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Acquire lock before unmapping vlog files #1050

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merged 2 commits into from
Sep 24, 2019
Merged

Acquire lock before unmapping vlog files #1050

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61a1140
Acquire lock before unmapping vlog files
Sep 23, 2019
1e2b78e
Fix typo
Sep 23, 2019
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9 changes: 8 additions & 1 deletion value.go
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Original file line number Diff line number Diff line change
Expand Up @@ -141,9 +141,16 @@ func (lf *logFile) doneWriting(offset uint32) error {
return errors.Wrapf(err, "Unable to sync value log: %q", lf.path)
}

// Before we were acquiring a lock here on lf.lock, because we were invalidating the file
// descriptor due to reopening it as read-only. Now, we don't invalidate the fd, but unmap it,
// truncate it and remap it. That creates a window where we have segfaults because the mmap is
// no longer valid, while someone might be reading it. Therefore, we need a lock here again.
lf.lock.Lock()
defer lf.lock.Unlock()

// Unmap file before we truncate it. Windows cannot truncate a file that is mmapped.
if err := lf.munmap(); err != nil {
return errors.Wrapf(err, "failed to mumap vlog file %s", lf.fd.Name())
return errors.Wrapf(err, "failed to munmap vlog file %s", lf.fd.Name())
}

// TODO: Confirm if we need to run a file sync after truncation.
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