记一次go中map并发引起的事故-白红宇

记一次go中map并发引起的事故

阅读量：456 次

发布时间：2019-03-06

本文共 6793 字，大约阅读时间需要 22 分钟。

错误使用map引发的血案

前言

最近业务中，同事使用map来接收返回的结果，使用waitGroup来并发的处理执行返回的结果，结果上线之后，直接崩了。

日志大量的数据库缓存池连接失败

{"ecode":-500,"message":"timed out while checking out a connection from connection pool"}{"ecode":-500,"message":"connection(xxxxxxxxx:xxxxx) failed to write: context deadline exceeded"}

场景复原

先来看来伪代码

一个全局的map，然后WaitGroup开启一组协程并发的读写数据，写入内容到map中。

package mainimport (	"fmt"	"sync"	"time")var count = 300func main() {	var data = make(map[int]string, count)	var wg sync.WaitGroup	for i := 0; i < count; i++ {		wg.Add(1)		go func(i int) {			defer wg.Done()			time.Sleep(time.Second * 1)			mockSqlPool()			data[i] = "test"		}(i)	}	fmt.Println("-----------WaitGroup执行结束了-----------")	wg.Wait()}// 模拟数据库的连接和释放func mockSqlPool() {	defer fmt.Println("关闭pool")	fmt.Println("我是pool")}

运行的输出

...我是pool关闭pool我是poolfatal error: 关闭poolconcurrent map writes我是poolgoroutine 56 [running]:runtime.throw(0x10d3923, 0x15)        /usr/local/go/src/runtime/panic.go:774 +0x72 fp=0xc00023cf20 sp=0xc00023cef0 pc=0x10298d2runtime.mapassign_fast64(0x10b29e0, 0xc000066180, 0x16, 0x0)        /usr/local/go/src/runtime/map_fast64.go:101 +0x350 fp=0xc00023cf60 sp=0xc00023cf20 pc=0x100f620main.main.func1(0xc00008c004, 0xc000066180, 0x16)        /Users/yj/Go/src/Go-POINT/map/main.go:23 +0x87 fp=0xc00023cfc8 sp=0xc00023cf60 pc=0x109a297runtime.goexit()        /usr/local/go/src/runtime/asm_amd64.s:1357 +0x1 fp=0xc00023cfd0 sp=0xc00023cfc8 pc=0x1053a51created by main.main        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0xbbgoroutine 1 [semacquire]:sync.runtime_Semacquire(0xc00008c004)        /usr/local/go/src/runtime/sema.go:56 +0x42sync.(*WaitGroup).Wait(0xc00008c004)        /usr/local/go/src/sync/waitgroup.go:130 +0x64main.main()        /Users/yj/Go/src/Go-POINT/map/main.go:27 +0x138goroutine 22 [semacquire]:internal/poll.runtime_Semacquire(0xc00008606c)        /usr/local/go/src/runtime/sema.go:61 +0x42internal/poll.(*fdMutex).rwlock(0xc000086060, 0xc000030500, 0x1097137)        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xadinternal/poll.(*FD).writeLock(...)        /usr/local/go/src/internal/poll/fd_mutex.go:239internal/poll.(*FD).Write(0xc000086060, 0xc000226030, 0xb, 0x10, 0x0, 0x0, 0x0)        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x5eos.(*File).write(...)        /usr/local/go/src/os/file_unix.go:276os.(*File).Write(0xc000084008, 0xc000226030, 0xb, 0x10, 0xc0000306b0, 0x103d37e, 0xc00000c060)        /usr/local/go/src/os/file.go:153 +0x77fmt.Fprintln(0x10ec4e0, 0xc000084008, 0xc000030730, 0x1, 0x1, 0x10459b6, 0xc00000c060, 0x3)        /usr/local/go/src/fmt/print.go:265 +0x8bfmt.Println(...)        /usr/local/go/src/fmt/print.go:274main.mockSqlPool()        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x104main.main.func1(0xc00008c004, 0xc000066180, 0x4)        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x63created by main.main        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0xbbgoroutine 192 [semacquire]:internal/poll.runtime_Semacquire(0xc00009e06c)        /usr/local/go/src/runtime/sema.go:61 +0x42internal/poll.(*fdMutex).rwlock(0xc00009e060, 0x10fae00, 0xc00023ad00)        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xe9internal/poll.(*FD).writeLock(...)        /usr/local/go/src/internal/poll/fd_mutex.go:239internal/poll.(*FD).Write(0xc00009e060, 0xc000246100, 0xb, 0x10, 0x0, 0x0, 0x0)        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x6fos.(*File).write(...)        /usr/local/go/src/os/file_unix.go:276os.(*File).Write(0xc00009c008, 0xc000246100, 0xb, 0x10, 0xc000124580, 0x40, 0x0)        /usr/local/go/src/os/file.go:153 +0xa7fmt.Fprintln(0x1158520, 0xc00009c008, 0xc00014d728, 0x1, 0x1, 0x107e3e6, 0xc0000d8100, 0x16)        /usr/local/go/src/fmt/print.go:265 +0xb3fmt.Println(...)        /usr/local/go/src/fmt/print.go:274main.mockSqlPool()        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x129main.main.func1(0xc0000a0004, 0xc000088180, 0x8f)        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x75created by main.main        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0x102goroutine 193 [semacquire]:internal/poll.runtime_Semacquire(0xc00009e06c)        /usr/local/go/src/runtime/sema.go:61 +0x42internal/poll.(*fdMutex).rwlock(0xc00009e060, 0x10fae00, 0xc000286410)        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xe9internal/poll.(*FD).writeLock(...)        /usr/local/go/src/internal/poll/fd_mutex.go:239internal/poll.(*FD).Write(0xc00009e060, 0xc0000a01a0, 0xb, 0x10, 0x0, 0x0, 0x0)        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x6fos.(*File).write(...)        /usr/local/go/src/os/file_unix.go:276os.(*File).Write(0xc00009c008, 0xc0000a01a0, 0xb, 0x10, 0xc0001245c0, 0x40, 0x0)        /usr/local/go/src/os/file.go:153 +0xa7fmt.Fprintln(0x1158520, 0xc00009c008, 0xc00014df28, 0x1, 0x1, 0x107e3e6, 0xc0000d8100, 0x17)        /usr/local/go/src/fmt/print.go:265 +0xb3fmt.Println(...)        /usr/local/go/src/fmt/print.go:274main.mockSqlPool()        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x129main.main.func1(0xc0000a0004, 0xc000088180, 0x90)        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x75created by main.main        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0x102goroutine 194 [semacquire]:internal/poll.runtime_Semacquire(0xc00009e06c)        /usr/local/go/src/runtime/sema.go:61 +0x42internal/poll.(*fdMutex).rwlock(0xc00009e060, 0x10fae00, 0xc00023add0)        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xe9internal/poll.(*FD).writeLock(...)        /usr/local/go/src/internal/poll/fd_mutex.go:239internal/poll.(*FD).Write(0xc00009e060, 0xc000246110, 0xb, 0x10, 0x0, 0x0, 0x0)        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x6fos.(*File).write(...)        /usr/local/go/src/os/file_unix.go:276os.(*File).Write(0xc00009c008, 0xc000246110, 0xb, 0x10, 0xc000124600, 0x40, 0x0)        /usr/local/go/src/os/file.go:153 +0xa7fmt.Fprintln(0x1158520, 0xc00009c008, 0xc000146728, 0x1, 0x1, 0x107e3e6, 0xc0000d8100, 0x18)        /usr/local/go/src/fmt/print.go:265 +0xb3fmt.Println(...)        /usr/local/go/src/fmt/print.go:274main.mockSqlPool()        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x129main.main.func1(0xc0000a0004, 0xc000088180, 0x91)        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x75created by main.main        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0x102

会发现很多goroutine处于semacquire状态，说明这些goroutine正在等待被信号量唤醒。但是这时候waitGroup已经因为panic退出了，这些goroutine不会在通过waitGroup.Done()退出，造成这些goroutine一直阻塞到这，最后的结果就是这些goroutine占用的数据库连接不能被释放。

关于waitGroup的信号量

整个Wait()会被runtime_Semacquire阻塞，直到等到全部退出的信号量；

Done()会在最后一次的时候通过runtime_Semrelease发出取消阻塞的信号，然后被runtime_Semacquire阻塞的Wait()就可以退出了；

上面涉及到的几种状态

semacquire 状态，这个状态表示等待调用

Waiting 等待状态。线程在等待某件事的发生。例如等待网络数据、硬盘；调用操作系统 API；等待内存同步访问条件 ready，如 atomic, mutexes

Runnable 就绪状态。只要给 CPU 资源我就能运行

原因

上面的错误原因有两个：

1、map不是并发安全，并发写的时候会触发panic；

2、避免在循环中连接数据库；

参考

【map 并发崩溃一例】

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