Hi there,
I'm not sure whether this is an epoll bug:
- I have a UDP socket which is non-blocking and watched by epoll with
(EPOLLOUT | EPOLLET).
- EPOLLOUT is triggered after registering the file descriptor with
epoll_add, which is expected.
- After calling sendto on the UDP socket with a very small message(5
bytes), sendto returns the exact number of bytes sent and no EAGAIN is
generated.
- *but* calling epoll_wait still returns EPOLLOUT.
Shouldn't that EPOLLOUT be only triggered when an EAGAIN is generated
after any writing operation?
Here is the code I use:
==================
We have very simple wrapper for socket and epoll operations, and you
can easily guess what they're doing
TEST(EpollService, UdpWriteable) {
Socket client(Socket::UDP());
Socket server(Socket::UDP());
// Ask os to pick random port
CHECK_ERR(server.Bind(SocketAddress(SocketAddress::LOOPBACK, 0)));
const SocketAddress server_addr(server.GetMyAddress());
ASSERT_TRUE(SocketOption::SetBlocking(client.fd(), false));
EpollService eps;
eps.Add(client.fd(), EPOLLOUT | EPOLLET, NULL);
epoll_event event;
// The fd should be writable.
ASSERT_EQ(1, eps.Wait(&event, 1, 0));
// No more writable event.
ASSERT_EQ(0, eps.Wait(&event, 1, 0));
const char buffer[] = "abcd";
CHECK_ERR(::sendto(client.fd(), buffer, ARRAYSIZE(buffer), 0,
server_addr.addr(), server_addr.length()))1;
EXPECT_EQ(0, eps.Wait(&event, 1, 0)) << "Got unexpect event " << event.events;
EXPECT_EQ(0, eps.Wait(&event, 1, 0)) << "Got unexpect event " << event.events;
client.Close();
server.Close();
}
And strace output:
===============
write(1, "\33[0;32m[ RUN ] \33[mEpollServ"..., 49[ RUN ]
EpollService.UdpWriteable
) = 49
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 4
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 5
bind(5, {sa_family=AF_INET, sin_port=htons(0),
sin_addr=inet_addr("127.0.0.1")}, 16) = 0
getsockname(5, {sa_family=AF_INET, sin_port=htons(51019),
sin_addr=inet_addr("127.0.0.1")}, [16]) = 0
fcntl(4, F_GETFL) = 0x2 (flags O_RDWR)
fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0
epoll_create(1024) = 6
epoll_ctl(6, EPOLL_CTL_ADD, 4, {EPOLLOUT|EPOLLET, {u32=0, u64=0}}) = 0
epoll_wait(6, {{EPOLLOUT, {u32=0, u64=0}}}, 1, 0) = 1
epoll_wait(6, {}, 1, 0) = 0
sendto(4, "abcd\0", 5, 0, {sa_family=AF_INET, sin_port=htons(51019),
sin_addr=inet_addr("127.0.0.1")}, 16) = 5
epoll_wait(6, {{EPOLLOUT, {u32=0, u64=0}}}, 1, 0) = 1
write(1, "net/base/eventmanager_test.cc:50"...,
99net/base/eventmanager_test.cc:50: Failure
Value of: eps.Wait(&event, 1, 0)
Actual: 1
Expected: 0
) = 99
write(1, "Got unexpect event 4\n", 21Got unexpect event 4
) = 21
epoll_wait(6, {}, 1, 0) = 0
close(4) = 0
close(5) = 0
close(6) = 0
write(1, "\33[0;31m[ FAILED ] \33[mEpollServ"..., 56[ FAILED ]
EpollService.UdpWriteable (2 ms)
Thanks you for your feedback!
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