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internal/trace: emit sync event before deferred spilled error

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CL 648315 and CL 648195 fixed #71615 in the case where we fail to read
the next generation by emitting an extra sync event before returning an
error. But, it's possible we failed to even read the next spilled batch
when we read the first generation, and have been carrying the error from
trying to read a spilled batch since the last generation. In this case,
we don't emit a final sync event, meaning that there are still some
cases where #71615 happens.

This change emits the final sync event in this corner case. I believe
this is the final corner case. I could previously reproduce the issue
by running the test under stress2, but I can no longer reproduce any
failures after this change.

Fixes #71615, for real this time.

Change-Id: I10688a3c0e4b8327a95f31add365338c77c091ab
Reviewed-on: https://go-review.googlesource.com/c/go/+/649259
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Michael Anthony Knyszek 2025-02-13 19:45:52 +00:00 • committed by Gopher Robot
parent 242ef7cb05
commit 85f8e240fe
1 changed files with 19 additions and 12 deletions
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7
src/internal/trace/reader.go
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@ -28,6 +28,7 @@ type Reader struct {
gen *generation
spill *spilledBatch
spillErr error // error from reading spill
spillErrSync bool // whether we emitted a Sync before reporting spillErr
frontier []*batchCursor
cpuSamples []cpuSample
order ordering
@ -139,8 +140,13 @@ func (r *Reader) ReadEvent() (e Event, err error) {
// Check if we need to refresh the generation.
if len(r.frontier) == 0 && len(r.cpuSamples) == 0 {
if r.spillErr != nil {
if r.spillErrSync {
return Event{}, r.spillErr
}
r.spillErrSync = true
r.syncs++
return syncEvent(nil, r.lastTs, r.syncs), nil
}
if r.gen != nil && r.spill == nil {
// If we have a generation from the last read,
// and there's nothing left in the frontier, and
@ -154,6 +160,7 @@ func (r *Reader) ReadEvent() (e Event, err error) {
// Read the next generation.
r.gen, r.spill, r.spillErr = readGeneration(r.r, r.spill)
if r.gen == nil {
r.spillErrSync = true
r.syncs++
return syncEvent(nil, r.lastTs, r.syncs), nil
}