util: global lock for certain MySQL operations

Even the reentrant libmysqlclient_r has some non-threadsafe operations,
which need to be protected by a global mutex.
<http://dev.mysql.com/doc/refman/5.5/en/c-api-threaded-clients.html>

Change-Id: I444e42f82cf982a6c8f8f2596e8991d0a5009b28

src/core/util/Database.cc

@@ -8,7 +8,15 @@ static fail::Logger LOG("Database", true);
 
 using namespace fail;
 
+#ifndef __puma
+boost::mutex Database::m_global_lock;
+#endif
+
 Database::Database(const std::string &username, const std::string &host, const std::string &database) {
+#ifndef __puma
+	boost::lock_guard<boost::mutex> guard(m_global_lock);
+#endif
+
 	handle = mysql_init(0);
 	last_result = 0;
 	mysql_options(handle, MYSQL_READ_DEFAULT_FILE, "~/.my.cnf");
@@ -26,6 +34,9 @@ Database::~Database()
 	// flush cached INSERTs if available
 	insert_multiple();
 
+#ifndef __puma
+	boost::lock_guard<boost::mutex> guard(m_global_lock);
+#endif
 	mysql_close(handle);
 }
 

src/core/util/Database.hpp

@@ -23,6 +23,7 @@ namespace fail {
 		MYSQL_RES *last_result; // !< Used for mysql_result_free
 #ifndef __puma
 		boost::mutex m_handle_lock;
+		static boost::mutex m_global_lock;
 #endif
 		std::string m_insertquery;
 		std::vector<std::string> m_insertquery_values;