I don't like the spec docs for panic/recover in Golang, for the spec docs
is vague and not clear on when recover will take effect.
So I wrote some examples to get the mechanism of panic/recover in Golang.
// example A
func main() {
defer func() {
fmt.Println(recover())
}()
panic(1) // recovered
}
========= result:
1
// example B
func main() {
defer func() {
defer func() {
fmt.Println(recover())
}()
panic(2) // recovered
}()
panic(1) // not recover
}
========= result:
2
panic: 1
// example c
func main() {
defer func() {
defer func() {
recover()
panic(3)
}()
panic(2)
}()
panic(1)
}
========= result:
2
panic: 1
panic: 2 [recovered]
panic: 3
// example D
func main() {
defer func() {
recover()
}()
defer func() {
panic(2) // recovered, (overwrite 1)
}()
defer func() {
panic(1) // recovered, (overwritten by 2)
}()
}
========= result:
2
// example E
func main() {
defer func() {
defer func() {
fmt.Println(recover())
}()
}()
panic(1) // not recover
}
========= result:
<nil>
panic: 1
// example F
func main() {
defer func() {
func() {
fmt.Println(recover())
}()
}()
panic(1) // not recover
}
========= result (same as last one):
<nil>
panic: 1
// example G
func main() {
defer fmt.Println(recover())
panic(1) // not recover
}
========= result:
<nil>
panic: 1
// example H
func main() {
defer func() {
fmt.Println(recover())
}()
func() {
func() {
panic(1) // recovered
}()
}()
}
========= result:
1
So, it looks the calling of recover only takes effect only when both of the
following two conditions are met:
1. the caller of calling recover must be a deferred function calling .
2. the panic must happened in (may not originate from) the caller function
of caller of calling recover.
Where or not the calling of recover is deferred or not is not important.
Is the conclusion right?
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