On Tue, 17 Jul 2007, Michael Kerrisk wrote: > Hi Davide, > > Working on the signalfd man page, another question comes up: > > What are the intended semantics for a signalfd file descriptor with respect > to threads? I have not yet tested the behavior, but in any case, I better > check what is expected. > > A signal can be directed to the process as a whole (e.g., using kill(2)), > or to a particular thread (using, e.g., pthread_kill(2), or tgkill(2)). > > So that raises the question: If a thread calls signalfd(), does the > resulting file descriptor return just those signals directed to [the thread > and the process as a whole], or will it also receive signals that are > targeted at other threads in the process? I would hope the former is the > case, but I'm not sure what has been implemented (or intended).
If thread A calls signalfd(), a read() from the signalfd will return thread A private (tgkill) signals (only when called by thread A) and thread A shared (kill) signals (readable from any thread). So a call to signalfd() virtually attaches the fd to the calling thread signal context. This is the reason of the "virtual connection" dropped I was talking about in the other email. If the signal context the fd is attached to (struct sighand), goes away, the fd becomes like a disconnected socket with no peer to read form. - Davide - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
