Issue #11408: In threading.Lock.acquire(), only call gettimeofday() when
really necessary.  Patch by Charles-François Natali.
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index 14ed55e..57d08d3 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -54,8 +54,8 @@
     _PyTime_timeval endtime;
 
 
-    _PyTime_gettimeofday(&endtime);
     if (microseconds > 0) {
+        _PyTime_gettimeofday(&endtime);
         endtime.tv_sec += microseconds / (1000 * 1000);
         endtime.tv_usec += microseconds % (1000 * 1000);
     }
@@ -76,7 +76,7 @@
 
             /* If we're using a timeout, recompute the timeout after processing
              * signals, since those can take time.  */
-            if (microseconds >= 0) {
+            if (microseconds > 0) {
                 _PyTime_gettimeofday(&curtime);
                 microseconds = ((endtime.tv_sec - curtime.tv_sec) * 1000000 +
                                 (endtime.tv_usec - curtime.tv_usec));