Re: [libvirt] [PATCH 0/6] virObject for reference-counting

On 04/06/2011 01:18 AM, Hu Tao wrote: > This series adds a virObject structure that manages reference-counting. > > Some notes about referece-counting introduced by this series: > > A thread owns a virObject by incrementing its reference-count by 1. > If a thread owns a virObject, the virObject is guarenteed not be > freed until the thread releases ownership by decrementing its > reference-count by 1. A thread can't access a virObject after it > releases the ownership of virObject because it can be freed at > anytime. > > A thread can own a virObject legally in these ways: > > - a thread owns a virObject that it creates. > - a thread owns a virObject if another thread passes the ownership > to it. Example: qemuMonitorOpen > - a thread gets a virObject from a container. > Example: virDomainFindByUUID > - a container owns a virObject by incrementing its reference-count > by 1 before adding it to the container > - if a virObject is removed from a container its reference-count > must be decremented by 1 > > By following these rules, there is no need to protect operations on > an object's reference-count by an external lock. (like in old ways > virDomainObj lock protects qemu monitor's ref-count.) These rules _need_ to be part of the patch series, preferably added at the same time as patch 1/6 (see for example how src/qemu/THREADS.txt documents threading issues related to qemu). I don't know whether virobject.h or a standalone document is better (but if you do a standalone document, then virobject.h should at least mention it).

-- Eric Blake eblake(a)redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org