1 // Copyright 2013 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef V8_PROFILER_SAMPLER_H_
6 #define V8_PROFILER_SAMPLER_H_
7 
8 #include "include/v8.h"
9 
10 #include "src/base/atomicops.h"
11 #include "src/base/platform/time.h"
12 #include "src/frames.h"
13 #include "src/globals.h"
14 
15 namespace v8 {
16 namespace internal {
17 
18 class Isolate;
19 
20 // ----------------------------------------------------------------------------
21 // Sampler
22 //
23 // A sampler periodically samples the state of the VM and optionally
24 // (if used for profiling) the program counter and stack pointer for
25 // the thread that created it.
26 
27 // TickSample captures the information collected for each sample.
28 struct TickSample {
29   // Internal profiling (with --prof + tools/$OS-tick-processor) wants to
30   // include the runtime function we're calling. Externally exposed tick
31   // samples don't care.
32   enum RecordCEntryFrame { kIncludeCEntryFrame, kSkipCEntryFrame };
33 
TickSampleTickSample34   TickSample()
35       : state(OTHER),
36         pc(NULL),
37         external_callback(NULL),
38         frames_count(0),
39         has_external_callback(false),
40         top_frame_type(StackFrame::NONE) {}
41   void Init(Isolate* isolate, const v8::RegisterState& state,
42             RecordCEntryFrame record_c_entry_frame);
43   static void GetStackSample(Isolate* isolate, const v8::RegisterState& state,
44                              RecordCEntryFrame record_c_entry_frame,
45                              void** frames, size_t frames_limit,
46                              v8::SampleInfo* sample_info);
47   StateTag state;  // The state of the VM.
48   Address pc;      // Instruction pointer.
49   union {
50     Address tos;   // Top stack value (*sp).
51     Address external_callback;
52   };
53   static const unsigned kMaxFramesCountLog2 = 8;
54   static const unsigned kMaxFramesCount = (1 << kMaxFramesCountLog2) - 1;
55   Address stack[kMaxFramesCount];  // Call stack.
56   base::TimeTicks timestamp;
57   unsigned frames_count : kMaxFramesCountLog2;  // Number of captured frames.
58   bool has_external_callback : 1;
59   StackFrame::Type top_frame_type : 4;
60 };
61 
62 class Sampler {
63  public:
64   // Initializes the Sampler support. Called once at VM startup.
65   static void SetUp();
66   static void TearDown();
67 
68   // Initialize sampler.
69   Sampler(Isolate* isolate, int interval);
70   virtual ~Sampler();
71 
isolate()72   Isolate* isolate() const { return isolate_; }
interval()73   int interval() const { return interval_; }
74 
75   // Performs stack sampling.
76   void SampleStack(const v8::RegisterState& regs);
77 
78   // Start and stop sampler.
79   void Start();
80   void Stop();
81 
82   // Whether the sampling thread should use this Sampler for CPU profiling?
IsProfiling()83   bool IsProfiling() const {
84     return base::NoBarrier_Load(&profiling_) > 0 &&
85         !base::NoBarrier_Load(&has_processing_thread_);
86   }
87   void IncreaseProfilingDepth();
88   void DecreaseProfilingDepth();
89 
90   // Whether the sampler is running (that is, consumes resources).
IsActive()91   bool IsActive() const { return base::NoBarrier_Load(&active_); }
92 
93   void DoSample();
94   // If true next sample must be initiated on the profiler event processor
95   // thread right after latest sample is processed.
SetHasProcessingThread(bool value)96   void SetHasProcessingThread(bool value) {
97     base::NoBarrier_Store(&has_processing_thread_, value);
98   }
99 
100   // Used in tests to make sure that stack sampling is performed.
js_and_external_sample_count()101   unsigned js_and_external_sample_count() const {
102     return js_and_external_sample_count_;
103   }
StartCountingSamples()104   void StartCountingSamples() {
105       is_counting_samples_ = true;
106       js_and_external_sample_count_ = 0;
107   }
108 
109   class PlatformData;
platform_data()110   PlatformData* platform_data() const { return data_; }
111 
112  protected:
113   // This method is called for each sampling period with the current
114   // program counter.
115   virtual void Tick(TickSample* sample) = 0;
116 
117  private:
SetActive(bool value)118   void SetActive(bool value) { base::NoBarrier_Store(&active_, value); }
119 
120   Isolate* isolate_;
121   const int interval_;
122   base::Atomic32 profiling_;
123   base::Atomic32 has_processing_thread_;
124   base::Atomic32 active_;
125   PlatformData* data_;  // Platform specific data.
126   bool is_counting_samples_;
127   // Counts stack samples taken in JS VM state.
128   unsigned js_and_external_sample_count_;
129   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
130 };
131 
132 
133 }  // namespace internal
134 }  // namespace v8
135 
136 #endif  // V8_PROFILER_SAMPLER_H_
137