Hello Fabien, On Fri, 14 Jul 2023 20:32:01 +0900 Yugo NAGATA <nag...@sraoss.co.jp> wrote:
I attached the updated patch. > Hello Fabien, > > Thank you for your review! > > On Mon, 3 Jul 2023 20:39:23 +0200 (CEST) > Fabien COELHO <coe...@cri.ensmp.fr> wrote: > > > > > Yugo-san, > > > > Some feedback about v1 of this patch. > > > > Patch applies cleanly, compiles. > > > > There are no tests, could there be one? ISTM that one could be done with a > > "SELECT pg_sleep(...)" script?? > > Agreed. I will add the test. I added a TAP test. > > > The global name "all_state" is quite ambiguous, what about "client_states" > > instead? Or maybe it could be avoided, see below. > > > > Instead of renaming "state" to "all_state" (or client_states as suggested > > above), I'd suggest to minimize the patch by letting "state" inside the > > main and adding a "client_states = state;" just after the allocation, or > > another approach, see below. > > Ok, I'll fix to add a global variable "client_states" and make this point to > "state" instead of changing "state" to global. Done. > > > Should PQfreeCancel be called on deconnections, in finishCon? I think that > > there may be a memory leak with the current implementation?? > > Agreed. I'll fix. Done. Regards, Yugo Nagata > > > Maybe it should check that cancel is not NULL before calling PQcancel? > > I think this is already checked as below, but am I missing something? > > + if (all_state[i].cancel != NULL) > + (void) PQcancel(all_state[i].cancel, errbuf, sizeof(errbuf)); > > > After looking at the code, I'm very unclear whether they may be some > > underlying race conditions, or not, depending on when the cancel is > > triggered. I think that some race conditions are still likely given the > > current thread 0 implementation, and dealing with them with a barrier or > > whatever is not desirable at all. > > > > In order to work around this issue, ISTM that we should go away from the > > simple and straightforward thread 0 approach, and the only clean way is > > that the cancelation should be managed by each thread for its own client. > > > > I'd suggest to have the advanceState to call PQcancel when CancelRequested > > is set and switch to CSTATE_ABORTED to end properly. This means that there > > would be no need for the global client states pointer, so the patch should > > be smaller and simpler. Possibly there would be some shortcuts added here > > and there to avoid lingering after the control-C, in threadRun. > > I am not sure this approach is simpler than mine. > > In multi-threads, only one thread can catches the signal and other threads > continue to run. Therefore, if Ctrl+C is pressed while threads are waiting > responses from the backend in wait_on_socket_set, only one thread can be > interrupted and return, but other threads will continue to wait and cannot > check CancelRequested. So, for implementing your suggestion, we need any hack > to make all threads return from wait_on_socket_set when the event occurs, but > I don't have idea to do this in simpler way. > > In my patch, all threads can return from wait_on_socket_set at Ctrl+C > because when thread #0 cancels all connections, the following error is > sent to all sessions: > > ERROR: canceling statement due to user request > > and all threads will receive the response from the backend. > > Regards, > Yugo Nagata > > -- > Yugo NAGATA <nag...@sraoss.co.jp> > > -- Yugo NAGATA <nag...@sraoss.co.jp>
