If the compiler doesn’t provide modern (C++11) atomic builtins (which is
now quite unlikely), we implement our own using the `__sync_synchronize()`
memory barrier. As Behdad and others have pointed out, though, the
implementation didn’t follow the same semantics as we use with the C++11
builtins — `__ATOMIC_SEQ_CST`.
Fix the use of memory barriers to provide `__ATOMIC_SEQ_CST` semantics.
In particular, this fixes the following common pattern:
```
GObject *obj = my_object_new ();
g_atomic_pointer_set (&shared_ptr, obj);
```
Previously this would have expanded to:
```
GObject *obj = my_object_new ();
*shared_ptr = obj;
__sync_synchronize ();
```
While the compiler would not have reordered the stores to `obj` and
`shared_ptr` within the code on one thread (due to the dependency
between them), the memory system might have made the write to
`shared_ptr` visible to other threads before the write to `obj` — if
they then dereferenced `shared_ptr` before seeing the write to `obj`,
that would be a bug.
Instead, the expansion is now:
```
GObject *obj = my_object_new ();
__sync_synchronize ();
*shared_ptr = obj;
```
This ensures that the write to `obj` is visible to all threads before
any write to `shared_ptr` is visible to any threads. For completeness,
`__sync_synchronize()` is augmented with a compiler barrier to ensure
that no loads/stores can be reordered locally before or after it.
Tested by disabling the C++11 atomic implementation and running:
```
meson test --repeat 1000 atomic atomic-test
```
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Fixes: #1449
`g_assert_*()` provide more useful failure messages, and aren’t compiled
out when building with `G_DISABLE_ASSERT`, unlike `g_assert()`.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
When compiling GLib with `-Wsign-conversion`, we get various warnings
about the atomic calls. A lot of these were fixed by
3ad375a629, but some remain. Fix them by
adding appropriate casts at the call sites.
Note that `g_atomic_int_{and,or,xor}()` actually all operate on `guint`s
rather than `gint`s (which is what the rest of the `g_atomic_int_*()`
functions operate on). I can’t find any written reasoning for this, but
assume that it’s because signedness is irrelevant when you’re using an
integer as a bit field. It’s unfortunate that they’re named a
`g_atomic_int_*()` rather than `g_atomic_uint_*()` functions.
Tested by compiling GLib as:
```
CFLAGS=-Wsign-conversion jhbuild make -ac |& grep atomic
```
I’m not going to add `-Wsign-conversion` to the set of default warnings
for building GLib, because it mostly produces false positives throughout
the rest of GLib.
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Fixes: #1565
While the introspection scanner can glean the transfer rule for the
return values by looking at their constness, adding an explicit
annotation has the advantage of gtk-doc writing out the transfer rule as
an additional bit of documentation, making the life of the documentation
reader easier.
It was possible to pass in (for example) an invalid hour to
g_date_time_new_ordinal(), which would be passed on to
g_date_time_new(), which would (correctly) return `NULL` — but then
g_date_time_new_ordinal() would try to dereference that.
Includes some test cases.
oss-fuzz#16103
oss-fuzz#17183
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Support for custom allocators was dropped in
commit 3be6ed60aa
Author: Alexander Larsson <alexl@redhat.com>
Date: Sat Jun 27 18:38:42 2015 +0200
Deprecate and drop support for memory vtables
The introductory doc text for the gmem APIs still warns against mixing
malloc/free with g_malloc/g_free. Clarify upfront in the docs that these
two sets of APIs are now guaranteed to use the same memory allocator &
can thus their usage can be freely mixed.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
g_utf8_get_char_validated() was not exactly matching its
documentation. The function was not checking if the sequence of
unicode characters was free of null bytes before performing a more
in-depth validation.
Fix issue #1052
