Re: [libvirt PATCH 6/7] virMutex*: Warn on error

On Thu, Aug 05, 2021 at 16:48:59 +0100, Daniel P. Berrangé wrote: > On Thu, Aug 05, 2021 at 05:44:15PM +0200, Peter Krempa wrote: > > On Thu, Aug 05, 2021 at 16:33:57 +0100, Daniel P. Berrangé wrote: > > > On Thu, Aug 05, 2021 at 05:29:24PM +0200, Peter Krempa wrote: [...] > Lock state tracking doesn't sound very appealing to me. > > QEMU makes use of g_auto for unlocking mutexes within scopes > > WITH_QEMU_LOCK_GUARD(&mutex) { > ... > if (error) { > return; <-- mutex is automatically unlocked > } > > if (early_exit) { > break; <-- leave this scope early, unlocking > } > ... > } > > > and another pattern > > ... <-- mutex not locked > QEMU_LOCK_GUARD(&mutex); <-- mutex locked from here onwards > ... > if (error) { > return; <-- mutex is automatically unlocked > } > > This would work for libvirt too, at least for cases where the > lock+unlock are in the same scope (which should be the majority). Yes I thought about this some time ago, but unfortunately in this very specific case it doesn't work. For some specific/historic reason 'virDomainObjNew' returns a locked mutex. Caller is expected then to attach the object into the list or dispose of it, so this doesn't happen in the same context.