go内存泄露
November 3, 2020今天同事遇到一个问题，是关于goroutine的泄露。
问题和分析
代码简化后如下：
package main
import (
"errors"
"fmt"
"github.com/gin-contrib/pprof"
"github.com/gin-gonic/gin"
"log"
"net/http"
)
func leakGrs() error {
s := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
ch := make(chan error)
for i := range s {
go func(i int) {
var err error
if i == 3 {
err = errors.New("something wrong")
}
ch <- err
}(i)
}
for range s {
err := <-ch
if err != nil {
return err
}
}
return nil
}
func handlerLeakGrs(c *gin.Context) {
err := leakGrs()
c.JSON(http.StatusOK, gin.H{
"err": fmt.Sprintf("%+v", err),
})
}
func main() {
engine := gin.Default()
pprof.Register(engine)
engine.GET("/", handlerLeakGrs)
server := http.Server{
Addr: ":8080",
Handler: engine,
}
if err := server.ListenAndServe(); err != nil {
log.Fatalf("cannot start server: %+v", err)
}
}
由于引入了pprof，所以我们可以通过http://localhost:8080/debug/pprof/goroutine?debug=1访问到goroutine状况——
在一开始，一共有三个goroutine，分别是一个主G和两个net/http的G：
goroutine profile: total 3
1 @ 0x1038170 0x103178a 0x1030d55 0x10ca245 0x10cb141 0x10cb123 0x11a389f 0x11b684e 0x12c9a88 0x10677b1
# 0x1030d54 internal/poll.runtime_pollWait+0x54 /Users/yuchanns/go/go1.14/src/runtime/netpoll.go:203
# 0x10ca244 internal/poll.(*pollDesc).wait+0x44 /Users/yuchanns/go/go1.14/src/internal/poll/fd_poll_runtime.go:87
# 0x10cb140 internal/poll.(*pollDesc).waitRead+0x200 /Users/yuchanns/go/go1.14/src/internal/poll/fd_poll_runtime.go:92
# 0x10cb122 internal/poll.(*FD).Read+0x1e2 /Users/yuchanns/go/go1.14/src/internal/poll/fd_unix.go:169
# 0x11a389e net.(*netFD).Read+0x4e /Users/yuchanns/go/go1.14/src/net/fd_unix.go:202
# 0x11b684d net.(*conn).Read+0x8d /Users/yuchanns/go/go1.14/src/net/net.go:184
# 0x12c9a87 net/http.(*connReader).backgroundRead+0x57 /Users/yuchanns/go/go1.14/src/net/http/server.go:678
1 @ 0x1038170 0x103178a 0x1030d55 0x10ca245 0x10ccaa4 0x10cca86 0x11a4152 0x11bf2a2 0x11be0e4 0x12d42dd 0x12d4027 0x15882d9 0x1037d92 0x10677b1
# 0x1030d54 internal/poll.runtime_pollWait+0x54 /Users/yuchanns/go/go1.14/src/runtime/netpoll.go:203
# 0x10ca244 internal/poll.(*pollDesc).wait+0x44 /Users/yuchanns/go/go1.14/src/internal/poll/fd_poll_runtime.go:87
# 0x10ccaa3 internal/poll.(*pollDesc).waitRead+0x1d3 /Users/yuchanns/go/go1.14/src/internal/poll/fd_poll_runtime.go:92
# 0x10cca85 internal/poll.(*FD).Accept+0x1b5 /Users/yuchanns/go/go1.14/src/internal/poll/fd_unix.go:384
# 0x11a4151 net.(*netFD).accept+0x41 /Users/yuchanns/go/go1.14/src/net/fd_unix.go:238
# 0x11bf2a1 net.(*TCPListener).accept+0x31 /Users/yuchanns/go/go1.14/src/net/tcpsock_posix.go:139
# 0x11be0e3 net.(*TCPListener).Accept+0x63 /Users/yuchanns/go/go1.14/src/net/tcpsock.go:261
# 0x12d42dc net/http.(*Server).Serve+0x25c /Users/yuchanns/go/go1.14/src/net/http/server.go:2901
# 0x12d4026 net/http.(*Server).ListenAndServe+0xb6 /Users/yuchanns/go/go1.14/src/net/http/server.go:2830
# 0x15882d8 main.main+0x138 /Users/yuchanns/Coding/golang/gobyexample/main.go:51
# 0x1037d91 runtime.main+0x211 /Users/yuchanns/go/go1.14/src/runtime/proc.go:203
1 @ 0x13603a5 0x13601c0 0x135cf8a 0x136a3aa 0x1587ef8 0x1587ea7 0x157245b 0x1585cb0 0x157245b 0x1584de1 0x157245b 0x157c346 0x157ba1e 0x12d3f33 0x12cf8ac 0x10677b1
# 0x13603a4 runtime/pprof.writeRuntimeProfile+0x94 /Users/yuchanns/go/go1.14/src/runtime/pprof/pprof.go:694
# 0x13601bf runtime/pprof.writeGoroutine+0x9f /Users/yuchanns/go/go1.14/src/runtime/pprof/pprof.go:656
# 0x135cf89 runtime/pprof.(*Profile).WriteTo+0x3d9 /Users/yuchanns/go/go1.14/src/runtime/pprof/pprof.go:329
# 0x136a3a9 net/http/pprof.handler.ServeHTTP+0x339 /Users/yuchanns/go/go1.14/src/net/http/pprof/pprof.go:248
# 0x1587ef7 net/http.HandlerFunc.ServeHTTP+0x77 /Users/yuchanns/go/go1.14/src/net/http/server.go:2012
# 0x1587ea6 github.com/gin-contrib/pprof.pprofHandler.func1+0x26 /Users/yuchanns/go/pkg/mod/github.com/gin-contrib/pprof@v1.3.0/pprof.go:56
# 0x157245a github.com/gin-gonic/gin.(*Context).Next+0x3a /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/context.go:156
# 0x1585caf github.com/gin-gonic/gin.RecoveryWithWriter.func1+0x5f /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/recovery.go:83
# 0x157245a github.com/gin-gonic/gin.(*Context).Next+0x3a /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/context.go:156
# 0x1584de0 github.com/gin-gonic/gin.LoggerWithConfig.func1+0xe0 /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/logger.go:241
# 0x157245a github.com/gin-gonic/gin.(*Context).Next+0x3a /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/context.go:156
# 0x157c345 github.com/gin-gonic/gin.(*Engine).handleHTTPRequest+0x665 /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/gin.go:409
# 0x157ba1d github.com/gin-gonic/gin.(*Engine).ServeHTTP+0x17d /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/gin.go:367
# 0x12d3f32 net/http.serverHandler.ServeHTTP+0xa2 /Users/yuchanns/go/go1.14/src/net/http/server.go:2807
# 0x12cf8ab net/http.(*conn).serve+0x86b /Users/yuchanns/go/go1.14/src/net/http/server.go:1895
然后对http://localhost:8080/debug/pprof/goroutine?debug=1进行多次访问，再次查看goroutine状态，发现G的数量多达153，其中150个全是main.leakGrs这个方法的：
goroutine profile: total 153
150 @ 0x1038170 0x1006dfd 0x1006bc5 0x15883ee 0x10677b1
# 0x15883ed main.leakGrs.func1+0x4d /Users/yuchanns/Coding/golang/gobyexample/main.go:22
1 @ 0x1038170 0x103178a 0x1030d55 0x10ca245 0x10ccaa4 0x10cca86 0x11a4152 0x11bf2a2 0x11be0e4 0x12d42dd 0x12d4027 0x15882d9 0x1037d92 0x10677b1
# 0x1030d54 internal/poll.runtime_pollWait+0x54 /Users/yuchanns/go/go1.14/src/runtime/netpoll.go:203
# 0x10ca244 internal/poll.(*pollDesc).wait+0x44 /Users/yuchanns/go/go1.14/src/internal/poll/fd_poll_runtime.go:87
# 0x10ccaa3 internal/poll.(*pollDesc).waitRead+0x1d3 /Users/yuchanns/go/go1.14/src/internal/poll/fd_poll_runtime.go:92
# 0x10cca85 internal/poll.(*FD).Accept+0x1b5 /Users/yuchanns/go/go1.14/src/internal/poll/fd_unix.go:384
# 0x11a4151 net.(*netFD).accept+0x41 /Users/yuchanns/go/go1.14/src/net/fd_unix.go:238
# 0x11bf2a1 net.(*TCPListener).accept+0x31 /Users/yuchanns/go/go1.14/src/net/tcpsock_posix.go:139
# 0x11be0e3 net.(*TCPListener).Accept+0x63 /Users/yuchanns/go/go1.14/src/net/tcpsock.go:261
# 0x12d42dc net/http.(*Server).Serve+0x25c /Users/yuchanns/go/go1.14/src/net/http/server.go:2901
# 0x12d4026 net/http.(*Server).ListenAndServe+0xb6 /Users/yuchanns/go/go1.14/src/net/http/server.go:2830
# 0x15882d8 main.main+0x138 /Users/yuchanns/Coding/golang/gobyexample/main.go:51
# 0x1037d91 runtime.main+0x211 /Users/yuchanns/go/go1.14/src/runtime/proc.go:203
1 @ 0x1054a5e 0x10b3ee6 0x10cb071 0x10cb03a 0x11a389f 0x11b684e 0x12c9a88 0x10677b1
# 0x1054a5d syscall.syscall+0x2d /Users/yuchanns/go/go1.14/src/runtime/sys_darwin.go:63
# 0x10b3ee5 syscall.read+0x65 /Users/yuchanns/go/go1.14/src/syscall/zsyscall_darwin_amd64.go:1242
# 0x10cb070 syscall.Read+0x130 /Users/yuchanns/go/go1.14/src/syscall/syscall_unix.go:189
# 0x10cb039 internal/poll.(*FD).Read+0xf9 /Users/yuchanns/go/go1.14/src/internal/poll/fd_unix.go:165
# 0x11a389e net.(*netFD).Read+0x4e /Users/yuchanns/go/go1.14/src/net/fd_unix.go:202
# 0x11b684d net.(*conn).Read+0x8d /Users/yuchanns/go/go1.14/src/net/net.go:184
# 0x12c9a87 net/http.(*connReader).backgroundRead+0x57 /Users/yuchanns/go/go1.14/src/net/http/server.go:678
1 @ 0x13603a5 0x13601c0 0x135cf8a 0x136a3aa 0x1587ef8 0x1587ea7 0x157245b 0x1585cb0 0x157245b 0x1584de1 0x157245b 0x157c346 0x157ba1e 0x12d3f33 0x12cf8ac 0x10677b1
# 0x13603a4 runtime/pprof.writeRuntimeProfile+0x94 /Users/yuchanns/go/go1.14/src/runtime/pprof/pprof.go:694
# 0x13601bf runtime/pprof.writeGoroutine+0x9f /Users/yuchanns/go/go1.14/src/runtime/pprof/pprof.go:656
# 0x135cf89 runtime/pprof.(*Profile).WriteTo+0x3d9 /Users/yuchanns/go/go1.14/src/runtime/pprof/pprof.go:329
# 0x136a3a9 net/http/pprof.handler.ServeHTTP+0x339 /Users/yuchanns/go/go1.14/src/net/http/pprof/pprof.go:248
# 0x1587ef7 net/http.HandlerFunc.ServeHTTP+0x77 /Users/yuchanns/go/go1.14/src/net/http/server.go:2012
# 0x1587ea6 github.com/gin-contrib/pprof.pprofHandler.func1+0x26 /Users/yuchanns/go/pkg/mod/github.com/gin-contrib/pprof@v1.3.0/pprof.go:56
# 0x157245a github.com/gin-gonic/gin.(*Context).Next+0x3a /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/context.go:156
# 0x1585caf github.com/gin-gonic/gin.RecoveryWithWriter.func1+0x5f /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/recovery.go:83
# 0x157245a github.com/gin-gonic/gin.(*Context).Next+0x3a /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/context.go:156
# 0x1584de0 github.com/gin-gonic/gin.LoggerWithConfig.func1+0xe0 /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/logger.go:241
# 0x157245a github.com/gin-gonic/gin.(*Context).Next+0x3a /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/context.go:156
# 0x157c345 github.com/gin-gonic/gin.(*Engine).handleHTTPRequest+0x665 /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/gin.go:409
# 0x157ba1d github.com/gin-gonic/gin.(*Engine).ServeHTTP+0x17d /Users/yuchanns/go/pkg/mod/github.com/gin-gonic/gin@v1.6.2/gin.go:367
# 0x12d3f32 net/http.serverHandler.ServeHTTP+0xa2 /Users/yuchanns/go/go1.14/src/net/http/server.go:2807
# 0x12cf8ab net/http.(*conn).serve+0x86b /Users/yuchanns/go/go1.14/src/net/http/server.go:1895
同事贴出他的代码，询问错误在哪里。实际代码比较复杂，特别是在循环返回错误那块，因此一时之间大家也没看出问题所在。
幸好因为事先知道问题在于这段代码造成的泄露，经过简化，很快大家就弄清楚了问题在于使用了go关键字的循环中，往无缓冲的通道写数据，而下面的通道读数据却并不总是全部读完，就会返回。这就造成了多个goroutine阻塞等待通道让位可以写入数据。
而goroutine都是平等而独立的，并且不会被gc所回收，一旦发生阻塞，就会一直存在，也就形成了事实上的“goroutine泄露”。更可怕的就是一次请求产生少量的泄露，一天下来的大量请求则会造成海量的goroutine泄露，数量飙升，后果就会变得严重，导致监控告警。
解决方法
代码中有两处错误，第一处是使用无缓冲通道。
使用无缓冲通道，通道只能容纳一个单位类型的数据；当存在多个写入成员时，需要等待原有的数据被读取后才能再次写入，造成阻塞排队。
所以提倡应该使用有缓冲的通道，并且把通道长度设置成写入成员的个数。
func leakGrs() error {
s := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
ch := make(chan error, 9)
将ch := make(chan error)加上长度9，就不会发生泄露的问题了。所有的goroutine完成了通道写入，自动退出；而尽管读取通道并没有用到那么多数据，随着方法的结束，通道也将被gc回收。
第二处错误则是遇到错误直接return。
这种错误写法源于对常驻进程的不了解。这位同事和我一样是从php转语言而来的。习惯于php-fpm的程序员一般认为变量的生命周期仅在于一次请求当中；当请求结束后，代码内容全被清空，自然也就不存在链接忘记回收、goroutine阻塞等泄露问题。
所以即使发生了错误，正确的做法也应该是收集全部错误信息，或者及时通知goroutine退出。
总结
goroutine很好用，可以以极小的资源轻松创建成千上万，但这并不意味着可以被滥用。
防止goroutine泄露，一定要做好协程的退出准备和意外退出处理。
无缓冲通道会造成写入阻塞。