-#define grep_lock() pthread_mutex_lock(&grep_mutex)
-#define grep_unlock() pthread_mutex_unlock(&grep_mutex)
-#define read_sha1_lock() pthread_mutex_lock(&read_sha1_mutex)
-#define read_sha1_unlock() pthread_mutex_unlock(&read_sha1_mutex)
+#define WHEN_THREADED(x) do { if (use_threads) (x); } while (0)
+#define grep_lock() WHEN_THREADED(pthread_mutex_lock(&grep_mutex))
+#define grep_unlock() WHEN_THREADED(pthread_mutex_unlock(&grep_mutex))
+#define read_sha1_lock() WHEN_THREADED(pthread_mutex_lock(&read_sha1_mutex))
+#define read_sha1_unlock() WHEN_THREADED(pthread_mutex_unlock(&read_sha1_mutex))