Fix concurrent HashSet modification when serializing archive meta#618
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UpdateMeta, UpdateTags and Update(ExchangeInfo) all touched _archiveMetaInformation.Tags but guarded it with two different locks (one on the path string, another on the meta object itself), so a thread adding a tag could race a thread serializing the meta file and trip "Collection was modified" inside JsonSerializer. Route every access through a single _metaLock and keep UpdateMeta inside the lock.
This was referenced Apr 13, 2026
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Summary
DirectoryArchiveWriterguarded_archiveMetaInformation.Tagswith two different locks:UpdateMetaandUpdateTagslocked on the path string, whileUpdate(ExchangeInfo)locked on the meta object itself. That meant two threads could be inside the tag code at the same time, one adding to the HashSet while the other was enumerating it throughJsonSerializer.Serialize, which throws "Collection was modified; enumeration operation may not execute".The issue shows up more often when
UseDnsOverHttpsActionis enabled because every DoH query becomes its own captured exchange, roughly doubling the concurrent write traffic through the archive writer.This PR routes every access through a single
_metaLockand keeps theUpdateMeta(true)call inside the lock so the Add and the serialize never interleave. The lock on an interned string was also a latent issue and is gone.