On Thu, Apr 27, 2006 at 06:10:07PM +0300, Denis Vlasenko wrote:
> On Tuesday 25 April 2006 20:53, Avi Kivity wrote:
> > Very often one needs to acquire a resource, do something with it, and
> > then free the resource. Here, "resource" can mean a file descriptor, a
> > reference into a reference counted object, or, in our case, a spinlock.
> > And we want "free" to mean "free no matter what", e.g. on a normal path
> > or an exception path.
>
> ...
>
> > Additionally, C++ guarantees that if an exception is thrown after
> > spin_lock() is called, then the spin_unlock() will also be called.
> > That's an interesting mechanism by itself.
>
> Life gets even more interesting when you hit another exception
> inside destructor(s) being executed due to first one.
> Say, spin_unlock() discovers that lock is already unlocked
> and does "throw BUG_double_unlock".
>
> Even if you
> (a) remember what standard says about it
> (b) implemented nested exception handling correctly,
> then you are still left with
> (c) let's pray gcc has no bugs in stack unwinding
> and nested exceptions and nested destructor calls.
>
> Mozilla crashes over such things. For Mozilla, crash is not
> *that* catastrophic. For OS kernel, it is.
Mozilla is written in C++ ? I start to better understand where the
160 MB bloat comes from...
> vda
Cheers,
Willy
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