Quoting Serge Hallyn (serge.hal...@ubuntu.com): > The problem: if a task is killed while holding a posix semaphore, > there appears to be no way to have the semaphore be reliably > autmoatically released. The only trick which seemed promising > is to store the pid of the lock holder in some file and have > later lock seekers check whether that task has died. > > Instead of going down that route, this patch switches from a > named posix semaphore to flock. The advantage is that when > the task is killed, its fds are closed and locks are automatically > released. > > The disadvantage of flock is that we can't rely on it to exclude > threads. Therefore c->slock must now always be wrapped inside > c->privlock. > > This patch survived basic testing with the lxcapi_create patchset, > where now killing lxc-create while it was holding the lock did > not lock up future api commands.
Two more notes: 1. the new lock doesn't support timeouts like the old one did. There's no caller which is currently using timeouts, so I will probably remove timeouts from the private semaphore as well. 2. It doesn't seem necessary to require everyone to understand the details, so I may abstrace away knowledge of c->privlock and c->slock behind two helpers. Not sure what good names would be, maybe c->memlock() and c->disklock() ? c->threadlock() and c->globallock()? Something to indicate that the first is to protect the struct lxc_container from simultaneous updates from other threads, while the latter is to protect the on-disk container. -serge ------------------------------------------------------------------------------ Try New Relic Now & We'll Send You this Cool Shirt New Relic is the only SaaS-based application performance monitoring service that delivers powerful full stack analytics. Optimize and monitor your browser, app, & servers with just a few lines of code. Try New Relic and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may _______________________________________________ Lxc-devel mailing list Lxc-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lxc-devel
