To see the escape analysis results, compile with -gcflags "-m -m -m -m". The code in each of the example should be relatively similar, which is why it is a bug that one of them causes the variable to escape to the heap.
On Wed, Oct 5, 2016 at 4:46 PM, 刘桂祥 <liuguixiang...@gmail.com> wrote: > 1: In example2_modified.go (y=x line should be *y=x ?) and that is the > same as example1.go ??? > but in example1.go y is escapted and example2.go is not. > 2:how do I see the compile handle closure call results ? compile para ? > > 在 2016年10月5日星期三 UTC+8下午11:38:42，Chris Manghane写道： >> >> Sorry, poor explanation again. >> >> When a variable is used from outside a closure's scope, it is *captured* >> by the closure. Usually that means that the closure function is modified to >> include a reference to that variable when it is called as a regular >> function. An example from the compiler: https://github.com/g >> olang/go/blob/master/src/cmd/compile/internal/gc/closure.go#L311. >> >> In example2, this >> >> // example2.go >> >> package main >> >> func main() { >> var y int >> func(x int) { >> y = x >> }(42) >> } >> >> is transformed into something like >> >> // example2_modified.go >> >> package main >> >> func main() { >> var y int >> func(y *int, x int) { >> y = x >> }(&y, 42) >> } >> >> and then the same analysis from above is applied. y should not escape to >> the heap here, similar to example3.go. >> >> Hope that clarifies, >> Chris >> >> On Wed, Oct 5, 2016 at 6:18 AM, 刘桂祥 <liuguix...@gmail.com> wrote: >> >>> In go when closure call the out varible will pass pointer to the >>> closure func so I doubt in example2.go y is passed &y to closure >>> >>> I don't know the compile how to analysis this and decide that can be >>> allocated in stack correctly ? >>> >>> 在 2016年10月4日星期二 UTC+8下午11:54:02，Chris Manghane写道： >>>> >>>> In example1, the // BAD: y escapes is there because y should not >>>> escape from that function, but the current algorithm needs to be improved >>>> for this case. In that closure, the address of y is captured as the closure >>>> argument p and since p is only dereferenced, the analysis should not >>>> consider it to escape. >>>> >>>> In example3, the analysis above applies and y should not escape. y is >>>> closed over and dereferenced, but we correctly do not mark it as escaping. >>>> >>>> In example2, y contains no pointers; it can never escape. The test was >>>> to see if capturing/closing over a non-pointer value would cause it to >>>> escape. >>>> >>>> It's a bit confusing, but to restate, in example1, y should not escape >>>> even though it currently does. >>>> >>>> On Mon, Oct 3, 2016 at 11:09 PM, 刘桂祥 <liuguix...@gmail.com> wrote: >>>> >>>>> // example1.go >>>>> >>>>> package main >>>>> >>>>> >>>>> func main() { >>>>> var y int // BAD: y escapes >>>>> func(p *int, x int) { >>>>> *p = x >>>>> }(&y, 42) >>>>> } >>>>> >>>>> example1.go y escape to the heap >>>>> >>>>> // example2.go >>>>> >>>>> package main >>>>> >>>>> func main() { >>>>> var y int >>>>> func(x int) { >>>>> y = x >>>>> }(42) >>>>> } >>>>> >>>>> example2.go y is not escaped and why ?? >>>>> >>>>> // example3.go >>>>> >>>>> package main >>>>> >>>>> func main() { >>>>> a := 100 >>>>> y := &a >>>>> func(x int) { >>>>> *y = x >>>>> }(42) >>>>> } >>>>> >>>>> example3.go y is not escaped and why ?? >>>>> >>>>> -- >>>>> 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...@googlegroups.com. >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>> >>>> -- >>> 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...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- > 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. > For more options, visit https://groups.google.com/d/optout. > -- 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. For more options, visit https://groups.google.com/d/optout.
