On Tue, 1 Dec 2020 14:19:15 GMT, Coleen Phillimore <cole...@openjdk.org> wrote:
>> The JvmtiTagMap can be deleted while it is posting. The JvmtiEnv is still >> on the list but the env is "disposed" of and the tag_map is deleted to save >> memory until the JvmtiEnv can be reclaimed at a safepoint and taken off the >> list. >> >> There's a check JvmtiEnvBase::check_for_periodic_clean_up() that determines >> whether the JvmtiEnv can be taken off the list and that check looks for >> whether threads are in the middle of JvmtiEnvIterator which sets >> Thread::jvmti_env_iteration_count. So this part is safe for the JvmtiTagMap >> changes. >> >> The fix is to clear the JvmtiTagMapTable of the entries inside the table >> lock to save memory but leave JvmtiTagMap intact so that we can load a valid >> pointer when iterating through JvmtiEnvIterator. We could also not do this >> at all and let the JvmtiTagMap destructor delete the table when the JvmtiEnv >> is also deleted, but we don't know what customer situation led to this code >> in the first place. > > Coleen Phillimore has updated the pull request with a new target base due to > a merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains three additional > commits since the last revision: > > - Merge branch 'master' into more-jvmti-table > - Rename JvmtiTagMap::clear() and fix JvmtiTagMapTable::clear() to null out > deleted entries. > - 8257140: Crash in JvmtiTagMap::flush_object_free_events() Hi Coleen, The JVMTI environment can be disposed with DisposeEnvironment: https://docs.oracle.com/en/java/javase/15/docs/specs/jvmti.html#DisposeEnvironment It seems to me that this operation is better to wait until posting is finished. Otherwise, the information is going to be lost in the report. Of course, we could blame the agent to call the DisposeEnvironment too early but then the agent needs a way to check if posting is finished. Thanks, Serguei ------------- PR: https://git.openjdk.java.net/jdk/pull/1539
