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gmem: Only evaluate pointer argument to g_clear_pointer() once

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The new typeof() macro version of g_clear_pointer() was evaluating its
pointer argument more than once, meaning any side effects would be
evaluated multiple times.

The existing (other) macro version of g_clear_pointer() was evaluating
its argument exactly once. This mismatch could have confused people or
lead to subtle bugs.

See https://gitlab.gnome.org/GNOME/glib/issues/1494.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
This commit is contained in:
Philip Withnall 2018-08-22 14:47:52 +01:00
parent 9a72ebe016
commit 2e9c31af11
2 changed files with 30 additions and 2 deletions
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5
glib/gmem.h
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@ -114,8 +114,9 @@ gpointer g_try_realloc_n (gpointer mem,
#define g_clear_pointer(pp, destroy) \
G_STMT_START { \
G_STATIC_ASSERT (sizeof *(pp) == sizeof (gpointer)); \
__typeof__(*(pp)) _ptr = *(pp); \
*(pp) = NULL; \
__typeof__((pp)) _pp = (pp); \
__typeof__(*(pp)) _ptr = *_pp; \
*_pp = NULL; \
if (_ptr) \
(destroy) (_ptr); \
} G_STMT_END

27
glib/tests/utils.c
View File

@ -533,6 +533,32 @@ test_clear_pointer_cast (void)
g_assert_null (hash_table);
}
/* Test that the macro version of g_clear_pointer() only evaluates its argument
* once, just like the function version would. */
static void
test_clear_pointer_side_effects (void)
{
gchar **my_string_array, **i;
my_string_array = g_new0 (gchar*, 3);
my_string_array[0] = g_strdup ("hello");
my_string_array[1] = g_strdup ("there");
my_string_array[2] = NULL;
i = my_string_array;
g_clear_pointer (i++, g_free);
g_assert_true (i == &my_string_array[1]);
g_assert_null (my_string_array[0]);
g_assert_nonnull (my_string_array[1]);
g_assert_null (my_string_array[2]);
g_free (my_string_array[1]);
g_free (my_string_array[2]);
g_free (my_string_array);
}
static int obj_count;
static void
@ -673,6 +699,7 @@ main (int argc,
g_test_add_func ("/utils/specialdir/desktop", test_desktop_special_dir);
g_test_add_func ("/utils/clear-pointer", test_clear_pointer);
g_test_add_func ("/utils/clear-pointer-cast", test_clear_pointer_cast);
g_test_add_func ("/utils/clear-pointer/side-effects", test_clear_pointer_side_effects);
g_test_add_func ("/utils/take-pointer", test_take_pointer);
g_test_add_func ("/utils/clear-source", test_clear_source);
g_test_add_func ("/utils/misc-mem", test_misc_mem);