Add WFFacilities::WaitGroup::add(). (sogou#1751)

Author: Barenboim

src/manager/WFFacilities.h

@@ -66,9 +66,10 @@ class WFFacilities
 		WaitGroup(int n);
 		~WaitGroup();
 
-		void done();
 		void wait() const;
 		std::future_status wait(int timeout) const;
+		void add(int n);
+		void done();
 
 	private:
 		static void __wait_group_callback(WFCounterTask *task);

src/manager/WFFacilities.inl

@@ -192,14 +192,6 @@ inline WFFacilities::WaitGroup::~WaitGroup()
 		this->task->count();
 }
 
-inline void WFFacilities::WaitGroup::done()
-{
-	if (--this->nleft == 0)
-	{
-		this->task->count();
-	}
-}
-
 inline void WFFacilities::WaitGroup::wait() const
 {
 	if (this->nleft < 0)
@@ -222,6 +214,19 @@ inline std::future_status WFFacilities::WaitGroup::wait(int timeout) const
 	return this->future.wait_for(std::chrono::milliseconds(timeout));
 }
 
+inline void WFFacilities::WaitGroup::add(int n)
+{
+	if ((this->nleft += n) == 0)
+	{
+		this->task->count();
+	}
+}
+
+inline void WFFacilities::WaitGroup::done()
+{
+	this->add(-1);
+}
+
 inline void WFFacilities::WaitGroup::__wait_group_callback(WFCounterTask *task)
 {
 	auto *pr = static_cast<WFPromise<void> *>(task->user_data);