Aias00 opened a new pull request, #3543:
URL: https://github.com/apache/dubbo-go/pull/3543
## What
`apolloListener.listeners` was a plain `map` with no mutex; `OnNewestChange`
ranges it on agollo's long-poll goroutine while `AddListener`/`RemoveListener`
mutate it on router goroutines — a fatal concurrent map read+write. Same class
as the zk config_center `CacheListener` fix (#3539/#3540).
## Why
```go
// config_center/apollo/listener.go (before)
type apolloListener struct {
listeners map[config_center.ConfigurationListener]struct{} // no lock
}
func (a *apolloListener) OnNewestChange(...) {
for listener := range a.listeners { listener.Process(...) } // agollo
goroutine
}
func (a *apolloListener) AddListener(l ...) { a.listeners[l] = struct{}{} }
// router goroutine
func (a *apolloListener) RemoveListener(l ...) { delete(a.listeners, l) }
// router goroutine
func (a *apolloListener) IsEmpty() bool { return len(a.listeners) ==
0 } // router goroutine
```
A config push from Apollo arriving while a router subscribes/unsubscribes
(or `IsEmpty` runs inside `RemoveListener`'s `RemoveChangeListener` decision) →
`fatal error: concurrent map read and map write`.
## Fix
Add a `sync.RWMutex` to `apolloListener`. `AddListener`/`RemoveListener`
take the write lock; `IsEmpty` takes the read lock; `OnNewestChange` snapshots
the set under the read lock and dispatches `Process` outside it (so a slow
consumer cannot block agollo's long-poll goroutine).
## Tests
Added `TestApolloListenerConcurrency`: 100 rounds of concurrent
`OnNewestChange` vs `Add`/`Remove`, passing under `-race`.
`config_center/apollo` passes under `-race`.
Fixes #3542
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