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JDK 11 updates will be delivered in a quarterly cylecycle. Usually releases happen mid of January, April, July and October.
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Fixes to the OpenJDK must generally be done in the upstream development repository jdk/jdk first. As a matter of fact, changes to JDK11 JDK 11 updates will mostly be backports of issues from upstream. There are exceptions when there's the need for a fix that only applies to JDK 11 updates.
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Should you not be willing or not be able to drive a fix into OpenJDK JDK 11 updates, you can still suggest changes by dropping a mail to the jdk-updates-dev mailing list. But by only doing that, you are at the grace of the community to pick up your suggestion.
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When a JDK 11 update release is in ramp down (that is, it was brought to jdk11u already), push approval can still be requested using the jdk11u-critical-request label. However, the maintainers will only consider fixes that Oracle have brought to their correspondent JDK11 corresponding JDK 11 update release, fixes for high priority issues or important test fixes at this point. The maintainers may approve with jdk11u-critical-yes, defer to jdk11u-dev or reject. Outstanding approvals for critical fixes can be monitored here. If and only if the fix gets approved with jdk11u-critical-yes, it may be pushed to the jdk11u repository. If a bug shows up in this JBS filter (login required) it is allowed for being pushed to jdk11u.
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