Adding flow traces for blink scheduler events

Source/platform/scheduler/Scheduler.cpp

Index: Source/platform/scheduler/Scheduler.cpp
diff --git a/Source/platform/scheduler/Scheduler.cpp b/Source/platform/scheduler/Scheduler.cpp
index fb331ac6e3766aad23db042059ad0c43b549bb18..e66c49b351a996e9a6b39a9b1bc9312a56048b3e 100644
--- a/Source/platform/scheduler/Scheduler.cpp
+++ b/Source/platform/scheduler/Scheduler.cpp
@@ -73,8 +73,8 @@ public:
 class Scheduler::MainThreadPendingTaskRunner : public WebThread::Task {
 public:
     MainThreadPendingTaskRunner(
-        const Scheduler::Task& task, const TraceLocation& location)
-        : m_task(task, location)
+        const Scheduler::Task& task, const TraceLocation& location, const char* traceName, int flowTraceID)
+        : m_task(task, location, traceName, flowTraceID)
     {
         ASSERT(Scheduler::shared());
     }
@@ -90,7 +90,7 @@ public:
         m_task.run();
     }
 
-    Scheduler::TracedTask m_task;
+    TracedTask m_task;
 };
 
 Scheduler* Scheduler::s_sharedScheduler = nullptr;
@@ -115,6 +115,9 @@ Scheduler::Scheduler()
     : m_sharedTimerFunction(nullptr)
     , m_mainThread(blink::Platform::current()->currentThread())
     , m_highPriorityTaskCount(0)
+    // Flow trace ID begins as the 'this' pointer to help ensure different scheduler
+    // instances don't generate identical IDs
+    , m_nextFlowTraceID(static_cast<int>(reinterpret_cast<intptr_t>(this)))
     , m_highPriorityTaskRunnerPosted(false)
 {
 }
@@ -126,31 +129,39 @@ Scheduler::~Scheduler()
     }
 }
 
+int Scheduler::generateFlowTraceID()
+{
+    return atomicIncrement(&m_nextFlowTraceID);
+}
+
 void Scheduler::scheduleIdleTask(const TraceLocation& location, const IdleTask& idleTask)
 {
     // TODO: send a real allottedTime here.
     m_mainThread->postTask(new MainThreadIdleTaskAdapter(idleTask, 0, location));
 }
 
+void Scheduler::postHighPriorityTaskInternal(const TraceLocation& location, const Task& task, const char* traceName)
+{
+    Locker<Mutex> lock(m_pendingTasksMutex);
+
+    m_pendingHighPriorityTasks.append(TracedTask(task, location, traceName, generateFlowTraceID()));

[eseidel, 2014/09/02 16:19:25]

Unfortunate we always generate these trace ids.  atomicIncrement is non-trivial
cost no?

[picksi1, 2014/09/03 16:32:57]

I've moved ID generation into TracedTasks and only do the atomicIncrement if
tracing is enabled.

+    atomicIncrement(&m_highPriorityTaskCount);
+    maybePostMainThreadPendingHighPriorityTaskRunner();
+}
+
 void Scheduler::postTask(const TraceLocation& location, const Task& task)
 {
-    m_mainThread->postTask(new MainThreadPendingTaskRunner(task, location));
+    m_mainThread->postTask(new MainThreadPendingTaskRunner(task, location, "Scheduler::MainThreadTask", generateFlowTraceID()));
 }
 
 void Scheduler::postInputTask(const TraceLocation& location, const Task& task)
 {
-    Locker<Mutex> lock(m_pendingTasksMutex);
-    m_pendingHighPriorityTasks.append(TracedTask(task, location));
-    atomicIncrement(&m_highPriorityTaskCount);
-    maybePostMainThreadPendingHighPriorityTaskRunner();
+    postHighPriorityTaskInternal(location, task, "Scheduler::InputTask");
 }
 
 void Scheduler::postCompositorTask(const TraceLocation& location, const Task& task)
 {
-    Locker<Mutex> lock(m_pendingTasksMutex);
-    m_pendingHighPriorityTasks.append(TracedTask(task, location));
-    atomicIncrement(&m_highPriorityTaskCount);
-    maybePostMainThreadPendingHighPriorityTaskRunner();
+    postHighPriorityTaskInternal(location, task, "Scheduler::CompositorTask");
 }
 
 void Scheduler::maybePostMainThreadPendingHighPriorityTaskRunner()
@@ -256,12 +267,4 @@ bool Scheduler::hasPendingHighPriorityWork() const
     return acquireLoad(&m_highPriorityTaskCount) != 0;
 }
 
-void Scheduler::TracedTask::run()
-{
-    TRACE_EVENT2("blink", "TracedTask::run",
-        "src_file", m_location.fileName(),
-        "src_func", m_location.functionName());
-    m_task();
-}
-
 } // namespace blink