The longjmp() facility is a wild, dangerous, improper, and popular mechanism. It's premise is that the app can go back in time, like you waking up last week with no knowledge of what happened since then. If you can follow that analogy, then imagine your surprise when external things you did last week--ordering from Amazon or getting married--start showing up in your life by surprise or you fail to show up as you should in theirs, through ignorance, with consequences either way. So it will be with the relationship between C and Go. You'll leave many things hanging or abandoned when you longump() back to your application's youth.
(I imagine this is colorful terms, like getting a text on my phone reading "setjmp() returned 1" and having a paroxysm of imagined crises like "maybe I got married, had a daughter, and she's waiting for me now at daycare! OMG, I just don't know.") On Mon, Dec 9, 2019 at 10:30 AM <p...@cpan.org> wrote: > On Monday 09 December 2019 10:18:26 Ian Lance Taylor wrote: > > On Mon, Dec 9, 2019 at 8:57 AM <p...@cpan.org> wrote: > > > > > > I would like to ask some technical question about cgo and long jumps. > > > > > > In Go I have written shared library which exports C API and therefore > > > can be called by other C applications. This my library is compiling > with > > > cgo, more precisely via: go build -buildmode=c-shared -compiler gc > > > > > > Now I would like to call from my Go library some C function which may > > > call longjmp(). And setjmp() was already called by application which is > > > using my Go library. > > > > > > It is possible to call from Go C function which calls longjmp() which > > > jumps outside of that my Go library? What would happen with Go garbage > > > collector and "defer" code? > > > > > > To imagine, whole stack looks like this: > > > > > > +------------------------------------------+ > > > | C application | > > > | main(): | > > > | call setjmp() | > > > | call f1() from Go library | > > > | ... | > > > +------------------------------------------+ > > > | Go library with exported C f1() function | > > > | f1(): | > > > | do something in Go | > > > | call f2() from C library | > > > | ... | > > > | return from f1() | > > > +------------------------------------------+ > > > | C library with exported f2() function | > > > | f2(): | > > > | do something in C | > > > | if error call longjmp() | > > > | else return from f2() | > > > +------------------------------------------+ > > > > > > And if longjmp() is called then it jumps to main() where setjmp() was > > > called. So effectively f1() function (in Go) does not return. > > > > I'm pretty sure that won't work at all. Sorry. > > Hi Ian! Thank you for your answer. > > I was trying to find any resource on Internet about long jumps and > "import C" but neither in official Go documentation nor in any other > blog post is written about it. > > There are many resources how Go is (fully) compatible with C and can > call C functions, but absolutely zero information how it is implemented > nor what would happen with such core feature of C language as long jumps > or signals. > > > Certainly no Go deferred functions will be run. I don't think this > > would break the garbage collector as such, but I expect that it would > > break the Go scheduler. In the best case you'll be left with a > > dangling goroutine that will never be run and never go away. > > So should I interpret your answer as long jumps are not supported and > caller of C function from Go must ensure that called C function would > not call longjmp()? > > > And another interesting question, it is possible to call longjmp() from > Go code? To throw C exception back to the main C application. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/20191209183039.khrexxnpedzitepy%40pali > . > -- *Michael T. jonesmichael.jo...@gmail.com <michael.jo...@gmail.com>* -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CALoEmQzJ9hJXv%3DSmnsXHuiQtHHghBRwZcZMQBBQOD%2BfJADBrZA%40mail.gmail.com.
