The header has said since it was written that blocking queue operations
must never run under connections_mutex; three code paths did exactly that.
KeepaliveThread held it while sending a keepalive to every connection,
which blocks until the peer-liveness or backpressure timeout - so one
half-dead writer socket could stall SendImage and every /statistics poll
for up to a minute, from an idle-time heartbeat. AcceptorThread and
StartDataCollection held it across RemoveDeadConnections, which joins a
writer thread that may itself be inside such a send.
RemoveDeadConnections is split in two: DetachDeadConnections unlinks them
from the pool under the mutex, which is quick, and CloseDeadConnections
tears them down afterwards with the mutex released - safe because they are
no longer reachable by anyone else. The keepalive loop copies the pool out
and sends outside the lock, the pattern EndDataCollection already used.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
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