Implement tracing interface for v8

include/v8-tracing.h

+// 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.
+
+#ifndef INCLUDE_V8_TRACING_H_
+#define INCLUDE_V8_TRACING_H_
+
+#include <stdint.h>
+
+namespace v8 {
+
+// This will mark the trace event as disabled by default. The user will need
+// to explicitly enable the event.
+#define TRACE_DISABLED_BY_DEFAULT(name) "disabled-by-default-" name
+
+class EventTracer {
+ public:
+  typedef uint64_t Handle;
+
+  static EventTracer* GetInstance();
+
+  static void SetInstance(EventTracer* tracer) {
+    delete (EventTracer::instance);
+    EventTracer::instance = tracer;
+  }
+
+  virtual ~EventTracer() {}
+
+  // The pointer returned from GetCategoryGroupEnabled() points to a
+  // value with zero or more of the following bits. Used in this class only.
+  // The TRACE_EVENT macros should only use the value as a bool.
+  // These values must be in sync with macro values in trace_log.h in
+  // chromium.
+  enum CategoryGroupEnabledFlags {
+    // Category group enabled for the recording mode.
+    kEnabledForRecording_CategoryGroupEnabledFlags = 1 << 0,
+    // Category group enabled for the monitoring mode.
+    kEnabledForMonitoring_CategoryGroupEnabledFlags = 1 << 1,
+    // Category group enabled by SetEventCallbackEnabled().
+    kEnabledForEventCallback_CategoryGroupEnabledFlags = 1 << 2,
+    // Category group enabled to export events to ETW.
+    kEnabledForETWExport_CategoryGroupEnabledFlags = 1 << 3,
+  };
+
+  virtual const uint8_t* GetCategoryGroupEnabled(const char* name) = 0;
+  virtual const char* GetCategoryGroupName(
+      const uint8_t* categoryEnabledFlag) = 0;
+
+  virtual EventTracer::Handle AddTraceEvent(

[caseq, 2015/08/25 22:02:46]

I'm very positive about the CL in general, but rather than introducing
additional class for embedders to implement, can we just add these to
v8::Platform? Besides simplifying the API slightly, there's another small
advantage in that docs already stress well the need for InitializePlatform to be
called before v8 initialization, which I think is critical in case of tracing
(due to caching of category pointers).

[jochen (gone - plz use gerrit), 2015/09/08 14:20:34]

agreed.

Either it should be part of the platform, or passed via the
Isolate::CreateParams.

we shouldn't have a global static event tracer, but it should be scoped to an
isolate (eventually, the v8::Platform will also be passed to Isolate::New)

[caseq, 2015/09/08 17:57:49]

Current trace macros implementation relies on static variables for caching
pointers to category enable flags (see
https://code.google.com/p/chromium/codesearch#chromium/src/base/trace_event/t...)
-- so I'm afraid that allowing setting tracers per isolate may create a false
impression that one could use different tracer implementation for different
isolates, while we actually rely on tracer being a singleton.

+      char phase, const uint8_t* categoryEnabledFlag, const char* name,
+      uint64_t id, uint64_t context_id, uint64_t bind_id, int32_t numArgs,
+      const char** argNames, const uint8_t* argTypes, const uint64_t* argValues,
+      unsigned int flags) = 0;
+
+  virtual void UpdateTraceEventDuration(const uint8_t* categoryEnabledFlag,
+                                        const char* name,
+                                        EventTracer::Handle handle) = 0;
+
+ protected:
+  EventTracer() {}
+
+ private:
+  static EventTracer* instance;
+
+  // Disallow copying and assigning.
+  EventTracer(const EventTracer&);
+  void operator=(const EventTracer&);
+};
+
+}  // namespace v8
+
+#endif  // INCLUDE_V8_TRACING_H_