[glib: 1/2] atomic/tests: test g_atomic_pointer_compare_and_exchange() with const pointers

[Philip Withnall <pwithnall src gnome org>]

commit ef9ce8ea00ae9d043adc46275cf8cce4319efa7e
Author: Thomas Haller <thaller redhat com>
Date:   Fri Dec 13 13:57:42 2019 +0100

    atomic/tests: test g_atomic_pointer_compare_and_exchange() with const pointers
    
    g_atomic_pointer_compare_and_exchange() should work with const pointers.
    Add a test for that.
    
    It seems clang 9.0.0-2.fc32 does not like this:
    
        ../glib/tests/atomic.c:93:9: warning: incompatible pointer types passing 'typeof ((((void *)0))) *' 
(aka 'void **') to parameter of type 'const char **' [-Wincompatible-pointer-types]
          res = g_atomic_pointer_compare_and_exchange (&vp_str, NULL, str);
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        ../glib/gatomic.h:192:44: note: expanded from macro 'g_atomic_pointer_compare_and_exchange'
            __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, 
__ATOMIC_SEQ_CST) ? TRUE : FALSE; \
                                                   ^~~~~~~~~~~~~~
        ../glib/tests/atomic.c:96:9: warning: incompatible pointer types passing 'typeof ((((void *)0))) *' 
(aka 'void **') to parameter of type 'const char **' [-Wincompatible-pointer-types]
          res = g_atomic_pointer_compare_and_exchange (&vp_str_vol, NULL, str);
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        ../glib/gatomic.h:192:44: note: expanded from macro 'g_atomic_pointer_compare_and_exchange'
            __atomic_compare_exchange_n ((atomic), &gapcae_oldval, (newval), FALSE, __ATOMIC_SEQ_CST, 
__ATOMIC_SEQ_CST) ? TRUE : FALSE; \
                                                   ^~~~~~~~~~~~~~
    
    Note that this clang version already issues various compiler warnings for
    this test. This merely adds another case to check.
    
    Eventually g_atomic_pointer_compare_and_exchange() should be fixed to
    avoid compiler warnings.
    
    Actually there is a problem. When you try to use g_atomic_pointer_compare_and_exchange()
    with const pointers, it is also not working, because the implementation
    as a function expects "void *" arguments. As the test also shows. As such,
    it's probably not portable to use g_atomic_pointer_compare_and_exchange()
    with const pointers at all. However, the macro implementation is (with the right
    compiler) fine with that, so it's an easy "mistake" to make.

 glib/tests/atomic.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
---
diff --git a/glib/tests/atomic.c b/glib/tests/atomic.c
index 3ba7d553f..6b6cc7f3e 100644
--- a/glib/tests/atomic.c
+++ b/glib/tests/atomic.c
@@ -24,6 +24,9 @@ test_types (void)
   guint u, u2;
   gint s, s2;
   gpointer vp, vp2;
+  const char *vp_str;
+  const char *volatile vp_str_vol;
+  const char *str = "Hello";
   int *ip, *ip2;
   gsize gs, gs2;
   gboolean res;
@@ -87,6 +90,14 @@ test_types (void)
   g_assert_true (res);
   g_assert_true (vp == 0);
 
+  g_atomic_pointer_set (&vp_str, NULL);
+  res = g_atomic_pointer_compare_and_exchange (&vp_str, NULL, str);
+  g_assert_true (res);
+
+  g_atomic_pointer_set (&vp_str_vol, NULL);
+  res = g_atomic_pointer_compare_and_exchange (&vp_str_vol, NULL, str);
+  g_assert_true (res);
+
   g_atomic_pointer_set (&ip, 0);
   ip2 = g_atomic_pointer_get (&ip);
   g_assert_true (ip2 == 0);
@@ -195,6 +206,14 @@ G_GNUC_END_IGNORE_DEPRECATIONS
   g_assert_true (res);
   g_assert_true (vp == 0);
 
+  g_atomic_pointer_set (&vp_str, NULL);
+  res = g_atomic_pointer_compare_and_exchange (&vp_str, NULL, (char *) str);
+  g_assert_true (res);
+
+  g_atomic_pointer_set (&vp_str_vol, NULL);
+  res = g_atomic_pointer_compare_and_exchange (&vp_str_vol, NULL, (char *) str);
+  g_assert_true (res);
+
   g_atomic_pointer_set (&ip, 0);
   ip2 = g_atomic_pointer_get (&ip);
   g_assert_true (ip2 == 0);