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SubjectRe: [PATCH] /dev/epoll update ...

On 20-Sep-2001 Dan Kegel wrote:
> Davide Libenzi wrote:
>> 1) if (recv()/send() == FAIL)
>> 2) ioctl(EP_POLL);
>
> A lot of people, including me, were under the mistaken impression
> that /dev/epoll, like /dev/poll, provided an efficient way to
> retrieve the current readiness state of fd's. I understand from your post
> that /dev/epoll's purpose is to retrieve state changes; in other
> words, it's exactly like F_SETSIG/F_SETOWN/O_ASYNC except that
> the readiness change indications are picked up via an ioctl
> rather than via a signal.
>
> A scorecard for the confused (Davide, correct me if I'm wrong):
>
> * API's that allow you to retrieve the current readiness state of
> a set of fd's: poll(), select(), /dev/poll, kqueue().
> Buzzwords describing this kind of interface: level-triggered, multishot.
>
> * API's that allow you to retrieve *changes* to the readiness state of
> a set of fd's: F_SETSIG/F_SETOWN/O_ASYNC + sigtimedwait(), /dev/epoll, kqueue().
> Buzzwords describing this kind of interface: edge-triggered, single-shot.
>
> (Note that kqueue is in both camps.)
>
> Er, I guess that means I'll rip up the /dev/epoll support I based on my
> /dev/poll code, and replace it with some based on my O_ASYNC code...


Exactly :)
Here are examples basic functions when used with coroutines :


int dph_connect(struct dph_conn *conn, const struct sockaddr *serv_addr, socklen_t addrlen) {

if (connect(conn->sfd, serv_addr, addrlen) == -1) {
if (errno != EWOULDBLOCK && errno != EINPROGRESS)
return -1;
conn->events = POLLOUT | POLLERR | POLLHUP;
co_resume(conn);
if (conn->revents & (POLLERR | POLLHUP))
return -1;
}
return 0;
}

int dph_read(struct dph_conn *conn, char *buf, int nbyte) {
int n;

while ((n = read(conn->sfd, buf, nbyte)) < 0) {
if (errno == EINTR)
continue;
if (errno != EAGAIN && errno != EWOULDBLOCK)
return -1;
conn->events = POLLIN | POLLERR | POLLHUP;
co_resume(conn);
}
return n;
}

int dph_write(struct dph_conn *conn, char const *buf, int nbyte) {
int n;

while ((n = write(conn->sfd, buf, nbyte)) < 0) {
if (errno == EINTR)
continue;
if (errno != EAGAIN && errno != EWOULDBLOCK)
return -1;
conn->events = POLLOUT | POLLERR | POLLHUP;
co_resume(conn);
}
return n;
}

int dph_accept(struct dph_conn *conn, struct sockaddr *addr, int *addrlen) {
int sfd;

while ((sfd = accept(conn->sfd, addr, (socklen_t *) addrlen)) < 0) {
if (errno == EINTR)
continue;
if (errno != EAGAIN && errno != EWOULDBLOCK)
return -1;
conn->events = POLLIN | POLLERR | POLLHUP;
co_resume(conn);
}
return sfd;
}




- Davide

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