReadWriteExecute:
       return base::PageReadWriteExecute;
     case v8::PageAllocator::Permission::kReadExecute:
       return base::PageReadExecute;
     default:
       DCHECK_EQ(v8::PageAllocator::Permission::kNoAccess, permission);
       return base::PageInaccessible;
   }
 }

 class PageAllocator : public v8::PageAllocator {
  public:
   ~PageAllocator() override = default;

   size_t AllocatePageSize() override {
     return base::kPageAllocationGranularity;
   }

   size_t CommitPageSize() override { return base::kSystemPageSize; }

   void SetRandomMmapSeed(int64_t seed) override {
     base::SetMmapSeedForTesting(seed);
   }

   void* GetRandomMmapAddr() override { return base::GetRandomPageBase(); }

   void* AllocatePages(void* address,
                       size_t length,
                       size_t alignment,
                       v8::PageAllocator::Permission permissions) override {
     base::PageAccessibilityConfiguration config = GetPageConfig(permissions);
     bool commit = (permissions != v8::PageAllocator::Permission::kNoAccess);
     return base::AllocPages(address, length, alignment, config,
                             base::PageTag::kV8, commit);
   }

   bool FreePages(void* address, size_t length) override {
     base::FreePages(address, length);
     return true;
   }

   bool ReleasePages(void* address, size_t length, size_t new_length) override {
     DCHECK_LT(new_length, length);
     uint8_t* release_base = reinterpret_cast<uint8_t*>(address) + new_length;
     size_t release_size = length - new_length;
 #if defined(OS_POSIX) || defined(OS_FUCHSIA)
     // On POSIX, we can unmap the trailing pages.
     base::FreePages(release_base, release_size);
 #elif defined(OS_WIN)
     // On Windows, we can only de-commit the trailing pages. FreePages() will
     // still free all pages in the region including the released tail, so it's
     // safe to just decommit the tail.
     base::DecommitSystemPages(release_base, release_size);
 #else
 #error Unsupported platform
 #endif
     return true;
   }

   bool SetPermissions(void* address,
                       size_t length,
                       Permission permissions) override {
     // If V8 sets permissions to none, we can discard the memory.
     if (permissions == v8::PageAllocator::Permission::kNoAccess) {
       base::DecommitSystemPages(address, length);
       return true;
     } else {
       return base::TrySetSystemPagesAccess(address, length,
                                            GetPageConfig(permissions));
     }
   }

   bool DiscardSystemPages(void* address, size_t size) override {
     base::DiscardSystemPages(address, size);
     return true;
   }
 };

 base::LazyInstance<PageAllocator>::Leaky g_page_allocator =
     LAZY_INSTANCE_INITIALIZER;

 #endif  // BUILDFLAG(USE_PARTITION_ALLOC)

 }  // namespace

 }  // namespace gin

 // Allow std::unique_ptr<v8::ConvertableToTraceFormat> to be a valid
 // initialization value for trace macros.
 template <>
 struct base::trace_event::TraceValue::Helper<
     std::unique_ptr<v8::ConvertableToTraceFormat>> {
   static constexpr unsigned char kType = TRACE_VALUE_TYPE_CONVERTABLE;
   static inline void SetValue(
       TraceValue* v,
       std::unique_ptr<v8::ConvertableToTraceFormat> value) {
     // NOTE: |as_convertable| is an owning pointer, so using new here
     // is acceptable.
     v->as_convertable =
         new gin::ConvertableToTraceFormatWrapper(std::move(value));
   }
 };

 namespace gin {

 class V8Platform::TracingControllerImpl : public v8::TracingController {
  public:
   TracingControllerImpl() = default;
   ~TracingControllerImpl() override = default;

   // TracingController implementation.
   const uint8_t* GetCategoryGroupEnabled(const char* name) override {
     return TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(name);
   }
   uint64_t AddTraceEvent(
       char phase,
       const uint8_t* category_enabled_flag,
       const char* name,
       const char* scope,
       uint64_t id,
       uint64_t bind_id,
       int32_t num_args,
       const char** arg_names,
       const uint8_t* arg_types,
       const uint64_t* arg_values,
       std::unique_ptr<v8::ConvertableToTraceFormat>* arg_convertables,
       unsigned int flags) override {
     base::trace_event::TraceArguments args(
         num_args, arg_names, arg_types,
         reinterpret_cast<const unsigned long long*>(arg_values),
         arg_convertables);
     DCHECK_LE(num_args, 2);
     base::trace_event::TraceEventHandle handle =
         TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_BIND_ID(
             phase, category_enabled_flag, name, scope, id, bind_id, &args,
             flags);
     uint64_t result;
     memcpy(&result, &handle, sizeof(result));
     return result;
   }
   uint64_t AddTraceEventWithTimestamp(
       char phase,
       const uint8_t* category_enabled_flag,
       const char* name,
       const char* scope,
       uint64_t id,
       uint64_t bind_id,
       int32_t num_args,
       const char** arg_names,
       const uint8_t* arg_types,
       const uint64_t* arg_values,
       std::unique_ptr<v8::ConvertableToTraceFormat>* arg_convertables,
       unsigned int flags,
       int64_t timestampMicroseconds) override {
     base::trace_event::TraceArguments args(
         num_args, arg_names, arg_types,
         reinterpret_cast<const unsigned long long*>(arg_values),
         arg_convertables);
     DCHECK_LE(num_args, 2);
     base::TimeTicks timestamp =
         base::TimeTicks() +
         base::TimeDelta::FromMicroseconds(timestampMicroseconds);
     base::trace_event::TraceEventHandle handle =
         TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_THREAD_ID_AND_TIMESTAMP(
             phase, category_enabled_flag, name, scope, id, bind_id,
             TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, &args, flags);
     uint64_t result;
     memcpy(&result, &handle, sizeof(result));
     return result;
   }
   void UpdateTraceEventDuration(const uint8_t* category_enabled_flag,
                                 const char* name,
                                 uint64_t handle) override {
     base::trace_event::TraceEventHandle traceEventHandle;
     memcpy(&traceEventHandle, &handle, sizeof(handle));
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_enabled_flag, name,
                                                 traceEventHandle);
   }
   void AddTraceStateObserver(TraceStateObserver* observer) override {
     g_trace_state_dispatcher.Get().AddObserver(observer);
   }
   void RemoveTraceStateObserver(TraceStateObserver* observer) override {
     g_trace_state_dispatcher.Get().RemoveObserver(observer);
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(TracingControllerImpl);
 };

 // static
 V8Platform* V8Platform::Get() { return g_v8_platform.Pointer(); }

 V8Platform::V8Platform() : tracing_controller_(new TracingControllerImpl) {}

 V8Platform::~V8Platform() = default;

 #if BUILDFLAG(USE_PARTITION_ALLOC)
 v8::PageAllocator* V8Platform::GetPageAllocator() {
   return g_page_allocator.Pointer();
 }

 void V8Platform::OnCriticalMemoryPressure() {
 // We only have a reservation on 32-bit Windows systems.
 // TODO(bbudge) Make the #if's in BlinkInitializer match.
 #if defined(OS_WIN) && defined(ARCH_CPU_32_BITS)
   base::ReleaseReservation();
 #endif
 }
 #endif  // BUILDFLAG(USE_PARTITION_ALLOC)

 std::shared_ptr<v8::TaskRunner> V8Platform::GetForegroundTaskRunner(
     v8::Isolate* isolate) {
   PerIsolateData* data = PerIsolateData::From(isolate);
   return data->task_runner();
 }

 int V8Platform::NumberOfWorkerThreads() {
   // V8Platform assumes the scheduler uses the same set of workers for default
   // and user blocking tasks.
   const int num_foreground_workers =
       base::ThreadPoolInstance::Get()
           ->GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated(
               kDefaultTaskTraits);
   DCHECK_EQ(num_foreground_workers,
             base::ThreadPoolInstance::Get()
                 ->GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated(
                     kBlockingTaskTraits));
   return std::max(1, num_foreground_workers);
 }

 void V8Platform::CallOnWorkerThread(std::unique_ptr<v8::Task> task) {
   base::PostTask(FROM_HERE, kDefaultTaskTraits,
                  base::BindOnce(&v8::Task::Run, std::move(task)));
 }

 void V8Platform::CallBlockingTaskOnWorkerThread(
     std::unique_ptr<v8::Task> task) {
   base::PostTask(FROM_HERE, kBlockingTaskTraits,
                  base::BindOnce(&v8::Task::Run, std::move(task)));
 }

 void V8Platform::CallLowPriorityTaskOnWorkerThread(
     std::unique_ptr<v8::Task> task) {
   base::PostTask(FROM_HERE, kLowPriorityTaskTraits,
                  base::BindOnce(&v8::Task::Run, std::move(task)));
 }

 void V8Platform::CallDelayedOnWorkerThread(std::unique_ptr<v8::Task> task,
                                            double delay_in_seconds) {
   base::PostDelayedTask(FROM_HERE, kDefaultTaskTraits,
                         base::BindOnce(&v8::Task::Run, std::move(task)),
                         base::TimeDelta::FromSecondsD(delay_in_seconds));
 }

 void V8Platform::CallOnForegroundThread(v8::Isolate* isolate, v8::Task* task) {
   PerIsolateData* data = PerIsolateData::From(isolate);
   data->task_runner()->PostTask(std::unique_ptr<v8::Task>(task));
 }

 void V8Platform::CallDelayedOnForegroundThread(v8::Isolate* isolate,
                                                v8::Task* task,
                                                double delay_in_seconds) {
   PerIsolateData* data = PerIsolateData::From(isolate);
   data->task_runner()->PostDelayedTask(std::unique_ptr<v8::Task>(task),
                                        delay_in_seconds);
 }

 void V8Platform::CallIdleOnForegroundThread(v8::Isolate* isolate,
                                             v8::IdleTask* task) {
   PerIsolateData* data = PerIsolateData::From(isolate);
   data->task_runner()->PostIdleTask(std::unique_ptr<v8::IdleTask>(task));
 }

 bool V8Platform::IdleTasksEnabled(v8::Isolate* isolate) {
   return PerIsolateData::From(isolate)->task_runner()->IdleTasksEnabled();
 }

 double V8Platform::MonotonicallyIncreasingTime() {
   return base::TimeTicks::Now().ToInternalValue() /
       static_cast<double>(base::Time::kMicrosecondsPerSecond);
 }

 double V8Platform::CurrentClockTimeMillis() {
   double now_seconds = base::Time::Now().ToJsTime() / 1000;
   return g_time_clamper.Get().ClampTimeResolution(now_seconds) * 1000;
 }

 v8::TracingController* V8Platform::GetTracingController() {
   return tracing_controller_.get();
 }

 v8::Platform::StackTracePrinter V8Platform::GetStackTracePrinter() {
   return PrintStackTrace;
 }

 }  // namespace gin
	// Copyright 2014 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "gin/public/v8_platform.h"

	#include <algorithm>

	#include "base/allocator/partition_allocator/address_space_randomization.h"
	#include "base/allocator/partition_allocator/page_allocator.h"
	#include "base/allocator/partition_allocator/random.h"
	#include "base/bind.h"
	#include "base/bit_cast.h"
	#include "base/bits.h"
	#include "base/debug/stack_trace.h"
	#include "base/location.h"
	#include "base/logging.h"
	#include "base/rand_util.h"
	#include "base/system/sys_info.h"
	#include "base/task/post_task.h"
	#include "base/task/task_traits.h"
	#include "base/task/thread_pool/thread_pool_instance.h"
	#include "base/trace_event/trace_event.h"
	#include "build/build_config.h"
	#include "gin/per_isolate_data.h"

	namespace gin {

	namespace {

	base::LazyInstance<V8Platform>::Leaky g_v8_platform = LAZY_INSTANCE_INITIALIZER;

	constexpr base::TaskTraits kLowPriorityTaskTraits = {
	base::ThreadPool(), base::TaskPriority::BEST_EFFORT};

	constexpr base::TaskTraits kDefaultTaskTraits = {
	base::ThreadPool(), base::TaskPriority::USER_VISIBLE};

	constexpr base::TaskTraits kBlockingTaskTraits = {
	base::ThreadPool(), base::TaskPriority::USER_BLOCKING};

	void PrintStackTrace() {
	base::debug::StackTrace trace;
	trace.Print();
	}

	class ConvertableToTraceFormatWrapper final
	: public base::trace_event::ConvertableToTraceFormat {
	public:
	explicit ConvertableToTraceFormatWrapper(
	std::unique_ptr<v8::ConvertableToTraceFormat> inner)
	: inner_(std::move(inner)) {}
	~ConvertableToTraceFormatWrapper() override = default;
	void AppendAsTraceFormat(std::string* out) const final {
	inner_->AppendAsTraceFormat(out);
	}

	private:
	std::unique_ptr<v8::ConvertableToTraceFormat> inner_;

	DISALLOW_COPY_AND_ASSIGN(ConvertableToTraceFormatWrapper);
	};

	class EnabledStateObserverImpl final
	: public base::trace_event::TraceLog::EnabledStateObserver {
	public:
	EnabledStateObserverImpl() {
	base::trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(this);
	}

	~EnabledStateObserverImpl() override {
	base::trace_event::TraceLog::GetInstance()->RemoveEnabledStateObserver(
	this);
	}

	void OnTraceLogEnabled() final {
	base::AutoLock lock(mutex_);
	for (auto* o : observers_) {
	o->OnTraceEnabled();
	}
	}

	void OnTraceLogDisabled() final {
	base::AutoLock lock(mutex_);
	for (auto* o : observers_) {
	o->OnTraceDisabled();
	}
	}

	void AddObserver(v8::TracingController::TraceStateObserver* observer) {
	{
	base::AutoLock lock(mutex_);
	DCHECK(!observers_.count(observer));
	observers_.insert(observer);
	}

	// Fire the observer if recording is already in progress.
	if (base::trace_event::TraceLog::GetInstance()->IsEnabled())
	observer->OnTraceEnabled();
	}

	void RemoveObserver(v8::TracingController::TraceStateObserver* observer) {
	base::AutoLock lock(mutex_);
	DCHECK(observers_.count(observer) == 1);
	observers_.erase(observer);
	}

	private:
	base::Lock mutex_;
	std::unordered_set<v8::TracingController::TraceStateObserver*> observers_;

	DISALLOW_COPY_AND_ASSIGN(EnabledStateObserverImpl);
	};

	base::LazyInstance<EnabledStateObserverImpl>::Leaky g_trace_state_dispatcher =
	LAZY_INSTANCE_INITIALIZER;

	// TODO(skyostil): Deduplicate this with the clamper in Blink.
	class TimeClamper {
	public:
	// As site isolation is enabled on desktop platforms, we can safely provide
	// more timing resolution. Jittering is still enabled everywhere.
	#if defined(OS_ANDROID)
	static constexpr double kResolutionSeconds = 100e-6;
	#else
	static constexpr double kResolutionSeconds = 5e-6;
	#endif

	TimeClamper() : secret_(base::RandUint64()) {}

	double ClampTimeResolution(double time_seconds) const {
	bool was_negative = false;
	if (time_seconds < 0) {
	was_negative = true;
	time_seconds = -time_seconds;
	}
	// For each clamped time interval, compute a pseudorandom transition
	// threshold. The reported time will either be the start of that interval or
	// the next one depending on which side of the threshold \|time_seconds\| is.
	double interval = floor(time_seconds / kResolutionSeconds);
	double clamped_time = interval * kResolutionSeconds;
	double tick_threshold = ThresholdFor(clamped_time);

	if (time_seconds >= tick_threshold)
	clamped_time = (interval + 1) * kResolutionSeconds;
	if (was_negative)
	clamped_time = -clamped_time;
	return clamped_time;
	}

	private:
	inline double ThresholdFor(double clamped_time) const {
	uint64_t time_hash = MurmurHash3(bit_cast<int64_t>(clamped_time) ^ secret_);
	return clamped_time + kResolutionSeconds * ToDouble(time_hash);
	}

	static inline double ToDouble(uint64_t value) {
	// Exponent for double values for [1.0 .. 2.0]
	static const uint64_t kExponentBits = uint64_t{0x3FF0000000000000};
	static const uint64_t kMantissaMask = uint64_t{0x000FFFFFFFFFFFFF};
	uint64_t random = (value & kMantissaMask) \| kExponentBits;
	return bit_cast<double>(random) - 1;
	}

	static inline uint64_t MurmurHash3(uint64_t value) {
	value ^= value >> 33;
	value *= uint64_t{0xFF51AFD7ED558CCD};
	value ^= value >> 33;
	value *= uint64_t{0xC4CEB9FE1A85EC53};
	value ^= value >> 33;
	return value;
	}

	const uint64_t secret_;
	DISALLOW_COPY_AND_ASSIGN(TimeClamper);
	};

	base::LazyInstance<TimeClamper>::Leaky g_time_clamper =
	LAZY_INSTANCE_INITIALIZER;

	#if BUILDFLAG(USE_PARTITION_ALLOC)
	base::PageAccessibilityConfiguration GetPageConfig(
	v8::PageAllocator::Permission permission) {
	switch (permission) {
	case v8::PageAllocator::Permission::kRead:
	return base::PageRead;
	case v8::PageAllocator::Permission::kReadWrite:
	return base::PageReadWrite;
	case v8::PageAllocator::Permission::kReadWriteExecute:
	return base::PageReadWriteExecute;
	case v8::PageAllocator::Permission::kReadExecute:
	return base::PageReadExecute;
	default:
	DCHECK_EQ(v8::PageAllocator::Permission::kNoAccess, permission);
	return base::PageInaccessible;
	}
	}

	class PageAllocator : public v8::PageAllocator {
	public:
	~PageAllocator() override = default;

	size_t AllocatePageSize() override {
	return base::kPageAllocationGranularity;
	}

	size_t CommitPageSize() override { return base::kSystemPageSize; }

	void SetRandomMmapSeed(int64_t seed) override {
	base::SetMmapSeedForTesting(seed);
	}

	void* GetRandomMmapAddr() override { return base::GetRandomPageBase(); }

	void* AllocatePages(void* address,
	size_t length,
	size_t alignment,
	v8::PageAllocator::Permission permissions) override {
	base::PageAccessibilityConfiguration config = GetPageConfig(permissions);
	bool commit = (permissions != v8::PageAllocator::Permission::kNoAccess);
	return base::AllocPages(address, length, alignment, config,
	base::PageTag::kV8, commit);
	}

	bool FreePages(void* address, size_t length) override {
	base::FreePages(address, length);
	return true;
	}

	bool ReleasePages(void* address, size_t length, size_t new_length) override {
	DCHECK_LT(new_length, length);
	uint8_t* release_base = reinterpret_cast<uint8_t*>(address) + new_length;
	size_t release_size = length - new_length;
	#if defined(OS_POSIX) \|\| defined(OS_FUCHSIA)
	// On POSIX, we can unmap the trailing pages.
	base::FreePages(release_base, release_size);
	#elif defined(OS_WIN)
	// On Windows, we can only de-commit the trailing pages. FreePages() will
	// still free all pages in the region including the released tail, so it's
	// safe to just decommit the tail.
	base::DecommitSystemPages(release_base, release_size);
	#else
	#error Unsupported platform
	#endif
	return true;
	}

	bool SetPermissions(void* address,
	size_t length,
	Permission permissions) override {
	// If V8 sets permissions to none, we can discard the memory.
	if (permissions == v8::PageAllocator::Permission::kNoAccess) {
	base::DecommitSystemPages(address, length);
	return true;
	} else {
	return base::TrySetSystemPagesAccess(address, length,
	GetPageConfig(permissions));
	}
	}

	bool DiscardSystemPages(void* address, size_t size) override {
	base::DiscardSystemPages(address, size);
	return true;
	}
	};

	base::LazyInstance<PageAllocator>::Leaky g_page_allocator =
	LAZY_INSTANCE_INITIALIZER;

	#endif // BUILDFLAG(USE_PARTITION_ALLOC)

	} // namespace

	} // namespace gin

	// Allow std::unique_ptr<v8::ConvertableToTraceFormat> to be a valid
	// initialization value for trace macros.
	template <>
	struct base::trace_event::TraceValue::Helper<
	std::unique_ptr<v8::ConvertableToTraceFormat>> {
	static constexpr unsigned char kType = TRACE_VALUE_TYPE_CONVERTABLE;
	static inline void SetValue(
	TraceValue* v,
	std::unique_ptr<v8::ConvertableToTraceFormat> value) {
	// NOTE: \|as_convertable\| is an owning pointer, so using new here
	// is acceptable.
	v->as_convertable =
	new gin::ConvertableToTraceFormatWrapper(std::move(value));
	}
	};

	namespace gin {

	class V8Platform::TracingControllerImpl : public v8::TracingController {
	public:
	TracingControllerImpl() = default;
	~TracingControllerImpl() override = default;

	// TracingController implementation.
	const uint8_t* GetCategoryGroupEnabled(const char* name) override {
	return TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(name);
	}
	uint64_t AddTraceEvent(
	char phase,
	const uint8_t* category_enabled_flag,
	const char* name,
	const char* scope,
	uint64_t id,
	uint64_t bind_id,
	int32_t num_args,
	const char** arg_names,
	const uint8_t* arg_types,
	const uint64_t* arg_values,
	std::unique_ptr<v8::ConvertableToTraceFormat>* arg_convertables,
	unsigned int flags) override {
	base::trace_event::TraceArguments args(
	num_args, arg_names, arg_types,
	reinterpret_cast<const unsigned long long*>(arg_values),
	arg_convertables);
	DCHECK_LE(num_args, 2);
	base::trace_event::TraceEventHandle handle =
	TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_BIND_ID(
	phase, category_enabled_flag, name, scope, id, bind_id, &args,
	flags);
	uint64_t result;
	memcpy(&result, &handle, sizeof(result));
	return result;
	}
	uint64_t AddTraceEventWithTimestamp(
	char phase,
	const uint8_t* category_enabled_flag,
	const char* name,
	const char* scope,
	uint64_t id,
	uint64_t bind_id,
	int32_t num_args,
	const char** arg_names,
	const uint8_t* arg_types,
	const uint64_t* arg_values,
	std::unique_ptr<v8::ConvertableToTraceFormat>* arg_convertables,
	unsigned int flags,
	int64_t timestampMicroseconds) override {
	base::trace_event::TraceArguments args(
	num_args, arg_names, arg_types,
	reinterpret_cast<const unsigned long long*>(arg_values),
	arg_convertables);
	DCHECK_LE(num_args, 2);
	base::TimeTicks timestamp =
	base::TimeTicks() +
	base::TimeDelta::FromMicroseconds(timestampMicroseconds);
	base::trace_event::TraceEventHandle handle =
	TRACE_EVENT_API_ADD_TRACE_EVENT_WITH_THREAD_ID_AND_TIMESTAMP(
	phase, category_enabled_flag, name, scope, id, bind_id,
	TRACE_EVENT_API_CURRENT_THREAD_ID, timestamp, &args, flags);
	uint64_t result;
	memcpy(&result, &handle, sizeof(result));
	return result;
	}
	void UpdateTraceEventDuration(const uint8_t* category_enabled_flag,
	const char* name,
	uint64_t handle) override {
	base::trace_event::TraceEventHandle traceEventHandle;
	memcpy(&traceEventHandle, &handle, sizeof(handle));
	TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_enabled_flag, name,
	traceEventHandle);
	}
	void AddTraceStateObserver(TraceStateObserver* observer) override {
	g_trace_state_dispatcher.Get().AddObserver(observer);
	}
	void RemoveTraceStateObserver(TraceStateObserver* observer) override {
	g_trace_state_dispatcher.Get().RemoveObserver(observer);
	}

	private:
	DISALLOW_COPY_AND_ASSIGN(TracingControllerImpl);
	};

	// static
	V8Platform* V8Platform::Get() { return g_v8_platform.Pointer(); }

	V8Platform::V8Platform() : tracing_controller_(new TracingControllerImpl) {}

	V8Platform::~V8Platform() = default;

	#if BUILDFLAG(USE_PARTITION_ALLOC)
	v8::PageAllocator* V8Platform::GetPageAllocator() {
	return g_page_allocator.Pointer();
	}

	void V8Platform::OnCriticalMemoryPressure() {
	// We only have a reservation on 32-bit Windows systems.
	// TODO(bbudge) Make the #if's in BlinkInitializer match.
	#if defined(OS_WIN) && defined(ARCH_CPU_32_BITS)
	base::ReleaseReservation();
	#endif
	}
	#endif // BUILDFLAG(USE_PARTITION_ALLOC)

	std::shared_ptr<v8::TaskRunner> V8Platform::GetForegroundTaskRunner(
	v8::Isolate* isolate) {
	PerIsolateData* data = PerIsolateData::From(isolate);
	return data->task_runner();
	}

	int V8Platform::NumberOfWorkerThreads() {
	// V8Platform assumes the scheduler uses the same set of workers for default
	// and user blocking tasks.
	const int num_foreground_workers =
	base::ThreadPoolInstance::Get()
	->GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated(
	kDefaultTaskTraits);
	DCHECK_EQ(num_foreground_workers,
	base::ThreadPoolInstance::Get()
	->GetMaxConcurrentNonBlockedTasksWithTraitsDeprecated(
	kBlockingTaskTraits));
	return std::max(1, num_foreground_workers);
	}

	void V8Platform::CallOnWorkerThread(std::unique_ptr<v8::Task> task) {
	base::PostTask(FROM_HERE, kDefaultTaskTraits,
	base::BindOnce(&v8::Task::Run, std::move(task)));
	}

	void V8Platform::CallBlockingTaskOnWorkerThread(
	std::unique_ptr<v8::Task> task) {
	base::PostTask(FROM_HERE, kBlockingTaskTraits,
	base::BindOnce(&v8::Task::Run, std::move(task)));
	}

	void V8Platform::CallLowPriorityTaskOnWorkerThread(
	std::unique_ptr<v8::Task> task) {
	base::PostTask(FROM_HERE, kLowPriorityTaskTraits,
	base::BindOnce(&v8::Task::Run, std::move(task)));
	}

	void V8Platform::CallDelayedOnWorkerThread(std::unique_ptr<v8::Task> task,
	double delay_in_seconds) {
	base::PostDelayedTask(FROM_HERE, kDefaultTaskTraits,
	base::BindOnce(&v8::Task::Run, std::move(task)),
	base::TimeDelta::FromSecondsD(delay_in_seconds));
	}

	void V8Platform::CallOnForegroundThread(v8::Isolate* isolate, v8::Task* task) {
	PerIsolateData* data = PerIsolateData::From(isolate);
	data->task_runner()->PostTask(std::unique_ptr<v8::Task>(task));
	}

	void V8Platform::CallDelayedOnForegroundThread(v8::Isolate* isolate,
	v8::Task* task,
	double delay_in_seconds) {
	PerIsolateData* data = PerIsolateData::From(isolate);
	data->task_runner()->PostDelayedTask(std::unique_ptr<v8::Task>(task),
	delay_in_seconds);
	}

	void V8Platform::CallIdleOnForegroundThread(v8::Isolate* isolate,
	v8::IdleTask* task) {
	PerIsolateData* data = PerIsolateData::From(isolate);
	data->task_runner()->PostIdleTask(std::unique_ptr<v8::IdleTask>(task));
	}

	bool V8Platform::IdleTasksEnabled(v8::Isolate* isolate) {
	return PerIsolateData::From(isolate)->task_runner()->IdleTasksEnabled();
	}

	double V8Platform::MonotonicallyIncreasingTime() {
	return base::TimeTicks::Now().ToInternalValue() /
	static_cast<double>(base::Time::kMicrosecondsPerSecond);
	}

	double V8Platform::CurrentClockTimeMillis() {
	double now_seconds = base::Time::Now().ToJsTime() / 1000;
	return g_time_clamper.Get().ClampTimeResolution(now_seconds) * 1000;
	}

	v8::TracingController* V8Platform::GetTracingController() {
	return tracing_controller_.get();
	}

	v8::Platform::StackTracePrinter V8Platform::GetStackTracePrinter() {
	return PrintStackTrace;
	}

	} // namespace gin