问题
I have a nested struct.
type ConfigOne struct {
// Daemon section from config file.
Daemon daemon
}
type daemon struct {
Loglevel int
Logfile string
}
And I have a String() string
method on that type, which I am trying to return the nested struct elements as
func (c ConfigOne)String() string{
return fmt.Sprintf("%+v\n", c)
}
When I am trying to print it as
c := &modules.ConfigOne{}
c.Daemon.Loglevel = 1
c.Daemon.Logfile = "/tmp/test.log"
modules.Logger.Infoln(c.String())
I am getting the error
runtime: goroutine stack exceeds 1000000000-byte limit fatal error: stack overflow
runtime stack: runtime.throw(0x6ea3b7, 0xe) ...
After going through the error, I could see repeated lines similar to the below one
modules/structs.go:31 +0x77 fp=0xc440100398 sp=0xc440100328 go-consume/modules.(*ConfigOne).String(0xc42abcb4e0, 0x70bc08, 0xc42abd6300) :1 +0x64 fp=0xc4401003d8 sp=0xc440100398 fmt.(*pp).handleMethods(0xc42abd6300, 0xc400000076, 0x410301)
and finally, before dying,
modules/structs.go:31 +0xc0 fp=0xc440103d18 sp=0xc440103ca8 ...additional frames elided...
goroutine 17 [syscall, locked to thread]: runtime.goexit()
which I believe is caused by going into some infinite recursion.
I tried my luck to find the cause and reached here, which I believe is the same issue. However I couldn't understand the explanation in that thread.
If I try to print the individual nested struct as
func (c ConfigOne)String() string{
//return fmt.Sprintf("%+v\n", c.Daemon.Loglevel)
return fmt.Sprintf("%+v\n", c.Daemon)
}
it is working fine, and log shows the fields as
2017/03/05 01:28:25 go-consume.go:38: INFO: {Loglevel:1 Logfile:/tmp/test.log}
Can someone kindly explain how the former String()
method is resulting in an infinite recursion and a stackoverflow, and what is the best way to overcome this?
回答1:
The %v
and %+v
formats use the value of String()
if the type implements it. Therefore, using %+v
on a type within the String()
function for that type causes infinite recursion. Instead of using %+v
in the String()
function, you'll have to construct your own string, showing the contents of the structure in whatever way you see fit.
来源:https://stackoverflow.com/questions/42600920/runtime-goroutine-stack-exceeds-1000000000-byte-limit-fatal-error-stack-overf