On Tue, Jun 11, 2024 at 2:36 AM Dominique Devienne <ddevienne@xxxxxxxxx> wrote: > Hi. I've noticed [that libpq API in v17 beta1][1], and wanted to use > it to replace an existing Boost.ASIO-based async polling of the > connection's socket, waiting for notifications. The use case being > using PostgreSQL LISTEN/NOTIFY for a simple message queue. The code > needs to be cross-platform Windows and Linux. My goal would be to > eliminate that Boost.ASIO dependency for that, to use just libpq. One idea I have wondered about is why you wouldn't just use poll() directly, if you want a facility that works on all known operating systems without extra portability libraries. Windows has WSApoll(), which AFAIK was designed to be Unix-compatible and a drop-in replacement, requiring just a rename but otherwise having the same macros and struct etc. For some period of time, people who had to deal with socket connection events (that includes us) avoided it, with the Curl guys' blog being the most often cited public explanation for why: https://daniel.haxx.se/blog/2012/10/10/wsapoll-is-broken/ However, as far as I know, that was fixed ~4 years ago: https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsapoll "Note As of Windows 10 version 2004, when a TCP socket fails to connect, (POLLHUP \| POLLERR \| POLLWRNORM) is indicated." I wonder if that means that it's now completely usable on all reasonable versions of the OS. I think so? I don't use Windows myself, my interest in this topic is that I have a slow moving background project to figure out how and when to remove all remaining uses of select() from our tree, and this one is on my hit list. > PQsocketPoll() being based on time_t, it has only second resolution, AFAIK. > Despite the [underlying implementation in fe-misc.c][2] supporting at > least milliseconds. Yeah, that is not nice and your complaint is very reasonable, and we should probably do something like what Tom suggested. Hmm, but if what I speculated above is true, I wonder if the extern function is even worth its bits... but I don't know how to determine that completely.
