[tarantool-patches] Re: [PATCH] Fix lua socket polling in case of a spurious wakeup
Vladislav Shpilevoy
v.shpilevoy at tarantool.org
Mon Aug 6 17:27:39 MSK 2018
Hi! See 7 comments below. Last 6 of them I've fixed on the branch
in a separate commit. Please, look, squash and fix the first comment
yourself.
On 02/08/2018 18:44, Georgy Kirichenko wrote:
> socket_writable/socket_readable handles socket.iowait spurious wakeup
> until event is happened or timeout is exceeded.
>
> Fixes #3344
> ---
> Issue: https://github.com/tarantool/tarantool/issues/3344
> Branch: https://github.com/tarantool/tarantool/tree/g.kirichenko/gh-3344-socket-io-spurios-wakeup
1. The test constantly fails:
======================================================================================
WORKR TEST PARAMS RESULT
---------------------------------------------------------------------------------
[001] app/socket.test.lua [ fail ]
[001]
[001] Test failed! Result content mismatch:
[001] --- app/socket.result Mon Aug 6 16:36:23 2018
[001] +++ app/socket.reject Mon Aug 6 17:06:23 2018
[001] @@ -2294,7 +2294,7 @@
[001] ...
[001] client:read(1, 0.1) == ''
[001] ---
[001] -- true
[001] +- false
[001] ...
[001] server:close()
[001] ---
I have tried to fix it and it looks like socket close event is not
triggered or checked in socket_read() function. Please, fix.
> src/lua/socket.lua | 67 ++++++++++++++++++++------------------
> test/app/socket.result | 70 ++++++++++++++++++++++++++++++++++++++++
> test/app/socket.test.lua | 29 +++++++++++++++++
> 3 files changed, 135 insertions(+), 31 deletions(-)
>
> diff --git a/src/lua/socket.lua b/src/lua/socket.lua
> index 06306eae2..9fcaee0e8 100644
> --- a/src/lua/socket.lua
> +++ b/src/lua/socket.lua
> @@ -328,12 +328,18 @@ local function do_wait(self, what, timeout)
> self._errno = nil
> timeout = timeout or TIMEOUT_INFINITY
>
> - local res = internal.iowait(fd, what, timeout)
> - if res == 0 then
> - self._errno = boxerrno.ETIMEDOUT
> - return 0
> + local deadline = fiber.clock() + timeout
> + local events
> +
> + while fiber.clock() <= deadline do
> + events = internal.iowait(fd, what, deadline - fiber.clock())
> + fiber.testcancel()
> + if events ~= 0 and events ~= '' then> + return events
> + end
> end
> - return res
> + self._errno = boxerrno.ETIMEDOUT
> + return events
2. Is it possible that you have an event after timeout? I believe,
events here is always 0. So you can return 0, and put 'local events'
declaration inside the 'while' loop above.
> end
>
> local function socket_readable(self, timeout)
> @@ -935,16 +934,19 @@ local function socket_tcp_connect(s, address, port, timeout)
> -- Wait until the connection is established or ultimately fails.
> -- In either condition the socket becomes writable. To tell these
> -- conditions appart SO_ERROR must be consulted (man connect).
> - if socket_writable(s, timeout) then
> - s._errno = socket_getsockopt(s, 'SOL_SOCKET', 'SO_ERROR')
> - else
> - s._errno = boxerrno.ETIMEDOUT
> - end
> - if s._errno ~= 0 then
> - return nil
> + local deadline = timeout + fiber.clock()
> + while deadline - fiber.clock() >= 0 do
3. This 'while' can be removed since the wait is done inside
socket_writable.
> + if socket_writable(s, deadline - fiber.clock()) then
> + s._errno = socket_getsockopt(s, 'SOL_SOCKET', 'SO_ERROR')
> + if s._errno == 0 then
> + return true
> + else
> + return nil
> + end
> + end
> end
> - -- Connected
> - return true
> + s._errno = boxerrno.ETIMEDOUT
4. Socket_writable already sets errno.
> + return nil
> end
>
> local function tcp_connect(host, port, timeout)
> @@ -1005,7 +1007,8 @@ end
> local function tcp_server_loop(server, s, addr)
> fiber.name(format("%s/%s:%s", server.name, addr.host, addr.port), {truncate = true})
> log.info("started")
> - while socket_readable(s) do
> + while true do
> + socket_readable(s)
5. If the socket is not writable you should not accept anything.
The previous version was right.
> local sc, from = socket_accept(s)
> if sc == nil then
> local errno = s._errno
> @@ -1325,7 +1328,8 @@ end
> local function lsocket_tcp_accept(self)
> check_socket(self)
> local deadline = fiber.clock() + (self.timeout or TIMEOUT_INFINITY)
> - repeat
> + while deadline - fiber.clock() >= 0 do
> + socket_readable(self, deadline - fiber.clock())
6. The same. If the socket is not writable, here is nothing to
accept.
> local client = socket_accept(self)
> if client then
> setmetatable(client, lsocket_tcp_client_mt)
> @@ -1390,7 +1394,8 @@ local function lsocket_tcp_receive(self, pattern, prefix)
> elseif pattern == "*a" then
> local result = { prefix }
> local deadline = fiber.clock() + (self.timeout or TIMEOUT_INFINITY)
> - repeat
> + while deadline - fiber.clock() >= 0 do
> + socket_readable(self, deadline - fiber.clock())
7. The same.
> local data = socket_sysread(self)
> if data == nil then
> if not errno_is_transient[self._errno] then
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