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consultopo: Enforce a connection heartbeat for Watch(). #5673

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Merged
enisoc merged 1 commit into from
Jan 9, 2020
Merged

consultopo: Enforce a connection heartbeat for Watch(). #5673

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19 changes: 17 additions & 2 deletions go/vt/topo/consultopo/watch.go
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,12 @@ func (s *Server) Watch(ctx context.Context, filePath string) (*topo.WatchData, <
go func() {
defer close(notifications)

var getCtx context.Context
// Initialize to no-op function to avoid having to check for nil.
cancelGetCtx := func() {}

defer cancelGetCtx()

for {
// Wait/poll until we get a new version.
// Get with a WaitIndex and WaitTime will return
Expand All @@ -69,9 +75,18 @@ func (s *Server) Watch(ctx context.Context, filePath string) (*topo.WatchData, <
WaitIndex: waitIndex,
WaitTime: *watchPollDuration,
}
pair, _, err = s.kv.Get(nodePath, opts.WithContext(watchCtx))

// Make a new Context for just this one Get() call.
// The server should send us something after WaitTime at the latest.
// If it takes more than 2x that long, assume we've lost contact.
// This essentially uses WaitTime as a heartbeat interval to detect
// a dead connection.
cancelGetCtx()
getCtx, cancelGetCtx = context.WithTimeout(watchCtx, 2*opts.WaitTime)

pair, _, err = s.kv.Get(nodePath, opts.WithContext(getCtx))
if err != nil {
// Serious error or context cancelled.
// Serious error or context timeout/cancelled.
notifications <- &topo.WatchData{
Err: convertError(err, nodePath),
}
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