Avoid listener is not called

Author: BewareMyPower

lib/Future.h

@@ -39,7 +39,8 @@ class InternalState {
     {
         INITIAL,
         COMPLETING,
-        COMPLETED
+        COMPLETED,
+        LISTENERS_EMPTY
     };
 
     // NOTE: Add the constructor explicitly just to be compatible with GCC 4.8
@@ -54,6 +55,15 @@ class InternalState {
             listener(result, value);
         } else {
             tailListener_ = listeners_.emplace_after(tailListener_, std::move(listener));
+            if (status_ == LISTENERS_EMPTY) {
+                auto listeners = std::move(listeners_);
+                auto result = result_;
+                auto value = value_;
+                lock.unlock();
+                for (auto &&listener : listeners) {
+                    listener(result, value);
+                }
+            }
         }
     }
 
@@ -70,9 +80,12 @@ class InternalState {
         value_ = value;
         status_ = COMPLETED;
         cond_.notify_all();
+        lock.unlock();
 
+        lock.lock();
         if (!listeners_.empty()) {
             auto listeners = std::move(listeners_);
+            status_ = LISTENERS_EMPTY;
             lock.unlock();
             for (auto &&listener : listeners) {
                 listener(result, value);
@@ -82,7 +95,7 @@ class InternalState {
         return true;
     }
 
-    bool completed() const noexcept { return status_.load() == COMPLETED; }
+    bool completed() const noexcept { return status_.load() >= COMPLETED; }
 
     Result get(Type &value) const {
         Lock lock{mutex_};