Use higher resolution timer for random client id generation.

ChangeLog.txt

@@ -6,6 +6,10 @@ Broker:
   case where a client connects using a username, and the anonymous ACL list is
   defined but specific user ACLs are not defined. Closes #1162.
 
+Library:
+- Use higher resolution timer for random initialisation of client id
+  generation. Closes #1177.
+
 
 1.5.7 - 20190213
 ================

lib/mosquitto.c

@@ -46,6 +46,16 @@ int mosquitto_lib_init(void)
 {
 #ifdef WIN32
 	srand(GetTickCount64());
+#elif _POSIX_TIMERS>0 && defined(_POSIX_MONOTONIC_CLOCK)
+	struct timespec tp;
+
+	clock_gettime(CLOCK_MONOTONIC, &tp);
+	srand(tp.tv_nsec);
+#elif defined(__APPLE__)
+	uint64_t ticks;
+
+	ticks = mach_absolute_time();
+	srand((unsigned int)ticks);
 #else
 	struct timeval tv;