+#if HAVE_PTHREAD_SIGMASK
+ int ret = pthread_sigmask (how, new_mask, old_mask);
+# if PTHREAD_SIGMASK_INEFFECTIVE
+ if (ret == 0)
+ {
+ /* Detect whether pthread_sigmask is currently ineffective.
+ Don't cache the information: libpthread.so could be dynamically
+ loaded after the program started and after pthread_sigmask was
+ called for the first time. */
+ if (pthread_sigmask (1729, NULL, NULL) == 0)
+ {
+ /* pthread_sigmask is currently ineffective. The program is not
+ linked to -lpthread. So use sigprocmask instead. */
+ return (sigprocmask (how, new_mask, old_mask) < 0 ? errno : 0);
+ }
+ }
+# endif
+ return ret;
+#else