How EPOLLHUP event is received on a socket fd

saurabhth · External Since: Aug 12, 2009 Posts: 2

Hi,

I have developed a simple server that uses epoll_wait with TCP
sockets. The server program listens to incoming connections on
listening socket and on acceptiong incoming connections adds them to
the pollset to be waited upon by epoll_wait.

I would like to know how can I produce a condition by which the event
EPOLLHUP is generated and returned by epoll_wait for a socket fd ?

Pls guide.

Loïc_Domaigné · External Since: Jul 28, 2009 Posts: 4

Hi,

> I have developed a simple server that uses epoll_wait with TCP
> sockets. The server program listens to incoming connections on
> listening socket and on acceptiong incoming connections adds them to
> the pollset to be waited upon by epoll_wait.
>
> I would like to know how can I produce a condition by which the event
> EPOLLHUP is generated and returned by epoll_wait for a socket fd ?
>
> Pls guide.

my guess would be that EPOLLHUP is the "epoll" version of POLLHUP...
for TCP socket, this means that the socket is half-closed as result of
a shutdown().

HTH,
Loïc
--
My Blog: http://www.domaigne.com/blog

"One of the main causes of the fall of the Roman Empire was that–
lacking zero–they had no way to indicate successful termination of
their C programs." -- Robert Firth

saurabhth · External Since: Aug 12, 2009 Posts: 2

On Aug 12, 4:50 pm, Loïc Domaigné <loic.domai....TakeThisOut@googlemail.com>
wrote:
> Hi,
>
> > I have developed a simple server that uses epoll_wait with TCP
> > sockets. The server program listens to incoming connections on
> > listening socket and on acceptiong incoming connections adds them to
> > the pollset to be waited upon by epoll_wait.
>
> > I would like to know how can I produce a condition by which the event
> > EPOLLHUP is generated and returned by epoll_wait for a socket fd ?
>
> > Pls guide.
>
> my guess would be that EPOLLHUP is the "epoll" version of POLLHUP...
> for TCP socket, this means that the socket is half-closed as result of
> a shutdown().
>
> HTH,
> Loïc
> --
> My Blog:http://www.domaigne.com/blog
>
> "One of the main causes of the fall of the Roman Empire was that–
> lacking zero–they had no way to indicate successful termination of
> their C programs." -- Robert Firth

Hi Loic,

I tried simulating the behaviour by writing a client program that
connects to the server and after the connection has been made, half
closes the connection with shutdown(SHUT_WR).

The server still receives the EPOLLIN event, no EPOLLHUP event is
received.

Kindly help

Loïc_Domaigné · External Since: Jul 28, 2009 Posts: 4

Hi,

> > > I have developed a simple server that uses epoll_wait with TCP
> > > sockets. The server program listens to incoming connections on
> > > listening socket and on acceptiong incoming connections adds them to
> > > the pollset to be waited upon by epoll_wait.
>
> > > I would like to know how can I produce a condition by which the event
> > > EPOLLHUP is generated and returned by epoll_wait for a socket fd ?
>
> > > Pls guide.
>
> > my guess would be that EPOLLHUP is the "epoll" version of POLLHUP...
> > for TCP socket, this means that the socket is half-closed as result of
> > a shutdown().
>
> > HTH,
> > Loïc
> > --
> > My Blog:http://www.domaigne.com/blog
>
> > "One of the main causes of the fall of the Roman Empire was that–
> > lacking zero–they had no way to indicate successful termination of
> > their C programs." -- Robert Firth
>
> Hi Loic,
>
> I tried simulating the behaviour by writing a client program that
> connects to the server and after the connection has been made, half
> closes the connection with shutdown(SHUT_WR).
>
> The server still receives the EPOLLIN event, no EPOLLHUP event is
> received.

From the experiments I made (using poll, not epoll), I found out that
you get a POLLHUP only after receiving a RST segment. This means that
the client has closed the socket (e.g. due to a crash), and the server
has performed one write on the closed socket.

HTH,
Loïc.
--
My Blog: http://www.domaigne.com/blog

"The first 90% of the code accounts for the first 90% of the
development time. The remaining 10% of the code accounts for the other
90% of the development time." -- Tom Cargill