libfuse: exiting fuse_session_loop

Question

Context: Ubuntu 11.10 and libfuse 2.8.4-1.4ubuntu1 Linux 3.0.0-14-generic #23-Ubuntu SMP Mon Nov 21 20:28:43 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux

I'm trying to use libfuse. I want to cause fuse_session_loop to exit (from a signal handler or a different thread), but when I call fuse_session_exit nothing happens until the session receives a new request.

fuse_session_exit sets a flag that is read by fuse_session_exited. Debugging into fuse_session_loop it appears to block on fuse_chan_recv, so it doesn't check fuse_session_exited again until the top of the loop...

int fuse_session_loop(struct fuse_session *se)
{
    int res = 0;
    struct fuse_chan *ch = fuse_session_next_chan(se, NULL);
    size_t bufsize = fuse_chan_bufsize(ch);
    char *buf = (char *) malloc(bufsize);
    if (!buf) {
        fprintf(stderr, "fuse: failed to allocate read buffer\n");
        return -1;
    }

    while (!fuse_session_exited(se)) {
        struct fuse_chan *tmpch = ch;
        res = fuse_chan_recv(&tmpch, buf, bufsize); <--- BLOCKING
        if (res == -EINTR)
            continue;
        if (res <= 0)
            break;
        fuse_session_process(se, buf, res, tmpch);
    }

    free(buf);
    fuse_session_reset(se);
    return res < 0 ? -1 : 0;
}

fuse_chan_recv calls fuse_kern_chan_receive which blocks on the "read" syscall of the "/dev/fuse" device, so even though the fuse_session_exited flag is set nothing happens yet.

static int fuse_kern_chan_receive(struct fuse_chan **chp, char *buf,
                  size_t size)
{
    struct fuse_chan *ch = *chp;
    int err;
    ssize_t res;
    struct fuse_session *se = fuse_chan_session(ch);
    assert(se != NULL);

restart:
    res = read(fuse_chan_fd(ch), buf, size); <--- BLOCKING
    err = errno;

    if (fuse_session_exited(se))
        return 0;
    if (res == -1) {
        /* ENOENT means the operation was interrupted, it's safe
           to restart */
        if (err == ENOENT)
            goto restart;

        if (err == ENODEV) {
            fuse_session_exit(se);
            return 0;
        }
        /* Errors occuring during normal operation: EINTR (read
           interrupted), EAGAIN (nonblocking I/O), ENODEV (filesystem
           umounted) */
        if (err != EINTR && err != EAGAIN)
            perror("fuse: reading device");
        return -err;
    }
    if ((size_t) res < sizeof(struct fuse_in_header)) {
        fprintf(stderr, "short read on fuse device\n");
        return -EIO;
    }
    return res;
}

This problem seems to effect the hello_ll.c example provided with libfuse as well as my program. It makes me think that perhaps there is some mechanism that is not working that should. Perhaps fuse_session_exit is supposed to be also doing something that interrupts the read call, that for some reason is not working on my system.

Any ideas?