Boost:1.82.0 ASIO changed its behavior

From: Nedelin Rusev (nedelin.rusev_at_[hidden])
Date: 2025-05-20 07:32:43

Hi,

Recently I inherited an old project, which uses boost 1.65.0 and ASIO, for
custom implementation of the SCTP protocol.
Technically it adapts the existing ASIO TCP for SCTP. Another
implementation uses this ASIO-SCTP to asynchronously send
and receive data. My task was to make both implementations work with any
boost version from 1.65.0 to 1.87.0.

I did the necessary changes and the project now compiles and runs, but I
face a test deviation with boost versions
1.82.0 and above.

The test is more or less simple:
- we have pre-generated data
- we start a server, which only receives data and stores it in file per
connected client
- we start multiple clients, each running in its own thread. Each client
sends its own data to the server at a random moment
- finally we check if the server has received the same data as the clients
have sent.

With boost versions up to 1.81.0 the test passes OK. But with boost version
1.82.0 we observe wrong order of the data stored
by the server. To illustrate it roughly:
Client sends:  0,1,2
Server stores: 0,2,1 (0 is OK, Next we should have 1, but we get 2).
Note: the real test data is hundreds of bytes long, not single digits.
Note: the test seems to have issues, but on the particular machine, the
behavior is consistent:
      test is OK with boost 1.81.0 and NOK with boost 1.82.0

I suspect the problem has something to do with the "on_immediate()"
extension, introduced in boost 1.82.0.
Somehow it speeds up the client threads execution and changes the order of
the sent data.
I failed to find any similar problems, reported in internet (git, boost
forums, etc)

I have enabled BOOST_ASIO_ENABLE_HANDLER_TRACKING and, if I get the log
right, client threads are executed faster.
I have attached the handler tracking logs for boost versions 1.81.0 and
1.82.0.

My question is how to keep the old code behavior (pre 1.82.0) with later
versions?
Is there any way to disable the "on_immediate()" functionality?
Are there any guidelines for using later versions of boost ASIO (1.82.0 and
later)?

Providing a simplified example test is hard, as the code-base is quite
large.
I will try to make something up, but this will take time.

Thank you!