Core/MySQL: wait for the DB to be ready (#1286)

* Core/MySQL: wait for the DB to be ready
- Closes #1285

* Fix build on windows

src/common/Database/MySQLConnection.cpp

@@ -14,6 +14,8 @@
 #include <mysql.h>
 #include <mysqld_error.h>
 #include <errmsg.h>
+#include <chrono>
+#include <thread>
 
 #include "MySQLConnection.h"
 #include "MySQLThreading.h"
@@ -24,6 +26,9 @@
 #include "Timer.h"
 #include "Log.h"
 
+using namespace std::this_thread;
+using namespace std::chrono;
+
 MySQLConnection::MySQLConnection(MySQLConnectionInfo& connInfo) :
 m_reconnecting(false),
 m_prepareError(false),
@@ -107,8 +112,21 @@ bool MySQLConnection::Open()
     }
     #endif
 
-    m_Mysql = mysql_real_connect(mysqlInit, m_connectionInfo.host.c_str(), m_connectionInfo.user.c_str(),
+    // Possible improvement for future: make ATTEMPTS and SECONDS configurable values
-        m_connectionInfo.password.c_str(), m_connectionInfo.database.c_str(), port, unix_socket, 0);
+    uint32 const ATTEMPTS = 180;
+    uint32 const SECONDS = 10;
+
+    uint32 count = 0;
+    do {
+        m_Mysql = mysql_real_connect(
+            mysqlInit,
+            m_connectionInfo.host.c_str(),
+            m_connectionInfo.user.c_str(),
+            m_connectionInfo.password.c_str(),
+            m_connectionInfo.database.c_str(),
+            port,
+            unix_socket,
+            0);
 
         if (m_Mysql)
         {
@@ -133,10 +151,20 @@ bool MySQLConnection::Open()
         }
         else
         {
+            count++;
             sLog->outError("Could not connect to MySQL database at %s: %s\n", m_connectionInfo.host.c_str(), mysql_error(mysqlInit));
+            sLog->outError("Retrying in 10 seconds...\n\n");
+            sleep_for(seconds(SECONDS));
+        }
+    } while (!m_Mysql && count < ATTEMPTS);
+
+    sLog->outError(
+        "Could not connect to MySQL database at %s: %s after %d attempts\n",
+        m_connectionInfo.host.c_str(),
+        mysql_error(mysqlInit),
+        ATTEMPTS);
     mysql_close(mysqlInit);
     return false;
-    }
 }
 
 bool MySQLConnection::PrepareStatements()