base: Factor task debug annotations out of MessageLoop

base/debug/task_annotator.cc

Index: base/debug/task_annotator.cc
diff --git a/base/debug/task_annotator.cc b/base/debug/task_annotator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c6576c829e83f1bb2bf4a2209afdd4a9b4e3f5e9
--- /dev/null
+++ b/base/debug/task_annotator.cc
@@ -0,0 +1,74 @@
+// Copyright 2014 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.
+
+#include "base/debug/task_annotator.h"
+
+#include "base/debug/alias.h"
+#include "base/debug/trace_event.h"
+#include "base/pending_task.h"
+#include "base/tracked_objects.h"
+
+namespace base {
+namespace debug {
+
+TaskAnnotator::TaskAnnotator() {
+}
+
+TaskAnnotator::~TaskAnnotator() {
+}
+
+void TaskAnnotator::DidQueueTask(const char* queue_function,
+                                 const PendingTask& pending_task) {
+  TRACE_EVENT_FLOW_BEGIN0(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
+                          queue_function,
+                          TRACE_ID_MANGLE(GetTaskTraceID(pending_task)));
+}
+
+void TaskAnnotator::RunTask(const char* queue_function,
+                            const char* run_function,
+                            const PendingTask& pending_task) {
+  tracked_objects::TrackedTime start_time =
+      tracked_objects::ThreadData::NowForStartOfRun(pending_task.birth_tally);
+  tracked_objects::Duration queue_duration =
+      start_time - pending_task.EffectiveTimePosted();
+
+  TRACE_EVENT_FLOW_END1(TRACE_DISABLED_BY_DEFAULT("toplevel.flow"),
+                        queue_function,
+                        TRACE_ID_MANGLE(GetTaskTraceID(pending_task)),
+                        "queue_duration",
+                        queue_duration.InMilliseconds());
+
+  // When tracing memory for posted tasks it's more valuable to attribute the
+  // memory allocations to the source function than generically to the task
+  // runner.
+  TRACE_EVENT_WITH_MEMORY_TAG2(
+      "toplevel",
+      run_function,
+      pending_task.posted_from.function_name(),  // Name for memory tracking.
+      "src_file",
+      pending_task.posted_from.file_name(),
+      "src_func",
+      pending_task.posted_from.function_name());
+
+  // Before running the task, store the program counter where it was posted
+  // and deliberately alias it to ensure it is on the stack if the task
+  // crashes. Be careful not to assume that the variable itself will have the
+  // expected value when displayed by the optimizer in an optimized build.
+  // Look at a memory dump of the stack.
+  const void* program_counter = pending_task.posted_from.program_counter();
+  debug::Alias(&program_counter);
+
+  pending_task.task.Run();
+
+  tracked_objects::ThreadData::TallyRunOnNamedThreadIfTracking(
+      pending_task, start_time, tracked_objects::ThreadData::NowForEndOfRun());
+}
+
+uint64 TaskAnnotator::GetTaskTraceID(const PendingTask& task) const {
+  return (static_cast<uint64>(task.sequence_num) << 32) |
+         ((static_cast<uint64>(reinterpret_cast<intptr_t>(this)) << 32) >> 32);
+}
+
+}  // namespace debug
+}  // namespace base