[erlang-questions] OTP 22.1 socket.erl somehow breaks message delivery or scheduler

[Jaka Bac]

Hi,

There were big improvements in compiler that were released with OTP 22.

If you are interested in details, see
http://blog.erlang.org/OTP-22-Highlights/

Jaka

On Mon, Oct 28, 2019, 16:39 Andreas Schultz <andreas.schultz@REDACTED>
wrote:

> Am Mo., 28. Okt. 2019 um 15:22 Uhr schrieb Björn Gustavsson <
> bjorn@REDACTED>:
>
>> Thanks for reporting this issue.
>>
>> We have investigated the issue and found that it is a bug in the compiler.
>>
>
> wow. I have to say I'm a bit scared of OTP 22.x at the moment because of
> all the "bugs in the compiler" changes lately.
> Did the rewrite of the compiler in 22.0 cause all this or was it present
> before and just went unnoticed?
>
> Anyway, many thanks for finding this,
> Andreas
>
>
>> https://bugs.erlang.org/browse/ERL-1076
>>
>> https://github.com/erlang/otp/pull/2434
>>
>> /Björn
>>
>> On Wed, Oct 23, 2019 at 3:53 PM Andreas Schultz
>> <andreas.schultz@REDACTED> wrote:
>> >
>> > Hi,
>> >
>> > After converting an application to socket.erl in OTP 22.1, the test
>> suites started to fail with random timeouts. It took me a while to figure
>> out that gen_server:calls arrived multiple seconds late in the server.
>> >
>> > I have a demonstration at
>> https://gist.github.com/RoadRunnr/311a7679fff6fbdf367c455b960f1ba8. It
>> implements a simple UDP echo server with socket.erl. The client uses
>> gen_udp to send messages and wait for the response.
>> > The client also sends Erlang ping message to the server and expects to
>> get a pong answer back. The socket.erl based server is supposed to not
>> block (and as far as I can tell, it does not), it therefore should be able
>> to answer the Erlang ping message all the time.
>> > There are also some simple busy loop process running to get some load.
>> Without them the problem is not reproducible.
>> >
>> > The sample is failing in about 20% off the test runs, when it does the
>> output is something like:
>> >
>> > $ ~/stest.escript
>> > Server Pid <0.78.0>
>> > Server Addr #{addr => {127,0,0,1},family => inet,port => 38959}
>> > ping timeout
>> >            round trip    Clnt/Srvr    Srvr/Clnt     ProcPing
>> > ...
>> >       85: ******** ns, ******** ns,    57675 ns,    42332 ns
>> > ...
>> >
>> > The failure happens because a 'ping' message is not see in time by the
>> receive clause in the server process. It seems that either the process is
>> not scheduled for some time (multiple seconds), or the scanning of the
>> mailbox is missing the message.
>> >
>> > I have ruled out that the UDP messages are being dropped, otherwise the
>> clients gen_udp:recv would never return.
>> >
>> > Does anyone have a clue what might cause this? Or point out where my
>> sample is broken.
>> >
>> > Many thanks
>> > Andreas
>> >
>> > --
>> >
>> > Andreas Schultz
>> >
>> >
>> >
>> > _______________________________________________
>> > erlang-questions mailing list
>> > erlang-questions@REDACTED
>> > http://erlang.org/mailman/listinfo/erlang-questions
>>
>>
>>
>> --
>> Björn Gustavsson, Erlang/OTP, Ericsson AB
>>
>
>
> --
>
> Andreas Schultz
>
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