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JEP 291: Deprecate the Concurrent Mark Sweep (CMS) Garbage Collector

Summary​

Deprecate the Concurrent Mark Sweep (CMS) garbage collector, with the intent to stop supporting it in a future major release.

Goals​

Accelerate the development of other garbage collectors in HotSpot.

Motivation​

Dropping support for CMS and then removing the CMS code, or at least more thoroughly segregating it, will reduce the maintenance burden of the GC code base and accelerate new development. The G1 garbage collector is intended, in the long term, to be a replacement for most uses of CMS.

Description​

Deprecate CMS so that a warning message is issued when it is requested on the command line, via the -XX:+UseConcMarkSweepGC option.

This JEP does not specify the major release in which support for CMS will be dropped. The decision of when to do that will be informed by the extent to which the G1 collector proves to be a suitable replacement for CMS. In the meantime, CMS users are encouraged to migrate to the G1 collector (-XX:+UseG1GC).

Testing​

Verify that the intended deprecation message is emitted when the CMS collector is requested.

Risk and Assumptions​

  • For some applications CMS is a very good fit and might always outperform G1.

  • When support of CMS is ended, CMS will not be available in new releases.