There’s an interesting behavioral difference between how the loopback works with ASIO on windows/linux. I have constructed a test that talks to an echo server across the loopback. The test steps are: 1) Open the socket using run_one(), verifying it is open 2) Start an async read 3) Start an async write 4) Call run_one, then verify the write succeeds 5) Call run_one, then verify that the data you write is received 6) Goto step 2 some number of times since the behavior is non-determinsitic One windows, this seems to consistently fail within the first 100 iterations, because on occasional you get the read callback with echoed data before the write success comes back!!!! This seems crazy that another process answers you before the OS/ASIO has even told you the write was successful. On Linux I have not been able to make this happen even with 10K’s of iterations. I can only assume that: 1) This can actually happen with Windows loopback + thread scheduling and my assumption that write callbacks will always occur before response data is invalid 2) There is a bug in the windows impl of ASIO that makes this possible. If anyone can shed some light on this I’d really appreciate it. I have code that wants to step through a series of states, and it makes things a lot more complicated if I can’t assume that the write callback will always occur before data received that’s a response to what I sent. Thanks! Adam Adam Crain Manager of R&D Green Energy Corp. 919-428-1002