RedisConnection#Connect(): get rid of spin lock

lib/base/io-engine.cpp

@@ -124,28 +124,50 @@ void IoEngine::RunEventLoop()
 	}
 }
 
-AsioConditionVariable::AsioConditionVariable(boost::asio::io_context& io, bool init)
+AsioEvent::AsioEvent(boost::asio::io_context& io, bool init)
 	: m_Timer(io)
 {
 	m_Timer.expires_at(init ? boost::posix_time::neg_infin : boost::posix_time::pos_infin);
 }
 
-void AsioConditionVariable::Set()
+void AsioEvent::Set()
 {
 	m_Timer.expires_at(boost::posix_time::neg_infin);
 }
 
-void AsioConditionVariable::Clear()
+void AsioEvent::Clear()
 {
 	m_Timer.expires_at(boost::posix_time::pos_infin);
 }
 
-void AsioConditionVariable::Wait(boost::asio::yield_context yc)
+void AsioEvent::Wait(boost::asio::yield_context yc)
 {
 	boost::system::error_code ec;
 	m_Timer.async_wait(yc[ec]);
 }
 
+AsioSymmetricEvent::AsioSymmetricEvent(boost::asio::io_context& io, bool init)
+	: m_IsTrue(io, init), m_IsFalse(io, !init)
+{
+}
+
+void AsioSymmetricEvent::Set()
+{
+	m_IsTrue.Set();
+	m_IsFalse.Clear();
+}
+
+void AsioSymmetricEvent::Clear()
+{
+	m_IsTrue.Clear();
+	m_IsFalse.Set();
+}
+
+void AsioSymmetricEvent::Wait(boost::asio::yield_context yc, bool desiredState)
+{
+	(desiredState ? m_IsTrue : m_IsFalse).Wait(std::move(yc));
+}
+
 /**
  * Cancels any pending timeout callback.
  *

lib/base/io-engine.hpp

@@ -145,14 +145,14 @@ class TerminateIoThread : public std::exception
 };
 
 /**
- * Condition variable which doesn't block I/O threads
+ * Awaitable flag which doesn't block I/O threads, inspired by threading.Event from Python
  *
  * @ingroup base
  */
-class AsioConditionVariable
+class AsioEvent
 {
 public:
-	AsioConditionVariable(boost::asio::io_context& io, bool init = false);
+	AsioEvent(boost::asio::io_context& io, bool init = false);
 
 	void Set();
 	void Clear();
@@ -162,6 +162,24 @@ class AsioConditionVariable
 	boost::asio::deadline_timer m_Timer;
 };
 
+/**
+ * Like AsioEvent, but additionally supports waiting for an event to be cleared
+ *
+ * @ingroup base
+ */
+class AsioSymmetricEvent
+{
+public:
+	AsioSymmetricEvent(boost::asio::io_context& io, bool init = false);
+
+	void Set();
+	void Clear();
+	void Wait(boost::asio::yield_context yc, bool desiredState = true);
+
+private:
+	AsioEvent m_IsTrue, m_IsFalse;
+};
+
 /**
  * I/O timeout emulator
  *

lib/icingadb/redisconnection.cpp

@@ -302,12 +302,6 @@ void RedisConnection::Connect(asio::yield_context& yc)
 
 	boost::asio::deadline_timer timer (m_Strand.context());
 
-	auto waitForReadLoop ([this, &yc]() {
-		while (!m_Queues.FutureResponseActions.empty()) {
-			IoEngine::YieldCurrentCoroutine(yc);
-		}
-	});
-
 	for (;;) {
 		try {
 			if (m_Path.IsEmpty()) {
@@ -339,7 +333,7 @@ void RedisConnection::Connect(asio::yield_context& yc)
 					}
 
 					Handshake(conn, yc);
-					waitForReadLoop();
+					m_QueuedReads.Wait(yc, false);
 					m_TlsConn = std::move(conn);
 				} else {
 					Log(m_Parent ? LogNotice : LogInformation, "IcingaDB")
@@ -350,7 +344,7 @@ void RedisConnection::Connect(asio::yield_context& yc)
 
 					icinga::Connect(conn->next_layer(), m_Host, Convert::ToString(m_Port), yc);
 					Handshake(conn, yc);
-					waitForReadLoop();
+					m_QueuedReads.Wait(yc, false);
 					m_TcpConn = std::move(conn);
 				}
 			} else {
@@ -362,7 +356,7 @@ void RedisConnection::Connect(asio::yield_context& yc)
 
 				conn->next_layer().async_connect(Unix::endpoint(m_Path.CStr()), yc);
 				Handshake(conn, yc);
-				waitForReadLoop();
+				m_QueuedReads.Wait(yc, false);
 				m_UnixConn = std::move(conn);
 			}
 

lib/icingadb/redisconnection.hpp

@@ -262,7 +262,8 @@ namespace icinga
 		std::set<QueryPriority> m_SuppressedQueryKinds;
 
 		// Indicate that there's something to send/receive
-		AsioConditionVariable m_QueuedWrites, m_QueuedReads;
+		AsioEvent m_QueuedWrites;
+		AsioSymmetricEvent m_QueuedReads;
 
 		std::function<void(boost::asio::yield_context& yc)> m_ConnectedCallback;
 

lib/remote/jsonrpcconnection.hpp

@@ -75,8 +75,8 @@ class JsonRpcConnection final : public Object
 	double m_Seen;
 	boost::asio::io_context::strand m_IoStrand;
 	std::vector<String> m_OutgoingMessagesQueue;
-	AsioConditionVariable m_OutgoingMessagesQueued;
-	AsioConditionVariable m_WriterDone;
+	AsioEvent m_OutgoingMessagesQueued;
+	AsioEvent m_WriterDone;
 	Atomic<bool> m_ShuttingDown;
 	boost::asio::deadline_timer m_CheckLivenessTimer, m_HeartbeatTimer;