Add a task_scheduler tracing category which will record an extra event per task.

That event will contain ExecutionMode/SequenceToken and TaskPriority.

It would be better to tack an optional extra arg to the main task event but
tracing doesn't currently allow this (http://crbug.com/652692).

BUG=649084

Review-Url: https://codereview.chromium.org/2392903002
Cr-Commit-Position: refs/heads/master@{#423681}

base/sequence_token.cc

@@ -37,6 +37,10 @@ bool SequenceToken::IsValid() const {
   return token_ != kInvalidSequenceToken;
 }
 
+int SequenceToken::ToInternalValue() const {
+  return token_;
+}
+
 SequenceToken SequenceToken::Create() {
   return SequenceToken(g_sequence_token_generator.GetNext());
 }

base/sequence_token.h

@@ -29,6 +29,10 @@ class BASE_EXPORT SequenceToken {
   // Returns true if this is a valid SequenceToken.
   bool IsValid() const;
 
+  // Returns the integer uniquely representing this SequenceToken. This method
+  // should only be used for tracing and debugging.
+  int ToInternalValue() const;
+
   // Returns a valid SequenceToken which isn't equal to any previously returned
   // SequenceToken.
   static SequenceToken Create();

base/sequence_token_unittest.cc

@@ -62,6 +62,14 @@ TEST(SequenceTokenTest, GetForCurrentThread) {
   EXPECT_FALSE(SequenceToken::GetForCurrentThread().IsValid());
 }
 
+TEST(SequenceTokenTest, ToInternalValue) {
+  const SequenceToken token1 = SequenceToken::Create();
+  const SequenceToken token2 = SequenceToken::Create();
+
+  // Confirm that internal values are unique.
+  EXPECT_NE(token1.ToInternalValue(), token2.ToInternalValue());
+}
+
 // Expect a default-constructed TaskToken to be invalid and not equal to
 // another invalid TaskToken.
 TEST(TaskTokenTest, InvalidDefaultConstructed) {

base/task_scheduler/task_tracker.cc

@@ -8,7 +8,9 @@
 
 #include "base/callback.h"
 #include "base/debug/task_annotator.h"
+#include "base/json/json_writer.h"
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/sequence_token.h"
 #include "base/synchronization/condition_variable.h"
@@ -16,12 +18,49 @@
 #include "base/threading/thread_restrictions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event.h"
+#include "base/values.h"
 
 namespace base {
 namespace internal {
 
 namespace {
 
+// An immutable copy of a scheduler task's info required by tracing.
+class TaskTracingInfo : public trace_event::ConvertableToTraceFormat {
+ public:
+  TaskTracingInfo(const TaskTraits& task_traits,
+                  ExecutionMode execution_mode,
+                  const SequenceToken& sequence_token)
+      : task_traits_(task_traits),
+        execution_mode_(execution_mode),
+        sequence_token_(sequence_token) {}
+
+  // trace_event::ConvertableToTraceFormat implementation.
+  void AppendAsTraceFormat(std::string* out) const override;
+
+ private:
+  const TaskTraits task_traits_;
+  const ExecutionMode execution_mode_;
+  const SequenceToken sequence_token_;
+
+  DISALLOW_COPY_AND_ASSIGN(TaskTracingInfo);
+};
+
+void TaskTracingInfo::AppendAsTraceFormat(std::string* out) const {
+  DictionaryValue dict;
+
+  dict.SetString("task_priority",
+                 base::TaskPriorityToString(task_traits_.priority()));
+  dict.SetString("execution_mode",
+                 base::ExecutionModeToString(execution_mode_));
+  if (execution_mode_ != ExecutionMode::PARALLEL)
+    dict.SetInteger("sequence_token", sequence_token_.ToInternalValue());
+
+  std::string tmp;
+  JSONWriter::Write(dict, &tmp);
+  out->append(tmp);
+}
+
 const char kQueueFunctionName[] = "base::PostTask";
 
 // This name conveys that a Task is run by the task scheduler without revealing
@@ -203,6 +242,18 @@ bool TaskTracker::RunTask(const Task* task,
 
       TRACE_TASK_EXECUTION(kRunFunctionName, *task);
 
+      const ExecutionMode execution_mode =
+          task->single_thread_task_runner_ref
+              ? ExecutionMode::SINGLE_THREADED
+              : (task->sequenced_task_runner_ref ? ExecutionMode::SEQUENCED
+                                                 : ExecutionMode::PARALLEL);
+      // TODO(gab): In a better world this would be tacked on as an extra arg
+      // to the trace event generated above. This is not possible however until
+      // http://crbug.com/652692 is resolved.
+      TRACE_EVENT1("task_scheduler", "TaskTracker::RunTask", "task_info",
+                   MakeUnique<TaskTracingInfo>(task->traits, execution_mode,
+                                               sequence_token));
+
       debug::TaskAnnotator task_annotator;
       task_annotator.RunTask(kQueueFunctionName, *task);
     }

base/task_scheduler/task_traits.cc

@@ -8,6 +8,8 @@
 
 #include <ostream>
 
+#include "base/logging.h"
+
 namespace base {
 
 // Do not rely on defaults hard-coded below beyond the guarantees described in
@@ -36,34 +38,60 @@ TaskTraits& TaskTraits::WithShutdownBehavior(
   return *this;
 }
 
-std::ostream& operator<<(std::ostream& os, const TaskPriority& task_priority) {
+const char* TaskPriorityToString(TaskPriority task_priority) {
   switch (task_priority) {
     case TaskPriority::BACKGROUND:
-      os << "BACKGROUND";
-      break;
+      return "BACKGROUND";
     case TaskPriority::USER_VISIBLE:
-      os << "USER_VISIBLE";
-      break;
+      return "USER_VISIBLE";
     case TaskPriority::USER_BLOCKING:
-      os << "USER_BLOCKING";
-      break;
+      return "USER_BLOCKING";
   }
-  return os;
+  NOTREACHED();
+  return "";
 }
 
-std::ostream& operator<<(std::ostream& os,
-                         const TaskShutdownBehavior& shutdown_behavior) {
+const char* TaskShutdownBehaviorToString(
+    TaskShutdownBehavior shutdown_behavior) {
   switch (shutdown_behavior) {
     case TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN:
-      os << "CONTINUE_ON_SHUTDOWN";
-      break;
+      return "CONTINUE_ON_SHUTDOWN";
     case TaskShutdownBehavior::SKIP_ON_SHUTDOWN:
-      os << "SKIP_ON_SHUTDOWN";
-      break;
+      return "SKIP_ON_SHUTDOWN";
     case TaskShutdownBehavior::BLOCK_SHUTDOWN:
-      os << "BLOCK_SHUTDOWN";
-      break;
+      return "BLOCK_SHUTDOWN";
   }
+  NOTREACHED();
+  return "";
+}
+
+const char* ExecutionModeToString(ExecutionMode execution_mode) {
+  switch (execution_mode) {
+    case ExecutionMode::PARALLEL:
+      return "PARALLEL";
+    case ExecutionMode::SEQUENCED:
+      return "SEQUENCED";
+    case ExecutionMode::SINGLE_THREADED:
+      return "SINGLE_THREADED";
+  }
+  NOTREACHED();
+  return "";
+}
+
+std::ostream& operator<<(std::ostream& os, const TaskPriority& task_priority) {
+  os << TaskPriorityToString(task_priority);
+  return os;
+}
+
+std::ostream& operator<<(std::ostream& os,
+                         const TaskShutdownBehavior& shutdown_behavior) {
+  os << TaskShutdownBehaviorToString(shutdown_behavior);
+  return os;
+}
+
+std::ostream& operator<<(std::ostream& os,
+                         const ExecutionMode& execution_mode) {
+  os << ExecutionModeToString(execution_mode);
   return os;
 }
 

base/task_scheduler/task_traits.h

@@ -126,14 +126,22 @@ enum class ExecutionMode {
   SINGLE_THREADED,
 };
 
-// Stream operators so TaskPriority and TaskShutdownBehavior can be used in
-// DCHECK statements.
+// Returns string literals for the enums defined in this file. These methods
+// should only be used for tracing and debugging.
+BASE_EXPORT const char* TaskPriorityToString(TaskPriority task_priority);
+BASE_EXPORT const char* TaskShutdownBehaviorToString(
+    TaskShutdownBehavior task_priority);
+BASE_EXPORT const char* ExecutionModeToString(ExecutionMode task_priority);
+
+// Stream operators so that the enums defined in this file can be used in
+// DCHECK and EXPECT statements.
 BASE_EXPORT std::ostream& operator<<(std::ostream& os,
                                      const TaskPriority& shutdown_behavior);
-
 BASE_EXPORT std::ostream& operator<<(
     std::ostream& os,
     const TaskShutdownBehavior& shutdown_behavior);
+BASE_EXPORT std::ostream& operator<<(std::ostream& os,
+                                     const ExecutionMode& execution_mode);
 
 }  // namespace base