[英]How come this loop is considered a data race [Golang]
我有一个循环,我得到这个错误,我正在运行go run -race main.go
这是有问题的循环:
var wg sync.WaitGroup
for _, member := range p.Members { << Line 254
go func() {
wg.Add(1)
_, err := db.Exec("UPDATE party_members SET active = ? WHERE steamid = ?", false, member.SteamID) << Line 257
if err != nil {
log.Println(err)
}
_, err = db.Exec("INSERT INTO party_members SET belongs_to =?, active = ?, steamid = ?", partyUUID, true, member.SteamID)
if err != nil {
log.Println(err)
}
wg.Done()
}() << Line 266
}
然后这是我得到的错误:
WARNING: DATA RACE
Read by goroutine 44:
BLAH/controllers/partybot.func·001()
/Users/Dev/gocode/src/BLAH/controllers/partybot/partybot.go:257 +0x136
Previous write by goroutine 43:
BLAH/controllers/partybot.(*PartialParty).SendReadyCheck()
/Users/Dev/gocode/src/BLAH/controllers/partybot/partybot.go:254 +0xda5
Goroutine 44 (running) created at:
BLAH/controllers/partybot.(*PartialParty).SendReadyCheck()
/Users/Dev/gocode/src/BLAH/controllers/partybot/partybot.go:266 +0xf13
Goroutine 43 (finished) created at:
BLAH/controllers/partybot.(*PartyHub).SortMemberIntoParty()
/Users/Dev/gocode/src/BLAH/controllers/partybot/partybot.go:173 +0xdb9
BLAH/controllers/partybot.(*Connection).readPump()
/Users/Dev/gocode/src/BLAH/controllers/partybot/partybot.go:359 +0x1872
BLAH/controllers/partybot.WSPartyBot()
/Users/Dev/gocode/src/BLAH/controllers/partybot/partybot.go:440 +0x4f0
net/http.HandlerFunc.ServeHTTP()
/usr/local/go/src/net/http/server.go:1265 +0x4e
github.com/gorilla/mux.(*Router).ServeHTTP()
/Users/Dev/gocode/src/github.com/gorilla/mux/mux.go:98 +0x377
BLAH/controllers/common.func·001()
/Users/Dev/gocode/src/BLAH/controllers/common/common.go:36 +0xc2
net/http.HandlerFunc.ServeHTTP()
/usr/local/go/src/net/http/server.go:1265 +0x4e
net/http.(*ServeMux).ServeHTTP()
/usr/local/go/src/net/http/server.go:1541 +0x20c
net/http.serverHandler.ServeHTTP()
/usr/local/go/src/net/http/server.go:1703 +0x1f6
net/http.(*conn).serve()
/usr/local/go/src/net/http/server.go:1204 +0x1087
==================
我不知道为什么这是一场数据竞赛,因为如果有人能告诉我为什么这会很好,我对Go来说还是新手,我标记了有问题的线条。
问题是goroutine正在通过闭包访问变量'member',并且在go中它被到达时被评估(即它在goroutine执行时看到成员的值,而不是在它通过go创建时的值) func()... call。成员变量正在被循环更新,所以循环更新和你已经开始读取它们的goroutines之间存在竞争。(你会发现如果你进一步挖掘你的数据库没有'从集合中看到确切的成员集。)通常,您可以通过在循环中强制评估变量来解决此问题,方法是创建局部变量,或者将其作为参数添加到func中,例如
var wg sync.WaitGroup
for _, member := range p.Members {
wg.Add(1)
m := member
go func() {
_, err := db.Exec("UPDATE party_members SET active = ? WHERE steamid = ?", false, m.SteamID)
...
wg.Done()
}()
}
要么
var wg sync.WaitGroup
for _, member := range p.Members {
wg.Add(1)
go func(m memberType) {
_, err := db.Exec("UPDATE party_members SET active = ? WHERE steamid = ?", false, m.SteamID)
...
wg.Done()
}(member)
}
另请注意,您需要从循环中调用wg.Add(1),而不是从goroutine本身调用。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.