Implement IoBoundWorkSlot

lib/base/io-engine.cpp

@@ -64,6 +64,29 @@ void CpuBoundWork::Done()
 	}
 }
 
+IoBoundWorkSlot::IoBoundWorkSlot(boost::asio::yield_context yc)
+	: yc(yc)
+{
+	IoEngine::Get().m_CpuBoundSemaphore.fetch_add(1);
+}
+
+IoBoundWorkSlot::~IoBoundWorkSlot()
+{
+	auto& ioEngine (IoEngine::Get());
+
+	for (;;) {
+		auto availableSlots (ioEngine.m_CpuBoundSemaphore.fetch_sub(1));
+
+		if (availableSlots < 1) {
+			ioEngine.m_CpuBoundSemaphore.fetch_add(1);
+			ioEngine.m_AlreadyExpiredTimer.async_wait(yc);
+			continue;
+		}
+
+		break;
+	}
+}
+
 LazyInit<std::unique_ptr<IoEngine>> IoEngine::m_Instance ([]() { return std::unique_ptr<IoEngine>(new IoEngine()); });
 
 IoEngine& IoEngine::Get()

lib/base/io-engine.hpp

@@ -55,6 +55,25 @@ private:
 	bool m_Done;
 };
 
+/**
+ * Scope break for CPU-bound work done in an I/O thread
+ *
+ * @ingroup base
+ */
+class IoBoundWorkSlot
+{
+public:
+	IoBoundWorkSlot(boost::asio::yield_context yc);
+	IoBoundWorkSlot(const IoBoundWorkSlot&) = delete;
+	IoBoundWorkSlot(IoBoundWorkSlot&&) = delete;
+	IoBoundWorkSlot& operator=(const IoBoundWorkSlot&) = delete;
+	IoBoundWorkSlot& operator=(IoBoundWorkSlot&&) = delete;
+	~IoBoundWorkSlot();
+
+private:
+	boost::asio::yield_context yc;
+};
+
 /**
  * Async I/O engine
  *
@@ -63,6 +82,7 @@ private:
 class IoEngine
 {
 	friend CpuBoundWork;
+	friend IoBoundWorkSlot;
 
 public:
 	IoEngine(const IoEngine&) = delete;