Implement frame attribution (FrameBlamer)

base/debug/blame_context.h

+// Copyright 2016 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.
+
+#ifndef BASE_DEBUG_BLAME_CONTEXT_H_
+#define BASE_DEBUG_BLAME_CONTEXT_H_
+
+#include <inttypes.h>
+
+#include "base/macros.h"
+#include "base/strings/stringprintf.h"
+#include "base/trace_event/trace_event.h"
+#include "base/trace_event/trace_event_argument.h"
+
+namespace base {
+namespace debug {
+
+// A blame context represents a logical unit to which we want to attribute
+// different costs (CPU, network usage, memory, etc.). An example of a blame
+// context is an <iframe> element on a web page. Different subsystems can
+// "enter" and "leave" blame contexts to indicate that they are doing work which
+// should be accounted against this blame context.
+//
+// Each blame context can optionally have a parent blame context, forming a
+// blame context tree. When work is attributed to a particular blame context, it
+// is considered to count against all of that context's children too. This is
+// useful when work cannot be exactly attributed into a more specific context.
+// For example, Javascript garbage collection generally needs to inspect all
+// objects on a page instead looking at each <iframe> individually. In this case
+// the work should be attributed to a blame context which is the parent of all
+// <iframe> blame contexts.
+
+// Abstract blame context base class which can be used for attributing work.
+class BlameContextBase {
+ public:
+  // Indicate that the current thread is now doing work which should count
+  // against this blame context.
+  virtual void Enter() = 0;
+
+  // Leave and stop doing work for a previously entered blame context. If
+  // another blame context of the same type was entered prior to this one, it
+  // becomes the active blame context for this thread again.
+  virtual void Leave() = 0;
+
+ protected:
+  BlameContextBase() {}
+  virtual ~BlameContextBase() {}
+
+  DISALLOW_COPY_AND_ASSIGN(BlameContextBase);
+};
+
+// A concrete instance of a blame context which emits blame context trace
+// events. |category| is the tracing category this context belongs to and |name|
+// identifies the type of the blame context. |scope| defines the name space for
+// the |id| parameter (identical ids in different scopes are considered separate
+// blame context objects). Each string parameter must be a pointer to a constant
+// string with application lifetime.
+//
+// Note that the blame context is templatized to work around a trace event
+// limitation which prohibits a single trace event macro instantiation to be
+// used with more than one trace category.
+// TODO(skyostil): De-templatize this class.
+template <const char* category, const char* name, const char* scope>
+class BlameContext : public BlameContextBase,
+                     public trace_event::TraceLog::EnabledStateObserver {
+ public:
+  // Construct a blame context with the given |id| belonging to the |scope|
+  // namespace. The blame context will not have a parent.
+  explicit BlameContext(int64_t id)
+      : id_(id), parent_id_(0), parent_scope_(nullptr) {
+    Initialize();
+  }
+
+  // Construct a blame context with the given |id| belonging to the |scope|
+  // namespace. |parent_context| identifies the parent for this blame context.
+  // It must belong to the same blame context tree as this context, i.e., |name|
+  // must equal |parent_name|.
+  template <const char* parent_category,
+            const char* parent_name,
+            const char* parent_scope>
+  BlameContext(int64_t id,
+               const BlameContext<parent_category, parent_name, parent_scope>&
+                   parent_context)
+      : id_(id), parent_id_(parent_context.id()), parent_scope_(parent_scope) {
+    DCHECK(!strcmp(name, parent_name))
+        << "parent blame context must be of the same type";
+    Initialize();
+  }
+
+  // BlameContextBase implementation:
+  void Enter() override {
+    TRACE_EVENT_ENTER_CONTEXT(category, name, TRACE_ID_WITH_SCOPE(scope, id_));
+  }
+
+  void Leave() override {
+    TRACE_EVENT_LEAVE_CONTEXT(category, name, TRACE_ID_WITH_SCOPE(scope, id_));
+  }
+
+  // Record a snapshot of the blame context. This is normally only needed if a
+  // blame context subclass defines custom properties (see AsValueInto) and one
+  // or more of the properties have changed.
+  void TakeSnapshot() {
+    bool is_tracing = false;
+    TRACE_EVENT_CATEGORY_GROUP_ENABLED(category, &is_tracing);
+    if (!is_tracing)
+      return;
+    scoped_ptr<trace_event::TracedValue> snapshot(new trace_event::TracedValue);
+    AsValueInto(snapshot.get());
+    scoped_ptr<trace_event::ConvertableToTraceFormat> snapshot_data(
+        std::move(snapshot));
+    TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(category, name,
+                                        TRACE_ID_WITH_SCOPE(scope, id_),
+                                        std::move(snapshot_data));
+  }
+
+  int64_t id() const { return id_; }
+
+  // trace_event::TraceLog::EnabledStateObserver implementation:
+  void OnTraceLogEnabled() override { TakeSnapshot(); }
+
+  void OnTraceLogDisabled() override {}
+
+ protected:
+  virtual ~BlameContext() {
+    TRACE_EVENT_OBJECT_DELETED_WITH_ID(category, name,
+                                       TRACE_ID_WITH_SCOPE(scope, id_));
+    trace_event::TraceLog::GetInstance()->RemoveEnabledStateObserver(this);
+  }
+
+  // Serialize the properties of this blame context into |state|. Subclasses can
+  // override this method to record additional properties (e.g, the URL for an
+  // <iframe> blame context). Note that an overriden implementation must still
+  // call this base method.
+  virtual void AsValueInto(trace_event::TracedValue* state) {
+    if (!parent_id_)
+      return;
+    state->BeginDictionary("parent");
+    state->SetString("id_ref", StringPrintf("0x%" PRIx64, parent_id_));
+    state->SetString("scope", parent_scope_);
+    state->EndDictionary();
+  }
+
+ private:
+  void Initialize() {
+    TRACE_EVENT_OBJECT_CREATED_WITH_ID(category, name,
+                                       TRACE_ID_WITH_SCOPE(scope, id_));
+    trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(this);
+  }
+
+  const int64_t id_;
+  const int64_t parent_id_;
+  const char* parent_scope_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlameContext);
+};
+
+}  // namespace debug
+}  // namespace base
+
+#endif  // BASE_DEBUG_BLAME_CONTEXT_H_