Golang Go语言用切片实现队列遇到无法理解的问题
Golang Go语言用切片实现队列遇到无法理解的问题
package main
import (
“fmt”
“log”
“net/http”
“os”
“time”
)
var Q []string
func main() {
go func() {
time.Sleep(1 * time.Second)
for {
test()
}
}()
Q = append(Q, “233”)
Q = append(Q, “233”)
Q = append(Q, “233”)
time.Sleep(3 * time.Second)
Q = append(Q, "233")
Q = append(Q, "233")
Q = append(Q, "233")
Q = append(Q, "233")
Q = append(Q, "233")
time.Sleep(3 * time.Second)
Q = append(Q, "233")
time.Sleep(3 * time.Second)
Q = append(Q, "233")
http.HandleFunc("/", handle)
err := http.ListenAndServe(":8080", nil)
if err != nil {
log.Println("http port has been used.")
os.Exit(-1)
}
}
func handle(w http.ResponseWriter, r *http.Request) {
defer r.Body.Close()
_ = r.ParseForm()
_, _ = fmt.Fprint(w, “hello”)
}
func test() {
file := queueOut()
if file != “” {
log.Println(file)
}
}
func queueOut() string {
res := Q[0]
if len(Q) == 1 {
Q[0] = “”
return res
}
Q = Q[1:]
return res
}
我觉得我这样写没错啊. 但是运行的时候有几率出现
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1058fe5]
goroutine 19 [running]:
fmt.(*buffer).WriteString(…)
/opt/local/lib/go/src/fmt/print.go:82
fmt.(*fmt).padString(0xc000114040, 0x0, 0x3)
/opt/local/lib/go/src/fmt/format.go:110 +0x9d
fmt.(*fmt).fmtS(0xc000114040, 0x0, 0x3)
/opt/local/lib/go/src/fmt/format.go:328 +0x61
fmt.(*pp).fmtString(0xc000114000, 0x0, 0x3, 0x76)
/opt/local/lib/go/src/fmt/print.go:437 +0x122
fmt.(*pp).printArg(0xc000114000, 0x1247a20, 0xc000010050, 0x76)
/opt/local/lib/go/src/fmt/print.go:671 +0x878
fmt.(*pp).doPrintln(0xc000114000, 0xc0000cffa8, 0x1, 0x1)
/opt/local/lib/go/src/fmt/print.go:1146 +0xb1
fmt.Sprintln(0xc0000cffa8, 0x1, 0x1, 0x1247a20, 0x1)
/opt/local/lib/go/src/fmt/print.go:271 +0x52
log.Println(0xc0000cffa8, 0x1, 0x1)
/opt/local/lib/go/src/log/log.go:301 +0x3f
main.test()
/Users/licsber/go/src/test/main.go:52 +0xd7
main.main.func1()
/Users/licsber/go/src/test/main.go:17 +0x2f
created by main.main
/Users/licsber/go/src/test/main.go:14 +0x39
Process finished with exit code 2
小白表示无法理解 这个问题是几率出现. 每次运行不一定都有
更多关于Golang Go语言用切片实现队列遇到无法理解的问题的实战系列教程也可以访问 https://www.itying.com/category-94-b0.html
package main
import (
“fmt”
“log”
“net/http”
“os”
“sync”
“time”
)
var Q []string
var lock sync.RWMutex
func main() {
go func() {
time.Sleep(1 * time.Second)
for {
test()
}
}()
Q = append(Q, “233”)
Q = append(Q, “233”)
Q = append(Q, “233”)
time.Sleep(3 * time.Second)
Q = append(Q, “233”)
Q = append(Q, “233”)
Q = append(Q, “233”)
Q = append(Q, “233”)
Q = append(Q, “233”)
time.Sleep(3 * time.Second)
Q = append(Q, “233”)
time.Sleep(3 * time.Second)
Q = append(Q, “233”)
http.HandleFunc("/", handle)
err := http.ListenAndServe(":8080", nil)
if err != nil {
log.Println(“http port has been used.”)
os.Exit(-1)
}
}
func handle(w http.ResponseWriter, r *http.Request) {
defer r.Body.Close()
_ = r.ParseForm()
_, _ = fmt.Fprint(w, “hello”)
}
func test() {
file := queueOut()
if file != “” {
log.Println(file)
}
}
func queueOut() string {
// 加写锁
lock.Lock()
res := Q[0]
if len(Q) == 1 {
Q[0] = “”
return res
}
Q = Q[1:]
lock.Unlock()
return res
}
有 channel 不用非要用非线程安全的 slice
另外 slice 的 append 操作是会重新分配 slice 结构的，而且你的 slice 初始 len 为 0，每次扩容时存储数据的 array 也会重新分配，问题应该就出现在这里
Q = Q[1:]瞬间执行多次，这个并发直接把 Q 给 cut 没了，再访问 Q 的任意下标自然就崩了。
要非得用 slice 就别直接操作 slice，另外封装两个增删方法，加上锁。
func queueOut() string {
res := Q[0]
if len(Q) == 1 {
Q[0] = “”
return res
}
// 加写锁
lock.Lock()
Q = Q[1:]
lock.Unlock()
return res
}
