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// Copyright 2013 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_SAMPLER_H_
#define V8_SAMPLER_H_
#include "src/base/atomicops.h"
#include "src/frames.h"
#include "src/globals.h"
namespace v8 {
namespace internal {
class Isolate;
// ----------------------------------------------------------------------------
// Sampler
// A sampler periodically samples the state of the VM and optionally
// (if used for profiling) the program counter and stack pointer for
// the thread that created it.
struct RegisterState {
RegisterState() : pc(NULL), sp(NULL), fp(NULL) {}
Address pc; // Instruction pointer.
Address sp; // Stack pointer.
Address fp; // Frame pointer.
// TickSample captures the information collected for each sample.
struct TickSample {
: state(OTHER),
top_frame_type(StackFrame::NONE) {}
void Init(Isolate* isolate, const RegisterState& state);
StateTag state; // The state of the VM.
Address pc; // Instruction pointer.
union {
Address tos; // Top stack value (*sp).
Address external_callback;
static const int kMaxFramesCount = 64;
Address stack[kMaxFramesCount]; // Call stack.
TimeTicks timestamp;
int frames_count : 8; // Number of captured frames.
bool has_external_callback : 1;
StackFrame::Type top_frame_type : 4;
class Sampler {
// Initializes the Sampler support. Called once at VM startup.
static void SetUp();
static void TearDown();
// Initialize sampler.
Sampler(Isolate* isolate, int interval);
virtual ~Sampler();
Isolate* isolate() const { return isolate_; }
int interval() const { return interval_; }
// Performs stack sampling.
void SampleStack(const RegisterState& regs);
// Start and stop sampler.
void Start();
void Stop();
// Whether the sampling thread should use this Sampler for CPU profiling?
bool IsProfiling() const {
return base::NoBarrier_Load(&profiling_) > 0 &&
void IncreaseProfilingDepth();
void DecreaseProfilingDepth();
// Whether the sampler is running (that is, consumes resources).
bool IsActive() const { return base::NoBarrier_Load(&active_); }
void DoSample();
// If true next sample must be initiated on the profiler event processor
// thread right after latest sample is processed.
void SetHasProcessingThread(bool value) {
base::NoBarrier_Store(&has_processing_thread_, value);
// Used in tests to make sure that stack sampling is performed.
unsigned js_and_external_sample_count() const {
return js_and_external_sample_count_;
void StartCountingSamples() {
is_counting_samples_ = true;
js_and_external_sample_count_ = 0;
class PlatformData;
PlatformData* platform_data() const { return data_; }
// This method is called for each sampling period with the current
// program counter.
virtual void Tick(TickSample* sample) = 0;
void SetActive(bool value) { base::NoBarrier_Store(&active_, value); }
Isolate* isolate_;
const int interval_;
base::Atomic32 profiling_;
base::Atomic32 has_processing_thread_;
base::Atomic32 active_;
PlatformData* data_; // Platform specific data.
bool is_counting_samples_;
// Counts stack samples taken in JS VM state.
unsigned js_and_external_sample_count_;
} } // namespace v8::internal
#endif // V8_SAMPLER_H_