Introduce RunLoop::Delegate splitting RunLoop/MessageLoop some more.

base/run_loop.cc

Index: base/run_loop.cc
diff --git a/base/run_loop.cc b/base/run_loop.cc
index b7df5b23d8d72f737c5c6f468c508ec12ade8fd9..adf3b5a003d6f8f71d9794e680712bc11fe1ffbf 100644
--- a/base/run_loop.cc
+++ b/base/run_loop.cc
@@ -4,12 +4,9 @@
 
 #include "base/run_loop.h"
 
-#include <stack>
-
 #include "base/bind.h"
 #include "base/lazy_instance.h"
-#include "base/observer_list.h"
-#include "base/threading/thread_local_storage.h"
+#include "base/threading/thread_local.h"
 #include "base/tracked_objects.h"
 #include "build/build_config.h"
 
@@ -17,74 +14,52 @@ namespace base {
 
 namespace {
 
-class ThreadLocalRunLoopState {
- public:
-  // A vector-based stack is more memory efficient than the default deque-based
-  // stack as the active RunLoop stack isn't expected to ever have more than a
-  // few entries.
-  using RunLoopStack = std::stack<RunLoop*, std::vector<RunLoop*>>;
-
-  ThreadLocalRunLoopState()
-      : slot_(&ThreadLocalRunLoopState::OnTLSDestruction) {}
-
-  ~ThreadLocalRunLoopState() = delete;
-
-  RunLoopStack& GetActiveRunLoops() {
-    return GetOrCreateInternalState()->active_run_loops;
-  }
-
-  ObserverList<RunLoop::NestingObserver>& GetNestingObservers() {
-    InternalState* state = GetOrCreateInternalState();
-    CHECK(state->allow_nesting);
-    return state->nesting_observers;
-  }
-
-  bool IsNestingAllowed() { return GetOrCreateInternalState()->allow_nesting; }
-
-  void DisallowNesting() { GetOrCreateInternalState()->allow_nesting = false; }
-
-  void Reset() {
-    InternalState* state = static_cast<InternalState*>(slot_.Get());
-    if (state) {
-      slot_.Set(nullptr);
-      delete state;
-    }
-  }
+LazyInstance<ThreadLocalPointer<RunLoop::Delegate>>::Leaky tls_delegate =
+    LAZY_INSTANCE_INITIALIZER;
 
- private:
-  struct InternalState {
-    bool allow_nesting = true;
-    RunLoopStack active_run_loops;
-    ObserverList<RunLoop::NestingObserver> nesting_observers;
-  };
+}  // namespace
 
-  static void OnTLSDestruction(void* internal_state) {
-    delete static_cast<InternalState*>(internal_state);
-  }
+RunLoop::Delegate::Delegate() {
+  // The Delegate can be created on another thread. It is only bound in
+  // BindToCurrentThread().
+  DETACH_FROM_THREAD(bound_thread_checker_);
+}
 
-  InternalState* GetOrCreateInternalState() {
-    InternalState* state = static_cast<InternalState*>(slot_.Get());
-    if (!state) {
-      state = new InternalState;
-      slot_.Set(static_cast<void*>(state));
-    }
-    return state;
-  }
+RunLoop::Delegate::~Delegate() {
+  DCHECK_CALLED_ON_VALID_THREAD(bound_thread_checker_);
+  // A RunLoop::Delegate may be destroyed before it is bound, if so it may still
+  // be on its creation thread (e.g. a Thread that fails to start) and
+  // shouldn't disrupt that thread's state.
+  if (bound_)
+    tls_delegate.Get().Set(nullptr);
+}
 
-  ThreadLocalStorage::Slot slot_;
+bool RunLoop::Delegate::IsNested() const {
+  DCHECK_CALLED_ON_VALID_THREAD(bound_thread_checker_);
+  DCHECK(bound_);
+  return active_run_loops_.size() > 1;
+}
 
-  DISALLOW_COPY_AND_ASSIGN(ThreadLocalRunLoopState);
-};
+RunLoop* RunLoop::Delegate::GetTopMostRunLoop() const {
+  DCHECK_CALLED_ON_VALID_THREAD(bound_thread_checker_);
+  DCHECK(bound_);
+  return active_run_loops_.empty() ? nullptr : active_run_loops_.top();
+}
 
-LazyInstance<ThreadLocalRunLoopState>::Leaky tls_run_loop_state =
-    LAZY_INSTANCE_INITIALIZER;
+void RunLoop::Delegate::BindToCurrentThread() {
+  // Bind the checker to this thread.
+  DCHECK_CALLED_ON_VALID_THREAD(bound_thread_checker_);
 
-}  // namespace
+  // There can only be one RunLoop::Delegate per thread.
+  DCHECK(!tls_delegate.Get().Get());
+  DCHECK(!bound_);
+  tls_delegate.Get().Set(this);
+  bound_ = true;
+}
 
-RunLoop::RunLoop()
-    : loop_(MessageLoop::current()),
-      weak_factory_(this) {
-  DCHECK(loop_);
+RunLoop::RunLoop() : delegate_(tls_delegate.Get().Get()), weak_factory_(this) {
+  // A RunLoop::Delegate must be bound to this thread prior to using RunLoop.
+  DCHECK(delegate_);
 }
 
 RunLoop::~RunLoop() {
@@ -102,7 +77,7 @@ void RunLoop::Run() {
   // any.
   tracked_objects::TaskStopwatch stopwatch;
   stopwatch.Start();
-  loop_->RunHandler();
+  delegate_->Run();
   stopwatch.Stop();
 
   AfterRun();
@@ -119,9 +94,9 @@ void RunLoop::Quit() {
   DCHECK(thread_checker_.CalledOnValidThread());
 
   quit_called_ = true;
-  if (running_ && loop_->run_loop_ == this) {
+  if (running_ && delegate_->active_run_loops_.top() == this) {
     // This is the inner-most RunLoop, so quit now.
-    loop_->QuitNow();
+    delegate_->Quit();
   }
 }
 
@@ -143,38 +118,37 @@ base::Closure RunLoop::QuitWhenIdleClosure() {
 }
 
 // static
-void RunLoop::ResetTLSState() {
-  tls_run_loop_state.Get().Reset();
-}
-
-// static
 bool RunLoop::IsRunningOnCurrentThread() {
-  return !tls_run_loop_state.Get().GetActiveRunLoops().empty();
+  return !tls_delegate.Get().Get()->active_run_loops_.empty();
 }
 
 // static
 bool RunLoop::IsNestedOnCurrentThread() {
-  return tls_run_loop_state.Get().GetActiveRunLoops().size() > 1;
+  return tls_delegate.Get().Get()->active_run_loops_.size() > 1;
 }
 
 // static
 void RunLoop::AddNestingObserverOnCurrentThread(NestingObserver* observer) {
-  tls_run_loop_state.Get().GetNestingObservers().AddObserver(observer);
+  Delegate* delegate = tls_delegate.Get().Get();
+  CHECK(delegate->allow_nesting_);
+  delegate->nesting_observers_.AddObserver(observer);
 }
 
 // static
 void RunLoop::RemoveNestingObserverOnCurrentThread(NestingObserver* observer) {
-  tls_run_loop_state.Get().GetNestingObservers().RemoveObserver(observer);
+  Delegate* delegate = tls_delegate.Get().Get();
+  CHECK(delegate->allow_nesting_);
+  delegate->nesting_observers_.RemoveObserver(observer);
 }
 
 // static
 bool RunLoop::IsNestingAllowedOnCurrentThread() {
-  return tls_run_loop_state.Get().IsNestingAllowed();
+  return tls_delegate.Get().Get()->allow_nesting_;
 }
 
 // static
 void RunLoop::DisallowNestingOnCurrentThread() {
-  tls_run_loop_state.Get().DisallowNesting();
+  tls_delegate.Get().Get()->allow_nesting_ = false;
 }
 
 bool RunLoop::BeforeRun() {
@@ -187,19 +161,14 @@ bool RunLoop::BeforeRun() {
   if (quit_called_)
     return false;
 
-  auto& active_run_loops = tls_run_loop_state.Get().GetActiveRunLoops();
-  active_run_loops.push(this);
-
-  const bool is_nested = active_run_loops.size() > 1;
+  auto& active_run_loops_ = delegate_->active_run_loops_;
+  active_run_loops_.push(this);
 
-  // TODO(gab): Break the inter-dependency between MessageLoop and RunLoop
-  // further. http://crbug.com/703346
-  loop_->run_loop_ = this;
-  loop_->is_nested_ = is_nested;
+  const bool is_nested = active_run_loops_.size() > 1;
 
   if (is_nested) {
-    CHECK(tls_run_loop_state.Get().IsNestingAllowed());
-    for (auto& observer : tls_run_loop_state.Get().GetNestingObservers())
+    CHECK(delegate_->allow_nesting_);
+    for (auto& observer : delegate_->nesting_observers_)
       observer.OnBeginNestedRunLoop();
   }
 
@@ -212,18 +181,16 @@ void RunLoop::AfterRun() {
 
   running_ = false;
 
-  auto& active_run_loops = tls_run_loop_state.Get().GetActiveRunLoops();
-  DCHECK_EQ(active_run_loops.top(), this);
-  active_run_loops.pop();
+  auto& active_run_loops_ = delegate_->active_run_loops_;
+  DCHECK_EQ(active_run_loops_.top(), this);
+  active_run_loops_.pop();
 
   RunLoop* previous_run_loop =
-      active_run_loops.empty() ? nullptr : active_run_loops.top();
-  loop_->run_loop_ = previous_run_loop;
-  loop_->is_nested_ = active_run_loops.size() > 1;
+      active_run_loops_.empty() ? nullptr : active_run_loops_.top();
 
   // Execute deferred QuitNow, if any:
   if (previous_run_loop && previous_run_loop->quit_called_)
-    loop_->QuitNow();
+    delegate_->Quit();
 }
 
 }  // namespace base