[profiler] Implement POC Sampling Heap Profiler

src/profiler/sampling-heap-profiler.cc

+// Copyright 2015 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.
+
+#include "src/api.h"
+#include "src/frames-inl.h"
+#include "src/heap/heap.h"
+#include "src/isolate.h"
+#include "src/profiler/sampling-heap-profiler.h"
+#include "src/profiler/strings-storage.h"
+
+namespace v8 {
+namespace internal {
+
+SamplingHeapProfiler::SamplingHeapProfiler(Heap* heap, StringsStorage* names,
+                                           uint64_t rate, int stack_depth)
+    : InlineAllocationObserver(GetNextSampleInterval(
+          heap->isolate()->random_number_generator(), rate)),
+      isolate_(heap->isolate()),
+      heap_(heap),
+      random_(isolate_->random_number_generator()),
+      names_(names),
+      samples_(),
+      rate_(rate),
+      stack_depth_(stack_depth) {
+  heap->new_space()->AddInlineAllocationObserver(this);
+}
+
+
+SamplingHeapProfiler::~SamplingHeapProfiler() {
+  heap_->new_space()->RemoveInlineAllocationObserver(this);
+
+  // Clear samples and drop all the weak references we are keeping.
+  std::set<SampledAllocation*>::iterator it;
+  for (it = samples_.begin(); it != samples_.end(); ++it) {
+    delete *it;
+  }
+  std::set<SampledAllocation*> empty{};
+  samples_.swap(empty);
+}
+
+void SamplingHeapProfiler::Step(int bytes_allocated, Address soon_object,
+                                size_t size) {
+  DCHECK(heap_->gc_state() == Heap::NOT_IN_GC);
+  DCHECK(soon_object);
+  SampleObject(soon_object, size);
+}
+
+
+void SamplingHeapProfiler::SampleObject(Address soon_object, size_t size) {
+  DisallowHeapAllocation no_allocation;
+
+  HandleScope scope(isolate_);
+  HeapObject* heap_object = HeapObject::FromAddress(soon_object);
+  Handle<Object> obj(heap_object, isolate_);
+
+  // Mark the new block as FreeSpace to make sure the heap is iterable while we
+  // are taking the sample.
+  heap()->CreateFillerObjectAt(soon_object, static_cast<int>(size));
+
+  Local<v8::Value> loc = v8::Utils::ToLocal(obj);
+
+  SampledAllocation* sample =
+      new SampledAllocation(this, isolate_, loc, size, stack_depth_);
+  samples_.insert(sample);
+}
+
+
+// We sample with a Poisson process, with constant average sampling interval.
+// This follows the exponential probability distribution with parameter
+// λ = 1/rate where rate is the average number of bytes between samples.
+//
+// Let u be a uniformly distributed random number between 0 and 1, then
+// next_sample = (- ln u) / λ
+intptr_t SamplingHeapProfiler::GetNextSampleInterval(
+    base::RandomNumberGenerator* random, uint64_t rate) {
+  double u = random->NextDouble();
+  double next = (-std::log(u)) * rate;
+  return std::max(static_cast<intptr_t>(kPointerSize),
+                  static_cast<intptr_t>(next));
+}
+
+
+void SamplingHeapProfiler::GetHeapSample(OutputStream* stream) {
+  std::map<int, Script*> scripts;
+  {
+    Script::Iterator iterator(isolate_);
+    Script* script;
+    while ((script = iterator.Next())) {
+      scripts[script->id()] = script;
+    }
+  }
+
+  OutputStreamWriter writer(stream);
+  writer.AddString("[\n");
+  std::set<SampledAllocation*>::iterator it;
+  for (it = samples_.begin(); it != samples_.end(); ++it) {
+    auto sample = *it;
+    if (it != samples_.begin()) {
+      writer.AddString(",");
+    }
+    writer.AddString(" {\"size\": ");
+    writer.AddNumber(static_cast<unsigned>(sample->get_size()));
+    writer.AddString(", \"stack\": [\n");
+    List<FunctionInfo*>& stack = sample->get_stack();
+    for (int i = 0; i < stack.length(); ++i) {
+      FunctionInfo* info = stack[i];
+      int line = -1;
+      int column = -1;
+      if (info->script_id != -1) {
+        Handle<Script> script(scripts[info->script_id]);
+        line = Script::GetLineNumber(script, info->start_position);
+        column = Script::GetColumnNumber(script, info->start_position);
+      }
+
+      writer.AddString("\t{\"name\": \"");
+      writer.AddString(info->name);
+      writer.AddString("\"");
+      if (line != -1) {
+        DCHECK(column != -1);
+        writer.AddString(", \"line\": ");
+        writer.AddNumber(line);
+        writer.AddString(", \"column\": ");
+        writer.AddNumber(column);
+      }
+      writer.AddString(", \"scriptName\": \"");
+      writer.AddString(info->script_name);
+      if (i < (stack.length() - 1)) {
+        writer.AddString("\"},\n");
+      } else {
+        writer.AddString("\"}\n");
+      }
+    }
+    writer.AddString(" ]}\n");
+  }
+  writer.AddString("]\n");
+  writer.Finalize();
+}
+
+void SamplingHeapProfiler::SampledAllocation::OnWeakCallback(
+    const WeakCallbackInfo<SampledAllocation>& data) {
+  SampledAllocation* sample = data.GetParameter();
+  sample->shp_->samples_.erase(sample);
+  delete sample;
+}
+
+
+SamplingHeapProfiler::FunctionInfo::FunctionInfo(SharedFunctionInfo* shared,
+                                                 StringsStorage* names)
+    : name(names->GetFunctionName(shared->DebugName())),
+      script_name(""),
+      script_id(-1),
+      start_position(-1) {
+  if (shared->script()->IsScript()) {
+    Script* script = Script::cast(shared->script());
+    script_id = script->id();
+    start_position = shared->start_position();
+    if (script->name()->IsName()) {
+      Name* name = Name::cast(script->name());
+      script_name = names->GetName(name);
+    }
+  }
+}
+
+SamplingHeapProfiler::SampledAllocation::SampledAllocation(
+    SamplingHeapProfiler* shp, Isolate* isolate, Local<Value> local,
+    size_t size, int max_frames)
+    : shp_(shp),
+      global_(reinterpret_cast<v8::Isolate*>(isolate), local),
+      size_(size) {
+  global_.SetWeak(this, OnWeakCallback, WeakCallbackType::kParameter);
+
+
+  StackTraceFrameIterator it(isolate);
+  int frames_captured = 0;
+  while (!it.done() && frames_captured < max_frames) {
+    JavaScriptFrame* frame = it.frame();
+    SharedFunctionInfo* shared = frame->function()->shared();
+    stack_.Add(new FunctionInfo(shared, shp->names()));
+
+    frames_captured++;
+    it.Advance();
+  }
+}
+
+
+}  // namespace internal
+}  // namespace v8