Close oldest unactivated session at the session limit#1760
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kevinherron merged 1 commit intoJun 2, 2026
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When MaxSessions was reached, SessionManager.createSession always threw Bad_TooManySessions. OPC UA Part 4, 5.7.2 requires that the server shall close the oldest Session that has not yet been activated before rejecting a new request, returning Bad_TooManySessions only when every existing Session has already been activated. Evict the oldest unactivated session (by connection time) instead. The limit check, eviction, and registration now run under a single lock and after request validation, so concurrent CreateSession requests cannot exceed MaxSessions and a request that later fails validation never evicts another client's pending session. ActivateSession's created-to-active move takes the same lock and rejects a session evicted mid-activation. Fixes eclipse-milo#1759 Signed-off-by: Jooyoung Jung <livinglikekrillin@gmail.com>
kevinherron
approved these changes
Jun 2, 2026
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Summary
When the session limit (
MaxSessions) was reached,SessionManager.createSessionalways returned
Bad_TooManySessions. OPC UA Part 4, §5.7.2 requires that theserver shall close the oldest Session that has not yet been activated before
rejecting a new request, and return
Bad_TooManySessionsonly when every existingSession has already been activated.
This was raised in #1759 (from Discussion #1582), where the maintainer confirmed
no work was in progress and welcomed a PR.
Changes
instead of unconditionally throwing
Bad_TooManySessions.request validation, so concurrent
CreateSessionrequests cannot exceedMaxSessions, and a request that later fails validation never evicts anotherclient's pending session.
ActivateSession's created→active move takes the same lock and rejects a sessionthat was evicted mid-activation (
Bad_SessionIdInvalid).Tests
SessionEvictionTest: evicts the oldest unactivated session; still returnsBad_TooManySessionswhen all sessions are activated; never exceeds the limitunder a concurrent
CreateSessionburst.TestServer.create(OpcUaServerConfigLimits)overload to setMaxSessions.Fixes #1759
Developed with AI assistance (Anthropic Claude Opus 4.8); the human contributor
reviewed, verified, and tested all changes.