GWakeup: test fallback case

We need to test the case of eventfd in the libc but no kernel support.

In order to do that, we add a separate compile of the GWakeup testcase
that interposes an 'eventfd' symbol that always returns -1 with errno
set.  That will trigger the fallback case.

configure.ac

@@ -2641,6 +2641,7 @@ main (void)
 if test x"$glib_cv_eventfd" = x"yes"; then
   AC_DEFINE(HAVE_EVENTFD, 1, [we have the eventfd(2) system call])
 fi
+AM_CONDITIONAL(HAVE_EVENTFD, [test "$glib_cv_eventfd" = "yes"])
 
 dnl ****************************************
 dnl *** GLib POLL* compatibility defines ***

gthread/tests/Makefile.am

@@ -46,3 +46,10 @@ spawn_singlethread_LDADD    = $(progs_ldadd) $(top_builddir)/gthread/libgthread-
 
 TEST_PROGS += gwakeup
 gwakeup_LDADD    = $(progs_ldadd) $(top_builddir)/gthread/libgthread-2.0.la
+
+if HAVE_EVENTFD
+TEST_PROGS += gwakeup-fallback
+gwakeup_fallback_SOURCES = gwakeup.c
+gwakeup_fallback_CFLAGS = $(AM_CFLAGS) -DTEST_EVENTFD_FALLBACK
+gwakeup_fallback_LDADD    = $(progs_ldadd) $(top_builddir)/gthread/libgthread-2.0.la
+endif

gthread/tests/gwakeup.c

@@ -1,6 +1,32 @@
 #include <unistd.h>
 #include <glib.h>
 
+#ifdef TEST_EVENTFD_FALLBACK
+  #include <errno.h>
+
+  static gboolean we_broke_eventfd;
+
+  /* We interpose over the eventfd() call in the libc to ensure that a
+   * failed call to eventfd() gives us a working fallback.
+   *
+   * We need to do this because older kernel versions don't have eventfd
+   * support, and some of them have eventfd but without support for some
+   * of the flags we use.
+   *
+   * We use the we_broke_eventfd boolean to make sure that it actually
+   * worked.
+   */
+  int eventfd (void) {
+    we_broke_eventfd = TRUE;
+    errno = EINVAL;
+
+    return -1;
+  }
+  #define TESTNAME_SUFFIX "-fallback"
+#else
+  #define TESTNAME_SUFFIX ""
+#endif
+
 #ifdef _WIN32
 void alarm (int sec) { }
 #endif
@@ -32,9 +58,18 @@ test_semantics (void)
   /* prevent the test from deadlocking */
   alarm (30);
 
+#ifdef TEST_EVENTFD_FALLBACK
+  we_broke_eventfd = FALSE;
+#endif
+
   wakeup = g_wakeup_new ();
   g_assert (!check_signaled (wakeup));
 
+#ifdef TEST_EVENTFD_FALLBACK
+  /* make sure our interposed eventfd call worked */
+  g_assert (we_broke_eventfd);
+#endif
+
   g_wakeup_signal (wakeup);
   g_assert (check_signaled (wakeup));
 
@@ -261,8 +296,8 @@ main (int argc, char **argv)
 
   g_test_init (&argc, &argv, NULL);
 
-  g_test_add_func ("/gwakeup/semantics", test_semantics);
+  g_test_add_func ("/gwakeup/semantics" TESTNAME_SUFFIX, test_semantics);
-  g_test_add_func ("/gwakeup/threaded", test_threaded);
+  g_test_add_func ("/gwakeup/threaded" TESTNAME_SUFFIX, test_threaded);
 
   return g_test_run ();
 }