Why not to use a socket (Unix socket or TCP/IP socket), push your
"0123456789" in one side and retrieve the same from the other side?
You'll need different code to open/close the socket, but writing/reading
will look the same.
--- Omer
On Wed, 2013-06-19 at 09:01 +0300, Elazar Leibovich wrote:
> I think I didn't explain myself correctly, so let me give a different
> example.
>
> Let's make a file descriptor that counts to 9.
>
>
> I.e, we want to emulate the behavior:
>
>
> int fd = make_counter_fd();
> assert(write(fd, buf, 100) == 11);
> assert(strcmp(buf, "0123456789") == 0);
>
>
> Let me describe a very simple version of the main poll loop:
>
>
> struct poll_cb {
> int fd;
> int (*read_cb)(int fd);
> int (*write_cb)(int fd);
> };
> while (poll(&pfd, nr, -1) != -1) {
> for (int i=0; i < nr; i++) {
> if (pfd[i].revent |= POLLIN)
> poll_cbs[i].read_cb(pfd[i].fd);
> if (pfd[i].revent |= POLLOUT)
> poll_cbs[i].write_cb(pfd[i].fd);
>
> if (pfd[i].revent |= POLLHUP)
> pfds[i].fd = -1; // don't poll again
> }
> }
>
>
> Now, in order to emulate the 0-9 file descriptor, we'll associate to a
> "/dev/zero" a read callback function that looks roughly like
>
>
> int written = 0;
> char buf[10];
> int zero_to_nine_cb(int fd) {
> for (int i=0; i< 10; i++) buf[i] = '0' + i;
> close(fd); // note, we never touched the fd
> }
>
>
> But I have to use a file descriptor! Otherwise poll will have no
> reason to call my callback.
> On Jun 19, 2013 7:47 AM, "Shachar Shemesh" <shac...@shemesh.biz>
> wrote:
> On 18/06/13 22:16, Elazar Leibovich wrote:
>
> > I'm using it as a fake "always non-blocking" file
> > descriptor.
> >
> >
> > My main libevent-like poll loop looks like:
> >
> >
> > poll(fds)
> > for fd in fds:
> > if fd.revents | POLLIN:
> > fd.read_callback()
> > if fd.revents | POLLOUT:
> > fd.write_callback()
> >
> >
> > Now let's say I want a fake filedescriptor that always reads
> > 'z's (a sleepy fd).
> Why? What you just did was to turn the whole thing into a
> non-sleeping loop. If that's the case, simply call poll with a
> zero timeout, so it won't sleep, and call your callback at the
> end of each loop. No need to artificially introduce another
> file descriptor into the mix.
>
> Mind you, I still don't understand WHY you'd want such a
> thing. This code will, by definition, consume 100% CPU all the
> time.
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