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记一次go中map并发引起的事故

2022年07月19日138me-sa

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 main 
 
import ( 
	"fmt" 
	"sync" 
	"time" 
) 
 
var count = 300 
 
func 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pool 
fatal error: 关闭pool 
concurrent map writes 
我是pool 
 
goroutine 56 [running]: 
runtime.throw(0x10d3923, 0x15) 
        /usr/local/go/src/runtime/panic.go:774 +0x72 fp=0xc00023cf20 sp=0xc00023cef0 pc=0x10298d2 
runtime.mapassign_fast64(0x10b29e0, 0xc000066180, 0x16, 0x0) 
        /usr/local/go/src/runtime/map_fast64.go:101 +0x350 fp=0xc00023cf60 sp=0xc00023cf20 pc=0x100f620 
main.main.func1(0xc00008c004, 0xc000066180, 0x16) 
        /Users/yj/Go/src/Go-POINT/map/main.go:23 +0x87 fp=0xc00023cfc8 sp=0xc00023cf60 pc=0x109a297 
runtime.goexit() 
        /usr/local/go/src/runtime/asm_amd64.s:1357 +0x1 fp=0xc00023cfd0 sp=0xc00023cfc8 pc=0x1053a51 
created by main.main 
        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0xbb 
 
goroutine 1 [semacquire]: 
sync.runtime_Semacquire(0xc00008c004) 
        /usr/local/go/src/runtime/sema.go:56 +0x42 
sync.(*WaitGroup).Wait(0xc00008c004) 
        /usr/local/go/src/sync/waitgroup.go:130 +0x64 
main.main() 
        /Users/yj/Go/src/Go-POINT/map/main.go:27 +0x138 
 
goroutine 22 [semacquire]: 
internal/poll.runtime_Semacquire(0xc00008606c) 
        /usr/local/go/src/runtime/sema.go:61 +0x42 
internal/poll.(*fdMutex).rwlock(0xc000086060, 0xc000030500, 0x1097137) 
        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xad 
internal/poll.(*FD).writeLock(...) 
        /usr/local/go/src/internal/poll/fd_mutex.go:239 
internal/poll.(*FD).Write(0xc000086060, 0xc000226030, 0xb, 0x10, 0x0, 0x0, 0x0) 
        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x5e 
os.(*File).write(...) 
        /usr/local/go/src/os/file_unix.go:276 
os.(*File).Write(0xc000084008, 0xc000226030, 0xb, 0x10, 0xc0000306b0, 0x103d37e, 0xc00000c060) 
        /usr/local/go/src/os/file.go:153 +0x77 
fmt.Fprintln(0x10ec4e0, 0xc000084008, 0xc000030730, 0x1, 0x1, 0x10459b6, 0xc00000c060, 0x3) 
        /usr/local/go/src/fmt/print.go:265 +0x8b 
fmt.Println(...) 
        /usr/local/go/src/fmt/print.go:274 
main.mockSqlPool() 
        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x104 
main.main.func1(0xc00008c004, 0xc000066180, 0x4) 
        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x63 
created by main.main 
        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0xbb 
 
goroutine 192 [semacquire]: 
internal/poll.runtime_Semacquire(0xc00009e06c) 
        /usr/local/go/src/runtime/sema.go:61 +0x42 
internal/poll.(*fdMutex).rwlock(0xc00009e060, 0x10fae00, 0xc00023ad00) 
        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xe9 
internal/poll.(*FD).writeLock(...) 
        /usr/local/go/src/internal/poll/fd_mutex.go:239 
internal/poll.(*FD).Write(0xc00009e060, 0xc000246100, 0xb, 0x10, 0x0, 0x0, 0x0) 
        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x6f 
os.(*File).write(...) 
        /usr/local/go/src/os/file_unix.go:276 
os.(*File).Write(0xc00009c008, 0xc000246100, 0xb, 0x10, 0xc000124580, 0x40, 0x0) 
        /usr/local/go/src/os/file.go:153 +0xa7 
fmt.Fprintln(0x1158520, 0xc00009c008, 0xc00014d728, 0x1, 0x1, 0x107e3e6, 0xc0000d8100, 0x16) 
        /usr/local/go/src/fmt/print.go:265 +0xb3 
fmt.Println(...) 
        /usr/local/go/src/fmt/print.go:274 
main.mockSqlPool() 
        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x129 
main.main.func1(0xc0000a0004, 0xc000088180, 0x8f) 
        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x75 
created by main.main 
        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0x102 
 
goroutine 193 [semacquire]: 
internal/poll.runtime_Semacquire(0xc00009e06c) 
        /usr/local/go/src/runtime/sema.go:61 +0x42 
internal/poll.(*fdMutex).rwlock(0xc00009e060, 0x10fae00, 0xc000286410) 
        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xe9 
internal/poll.(*FD).writeLock(...) 
        /usr/local/go/src/internal/poll/fd_mutex.go:239 
internal/poll.(*FD).Write(0xc00009e060, 0xc0000a01a0, 0xb, 0x10, 0x0, 0x0, 0x0) 
        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x6f 
os.(*File).write(...) 
        /usr/local/go/src/os/file_unix.go:276 
os.(*File).Write(0xc00009c008, 0xc0000a01a0, 0xb, 0x10, 0xc0001245c0, 0x40, 0x0) 
        /usr/local/go/src/os/file.go:153 +0xa7 
fmt.Fprintln(0x1158520, 0xc00009c008, 0xc00014df28, 0x1, 0x1, 0x107e3e6, 0xc0000d8100, 0x17) 
        /usr/local/go/src/fmt/print.go:265 +0xb3 
fmt.Println(...) 
        /usr/local/go/src/fmt/print.go:274 
main.mockSqlPool() 
        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x129 
main.main.func1(0xc0000a0004, 0xc000088180, 0x90) 
        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x75 
created by main.main 
        /Users/yj/Go/src/Go-POINT/map/main.go:18 +0x102 
 
goroutine 194 [semacquire]: 
internal/poll.runtime_Semacquire(0xc00009e06c) 
        /usr/local/go/src/runtime/sema.go:61 +0x42 
internal/poll.(*fdMutex).rwlock(0xc00009e060, 0x10fae00, 0xc00023add0) 
        /usr/local/go/src/internal/poll/fd_mutex.go:154 +0xe9 
internal/poll.(*FD).writeLock(...) 
        /usr/local/go/src/internal/poll/fd_mutex.go:239 
internal/poll.(*FD).Write(0xc00009e060, 0xc000246110, 0xb, 0x10, 0x0, 0x0, 0x0) 
        /usr/local/go/src/internal/poll/fd_unix.go:255 +0x6f 
os.(*File).write(...) 
        /usr/local/go/src/os/file_unix.go:276 
os.(*File).Write(0xc00009c008, 0xc000246110, 0xb, 0x10, 0xc000124600, 0x40, 0x0) 
        /usr/local/go/src/os/file.go:153 +0xa7 
fmt.Fprintln(0x1158520, 0xc00009c008, 0xc000146728, 0x1, 0x1, 0x107e3e6, 0xc0000d8100, 0x18) 
        /usr/local/go/src/fmt/print.go:265 +0xb3 
fmt.Println(...) 
        /usr/local/go/src/fmt/print.go:274 
main.mockSqlPool() 
        /Users/yj/Go/src/Go-POINT/map/main.go:35 +0x129 
main.main.func1(0xc0000a0004, 0xc000088180, 0x91) 
        /Users/yj/Go/src/Go-POINT/map/main.go:21 +0x75 
created 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】https://xargin.com/map-concurrent-throw/


本文参考链接：https://www.cnblogs.com/ricklz/p/14693855.html
  文章来源：
  https://www.itguest.com/post/aaeh2b1.html
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