time: Allow using different clocks

On some systems it might be preferable to use e.g. CLOCK_BOOTTIME
instead of CLOCK_MONOTONIC, which is also not affected by time
adjustments but includes times when the system was suspended.

src/libstrongswan/threading/mutex.c

@@ -337,7 +337,7 @@ condvar_t *condvar_create(condvar_type_t type)
 				pthread_condattr_t condattr;
 				pthread_condattr_init(&condattr);
 #ifdef HAVE_CONDATTR_CLOCK_MONOTONIC
-				pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC);
+				pthread_condattr_setclock(&condattr, TIME_CLOCK_ID);
 #endif
 				pthread_cond_init(&this->condvar, &condattr);
 				pthread_condattr_destroy(&condattr);

src/libstrongswan/utils/utils/time.c

@@ -52,7 +52,7 @@ time_t time_monotonic(timeval_t *tv)
 	 * monotonic time source only if it is also supported by pthread. */
 	timespec_t ts;
 
-	if (clock_gettime(CLOCK_MONOTONIC, &ts) == 0)
+	if (clock_gettime(TIME_CLOCK_ID, &ts) == 0)
 	{
 		if (tv)
 		{

src/libstrongswan/utils/utils/time.h

@@ -32,6 +32,20 @@
  */
 #define TIME_32_BIT_SIGNED_MAX	0x7fffffff
 
+/**
+ * The clock that should be used for time_monotonic() and conditional variables
+ */
+#ifdef HAVE_CLOCK_GETTIME
+#ifdef HAVE_CONDATTR_CLOCK_MONOTONIC
+/* only can use different clocks if we can set it via attribute */
+#ifndef TIME_CLOCK_ID
+#define TIME_CLOCK_ID CLOCK_MONOTONIC
+#endif
+#else
+#define TIME_CLOCK_ID CLOCK_MONOTONIC
+#endif
+#endif
+
 /**
  * Handle struct timeval like an own type.
  */