Go语言的panic类型
1、数组越界(运行时错误)。
package main
import "fmt"
func main() {
var s []string
fmt.Println(s)
fmt.Println(s[0])
}
运行结果：
[]
panic: runtime error: index out of range
goroutine 1 [running]:
main.main()
index out of range：索引超出范围(数组越界)
2、空指针异常(运行时错误)。
package main
import "fmt"
type Person struct {
Name string
Age int
}
func main() {
var p *Person
fmt.Println(p)
fmt.Println(p.Name)
}
运行结果：
<nil>
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x10914c8]
goroutine 1 [running]:
main.main()
segmentation violation：内存段异常。
3、类型断言失败(接口转换异常)。
package main
import "fmt"
func main() {
add(20, 18)
add(1, "hello")
}
func add(a, b interface{}) {
i := a.(int)
j := b.(int)
fmt.Println(i+j)
}
运行结果：
panic: interface conversion: interface {} is string, not int
38
goroutine 1 [running]:
main.add(0x10a0f60, 0x10d6840, 0x10a1660, 0x10d6b90)
interface conversion: interface {} is string, not int：接口转换，接口是string，不是int。
4、通道为空，通道已关闭
package main
func main() {
var ch chan int
close(ch)
}
运行结果：
panic: close of nil channel
goroutine 1 [running]:
main.main()
close of nil channel关闭空的通道。
package main
func main() {
var ch chan int
ch = make(chan int,0)
close(ch)
ch <- 108
}
运行结果：
panic: send on closed channel
goroutine 1 [running]:
main.main()
send on closed channel：发送给已关闭的通道。
5、死锁，所有线程睡眠(致命错误)
这一条是致命错误，不属于panic，但是跟panic异常一样，会导致程序挂掉。
package main
func main() {
var ch chan int
ch = make(chan int)
ch <- 108
}
运行结果：
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [chan send]:
main.main()
fatal error: all goroutines are asleep - deadlock：指明错误，所有线程睡眠，死锁。
6、给空map赋值
package main
func main() {
var mm map[string]int
mm["a"] = 10
}
运行结果
panic: assignment to entry in nil map
goroutine 1 [running]:
main.main()
assignment to entry in nil map：赋值到空的map。
7、致命错误：并发的map写
package main
import (
"fmt"
"time"
)
func main() {
mm := make(map[string]int, 0)
mm["jack"] = 20
fmt.Println(mm)
for i := 0; i < 10; i++ {
name := fmt.Sprint(i)
go addMap(mm,name,i)
}
time.Sleep(time.Second)
fmt.Println(mm)
}
func addMap(m map[string]int, name string, age int) map[string]int {
m[name] = age
return m
}
运行结果
map[jack:20]
fatal error: concurrent map writes
goroutine 42 [running]:
runtime.throw(0x10c8fe1, 0x15)
/usr/local/Cellar/go/1.12.1/libexec/src/runtime/panic.go:617 +0x72 fp=0xc0000a6f18 sp=0xc0000a6ee8 pc=0x1027e52
runtime.mapassign_faststr(0x10ab2c0, 0xc000098000, 0x1162919, 0x1, 0x0)
/usr/local/Cellar/go/1.12.1/libexec/src/runtime/map_faststr.go:211 +0x42a fp=0xc0000a6f80 sp=0xc0000a6f18 pc=0x100fe9a
main.addMap(0xc000098000, 0x1162919, 0x1, 0x9, 0x0)
/Users/ElonJelinek/go/src/kongyixueyuan.com/prac0424/test09.go:21 +0x4b fp=0xc0000a6fb8 sp=0xc0000a6f80 pc=0x1093c0b
runtime.goexit()
concurrent map writes：并发map写。
Go语言中，map只能并发的读，不可以并发的写，如果要在多个线程中对map进行写操作，必须要加锁
8、递归死循环，堆栈溢出（运行时：goroutine堆栈超出限制，致命错误：堆栈溢出）
package main
import "fmt"
type People1 struct {
Name string
}
func (p *People1) String() string {
return fmt.Sprintf("print: %v", p)
}
func main() {
p := &People1{"杰克"}
s := p.String()
fmt.Println(s)
}
运行结果
runtime: goroutine stack exceeds 1000000000-byte limit
fatal error: stack overflow
runtime stack:
runtime.throw(0x10c8f32, 0xe)
/usr/local/Cellar/go/1.12.1/libexec/src/runtime/panic.go:617 +0x72
runtime.newstack()
/usr/local/Cellar/go/1.12.1/libexec/src/runtime/stack.go:1041 +0x6f0
runtime.morestack()
/usr/local/Cellar/go/1.12.1/libexec/src/runtime/asm_amd64.s:429 +0x8f
goroutine 1 [running]:
runtime.heapBitsSetType(0xc013a67380, 0xc0, 0xb8, 0x10bdce0)
/usr/local/Cellar/go/1.12.1/libexec/src/runtime/mbitmap.go:938 +0xa56 fp=0xc024000330 sp=0xc024000328 pc=0x1012b96
runtime.mallocgc(0xc0, 0x10bdce0, 0x1, 0x0)
这里出现了递归循环调用，即死循环，因为结构体people重写了官方包的String()方法，而fmt.Sprintf()中调用了String()方法，就出现了又回到p.String()方法，然后又调用fmt.Sprintf()方法，然后又回来，导致死循环，也导致堆栈溢出。
runtime: goroutine stack exceeds 1000000000-byte limit：运行时：goroutine堆栈超出1000000000字节限制
fatal error: stack overflow：
致命错误：堆栈溢出
这种错误在递归没有出口的时候出现，也就是递归死循环的时候出现
package main
import "fmt"
func main() {
n := fibonacci(5)
fmt.Println(n)
}
func fibonacci(n int) int {
//if n <= 1 {
// return n
//}
return fibonacci(n-1) + fibonacci(n-2)
}
运行结果
runtime: goroutine stack exceeds 1000000000-byte limit
fatal error: stack overflow
runtime stack:
runtime.throw(0x10c71e3, 0xe)
map并发加锁
package main
import (
"fmt"
"sync"
"time"
)
func main() {
mut := new(sync.Mutex)
mm := make(map[string]int, 0)
mm["jack"] = 20
fmt.Println(mm)
for i := 0; i < 20; i++ {
name := fmt.Sprint(i)
go addMap(mm,name,i,mut)
}
time.Sleep(time.Second)
fmt.Println(mm)
}
func addMap(m map[string]int, name string, age int,mu *sync.Mutex) map[string]int {
mu.Lock()
m[name] = age
mu.Unlock()
return m
}