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packagemain
import(
"sync/atomic"
"unsafe"
)
typeastruct{
xunsafe.Pointer
yuint64
}
funcmain(){
p:=new(a)
atomic.AddUint64(&p.y,1)
}
在32位计算机上运行改程序，会出现错误：
| panic: runtime error: invalid memory address or nil pointer dereference [signal 0xc0000005 code=0x0 addr=0x0 pc=0x4198bc] goroutine 1 [running]: runtime.panic(0x41c740,0x445e4f) C:/Users/ADMINI~1/AppData/Local/Temp/2/bindist550409343/go/src/pkg/runtime/panic.c:266 +0xa6 sync/atomic.AddUint64(0x114434ac,0×1,0×0,0x4107e3,0x397fcc) C:/Users/ADMINI~1/AppData/Local/Temp/2/bindist550409343/go/src/pkg/sync/atomic/asm_386.s:118 +0xc main.main() E:/Work/GoLang/src/demo/goBug/atomic/main.go:17 +0x4d |
查了资料具体原因如下：
| https://code.google.com/p/go/issues/detail?id=5278 On x86-32,the 64-bit functions use instructions unavailable before the Pentium MMX. On both ARM and x86-32,it is the caller’s responsibility to arrange for 64-bit alignment of 64-bit words accessed atomically. The first word in a global variable or in an allocated struct or slice can be relied upon to be 64-bit aligned. |
其大意是：
| 64位原子操作的调用者必须确保指针的地址是对齐到8字节的边界 |
的办法有两种：
1，修改uint64字段在struct 的位置确保字段地址出现在8字节的边界；
2，修改使用sync.RWMutex来实现互斥，如下
mutex.Lock() uint64+=1 mutex.Unlock()
建议使用办法2来彻底解决问题
