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p2p/discover: slow down lookups on empty table #20389

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merged 2 commits into from
Nov 26, 2019
Merged

p2p/discover: slow down lookups on empty table #20389

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88fe4b5
p2p/discover: slow down lookups on empty table
fjl Nov 25, 2019
e277669
p2p/discover: wake from slowdown sleep when table is closed
fjl Nov 26, 2019
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16 changes: 16 additions & 0 deletions p2p/discover/lookup.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ package discover

import (
"context"
"time"

"github.com/ethereum/go-ethereum/p2p/enode"
)
Expand Down Expand Up @@ -106,6 +107,12 @@ func (it *lookup) startQueries() bool {
it.tab.mutex.Lock()
closest := it.tab.closest(it.result.target, bucketSize, false)
it.tab.mutex.Unlock()
// Avoid finishing the lookup too quickly if table is empty. It'd be better to wait
// for the table to fill in this case, but there is no good mechanism for that
// yet.
if len(closest.entries) == 0 {
it.slowdown()
}
it.queries = 1
it.replyCh <- closest.entries
return true
Expand All @@ -124,6 +131,15 @@ func (it *lookup) startQueries() bool {
return it.queries > 0
}

func (it *lookup) slowdown() {
sleep := time.NewTimer(1 * time.Second)
defer sleep.Stop()
select {
case <-sleep.C:
case <-it.tab.closeReq:
}
}

func (it *lookup) query(n *node, reply chan<- []*node) {
fails := it.tab.db.FindFails(n.ID(), n.IP())
r, err := it.queryfunc(n)
Expand Down