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4685b9eaa9
There was another deadlock in the peer pool. Because we made the event handler asynchrnous, another deadlock popped up, as the loop locks the global peerpool lock before processing events. But the handlers also take the global look, effectively resulting in the same situation we had before, i.e the loop is not running. THE LOOP MUST BE RUNNING AT ALL TIMES OTHERWISE THE SERVER HANGS.
69 lines
2.5 KiB
Go
69 lines
2.5 KiB
Go
package node
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import (
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"context"
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"errors"
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"github.com/ethereum/go-ethereum/log"
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"github.com/ethereum/go-ethereum/node"
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"github.com/ethereum/go-ethereum/p2p"
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)
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// All general log messages in this package should be routed through this logger.
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var logger = log.New("package", "status-go/metrics/node")
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// SubscribeServerEvents subscribes to server and listens to
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// PeerEventTypeAdd and PeerEventTypeDrop events.
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func SubscribeServerEvents(ctx context.Context, node *node.Node) error {
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server := node.Server()
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if server == nil {
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return errors.New("server is unavailable")
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}
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ch := make(chan *p2p.PeerEvent, server.MaxPeers)
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subscription := server.SubscribeEvents(ch)
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defer subscription.Unsubscribe()
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logger.Debug("Subscribed to server events")
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for {
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select {
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case event := <-ch:
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if isAddDropPeerEvent(event.Type) {
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// We start a goroutine here because updateNodeMetrics
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// is calling a method on the p2p server, which
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// blocks until the server is available:
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// https://github.com/status-im/status-go/blob/e60f425b45d00d3880b42fdd77b460ec465a9f55/vendor/github.com/ethereum/go-ethereum/p2p/server.go#L301
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// https://github.com/status-im/status-go/blob/e60f425b45d00d3880b42fdd77b460ec465a9f55/vendor/github.com/ethereum/go-ethereum/p2p/server.go#L746
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// If there's back-pressure on the peer event feed
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// https://github.com/status-im/status-go/blob/e60f425b45d00d3880b42fdd77b460ec465a9f55/vendor/github.com/ethereum/go-ethereum/p2p/server.go#L783
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// The event channel above might become full while updateNodeMetrics
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// is called, which means is never consumed, the server blocks on publishing on
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// it, and the two will deadlock (server waits for the channel above to be consumed,
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// this code waits for the server to respond to peerCount, which is in the same
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// event loop).
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// Calling it in a different go-routine will allow this code to keep
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// processing peer added events, therefore the server will not lock and
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// keep processing requests.
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go func() {
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if err := updateNodeMetrics(node, event.Type); err != nil {
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logger.Error("failed to update node metrics", "err", err)
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}
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}()
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}
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case err := <-subscription.Err():
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if err != nil {
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logger.Error("Subscription failed", "err", err)
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}
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return err
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case <-ctx.Done():
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return nil
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}
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}
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}
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func isAddDropPeerEvent(eventType p2p.PeerEventType) bool {
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return eventType == p2p.PeerEventTypeAdd || eventType == p2p.PeerEventTypeDrop
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}
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