Add Semaphore class

A simple Semaphore class that makes it simpler and less
erroprone to use a semaphore.

server/core/semaphore.cc

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/semaphore.hh>
+#include <time.h>
+
+namespace maxscale
+{
+
+bool Semaphore::timedwait(time_t seconds,
+                          long nseconds,
+                          signal_approach_t signal_approach) const
+{
+    ss_dassert(nseconds <= 999999999);
+
+    timespec ts;
+
+    ss_debug(int rc=) clock_gettime(CLOCK_REALTIME, &ts);
+    ss_dassert(rc == 0);
+
+    ts.tv_sec += seconds;
+
+    uint64_t nseconds_sum = ts.tv_nsec + nseconds;
+
+    if (nseconds_sum > 1000000000)
+    {
+        ts.tv_sec += 1;
+        nseconds_sum -= 1000000000;
+    }
+
+    ts.tv_nsec = nseconds_sum;
+
+    return timedwait(ts, signal_approach);
+}
+
+}