On Tue, Dec 4, 2012 at 6:12 PM, Johannes Schindelin <johannes.schinde...@gmx.de> wrote: > Hi kusma, > > On Sat, 1 Dec 2012, Erik Faye-Lund wrote: > >> On Fri, Nov 30, 2012 at 6:58 PM, Johannes Schindelin >> <johannes.schinde...@gmx.de> wrote: >> > Hi, >> > >> > On Tue, 13 Nov 2012, Erik Faye-Lund wrote: >> > >> >> Set a control-handler to prevent the process from terminating, and >> >> simulate SIGINT so it can be handled by a signal-handler as usual. >> > >> > One thing you might want to mention is that the fgetc() handling is not >> > thread-safe, and intentionally so: if two threads read from the same >> > console, we are in trouble anyway. >> >> I'm not entirely sure if I know what you mean. Do you suggest that two >> threads can race for setting the console ctrl-handler? > > That was my idea, yes. > >> I don't think that's the case; "SetConsoleCtrlHandler(x, TRUE)" adds a >> console handler to the handler-chain, and SetConsoleCtrlHandler(x, >> FALSE) removes it. If two threads add handlers, it is my understanding >> that one of them will be run, only to report "no, no more ctrl-handling >> needed". Since both handlers block further ctrl-handling, I don't think >> there's a problem. > > My idea was that the SetConsoleCtrlHandler(x, FALSE) could remove the > handler prematurely iff another thread wanted to install the very same > handler (but it was already installed by the first thread). >
Yes, but that's not how SetConsoleCtrlHandler works; if a routine x gets added twice, it needs to be removed twice as well to not get called. This little C-program demonstrates that: ---8<--- #include <windows.h> #include <stdio.h> BOOL WINAPI HandlerRoutine1(DWORD dwCtrlType) { printf("Hello from handler1!\n"); return TRUE; } BOOL WINAPI HandlerRoutine2(DWORD dwCtrlType) { printf("Hello from handler2!\n"); return FALSE; } int main() { SetConsoleCtrlHandler(HandlerRoutine1, TRUE); SetConsoleCtrlHandler(HandlerRoutine2, TRUE); SetConsoleCtrlHandler(HandlerRoutine2, TRUE); SetConsoleCtrlHandler(HandlerRoutine2, FALSE); GenerateConsoleCtrlEvent(CTRL_C_EVENT, 0); SetConsoleCtrlHandler(HandlerRoutine2, FALSE); SetConsoleCtrlHandler(HandlerRoutine1, FALSE); } ---8<--- This program outputs: Hello from handler2! Hello from handler1! So since that other thread would add the console ctrl handler before it removed it again, this should still be thread-safe as far as I can tell. > But as I said: for this to happen, *two* threads need to want to access > the console for reading. In that case we'd be in bigger trouble than > thread unsafety... We cannot read two passwords from the same console at > the same time. I agree with that, but I'm saying that *even if* we didn't have this limitation, the code shouldn't be problematic. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html