[tarantool-patches] Re: [PATCH] Protect lua socket io against a spurious wakeup

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

Hello. Thanks for the patch! See 6 comments below.

On 18/07/2018 14:43, Georgy Kirichenko wrote:
> socket_readable/socket_writable might return until socket become a
> requested state in case of a spurious wakeup. Socket functions are
> refactored with considering that fact.
> 
> Old behavior leads to test failures.

Are you sure, that the only reason is the tests? Please,
explain here briefly, why it is important to track spurious
wakeups and cancels.

> ---
> Issue: https://github.com/tarantool/tarantool/issues/3344
> Branch:
> https://github.com/tarantool/tarantool/tree/g.kirichenko/gh-3344-socket-io-spurios-wakeup
>   src/lua/socket.lua        | 54 ++++++++++++++++++++++-----------------
>   test/box/net.box.result   |  3 +++
>   test/box/net.box.test.lua |  2 ++
>   3 files changed, 35 insertions(+), 24 deletions(-)
> 
> diff --git a/src/lua/socket.lua b/src/lua/socket.lua
> index 06306eae2..0b22bb91c 100644
> --- a/src/lua/socket.lua
> +++ b/src/lua/socket.lua
> @@ -689,12 +689,8 @@ local function read(self, limit, timeout, check, ...)
>               return nil
>           end
>   
> -        if not socket_readable(self, timeout) then
> -            return nil
> -        end
> -        if timeout <= 0 then
> -            break
> -        end
> +        socket_readable(self, timeout)
> +        fiber.testcancel()

1. I see that you put this testcancel after each wait in this
file. But why can not you just put it inside wait? This is
obvious code duplication.

>           timeout = timeout - ( fiber.clock() - started )
>       end
>       self._errno = boxerrno.ETIMEDOUT
> @@ -736,7 +732,7 @@ local function socket_write(self, octets, timeout)
>       end
>   
>       local started = fiber.clock()
> -    while true do
> +    while timeout > 0 do

2. Why? As I remember, Kostja said, that timeout 0 is ok and
means that we have only one attempt to do an action (like
write, read ...). And how is it linked with the patch?

>           local written = syswrite(self, p, e - p)
>           if written == 0 then
>               return p - s -- eof
> @@ -935,16 +930,21 @@ 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
> +        if socket_writable(s, deadline - fiber.clock()) then

3. If the socket became writable, and the fiber was canceled,
then you will return true/nil with no testcancel.

> +            s._errno = socket_getsockopt(s, 'SOL_SOCKET', 'SO_ERROR')
> +            if s._errno == 0 then
> +                return true
> +            else
> +                return nil
> +            end
> +        end
> +        -- timeout, spurious wakeup or cancel
> +        fiber.testcancel()
>       end
> -    -- Connected
> -    return true
> +    s._errno = boxerrno.ETIMEDOUT
> +    return nil
>   end
>   
>   local function tcp_connect(host, port, timeout)
> @@ -1005,7 +1005,9 @@ 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
> +        fiber.testcancel()
> +        socket_readable(s)

4. Why cancel() is before readable()?

>           local sc, from = socket_accept(s)
>           if sc == nil then
>               local errno = s._errno
> @@ -1335,7 +1339,7 @@ local function lsocket_tcp_accept(self)
>           if not errno_is_transient[errno] then
>               break
>           end
> -    until not socket_readable(self, deadline - fiber.clock())
> +    end
>       return nil, socket_error(self)
>   end
>   
> @@ -1390,7 +1394,9 @@ 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

5. Same as 2. We allow 0 timeout.

> +            socket_readable(self, deadline - fiber.clock())
> +            fiber.testcancel()
>               local data = socket_sysread(self)
>               if data == nil then
>                   if not errno_is_transient[self._errno] then
> diff --git a/test/box/net.box.result b/test/box/net.box.result
> index 21cff4a11..4bafabdcb 100644
> --- a/test/box/net.box.result
> +++ b/test/box/net.box.result
> @@ -20,6 +20,9 @@ test_run:cmd("push filter ".."'\\.lua.*:[0-9]+: ' to '.lua...\"]:<line>: '")
>   ---
>   - true
>   ...
> +fiber.wakeup(fiber.self())

6. No link to the issue. Both in the commit message and
before the test.

> +---
> +...
>   test_run:cmd("setopt delimiter ';'")
>   ---
>   - true