Re: [Qemu-devel] [RFC] [PATCHv8 13/30] aio / timers: Add aio_timer_new wrapper

[Paolo Bonzini]

Il 10/08/2013 00:57, Alex Bligh ha scritto:
> There are a large number of users of qemu_free_timer (now timer_free).
> 
> If someone does not call qemu_free_timer having called qemu_new_timer,
> the timer sits there and basically does nothing.

If you have called qemu_del_timer, it is a memory leak.  If you haven't,
you'll get almost the same crash you describe here:

> If we go to the timer_init model, the timer will either be on the
> stack or (more likely) inside some other struct on the heap, which
> will likely have been freed. This means walking the timer list will
> be dangerous.

With heap-allocated timers, the timer will exist on the heap, but likely
the opaque will not and you'll get a crash in the callback.

> This seems to add a good deal of fragility.

It is really the same.  The disadvantage is that you will not have a
hint of which timer was accessed erroneously (the callback is a useful
hint).  The advantage is that you cannot leak timers, and the crash
happens deterministically as soon as the object is deleted (rather than
only when the timer fires).

Paolo