[tarantool-patches] Re: [PATCH] Fix lua socket polling in case of a spurious wakeup

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

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