Could someone please give clarification values returned from the goroutine. Does the returned value from the goroutine is getting stored on stake.
example :
// function getNumber returns the "int i" and we can't use this returned value
// because this function is invoked as goroutine.
// We know that, to communicate between main and goroutine one could
// use the channel ( chan <- i), but I am interested to know about
// the use of return i in goroutine. Is it possible to get/ use this
// returned value.
func getNumber(i int) int {
return i
}
func main() {
for i:=0; i<10; i++ {
go printNumber(i)
}
time.Sleep(5)
}
Should we try to avoid the return valued in go routine ?
A quick bit of looking at the assembly output shows
$ go build -gcflags -S z.go
The getNumber() function does store its results to the stack
"".getNumber t=1 size=16 value=0 args=0x10 locals=0x0
0x0000 00000 (z.go:5) TEXT "".getNumber+0(SB),4,$0-16
0x0000 00000 (z.go:6) MOVQ "".i+8(FP),BX
0x0005 00005 (z.go:6) MOVQ BX,"".~r1+16(FP)
0x000a 00010 (z.go:6) RET ,
So when it is called from a goroutine, it does store its results to the stack. However this is a new stack which is destroyed when the goroutine ends so there is no possibility of retrieving the return value.
"".main t=1 size=96 value=0 args=0x0 locals=0x18
0x0000 00000 (z.go:9) TEXT "".main+0(SB),$24-0
0x0000 00000 (z.go:9) MOVQ (TLS),CX
0x0009 00009 (z.go:9) CMPQ SP,16(CX)
0x000d 00013 (z.go:9) JHI ,22
0x000f 00015 (z.go:9) CALL ,runtime.morestack_noctxt(SB)
0x0014 00020 (z.go:9) JMP ,0
0x0016 00022 (z.go:9) SUBQ $24,SP
0x001a 00026 (z.go:10) MOVQ $0,AX
0x001c 00028 (z.go:10) CMPQ AX,$10
0x0020 00032 (z.go:10) JGE $0,74
0x0022 00034 (z.go:11) MOVQ AX,"".i+16(SP)
0x0027 00039 (z.go:11) MOVQ AX,(SP)
0x002b 00043 (z.go:11) MOVQ $"".getNumber·f+0(SB),CX
0x0032 00050 (z.go:11) PUSHQ CX,
0x0033 00051 (z.go:11) PUSHQ $16,
0x0035 00053 (z.go:11) PCDATA $0,$0
0x0035 00053 (z.go:11) CALL ,runtime.newproc(SB)
0x003a 00058 (z.go:11) POPQ ,CX
0x003b 00059 (z.go:11) POPQ ,CX
0x003c 00060 (z.go:10) MOVQ "".i+16(SP),AX
0x0041 00065 (z.go:10) INCQ ,AX
0x0044 00068 (z.go:10) NOP ,
0x0044 00068 (z.go:10) CMPQ AX,$10
0x0048 00072 (z.go:10) JLT $0,34
0x004a 00074 (z.go:13) MOVQ $5,(SP)
0x0052 00082 (z.go:13) PCDATA $0,$0
0x0052 00082 (z.go:13) CALL ,time.Sleep(SB)
0x0057 00087 (z.go:14) ADDQ $24,SP
0x005b 00091 (z.go:14) RET ,
However there is no way of retrieving these results.