Make nesting/running states a RunLoop rather than a MessageLoop concept.

base/run_loop.cc

 // Copyright (c) 2012 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/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/tracked_objects.h"
 #include "build/build_config.h"
 
 namespace base {
 
+namespace {
+
+class ThreadLocalRunLoopState {
+ public:
+  ThreadLocalRunLoopState()
+      : slot_(&ThreadLocalRunLoopState::OnTLSDestruction) {}
+
+  ~ThreadLocalRunLoopState() = delete;
+
+  std::stack<RunLoop*>& 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; }
+
+ private:
+  struct InternalState {
+    bool allow_nesting = true;
+    std::stack<RunLoop*> active_run_loops;

[danakj, 2017/04/20 14:57:32]

stacks are deques by default which are terrible for wasting memory. the number
of things here is small, maybe make the stack backed by a vector?

[gab, 2017/04/20 16:22:02]

Good point, done.

+    ObserverList<RunLoop::NestingObserver> nesting_observers;
+  };
+
+  static void OnTLSDestruction(void* internal_state) {
+    delete static_cast<InternalState*>(internal_state);
+  }
+
+  InternalState* GetOrCreateInternalState() {
+    InternalState* state = static_cast<InternalState*>(slot_.Get());
+    if (!state) {
+      state = new InternalState;
+      slot_.Set(static_cast<void*>(state));
+    }
+    return state;
+  }
+
+  ThreadLocalStorage::Slot slot_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThreadLocalRunLoopState);
+};
+
+LazyInstance<ThreadLocalRunLoopState>::Leaky tls_run_loop_state =
+    LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
 RunLoop::RunLoop()
     : loop_(MessageLoop::current()),
-      previous_run_loop_(NULL),
-      run_depth_(0),
-      run_called_(false),
-      quit_called_(false),
-      running_(false),
-      quit_when_idle_received_(false),
       weak_factory_(this) {
   DCHECK(loop_);
 }
 
 RunLoop::~RunLoop() {
+  DCHECK(thread_checker_.CalledOnValidThread());
 }
 
 void RunLoop::Run() {
   DCHECK(thread_checker_.CalledOnValidThread());
+
   if (!BeforeRun())
     return;
 
   // Use task stopwatch to exclude the loop run time from the current task, if
   // any.
   tracked_objects::TaskStopwatch stopwatch;
   stopwatch.Start();
   loop_->RunHandler();
   stopwatch.Stop();
 
   AfterRun();
 }
 
 void RunLoop::RunUntilIdle() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
   quit_when_idle_received_ = true;
   Run();
 }
 
 void RunLoop::Quit() {
   DCHECK(thread_checker_.CalledOnValidThread());
+
   quit_called_ = true;
   if (running_ && loop_->run_loop_ == this) {
     // This is the inner-most RunLoop, so quit now.
     loop_->QuitNow();
   }
 }
 
 void RunLoop::QuitWhenIdle() {
   DCHECK(thread_checker_.CalledOnValidThread());
   quit_when_idle_received_ = true;
 }
 
 base::Closure RunLoop::QuitClosure() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   return base::Bind(&RunLoop::Quit, weak_factory_.GetWeakPtr());
 }
 
 base::Closure RunLoop::QuitWhenIdleClosure() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   return base::Bind(&RunLoop::QuitWhenIdle, weak_factory_.GetWeakPtr());
 }
 
+// static
+bool RunLoop::IsRunningOnCurrentThread() {
+  return !tls_run_loop_state.Get().GetActiveRunLoops().empty();
+}
+
+// static
+bool RunLoop::IsNestedOnCurrentThread() {
+  return tls_run_loop_state.Get().GetActiveRunLoops().size() > 1;
+}
+
+// static
+void RunLoop::AddNestingObserverOnCurrentThread(NestingObserver* observer) {
+  tls_run_loop_state.Get().GetNestingObservers().AddObserver(observer);
+}
+
+// static
+void RunLoop::RemoveNestingObserverOnCurrentThread(NestingObserver* observer) {
+  tls_run_loop_state.Get().GetNestingObservers().RemoveObserver(observer);
+}
+
+// static
+bool RunLoop::IsNestingAllowedOnCurrentThread() {
+  return tls_run_loop_state.Get().IsNestingAllowed();
+}
+
+// static
+void RunLoop::DisallowNestingOnCurrentThread() {
+  tls_run_loop_state.Get().DisallowNesting();
+}
+
 bool RunLoop::BeforeRun() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
   DCHECK(!run_called_);
   run_called_ = true;
 
   // Allow Quit to be called before Run.
   if (quit_called_)
     return false;
 
-  // Push RunLoop stack:
-  previous_run_loop_ = loop_->run_loop_;
-  run_depth_ = previous_run_loop_? previous_run_loop_->run_depth_ + 1 : 1;
+  std::stack<RunLoop*>& active_run_loops =

[danakj, 2017/04/20 14:57:32]

nit: auto?

[gab, 2017/04/20 16:22:01]

Done.

+      tls_run_loop_state.Get().GetActiveRunLoops();
+  active_run_loops.push(this);
+
+  const bool is_nested = active_run_loops.size() > 1;
+
+  // TODO(gab): Break the inter-dependency between MessageLoop and RunLoop
+  // further. http://crbug.com/703346
   loop_->run_loop_ = this;
+  loop_->is_nested_ = is_nested;
 
-  if (run_depth_ > 1)
-    loop_->NotifyBeginNestedLoop();
+  if (is_nested) {
+    CHECK(tls_run_loop_state.Get().IsNestingAllowed());
+    for (auto& observer : tls_run_loop_state.Get().GetNestingObservers())
+      observer.OnBeginNestedMessageLoop();
+  }
 
   running_ = true;
   return true;
 }
 
 void RunLoop::AfterRun() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
   running_ = false;
 
-  // Pop RunLoop stack:
-  loop_->run_loop_ = previous_run_loop_;
+  std::stack<RunLoop*>& active_run_loops =
+      tls_run_loop_state.Get().GetActiveRunLoops();
+  DCHECK_EQ(active_run_loops.top(), this);
+  active_run_loops.pop();
+
+  RunLoop* underlying_run_loop =

[danakj, 2017/04/20 14:57:32]

nit: i liked previous better than underlying as a name

[gab, 2017/04/20 16:22:01]

Done.

+      active_run_loops.empty() ? nullptr : active_run_loops.top();
+  loop_->run_loop_ = underlying_run_loop;
+  loop_->is_nested_ = active_run_loops.size() > 1;
 
   // Execute deferred QuitNow, if any:
-  if (previous_run_loop_ && previous_run_loop_->quit_called_)
+  if (underlying_run_loop && underlying_run_loop->quit_called_)
     loop_->QuitNow();
 }
 
 }  // namespace base