panic

I'm writing a framebuffer for an SPI LCD display on ARM. Before I complete that, I've written a memory only driver and trialled it under Ubuntu (Intel, Virtualbox). The driver works fine - I've allocated a block of memory using kmalloc, page aligned it (it's page aligned anyway actually), and used the framebuffer system to create a /dev/fb1. I have my own mmap function if that's relevant (deferred_io ignores it and uses its own by the look of it). I have set: info->screen_base = (u8 __iomem *)kmemptr; info->fix.smem_len = kmem_size; When I open /dev/fb1 with a test program and mmap it, it

I'm trying to wrap a general map (with interface{} as both key and value) as in-memory key-value store that I named MemStore . But it is not thread-safe, despite my use of a sync.RWMutex to lock access to the underlying map. I did verify that it works fine when used from a single goroutine. However, just two concurrent goroutines accessing it results in panic: runtime error: invalid memory address or nil pointer dereference . What is causing this problem, and what is the proper way to achieve thread-safety in Go? Whilst in this example, channels to a single goroutine interacting with the map

1. defer的使用 　　defer 延迟调用。我们先来看一下，有defer关键字的代码执行顺序： 1 func main() { 2 defer func() { 3 fmt.Println("1号输出") 4 }() 5 defer func() { 6 fmt.Println("2号输出") 7 }() 8 } 　　输出结果： 1 2号出来 2 1号出来 　　结论：多个defer的执行顺序是倒序执行（同入栈先进后出）。 　　由例子可以看出来，defer有延迟生效的作用，先使用defer的语句延迟到最后执行。 1.1 defer与返回值之间的顺序 1 func defertest() int 2 3 func main() { 4 fmt.Println("main:", defertest()) 5 } 6 7 func defertest() int { 8 var i int 9 defer func() { 10 i++ 11 fmt.Println("defer2的值:", i) 12 }() 13 defer func() { 14 i++ 15 fmt.Println("defer1的值:", i) 16 }() 17 return i 18 } 　　输出结果： 1 defer1的值: 1 2 defer2的值: 2 3 main: 0 　　结论

1. defer的使用 　　defer 延迟调用。我们先来看一下，有defer关键字的代码执行顺序： 1 func main() { 2 defer func() { 3 fmt.Println("1号输出") 4 }() 5 defer func() { 6 fmt.Println("2号输出") 7 }() 8 } 　　输出结果： 1 2号出来 2 1号出来 　　结论：多个defer的执行顺序是倒序执行（同入栈先进后出）。 　　由例子可以看出来，defer有延迟生效的作用，先使用defer的语句延迟到最后执行。 1.1 defer与返回值之间的顺序 1 func defertest() int 2 3 func main() { 4 fmt.Println("main:", defertest()) 5 } 6 7 func defertest() int { 8 var i int 9 defer func() { 10 i++ 11 fmt.Println("defer2的值:", i) 12 }() 13 defer func() { 14 i++ 15 fmt.Println("defer1的值:", i) 16 }() 17 return i 18 } 　　输出结果： 1 defer1的值: 1 2 defer2的值: 2 3 main: 0 　　结论

panic发生时， 会导致进程挂掉。为了处理panic， 可以使用recover捕获，然后处理。 下面以下标引用越界问题为例进行说明。 正常情况下，代码中如果出现下标越界，会直接触发panic， 导致进程挂掉。 例如下面的例子： package main import ( "fmt" ) func main() { fmt.Println( "start..." ) count := [] int {} fmt.Println(count [1 ]) fmt.Println( "1..." ) } output: start… panic: runtime error: index out of range goroutine 1 [running]: main.main() D:/work/go_exercise/t.go:29 +0xd4 recover的使用 进程crash后，无法再提供服务，必须设法避免。 Go语言中提供recover可以用于捕获panic。 当对某些代码质量问题存在疑问时，可使用recover进行异常处理。 另外，如果没有panic发生，调用recover会返回nil. package main import ( "fmt" ) func main() { defer func (){ if r := recover (); r != nil { fmt