IcingaDB: start initial sync after all child connections are established

Icinga started the initial config sync right after the first Redis connection
was established. If any other connections would take longer to connect than
when it's first needed, queries were discarded.

lib/icingadb/icingadb.cpp

@@ -73,22 +73,31 @@ void IcingaDB::Start(bool runtimeCreated)
 		if (!ctype)
 			continue;
 
-		m_Rcons[ctype] = new RedisConnection(GetHost(), GetPort(), GetPath(), GetPassword(), GetDbIndex(),
+		RedisConnection::Ptr con = new RedisConnection(GetHost(), GetPort(), GetPath(), GetPassword(), GetDbIndex(),
 			GetEnableTls(), GetInsecureNoverify(), GetCertPath(), GetKeyPath(), GetCaPath(), GetCrlPath(),
 			GetTlsProtocolmin(), GetCipherList(), GetConnectTimeout(), GetDebugInfo(), m_Rcon);
+
+		con->SetConnectedCallback([this, con](boost::asio::yield_context& yc) {
+			con->SetConnectedCallback(nullptr);
+
+			size_t pending = --m_PendingRcons;
+			Log(LogDebug, "IcingaDB") << pending << " pending child connections remaining";
+			if (pending == 0) {
+				m_WorkQueue.Enqueue([this]() { OnConnectedHandler(); });
+			}
+		});
+
+		m_Rcons[ctype] = std::move(con);
 	}
 
-	auto connectedCallback ([this](boost::asio::yield_context& yc) {
-		m_WorkQueue.Enqueue([this]() { OnConnectedHandler(); });
-	});
+	m_PendingRcons = m_Rcons.size();
+
+	m_Rcon->SetConnectedCallback([this](boost::asio::yield_context& yc) {
+		m_Rcon->SetConnectedCallback(nullptr);
 
-	m_Rcon->SetConnectedCallback([this, connectedCallback](boost::asio::yield_context& yc) {
 		for (auto& kv : m_Rcons) {
 			kv.second->Start();
 		}
-
-		m_Rcon->SetConnectedCallback(connectedCallback);
-		connectedCallback(yc);
 	});
 	m_Rcon->Start();
 

lib/icingadb/icingadb.hpp

@@ -13,6 +13,7 @@
 #include "icinga/downtime.hpp"
 #include "remote/messageorigin.hpp"
 #include <boost/thread/once.hpp>
+#include <atomic>
 #include <memory>
 #include <mutex>
 #include <set>
@@ -169,6 +170,7 @@ private:
 
 	RedisConnection::Ptr m_Rcon;
 	std::unordered_map<ConfigType*, RedisConnection::Ptr> m_Rcons;
+	std::atomic_size_t m_PendingRcons;
 
 	struct {
 		DumpedGlobals CustomVar, ActionUrl, NotesUrl, IconImage;