092be080c5
_object_unref_clear_weak_locations() is called twice during g_object_unref(). In both cases, it is when we expect that the reference count is 1 and we are either about to call dispose() or finalize(). At this point, we must check for GWeakRef to avoid a race that the ref count gets increased just at that point. However, we can do something better than to always take the global lock. On the object, whenever an object is set to a GWeakRef, set a flag OPTIONAL_FLAG_EVER_HAD_WEAK_REF. Most objects are not involved with weak references and won't have this flag set. If we reach _object_unref_clear_weak_locations() we just (atomically) checked that the ref count is one. If the object at this point never had a GWeakRef registered, we know that nobody else could have raced against obtaining another reference. In this case, we can skip taking the lock and checking for weak locations. As most object don't ever have a GWeakRef registered, this significantly avoids unnecessary work during _object_unref_clear_weak_locations(). This even fixes a hard to hit race in the do_unref=FALSE case. Previously, if do_unref=FALSE there were code paths where we avoided taking the global lock. We do so, when quark_weak_locations is unset. However, that is not race free. If we enter _object_unref_clear_weak_locations() with a ref-count of 1 and one GWeakRef registered, another thread can take a strong reference and unset the GWeakRef. Then quark_weak_locations will be unset, and _object_unref_clear_weak_locations() misses the fact that the ref count is now bumped to two. That is now fixed, because once OPTIONAL_FLAG_EVER_HAD_WEAK_REF is set, it will stick. Previously, there was an optimization to first take a read lock to check whether there are weak locations to clear. It's not clear that this is worth it, because we now already have a hint that there might be a weak location. Unfortunately, GRWLock does not support an upgradable lock, so we cannot take an (upgradable) read lock, and when necessary upgrade that to a write lock.
GLib
GLib is the low-level core library that forms the basis for projects such as GTK and GNOME. It provides data structure handling for C, portability wrappers, and interfaces for such runtime functionality as an event loop, threads, dynamic loading, and an object system.
The official download locations are: https://download.gnome.org/sources/glib
The official web site is: https://www.gtk.org/
Installation
See the file ‘INSTALL.md’. There is separate and more in-depth documentation for building GLib on Windows.
Supported versions
Upstream GLib only supports the most recent stable release series, the previous stable release series, and the current development release series. All older versions are not supported upstream and may contain bugs, some of which may be exploitable security vulnerabilities.
See SECURITY.md for more details.
Documentation
API documentation is available online for GLib for the:
Discussion
If you have a question about how to use GLib, seek help on GNOME’s Discourse
instance. Alternatively, ask a question
on StackOverflow and tag it glib.
Reporting bugs
Bugs should be reported to the GNOME issue tracking system. You will need to create an account for yourself. You may also submit bugs by e-mail (without an account) by e-mailing incoming+gnome-glib-658-issue-@gitlab.gnome.org, but this will give you a degraded experience.
Bugs are for reporting problems in GLib itself, not for asking questions about how to use it. To ask questions, use one of our discussion forums.
In bug reports please include:
- Information about your system. For instance:
- What operating system and version
- For Linux, what version of the C library
- And anything else you think is relevant.
- How to reproduce the bug.
- If you can reproduce it with one of the test programs that are built
in the
tests/subdirectory, that will be most convenient. Otherwise, please include a short test program that exhibits the behavior. As a last resort, you can also provide a pointer to a larger piece of software that can be downloaded.
- If you can reproduce it with one of the test programs that are built
in the
- If the bug was a crash, the exact text that was printed out when the crash occurred.
- Further information such as stack traces may be useful, but is not necessary.
Contributing to GLib
Please follow the contribution guide to know how to start contributing to GLib.
Patches should be submitted as merge requests to gitlab.gnome.org. If the patch fixes an existing issue, please refer to the issue in your commit message with the following notation (for issue 123):
Closes: #123
Otherwise, create a new merge request that introduces the change. Filing a separate issue is not required.