Add Callback::IsCancelled

base/callback_internal.cc

Index: base/callback_internal.cc
diff --git a/base/callback_internal.cc b/base/callback_internal.cc
index 303de4d71b84d148557f17bbf388cb35849e0622..e29dd694efb5e2fabc899ef1183fbac333b042b2 100644
--- a/base/callback_internal.cc
+++ b/base/callback_internal.cc
@@ -10,9 +10,12 @@ namespace base {
 namespace internal {
 
 BindStateBase::BindStateBase(InvokeFuncStorage polymorphic_invoke,
-                             void (*destructor)(BindStateBase*))
+                             void (*destructor)(BindStateBase*),
+                             bool (*is_cancelled)(const BindStateBase*))
       : polymorphic_invoke_(polymorphic_invoke),
-        ref_count_(0), destructor_(destructor) {}
+        ref_count_(0),
+        destructor_(destructor),
+        is_cancelled_(is_cancelled) {}
 
 void BindStateBase::AddRef() {
   AtomicRefCountInc(&ref_count_);
@@ -34,6 +37,11 @@ void CallbackBase<CopyMode::MoveOnly>::Reset() {
   bind_state_ = nullptr;
 }
 
+bool CallbackBase<CopyMode::MoveOnly>::IsCancelled() const {
+  DCHECK(bind_state_);

[alex clarke (OOO till 29th), 2016/09/07 15:53:53]

Can we do this instead of the DCHECK?

if (!bind_state_)
  return false;

[dcheng, 2016/09/07 21:40:27]

If there's a null callback posted to the task queue, we'll explode anyway when
we try to Run() it. So DCHECKing seems fine to me.

[tzik, 2016/09/08 03:55:10]

Hmm, right, it doesn't matter for the intended usage in the scheduler,  but I
feel it's natural to return false for a empty callback. Let me update this.

[dcheng, 2016/09/08 04:01:33]

What is the use case where we'd want to call this on an empty callback? I feel
pretty strongly about keeping this a DCHECK: IsCancelled() simply doesn't have
any meaning for an empty callback.

[tzik, 2016/09/08 05:21:45]

There will be no actual use case for it. I just think state query functions
should be always valid.
Anyway, I don't have strong opinion on this. And it's OK to me to revert this to
DCHECK.

+  return bind_state_->IsCancelled();
+}
+
 bool CallbackBase<CopyMode::MoveOnly>::EqualsInternal(
     const CallbackBase& other) const {
   return bind_state_ == other.bind_state_;