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fix: avoid potential hang when starting event listener

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It was possible for NewEvents to never return, blocked on waiting for a WaitGroup to be done.
The call to Done was in a goroutine that could exit before reaching the Done call.

Replace the WaitGroup with a channel that is closed to signal that initialisation is complete.
Also, while we are waiting on the channel, wait on the context so we can exit clealy if the
context is canceled.
This commit is contained in:
Ian Davis 2020-12-09 11:25:20 +00:00
parent a999e41677
commit 696469aae7
No known key found for this signature in database
GPG Key ID: F3B290C645FE1783
1 changed files with 25 additions and 14 deletions
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35
chain/events/events.go
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@ -20,8 +20,10 @@ import (
var log = logging.Logger("events")
// HeightHandler `curH`-`ts.Height` = `confidence`
type HeightHandler func(ctx context.Context, ts *types.TipSet, curH abi.ChainEpoch) error
type RevertHandler func(ctx context.Context, ts *types.TipSet) error
type (
HeightHandler func(ctx context.Context, ts *types.TipSet, curH abi.ChainEpoch) error
RevertHandler func(ctx context.Context, ts *types.TipSet) error
)
type heightHandler struct {
confidence int
@ -48,7 +50,7 @@ type Events struct {
tsc *tipSetCache
lk sync.Mutex
ready sync.WaitGroup
ready chan struct{}
readyOnce sync.Once
heightEvents
@ -76,15 +78,16 @@ func NewEvents(ctx context.Context, api eventAPI) *Events {
},
hcEvents: newHCEvents(ctx, api, tsc, uint64(gcConfidence)),
ready: make(chan struct{}),
}
e.ready.Add(1)
go e.listenHeadChanges(ctx)
e.ready.Wait()
// TODO: cleanup/gc goroutine
// Wait for the first tipset to be seen or bail if shutting down
select {
case <-e.ready:
case <-ctx.Done():
}
return e
}
@ -111,14 +114,22 @@ func (e *Events) listenHeadChangesOnce(ctx context.Context) error {
notifs, err := e.api.ChainNotify(ctx)
if err != nil {
// TODO: retry
// Retry is handled by caller
return xerrors.Errorf("listenHeadChanges ChainNotify call failed: %w", err)
}
cur, ok := <-notifs // TODO: timeout?
var cur []*api.HeadChange
var ok bool
// Wait for first tipset or bail
select {
case cur, ok = <-notifs:
if !ok {
return xerrors.Errorf("notification channel closed")
}
case <-ctx.Done():
return ctx.Err()
}
if len(cur) != 1 {
return xerrors.Errorf("unexpected initial head notification length: %d", len(cur))
@ -134,8 +145,8 @@ func (e *Events) listenHeadChangesOnce(ctx context.Context) error {
e.readyOnce.Do(func() {
e.lastTs = cur[0].Val
e.ready.Done()
// Signal that we have seen first tipset
close(e.ready)
})
for notif := range notifs {