[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/profiler/sampling-heap-profiler.h"
+
+#include <memory>
+#include "src/api.h"
+#include "src/frames-inl.h"
+#include "src/heap/heap.h"
+#include "src/isolate.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::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_(v8::UnboundScript::kNoScriptId),
+      start_position_(0) {
+  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_.push_back(new FunctionInfo(shared, shp->names()));
+
+    frames_captured++;
+    it.Advance();
+  }
+
+  if (frames_captured == 0) {
+    const char* name = nullptr;
+    switch (isolate->current_vm_state()) {
+      case GC:
+        name = "(GC)";
+        break;
+      case COMPILER:
+        name = "(COMPILER)";
+        break;
+      case OTHER:
+        name = "(V8 API)";
+        break;
+      case EXTERNAL:
+        name = "(EXTERNAL)";
+        break;
+      case IDLE:
+        name = "(IDLE)";
+        break;
+      case JS:
+        name = "(JS)";
+        break;
+    }
+    stack_.push_back(
+        new FunctionInfo(name, "", v8::UnboundScript::kNoScriptId, 0));
+  }
+}
+
+
+SamplingHeapProfiler::Node* SamplingHeapProfiler::AllocateNode(
+    v8::AllocationProfile& profile, const std::map<int, Script*>& scripts,
+    FunctionInfo* function_info) {
+  DCHECK(function_info->get_name());
+  DCHECK(function_info->get_script_name());
+
+  int line = v8::AllocationProfile::kNoLineNumberInfo;
+  int column = v8::AllocationProfile::kNoColumnNumberInfo;
+
+  if (function_info->get_script_id() != v8::UnboundScript::kNoScriptId) {
+    Handle<Script> script(scripts.at(function_info->get_script_id()));
+
+    line =
+        1 + Script::GetLineNumber(script, function_info->get_start_position());
+    column = 1 + Script::GetColumnNumber(script,
+                                         function_info->get_start_position());
+  }
+
+  profile.nodes.push_back(
+      Node({ToApiHandle<v8::String>(isolate_->factory()->InternalizeUtf8String(
+                function_info->get_name())),
+            ToApiHandle<v8::String>(isolate_->factory()->InternalizeUtf8String(
+                function_info->get_script_name())),
+            function_info->get_script_id(), function_info->get_start_position(),
+            line, column, std::vector<Node*>(),
+            std::vector<v8::AllocationProfile::Allocation>()}));
+
+  return &profile.nodes.back();
+}
+
+
+SamplingHeapProfiler::Node* SamplingHeapProfiler::FindOrAddChildNode(
+    v8::AllocationProfile& profile, const std::map<int, Script*>& scripts,
+    Node* parent, FunctionInfo* function_info) {
+  for (Node* child : parent->children) {
+    if (child->script_id == function_info->get_script_id() &&
+        child->start_position == function_info->get_start_position())
+      return child;
+  }
+  Node* child = AllocateNode(profile, scripts, function_info);
+  parent->children.push_back(child);
+  return child;
+}
+
+
+SamplingHeapProfiler::Node* SamplingHeapProfiler::AddStack(
+    v8::AllocationProfile& profile, const std::map<int, Script*>& scripts,
+    const std::vector<FunctionInfo*>& stack) {
+  Node* node = profile.GetRootNode();
+
+  // We need to process the stack in reverse order as the top of the stack is
+  // the first element in the list.
+  for (auto it = stack.rbegin(); it != stack.rend(); ++it) {
+    FunctionInfo* function_info = *it;
+    node = FindOrAddChildNode(profile, scripts, node, function_info);
+  }
+  return node;
+}
+
+
+v8::AllocationProfile SamplingHeapProfiler::GetAllocationProfile() {
+  // To resolve positions to line/column numbers, we will need to look up
+  // scripts. Build a map to allow fast mapping from script id to script.
+  std::map<int, Script*> scripts;
+  {
+    Script::Iterator iterator(isolate_);
+    Script* script;
+    while ((script = iterator.Next())) {
+      scripts[script->id()] = script;
+    }
+  }
+
+
+  v8::AllocationProfile profile;
+
+  // Create the root node.
+  FunctionInfo function_info("(root)", "", v8::UnboundScript::kNoScriptId, 0);
+  AllocateNode(profile, scripts, &function_info);
+
+  for (SampledAllocation* allocation : samples_) {
+    Node* node = AddStack(profile, scripts, allocation->get_stack());
+    node->allocations.push_back({allocation->get_size(), 1});
+  }
+
+  return profile;
+}
+
+
+}  // namespace internal
+}  // namespace v8