<html> <head> <base href="https://bugs.freedesktop.org/"> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW - Segmentation fault in _cairo_traps_compositor_glyphs" href="https://bugs.freedesktop.org/show_bug.cgi?id=103037#c9">Comment # 9</a> on <a class="bz_bug_link bz_status_NEW " title="NEW - Segmentation fault in _cairo_traps_compositor_glyphs" href="https://bugs.freedesktop.org/show_bug.cgi?id=103037">bug 103037</a> from <a class="email" href="mailto:psychon@znc.in" title="Uli Schlachter <psychon@znc.in>"> Uli Schlachter</a> <pre>> My colleague and me discussed it for quite a while, as it was not obvious at the first glance. The conclusion was that it should be ok. If for whatever reason it is not True after we read it, all the following reads/writes to it are atomic, so we should be fine. (Disclaimer: I have never actually used C11 atomics and I certainly am no expert on them, I just 'read some stuff') The only formal semantics for this kind of thing are C11 atomics (right?). There, you may never read an atomic variable non-atomicly (you are not even guaranteed to read a value that was written, it might be some intermediate garbage). Thus, this would at least need to be a relaxed atomic. However, a relaxed read is too weak: It is allowed to read the new value for the atomic variable, but continue to read other older memory for other locations. I.e. it is allowed that the current thread sees that initialisation was done, but does not see the actual memory stores of the initialisation (and AFAIK there are architectures were this can actually happen). Thus, in C11 semantics, this needs at least an acquire read (I'll ignore consume here, everyone else does) (and the memory store that sets the atomic variable needs to be at least a release store). Now, cairo does not use C11 atomic operations (yet). However, the C11 semantics are the way they are since there are architectures that allow such behaviour. Thus, something needs to be atomic here. So, short version: I disagree with the above and I think that this needs a _cairo_atomic_int_get. (Also: +1 for Adrian's proposed name change)</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the QA Contact for the bug.</li> </ul> </body> </html>