RFR: 8340826: Should not send unload notification for scratch classes [v2]
Leonid Mesnik
lmesnik at openjdk.org
Thu Sep 26 18:23:48 UTC 2024
> The jvmti class redefinition creates temporary scratch classes for it's own purposes. These classes are added to corresponding classloaders and might be unloaded.
> In this case the jvmti/jfr and log events are generated twice: for original class and for it's scratch.
>
> The bug could be reproduced by jfr test
> jdk/jfr/api/metadata/eventtype/TestUnloadingEventClass.java
> with '-Xcomp -XX:TieredStopAtLevel=1' or with '-Xcomp'
>
> The test log (modified slightly) shown
>
>
> [167.294s][info ][class,unload] unloading class jdk.jfr.api.metadata.eventtype.TestUnloadingEventClass$ToBeUnloaded 0x00000000af1006d8 allocated
> [167.294s][info ][class,unload] unloading class jdk.jfr.api.metadata.eventtype.TestUnloadingEventClass$ToBeUnloaded 0x00000000af100248 fully_initialized
> [167.345s][trace][class,unload] unlinking class (subclass): jdk.jfr.api.metadata.eventtype.TestUnloadingEventClass$ToBeUnloaded
> [167.872s][trace][gc ] GC(0) Restored 3597 marks, occupying 57552 B
> [167.924s][info ][gc ] GC(0) Pause Full (System.gc()) 34M->2M(136M) 691.041ms
> Unloaded count: 2
>
>
> instead of expected
>
>
>
> [159.737s][info ][class,unload] unloading class jdk.jfr.api.metadata.eventtype.TestUnloadingEventClass$ToBeUnloaded 0x0000000041100248 state: fully_initialized
> [159.800s][trace][class,unload] unlinking class (subclass): jdk.jfr.api.metadata.eventtype.TestUnloadingEventClass$ToBeUnloaded
> [160.341s][trace][gc ] GC(0) Restored 3597 marks, occupying 57552 B
> [160.384s][info ][gc ] GC(0) Pause Full (System.gc()) 34M->2M(136M) 710.422ms
>
>
>
> The test hang because got 2 events while waiting for one.
> The "allocated" version is the scratch class generated by JVMTI JFR agent that redefine classes.
>
> The fix is to don't send notification for scratch classes. The scratch classes shouldn't have dependency so added assertion. Also, we don't expect any other not loaded classes during unloaded.
>
> Thanks Coleen for details about scratch classed.
>
> Tested with tier1-5 and with :jdk_jfr with Xcomp and c1.
Leonid Mesnik has updated the pull request incrementally with one additional commit since the last revision:
space added
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/21166/files
- new: https://git.openjdk.org/jdk/pull/21166/files/e3a0b81f..86207f2e
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=21166&range=01
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=21166&range=00-01
Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
Patch: https://git.openjdk.org/jdk/pull/21166.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/21166/head:pull/21166
PR: https://git.openjdk.org/jdk/pull/21166
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