On Fri, Nov 17, 2017 at 10:04:35AM -0600, Chris Friesen wrote: > On 11/17/2017 06:37 AM, Daniel P. Berrange wrote: > > On Fri, Nov 17, 2017 at 01:34:54PM +0100, Markus Armbruster wrote: > > > "Daniel P. Berrange" <berrange@xxxxxxxxxx> writes: > > > > > > [...] > > > > Goroutines are basically a union of the thread + coroutine concepts. The > > > > Go runtime will create N OS level threads, where the default N currently > > > > matches the number of logical CPU cores you host has (but is tunable to > > > > other values). The application code just always creates Goroutines which > > > > are userspace threads just like coroutines. The Go runtime will dynamically > > > > switch goroutines at key points, and automatically pick suitable OS level > > > > threads to run them on to maximize concurrency. Most cleverly goroutines > > > > have a 2 KB default stack size, and runtime will dynamically grow the > > > > stack if that limit is reached. > > > > > > Does this work even when the stack limit is exceeded in a C function? > > > > When you make a C call in go, it runs in a separate stack. The goroutines > > own stack is managed by the garbage collector, so can't be exposed to C > > code. I'm unclear exactly what size the C stack would be, but it'll be > > the traditional fixed size, not the grow-on-demand behaviour of the Go > > stack. > > Based on > https://github.com/golang/go/blob/master/src/runtime/cgo/gcc_linux_amd64.c > it looks like they don't explicitly specify a stack size, at least on linux. That'll inherit the default from ulimit then, which will be 8MB > Are there limits as to what you're allowed to do in C code called from Go? > Can you fork processes, spawn threads, call setjmp/longjmp, handle signals, > sleep, etc.? The big caveats are around sharing memory between the Go & C layers. You generally need to copy data between the layers to avoid C code interacting with Go memory that can be garbage collected. In terms of whta C can do, I think pretty much anything is possible, within the constraints of safe C programming - eg careful wrt async signal safety as normal. You also have to be aware that if a C code called from goroutines makes the goroutine much heavier than normal, because of the extra C stack space. ie just because you can have 1000's of goroutines running go code, doesn't mean you can have 1000's of goroutines running C code, as stack size explodes from 2kb to 8 MB Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
