Joerg Hoh created SLING-13266:
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Summary: BundledScriptTracker can race on shutdown
Key: SLING-13266
URL: https://issues.apache.org/jira/browse/SLING-13266
Project: Sling
Issue Type: Improvement
Components: Servlets
Affects Versions: Servlets Resolver 3.0.6
Reporter: Joerg Hoh
h3. Summary
{{BundledScriptTracker.deactivate()}} is not synchronized against
{{refreshDispatcher()}}, so the two can run concurrently and both write the
shared {{dispatchers}} {{AtomicReference}}.
h3. Details
{{refreshDispatcher()}} is {{synchronized}} and reads {{dispatchers}} (with a
{{null}} check for the deactivated state), then swaps in a new map at the end.
{{deactivate()}} sets {{dispatchers}} to {{null}} but takes no lock. If
{{deactivate()}} runs after a concurrent {{refreshDispatcher()}} has passed its
null check but before its final swap, the refresh re-publishes a non-{{null}}
map after shutdown. The {{DispatcherServlet}} registrations in that map are
then leaked (never unregistered), and the refresh may also call {{register()}}
with an already-nulled {{BundleContext}}.
Shutdown-only, low severity.
h3. Fix
Make {{deactivate()}} {{synchronized}} so it cannot interleave with
{{refreshDispatcher()}}; a refresh then either completes before deactivation or
observes {{dispatchers == null}} and returns early.
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