Обсуждение: Is psSocketPoll doing the right thing?
Hello. While looking a patch, I found that pqSocketPoll passes through the result from poll(2) to the caller and throws away revents. If I understand it correctly, poll() *doesn't* return -1 nor errno by the reason it has set POLLERR, POLLHUP, POLLNVAL, and POLLRDHUP for some of the target sockets, and returns 0 unless poll() itself failed to work. It doesn't seem to be the intended behavior since the function sets POLLERR to pollfd.events. (but the bit is ignored by poll(), though) Is the above diagnosis correct? regards. -- Kyotaro Horiguchi NTT Open Source Software Center
On 2023/02/09 11:50, Kyotaro Horiguchi wrote: > Hello. > > While looking a patch, I found that pqSocketPoll passes through the > result from poll(2) to the caller and throws away revents. If I > understand it correctly, poll() *doesn't* return -1 nor errno by the > reason it has set POLLERR, POLLHUP, POLLNVAL, and POLLRDHUP for some > of the target sockets, and returns 0 unless poll() itself failed to > work. As far as I understand correctly, poll() returns >0 if "revents" has either of those bits, not 0 nor -1. You're thinking that pqSocketPoll() should check "revents" and return -1 if either of those bits is set? Regards, -- Fujii Masao Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
> Subject: is p*s*Socket.. Oops... At Thu, 9 Feb 2023 17:32:08 +0900, Fujii Masao <masao.fujii@oss.nttdata.com> wrote in > > > On 2023/02/09 11:50, Kyotaro Horiguchi wrote: > > Hello. > > While looking a patch, I found that pqSocketPoll passes through the > > result from poll(2) to the caller and throws away revents. If I > > understand it correctly, poll() *doesn't* return -1 nor errno by the > > reason it has set POLLERR, POLLHUP, POLLNVAL, and POLLRDHUP for some > > of the target sockets, and returns 0 unless poll() itself failed to > > work. > > As far as I understand correctly, poll() returns >0 if "revents" > has either of those bits, not 0 nor -1. Right. as my understanding. If any of the sockets is in any of the states, pqSocketPoll returns a positive, which makes pqSocketCheck return 1. Finally pqRead/WriteReady return "ready" even though the connection socket is in an error state. Actually that behavior doesn't harm since the succeeding actual read/write will "properly" fail. However, once we use this function to simply check the socket is sound without doing an actual read/write, that behavior starts giving a harm by the false answer. > You're thinking that pqSocketPoll() should check "revents" and > return -1 if either of those bits is set? In short, yes. pqSocketPoll() should somehow inform callers about that state. Fortunately pqSocketPoll is a private function thus we can refactor the function so that it can do that properly. If no one object to that change, I'll work on that. regards. -- Kyotaro Horiguchi NTT Open Source Software Center
On 2023-02-10 10:42, Kyotaro Horiguchi wrote: >> On 2023/02/09 11:50, Kyotaro Horiguchi wrote: >> > Hello. >> > While looking a patch, I found that pqSocketPoll passes through the >> > result from poll(2) to the caller and throws away revents. If I >> > understand it correctly, poll() *doesn't* return -1 nor errno by the >> > reason it has set POLLERR, POLLHUP, POLLNVAL, and POLLRDHUP for some >> > of the target sockets, and returns 0 unless poll() itself failed to >> > work. >> >> As far as I understand correctly, poll() returns >0 if "revents" >> has either of those bits, not 0 nor -1. > > Right. as my understanding. > > If any of the sockets is in any of the states, pqSocketPoll returns a > positive, which makes pqSocketCheck return 1. Finally > pqRead/WriteReady return "ready" even though the connection socket is > in an error state. Actually that behavior doesn't harm since the > succeeding actual read/write will "properly" fail. However, once we > use this function to simply check the socket is sound without doing an > actual read/write, that behavior starts giving a harm by the false > answer. I agree with you. Current pqScoketCheck could return a false result from a caller's point of view. >> You're thinking that pqSocketPoll() should check "revents" and >> return -1 if either of those bits is set? > > In short, yes. > > pqSocketPoll() should somehow inform callers about that > state. Fortunately pqSocketPoll is a private function thus we can > refactor the function so that it can do that properly. Does this mean that pqSocketPoll or pqSocketCheck somehow returns the poll's result including error conditions (POLLERR, POLLHUP, POLLNVAL) to callers? Then callers filter the result to make their final result. regards, -- Katsuragi Yuta Advanced Computing Technology Center Research and Development Headquarters NTT DATA CORPORATION
Dear Horiguchi-san, My comment may be no longer needed, but I can +1 to your opinion. > > On 2023/02/09 11:50, Kyotaro Horiguchi wrote: > > > Hello. > > > While looking a patch, I found that pqSocketPoll passes through the > > > result from poll(2) to the caller and throws away revents. If I > > > understand it correctly, poll() *doesn't* return -1 nor errno by the > > > reason it has set POLLERR, POLLHUP, POLLNVAL, and POLLRDHUP for > some > > > of the target sockets, and returns 0 unless poll() itself failed to > > > work. > > > > As far as I understand correctly, poll() returns >0 if "revents" > > has either of those bits, not 0 nor -1. > > Right. as my understanding. > > If any of the sockets is in any of the states, pqSocketPoll returns a > positive, which makes pqSocketCheck return 1. Finally > pqRead/WriteReady return "ready" even though the connection socket is > in an error state. Actually that behavior doesn't harm since the > succeeding actual read/write will "properly" fail. However, once we > use this function to simply check the socket is sound without doing an > actual read/write, that behavior starts giving a harm by the false > answer. I checked man page of poll(3), and it said that POLLERR, POLLHUP, POLLNVAL is only valid in revents. Moreover, poll() has is clarified that it returns natural number if revent is larger than zero. So revent should be checked even if the returned value > 0. Best Regards, Hayato Kuroda FUJITSU LIMITED