Introduce AsioConditionVariable

lib/base/io-engine.cpp

@@ -142,6 +142,28 @@ void AsioDualEvent::WaitForClear(boost::asio::yield_context yc)
 	m_IsFalse.Wait(std::move(yc));
 }
 
+AsioConditionVariable::AsioConditionVariable(boost::asio::io_context& io)
+	: m_Timer(io)
+{
+	m_Timer.expires_at(decltype(m_Timer)::clock_type::time_point::max());
+}
+
+void AsioConditionVariable::Wait(boost::asio::yield_context yc)
+{
+	boost::system::error_code ec;
+	m_Timer.async_wait(yc[ec]);
+}
+
+bool AsioConditionVariable::NotifyOne()
+{
+	return m_Timer.cancel_one();
+}
+
+size_t AsioConditionVariable::NotifyAll()
+{
+	return m_Timer.cancel();
+}
+
 /**
  * Cancels any pending timeout callback.
  *

lib/base/io-engine.hpp

@@ -23,6 +23,7 @@
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/io_context_strand.hpp>
 #include <boost/asio/spawn.hpp>
+#include <boost/asio/steady_timer.hpp>
 
 #if BOOST_VERSION >= 108700
 #	include <boost/asio/detached.hpp>
@@ -56,6 +57,24 @@ private:
 	bool m_Done;
 };
 
+/**
+ * Condition variable which doesn't block I/O threads
+ *
+ * @ingroup base
+ */
+class AsioConditionVariable
+{
+public:
+	AsioConditionVariable(boost::asio::io_context& io);
+
+	void Wait(boost::asio::yield_context yc);
+	bool NotifyOne();
+	size_t NotifyAll();
+
+private:
+	boost::asio::steady_timer m_Timer;
+};
+
 /**
  * Async I/O engine
  *