Date: Fri, 18 Oct 2019 21:44:58 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: broadcast fd On Tue, Oct 15, 2019 at 10:04:47AM -0700, Leonid Shamis wrote: > Hi Folks, > > TLDR: > > How do I broadcast a notification across processes, without a broker? > > Long story: > > I'm building an ipc-over-shm library with some unusual restrictions: > * There are multiple channels of communication (each in it's own shm). > * Each channel contains non-consumable resources (not a message queue). > * Multiple processes can produce resources on the same channel. > * Multiple consumers can access/use the resources. > * Resources are versioned and (some) old versions are kept available. > * Spurious wakeups are ok, but missing notifications (starvation) is not. > * The library must be robust (in the mutex sense), meaning a process may > crash without taking down the rest of the system. > > I'm trying to figure out how to notify a process that a new resource is > available on a channel. > > Right now, my library puts (the equivalent of) a robust conditional > variable in shared memory, for each channel. > Each process must spawn a thread per-channel, just to await the cv > broadcast. > > I'd ideally like to use a single thread with something like an epoll. > For this, I'd need to get an fd (maybe eventfd) per channel into the hands > of every process that wants to connect to a channel. > fds, as I understand, cannot be shared via shared memory, only pipes, but > I'm required to be brokerless. > futex_fd are very deprecated. > > Am I missing another approach? If you want the events associated with the shared memory objects, and you have file descriptors for these objects (they're POSIX shm or hand-rolled tmpfs shm, as opposed to sysvipc), perhaps there's a way to convey the event availability through the fd. For example is there a way you could use inotify to do it? Otherwise I think you already have the best way. Keep in mind the cv-waiting thread can be made tiny if you use a minimal stack size, run with signals blocked, and just have it convert cv events to self-pipe/eventfd/etc. Rich
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.