DOC: internal: commit notes about polling states and flags
Some detailed observations were made on polling general and POLLHUP more specifically, they can be useful later.
This commit is contained in:
Willy Tarreau
parent
e6ef4cd747
commit
c89f665cca
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@ -0,0 +1,281 @@
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tcp mode 8001->8008
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Remote test:
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============
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willy@up1:~$ echo bar | ncat -lp8008
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willy@wtap:haproxy$ echo foo | ncat 127.1 8001
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17:09:53.663154 epoll_wait(3, [{EPOLLIN, {u32=5, u64=5}}], 200, 1000) = 1
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17:09:54.582146 accept4(5, {sa_family=AF_INET, sin_port=htons(33378), sin_addr=inet_addr("127.0.0.1")}, [128->16], SOCK_NONBLOCK) = 8
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17:09:54.582299 setsockopt(8, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:09:54.582527 accept4(5, 0x7ffc4a8bf330, [128], SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
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17:09:54.582655 recvfrom(8, "foo\n", 15360, 0, NULL, NULL) = 4
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17:09:54.582727 recvfrom(8, "", 15356, 0, NULL, NULL) = 0
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17:09:54.582827 socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 9
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17:09:54.582878 setsockopt(9, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:09:54.582897 connect(9, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("10.0.3.82")}, 16) = -1 EINPROGRESS (Operation now in progress)
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17:09:54.582941 sendto(9, "foo\n", 4, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = -1 EAGAIN (Resource temporarily unavailable)
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17:09:54.582968 epoll_ctl(3, EPOLL_CTL_ADD, 9, {EPOLLOUT, {u32=9, u64=9}}) = 0
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17:09:54.582997 epoll_wait(3, [{EPOLLOUT, {u32=9, u64=9}}], 200, 1000) = 1
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17:09:54.583686 connect(9, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("10.0.3.82")}, 16) = 0
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17:09:54.583706 sendto(9, "foo\n", 4, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 4
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17:09:54.583733 recvfrom(9, 0x19c2300, 15360, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
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17:09:54.583755 shutdown(9, SHUT_WR) = 0
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17:09:54.583775 epoll_ctl(3, EPOLL_CTL_MOD, 9, {EPOLLIN|EPOLLRDHUP, {u32=9, u64=9}}) = 0
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17:09:54.583802 epoll_wait(3, [{EPOLLIN, {u32=9, u64=9}}], 200, 1000) = 1
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17:09:54.584672 recvfrom(9, "bar\n", 16384, 0, NULL, NULL) = 4
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17:09:54.584713 recvfrom(9, "", 16380, 0, NULL, NULL) = 0
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17:09:54.584743 sendto(8, "bar\n", 4, MSG_DONTWAIT|MSG_NOSIGNAL|MSG_MORE, NULL, 0) = 4
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17:09:54.584819 epoll_wait(3, [], 200, 0) = 0
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17:09:54.584901 epoll_wait(3, [], 200, 1000) = 0
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Notes:
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- we had data available to try the connect() (see first attempt), despite
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this during the retry we sent the connect again!
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- why do we wait before sending the shutw to the server if we already know
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it's needed ? missing CF_SHUTW_NOW ? Missing request forwarding ? Missing
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auto-close ?
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- response didn't feature HUP nor RDHUP
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Local:
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17:15:43.010786 accept4(5, {sa_family=AF_INET, sin_port=htons(33506), sin_addr=inet_addr("127.0.0.1")}, [128->16], SOCK_NONBLOCK) = 8
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17:15:43.011013 setsockopt(8, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:15:43.011181 accept4(5, 0x7ffcd9092cd0, [128], SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
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17:15:43.011231 recvfrom(8, "foo\n", 15360, 0, NULL, NULL) = 4
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17:15:43.011296 recvfrom(8, "", 15356, 0, NULL, NULL) = 0
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17:15:43.011318 socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 9
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17:15:43.011340 setsockopt(9, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:15:43.011353 connect(9, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)
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17:15:43.011395 sendto(9, "foo\n", 4, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 4
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17:15:43.011425 shutdown(9, SHUT_WR) = 0
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17:15:43.011459 recvfrom(9, "bar\n", 16384, 0, NULL, NULL) = 4
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17:15:43.011491 recvfrom(9, "", 16380, 0, NULL, NULL) = 0
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17:15:43.011525 sendto(8, "bar\n", 4, MSG_DONTWAIT|MSG_NOSIGNAL|MSG_MORE, NULL, 0) = 4
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17:15:43.011584 epoll_wait(3, [], 200, 0) = 0
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Notes:
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- the shutdown() was properly done right after the sendto(), proving that
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CF_SHUTW_NOW and auto-close were present. Maybe difference is sync vs async
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send.
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Local with delay before closing client:
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17:18:17.155349 epoll_wait(3, [{EPOLLIN, {u32=5, u64=5}}], 200, 1000) = 1
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17:18:17.727327 accept4(5, {sa_family=AF_INET, sin_port=htons(33568), sin_addr=inet_addr("127.0.0.1")}, [128->16], SOCK_NONBLOCK) = 8
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17:18:17.727553 setsockopt(8, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:18:17.727661 accept4(5, 0x7fff4eb9a0b0, [128], SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
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17:18:17.727798 recvfrom(8, 0xbda300, 15360, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
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17:18:17.727830 socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 9
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17:18:17.727858 setsockopt(9, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:18:17.727877 connect(9, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)
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17:18:17.727923 epoll_ctl(3, EPOLL_CTL_ADD, 8, {EPOLLIN|EPOLLRDHUP, {u32=8, u64=8}}) = 0
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17:18:17.727945 epoll_ctl(3, EPOLL_CTL_ADD, 9, {EPOLLOUT, {u32=9, u64=9}}) = 0
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17:18:17.727989 epoll_wait(3, [{EPOLLOUT, {u32=9, u64=9}}], 200, 1000) = 1
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17:18:17.728010 connect(9, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
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17:18:17.728027 recvfrom(9, "bar\n", 15360, 0, NULL, NULL) = 4
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17:18:17.728055 recvfrom(9, 0xbd62f4, 15356, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
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17:18:17.728073 sendto(8, "bar\n", 4, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 4
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17:18:17.728104 epoll_ctl(3, EPOLL_CTL_MOD, 9, {EPOLLIN|EPOLLRDHUP, {u32=9, u64=9}}) = 0
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17:18:17.728127 epoll_wait(3, [], 200, 1000) = 0
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17:18:18.729411 epoll_wait(3, [], 200, 1000) = 0
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17:18:19.730654 epoll_wait(3, [{EPOLLIN|EPOLLRDHUP, {u32=8, u64=8}}], 200, 1000) = 1
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17:18:20.299268 recvfrom(8, "", 16384, 0, NULL, NULL) = 0
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17:18:20.299336 epoll_ctl(3, EPOLL_CTL_DEL, 8, 0x7ff3a969f7d0) = 0
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17:18:20.299379 epoll_wait(3, [], 200, 0) = 0
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17:18:20.299401 shutdown(9, SHUT_WR) = 0
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17:18:20.299523 epoll_wait(3, [{EPOLLIN|EPOLLHUP|EPOLLRDHUP, {u32=9, u64=9}}], 200, 1000) = 1
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17:18:20.299678 recvfrom(9, "", 16384, 0, NULL, NULL) = 0
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17:18:20.299761 epoll_wait(3, [], 200, 0) = 0
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Notes: server sent the response in two parts ("bar" then EOF) just due to
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netcat's implementation. The second epoll_wait() caught it.
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Here we clearly see that :
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- read0 alone returns EPOLLIN|EPOLLRDHUP
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- read0 after shutw returns EPOLLIN|EPOLLRDHUP|EPOLLHUP
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=> difference indeed is "cannot write"
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Local with a delay before closing the server:
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17:30:32.527157 epoll_wait(3, [{EPOLLIN, {u32=5, u64=5}}], 200, 1000) = 1
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17:30:33.216827 accept4(5, {sa_family=AF_INET, sin_port=htons(33908), sin_addr=inet_addr("127.0.0.1")}, [128->16], SOCK_NONBLOCK) = 8
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17:30:33.216957 setsockopt(8, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:30:33.216984 accept4(5, 0x7ffc1a1fb0c0, [128], SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
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17:30:33.217071 recvfrom(8, "GET / HTTP/1.0\r\n\r\n\n", 15360, 0, NULL, NULL) = 19
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17:30:33.217115 recvfrom(8, "", 15341, 0, NULL, NULL) = 0
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17:30:33.217135 socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 9
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17:30:33.217176 setsockopt(9, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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17:30:33.217190 connect(9, {sa_family=AF_INET, sin_port=htons(8000), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)
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17:30:33.217233 sendto(9, "GET / HTTP/1.0\r\n\r\n\n", 19, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 19
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17:30:33.217272 shutdown(9, SHUT_WR) = 0
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17:30:33.217318 recvfrom(9, 0x109b2f0, 16384, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
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17:30:33.217332 epoll_ctl(3, EPOLL_CTL_ADD, 9, {EPOLLIN|EPOLLRDHUP, {u32=9, u64=9}}) = 0
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17:30:33.217355 epoll_wait(3, [{EPOLLIN|EPOLLHUP|EPOLLRDHUP, {u32=9, u64=9}}], 200, 1000) = 1
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17:30:33.217377 recvfrom(9, "HTTP/1.0 200\r\nContent-length: 0\r\nX-req: size=19, time=0 ms\r\nX-rsp: id=dummy, code=200, cache=1, size=0, time=0 ms (0 real)\r\n\r\n", 16384, 0, NULL, NULL) = 126
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17:30:33.217395 close(9) = 0
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17:30:33.217411 sendto(8, "HTTP/1.0 200\r\nContent-length: 0\r\nX-req: size=19, time=0 ms\r\nX-rsp: id=dummy, code=200, cache=1, size=0, time=0 ms (0 real)\r\n\r\n", 126, MSG_DONTWAIT|MSG_NOSIGNAL|MSG_MORE, NULL, 0) = 126
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17:30:33.217464 close(8) = 0
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17:30:33.217496 epoll_wait(3, [], 200, 0) = 0
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Notes:
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- RDHUP is properly present while some data remain pending.
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- HUP is present since RDHUP + shutw
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It could be concluded that HUP indicates RDHUP+shutw and in no way indicates
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the ability to avoid reading.
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Below HUP|ERR|OUT are reported on connection failures, thus WITHOUT read:
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accept4(5, {sa_family=AF_INET, sin_port=htons(39080), sin_addr=inet_addr("127.0.0.1")}, [128->16], SOCK_NONBLOCK) = 8
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setsockopt(8, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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accept4(5, 0x7ffffba55730, [128], SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
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recvfrom(8, "foo\n", 15360, 0, NULL, NULL) = 4
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recvfrom(8, 0x7f634dcfeff4, 15356, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
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socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 9
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fcntl(9, F_SETFL, O_RDONLY|O_NONBLOCK) = 0
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setsockopt(9, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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connect(9, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("10.0.3.82")}, 16) = -1 EINPROGRESS (Operation now in progress)
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sendto(9, "foo\n", 4, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = -1 EAGAIN (Resource temporarily unavailable)
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epoll_ctl(3, EPOLL_CTL_ADD, 8, {EPOLLIN|EPOLLRDHUP, {u32=8, u64=8}}) = 0
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epoll_ctl(3, EPOLL_CTL_ADD, 9, {EPOLLOUT, {u32=9, u64=9}}) = 0
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epoll_wait(3, [{EPOLLOUT|EPOLLERR|EPOLLHUP, {u32=9, u64=9}}], 200, 1000) = 1
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getsockopt(9, SOL_SOCKET, SO_ERROR, [111], [4]) = 0
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recvfrom(9, "", 15360, 0, NULL, NULL) = 0
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close(9) = 0
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On a failed connect attempt immediately followed by a failed recv (all flags
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set), we can see this:
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socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 8
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fcntl(8, F_SETFL, O_RDONLY|O_NONBLOCK) = 0
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setsockopt(8, SOL_TCP, TCP_NODELAY, [1], 4) = 0
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connect(8, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("10.0.3.82")}, 16) = -1 EINPROGRESS (Operation now in progress)
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recvfrom(8, 0x1084a20, 16384, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
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epoll_ctl(3, EPOLL_CTL_ADD, 8, {EPOLLIN|EPOLLOUT|EPOLLRDHUP, {u32=8, u64=8}}) = 0
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epoll_wait(3, [{EPOLLIN|EPOLLOUT|EPOLLERR|EPOLLHUP|EPOLLRDHUP, {u32=8, u64=8}}], 200, 1000) = 1
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connect(8, {sa_family=AF_INET, sin_port=htons(8008), sin_addr=inet_addr("10.0.3.82")}, 16) = -1 ECONNREFUSED (Connection refused)
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close(8) = 0
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=> all flags are reported in case of error.
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It's also interesting to note that POLLOUT is still reported after a shutw,
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and no send error is ever reported after shutw:
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shutdown(4, SHUT_WR) = 0
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poll([{fd=4, events=POLLIN|POLLOUT|POLLRDHUP}], 1, 0) = 1 ([{fd=4, revents=POLLOUT}])
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and:
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shutdown(4, SHUT_WR) = 0
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sendto(5, "foo", 3, MSG_NOSIGNAL, NULL, 0) = 3
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poll([{fd=4, events=POLLIN|POLLOUT|POLLRDHUP}], 1, 0) = 1 ([{fd=4, revents=POLLIN|POLLOUT}])
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and:
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shutdown(4, SHUT_WR) = 0
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sendto(4, "bar", 3, MSG_NOSIGNAL, NULL, 0) = -1 EPIPE (Broken pipe)
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poll([{fd=4, events=POLLIN|POLLOUT|POLLRDHUP}], 1, 0) = 1 ([{fd=4, revents=POLLOUT}])
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POLLOUT is still reported after a SHUTWR:
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socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
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setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
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bind(3, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
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listen(3, 1000) = 0
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getsockname(3, {sa_family=AF_INET, sin_port=htons(34729), sin_addr=inet_addr("0.0.0.0")}, [16]) = 0
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socket(AF_INET, SOCK_STREAM, IPPROTO_TCP) = 4
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connect(4, {sa_family=AF_INET, sin_port=htons(34729), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
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accept(3, 0x7ffcd6a68300, [0->16]) = 5
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fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
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brk(NULL) = 0xc4e000
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brk(0xc6f000) = 0xc6f000
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write(1, "\n", 1
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) = 1
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shutdown(4, SHUT_WR) = 0
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poll([{fd=4, events=POLLIN|POLLOUT|POLLRDHUP}], 1, 0) = 1 ([{fd=4, revents=POLLOUT}])
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write(1, "ret=1 ev={fd:4 ev:4}\n", 21ret=1 ev={fd:4 ev:4}
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) = 21
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close(5) = 0
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close(4) = 0
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close(3) = 0
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Performing a write() on it reports a SIGPIPE:
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shutdown(4, SHUT_WR) = 0
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sendto(4, "bar", 3, MSG_NOSIGNAL, NULL, 0) = -1 EPIPE (Broken pipe)
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poll([{fd=4, events=POLLIN|POLLOUT|POLLRDHUP}], 1, 0) = 1 ([{fd=4, revents=POLLOUT}])
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On SHUT_RD we see POLLIN|POLLOUT|POLLRDHUP (there's no data pending here) :
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shutdown(4, SHUT_RD) = 0
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poll([{fd=4, events=POLLIN|POLLOUT|POLLRDHUP}], 1, 0) = 1 ([{fd=4, revents=POLLIN|POLLOUT|POLLRDHUP}])
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What is observed in the end :
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- POLLOUT is always reported for anything SHUT_WR even if it would cause a broken pipe, including listeners if they're also SHUT_RD
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- POLLHUP is always reported for anything SHUT_WR + having a SHUT_RD pending with or without anything to read, including listeners
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- POLLIN is always reported for anything to read or a pending zero
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- POLLIN is NOT reported for SHUT_RD listeners, even with pending connections, only OUT+HUP are reported
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- POLLIN and POLLRDHUP are always reported after a SHUTR
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- POLLERR also enables IN,OUT,HUP,RHUP
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Currently there's a bit of an issue with connect() being too impatient to read:
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16:26:06.818521 connect(9, {sa_family=AF_INET, sin_port=htons(8000), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)
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16:26:06.818558 recvfrom(9, 0x1db9400, 16320, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
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16:26:06.818571 epoll_ctl(3, EPOLL_CTL_ADD, 9, {EPOLLIN|EPOLLOUT|EPOLLRDHUP, {u32=9, u64=9}}) = 0
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16:26:06.818588 epoll_wait(3, [{EPOLLOUT, {u32=9, u64=9}}], 200, 1000) = 1
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16:26:06.818603 connect(9, {sa_family=AF_INET, sin_port=htons(8000), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
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16:26:06.818617 sendto(9, "GET /?s=10k HTTP/1.1\r\nhost: 127.0.0.1:4445\r\nuser-agent: curl/7.54.1\r\naccept: */*\r\n\r\n", 84, MSG_DONTWAIT|MSG_NOSIGNAL, NULL, 0) = 84
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16:26:06.818660 epoll_ctl(3, EPOLL_CTL_MOD, 9, {EPOLLIN|EPOLLRDHUP, {u32=9, u64=9}}) = 0
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16:26:06.818696 epoll_wait(3, [{EPOLLIN, {u32=9, u64=9}}], 200, 1000) = 1
|
||||
16:26:06.818711 recvfrom(9, "HTTP/1.1 200\r\nContent-length: 10240\r\nX-req: size=84, time=0 ms\r\nX-rsp: id=dummy, code=200, cache=1, size=10240, time=0 ms (0 real)\r\n\r\n89.123456789.12345678\n.123456789.123456789.123456789.123456789.123"..., 16320, 0, NULL, NULL) = 10374
|
||||
16:26:06.818735 recvfrom(9, 0x1dd75f6, 5946, 0, NULL, NULL) = -1 EAGAIN (Resource temporarily unavailable)
|
||||
16:26:06.818790 epoll_ctl(3, EPOLL_CTL_DEL, 9, 0x7ffa818fd7d0) = 0
|
||||
16:26:06.818804 epoll_wait(3, [], 200, 0) = 0
|
||||
|
||||
|
||||
|
||||
|
||||
This one shows that the error is not definitive, it disappears once it's
|
||||
been signaled, then only shut remains! Also it's a proof that an error
|
||||
may well be reported after a shutw, so the r/w error may not be merged
|
||||
with a shutw since it may appear after an deliberate shutw.
|
||||
|
||||
$ ./contrib/debug/poll -v -c snd,shw -s pol,rcv,pol,rcv,pol,snd,lin,clo -c pol,rcv,pol,rcv,pol,rcv,pol
|
||||
#### BEGIN ####
|
||||
cmd #1 stp #1: do_snd(4): ret=3
|
||||
cmd #1 stp #2: do_shw(4): ret=0
|
||||
cmd #2 stp #0: do_acc(3): ret=5
|
||||
cmd #2 stp #1: do_pol(5): ret=1 ev=0x2005 (IN OUT RDHUP)
|
||||
cmd #2 stp #2: do_rcv(5): ret=3
|
||||
cmd #2 stp #3: do_pol(5): ret=1 ev=0x2005 (IN OUT RDHUP)
|
||||
cmd #2 stp #4: do_rcv(5): ret=0
|
||||
cmd #2 stp #5: do_pol(5): ret=1 ev=0x2005 (IN OUT RDHUP)
|
||||
cmd #2 stp #6: do_snd(5): ret=3
|
||||
cmd #2 stp #7: do_lin(5): ret=0
|
||||
cmd #2 stp #8: do_clo(5): ret=0
|
||||
cmd #3 stp #1: do_pol(4): ret=1 ev=0x201d (IN OUT ERR HUP RDHUP)
|
||||
cmd #3 stp #2: do_rcv(4): ret=3
|
||||
cmd #3 stp #3: do_pol(4): ret=1 ev=0x201d (IN OUT ERR HUP RDHUP)
|
||||
cmd #3 stp #4: do_rcv(4): ret=-1 (Connection reset by peer)
|
||||
cmd #3 stp #5: do_pol(4): ret=1 ev=0x2015 (IN OUT HUP RDHUP)
|
||||
cmd #3 stp #6: do_rcv(4): ret=0
|
||||
cmd #3 stp #7: do_pol(4): ret=1 ev=0x2015 (IN OUT HUP RDHUP)
|
||||
#### END ####
|
||||
|
|
@ -0,0 +1,192 @@
|
|||
2019-09-03
|
||||
|
||||
u8 fd.state;
|
||||
u8 fd.ev;
|
||||
|
||||
|
||||
ev = one of :
|
||||
#define FD_POLL_IN 0x01
|
||||
#define FD_POLL_PRI 0x02
|
||||
#define FD_POLL_OUT 0x04
|
||||
#define FD_POLL_ERR 0x08
|
||||
#define FD_POLL_HUP 0x10
|
||||
|
||||
Could we instead have :
|
||||
|
||||
FD_WAIT_IN 0x01
|
||||
FD_WAIT_OUT 0x02
|
||||
FD_WAIT_PRI 0x04
|
||||
FD_SEEN_HUP 0x08
|
||||
FD_SEEN_HUP 0x10
|
||||
FD_WAIT_CON 0x20 <<= shouldn't this be in the connection itself in fact ?
|
||||
|
||||
=> not needed, covered by the state instead.
|
||||
|
||||
What is missing though is :
|
||||
- FD_DATA_PENDING -- overlaps with READY_R, OK if passed by pollers only
|
||||
- FD_EOI_PENDING
|
||||
- FD_ERR_PENDING
|
||||
- FD_EOI
|
||||
- FD_SHW
|
||||
- FD_ERR
|
||||
|
||||
fd_update_events() could do that :
|
||||
|
||||
if ((fd_data_pending|fd_eoi_pending|fd_err_pending) && !(fd_err|fd_eoi))
|
||||
may_recv()
|
||||
|
||||
if (fd_send_ok && !(fd_err|fd_shw))
|
||||
may_send()
|
||||
|
||||
if (fd_err)
|
||||
wake()
|
||||
|
||||
the poller could do that :
|
||||
HUP+OUT => always indicates a failed connect(), it should not lack ERR. Is this err_pending ?
|
||||
|
||||
ERR HUP OUT IN
|
||||
0 0 0 0 => nothing
|
||||
0 0 0 1 => FD_DATA_PENDING
|
||||
0 0 1 0 => FD_SEND_OK
|
||||
0 0 1 1 => FD_DATA_PENDING|FD_SEND_OK
|
||||
0 1 0 0 => FD_EOI (|FD_SHW)
|
||||
0 1 0 1 => FD_DATA_PENDING|FD_EOI_PENDING (|FD_SHW)
|
||||
0 1 1 0 => FD_EOI |FD_ERR (|FD_SHW)
|
||||
0 1 1 1 => FD_EOI_PENDING (|FD_ERR_PENDING) |FD_DATA_PENDING (|FD_SHW)
|
||||
1 X 0 0 => FD_ERR | FD_EOI (|FD_SHW)
|
||||
1 X X 1 => FD_ERR_PENDING | FD_EOI_PENDING | FD_DATA_PENDING (|FD_SHW)
|
||||
1 X 1 0 => FD_ERR | FD_EOI (|FD_SHW)
|
||||
|
||||
OUT+HUP,OUT+HUP+ERR => FD_ERR
|
||||
|
||||
This reorders to:
|
||||
|
||||
IN ERR HUP OUT
|
||||
0 0 0 0 => nothing
|
||||
0 0 0 1 => FD_SEND_OK
|
||||
0 0 1 0 => FD_EOI (|FD_SHW)
|
||||
|
||||
0 X 1 1 => FD_ERR | FD_EOI (|FD_SHW)
|
||||
0 1 X 0 => FD_ERR | FD_EOI (|FD_SHW)
|
||||
0 1 X 1 => FD_ERR | FD_EOI (|FD_SHW)
|
||||
|
||||
1 0 0 0 => FD_DATA_PENDING
|
||||
1 0 0 1 => FD_DATA_PENDING|FD_SEND_OK
|
||||
1 0 1 0 => FD_DATA_PENDING|FD_EOI_PENDING (|FD_SHW)
|
||||
1 0 1 1 => FD_EOI_PENDING (|FD_ERR_PENDING) |FD_DATA_PENDING (|FD_SHW)
|
||||
1 1 X X => FD_ERR_PENDING | FD_EOI_PENDING | FD_DATA_PENDING (|FD_SHW)
|
||||
|
||||
Regarding "|SHW", it's normally useless since it will already have been done,
|
||||
except on connect() error where this indicates there's no need for SHW.
|
||||
|
||||
FD_EOI and FD_SHW could be part of the state (FD_EV_SHUT_R, FD_EV_SHUT_W).
|
||||
Then all states having these bit and another one would be transient and need
|
||||
to resync. We could then have "fd_shut_recv" and "fd_shut_send" to turn these
|
||||
states.
|
||||
|
||||
The FD's ev then only needs to update EOI_PENDING, ERR_PENDING, ERR, DATA_PENDING.
|
||||
With this said, these are not exactly polling states either, as err/eoi/shw are
|
||||
orthogonal to the other states and are required to update them so that the polling
|
||||
state really is DISABLED in the end. So we need more of an operational status for
|
||||
the FD containing EOI_PENDING, EOI, ERR_PENDING, ERR, SHW, CLO?. These could be
|
||||
classified in 3 categories: read:(OPEN, EOI_PENDING, EOI); write:(OPEN,SHW),
|
||||
ctrl:(OPEN,ERR_PENDING,ERR,CLO). That would be 2 bits for R, 1 for W, 2 for ctrl
|
||||
or total 5 vs 6 for individual ones, but would be harder to manipulate.
|
||||
|
||||
Proposal:
|
||||
- rename fdtab[].state to "polling_state"
|
||||
- rename fdtab[].ev to "status"
|
||||
|
||||
Note: POLLHUP is also reported is a listen() socket has gone in shutdown()
|
||||
TEMPORARILY! Thus we may not always consider this as a final error.
|
||||
|
||||
|
||||
Work hypothesis:
|
||||
|
||||
SHUT RDY ACT
|
||||
0 0 0 => disabled
|
||||
0 0 1 => active
|
||||
0 1 0 => stopped
|
||||
0 1 1 => ready
|
||||
1 0 0 => final shut
|
||||
1 0 1 => shut pending without data
|
||||
1 1 0 => shut pending, stopped
|
||||
1 1 1 => shut pending
|
||||
|
||||
PB: we can land into final shut if one thread disables the FD while another
|
||||
one that was waiting on it reports it as shut. Theorically it should be
|
||||
implicitly ready though, since reported. But if no data is reported, it
|
||||
will be reportedly shut only. And no event will be reported then. This
|
||||
might still make sense since it's not active, thus we don't want events.
|
||||
But it will not be enabled later either in this case so the shut really
|
||||
risks not to be properly reported. The issue is that there's no difference
|
||||
between a shut coming from the bottom and a shut coming from the top, and
|
||||
we need an event to report activity here. Or we may consider that a poller
|
||||
never leaves a final shut by itself (100) and always reports it as
|
||||
shut+stop (thus ready) if it was not active. Alternately, if active is
|
||||
disabled, shut should possibly be ignored, then a poller cannot report
|
||||
shut. But shut+stopped seems the most suitable as it corresponds to
|
||||
disabled->stopped transition.
|
||||
|
||||
Now let's add ERR. ERR necessarily implies SHUT as there doesn't seem to be a
|
||||
valid case of ERR pending without shut pending.
|
||||
|
||||
ERR SHUT RDY ACT
|
||||
0 0 0 0 => disabled
|
||||
0 0 0 1 => active
|
||||
0 0 1 0 => stopped
|
||||
0 0 1 1 => ready
|
||||
|
||||
0 1 0 0 => final shut, no error
|
||||
0 1 0 1 => shut pending without data
|
||||
0 1 1 0 => shut pending, stopped
|
||||
0 1 1 1 => shut pending
|
||||
|
||||
1 0 X X => invalid
|
||||
|
||||
1 1 0 0 => final shut, error encountered
|
||||
1 1 0 1 => error pending without data
|
||||
1 1 1 0 => error pending after data, stopped
|
||||
1 1 1 1 => error pending
|
||||
|
||||
So the algorithm for the poller is:
|
||||
- if (shutdown_pending or error) reported and ACT==0,
|
||||
report SHUT|RDY or SHUT|ERR|RDY
|
||||
|
||||
For read handlers :
|
||||
- if (!(flags & (RDY|ACT)))
|
||||
return
|
||||
- if (ready)
|
||||
try_to_read
|
||||
- if (err)
|
||||
report error
|
||||
- if (shut)
|
||||
read0
|
||||
|
||||
For write handlers:
|
||||
- if (!(flags & (RDY|ACT)))
|
||||
return
|
||||
- if (err||shut)
|
||||
report error
|
||||
- if (ready)
|
||||
try_to_write
|
||||
|
||||
For listeners:
|
||||
- if (!(flags & (RDY|ACT)))
|
||||
return
|
||||
- if (err||shut)
|
||||
pause
|
||||
- if (ready)
|
||||
try_to_accept
|
||||
|
||||
Kqueue reports events differently, it says EV_EOF() on READ or WRITE, that
|
||||
we currently map to FD_POLL_HUP and FD_POLL_ERR. Thus kqueue reports only
|
||||
POLLRDHUP and not POLLHUP, so for now a direct mapping of POLLHUP to
|
||||
FD_POLL_HUP does NOT imply write closed with kqueue while it does for others.
|
||||
|
||||
Other approach, use the {RD,WR}_{ERR,SHUT,RDY} flags to build a composite
|
||||
status in each poller and pass this to fd_update_events(). We normally
|
||||
have enough to be precise, and this latter will rework the events.
|
||||
|
||||
FIXME: Normally on KQUEUE we're supposed to look at kev[].fflags to get the error
|
||||
on EV_EOF() on read or write.
|
||||
Loading…
Reference in New Issue