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union: fix crash when using epff policy - fixes #5000 

Before this fix using the epff policy could double close a channel.

The fix refactors the code to make that impossible and cancels any
running queries when the first query is found.
This commit is contained in:
Nick Craig-Wood 2021-02-08 11:59:01 +00:00
parent 687a3b1832
commit 6b9e4f939d
1 changed files with 5 additions and 9 deletions
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14
backend/union/policy/epff.go
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@ -17,7 +17,9 @@ func init() {
type EpFF struct{}
func (p *EpFF) epff(ctx context.Context, upstreams []*upstream.Fs, filePath string) (*upstream.Fs, error) {
ch := make(chan *upstream.Fs)
ch := make(chan *upstream.Fs, len(upstreams))
ctx, cancel := context.WithCancel(ctx)
defer cancel()
for _, u := range upstreams {
u := u // Closure
go func() {
@ -30,16 +32,10 @@ func (p *EpFF) epff(ctx context.Context, upstreams []*upstream.Fs, filePath stri
}()
}
var u *upstream.Fs
for i := 0; i < len(upstreams); i++ {
for range upstreams {
u = <-ch
if u != nil {
// close remaining goroutines
go func(num int) {
defer close(ch)
for i := 0; i < num; i++ {
<-ch
}
}(len(upstreams) - 1 - i)
break
}
}
if u == nil {