RFR: 8259067: bootclasspath append takes out object lock [v2]

[Coleen Phillimore]

On Tue, 5 Jan 2021 21:10:45 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> Thanks Serguei.  Ioi convinced me offline to simplify and just use a mutex, so I updated the patch to do that.  I tested with jdi and jvmti tests and will rerun tier1-3.
>
> Coleen, the function `ClassLoader::add_to_boot_append_entries` is also called from `ClassLoader::update_class_path_entry_list` and `ClassLoaderExt::append_boot_classpath`. It is not clear why the `Bootclasspath_lock` is not used for sync in these contexts. Could you consider to move this `MutexLocker` from `JvmtiEnv::AddToBootstrapClassLoaderSearch` to `ClassLoader::add_to_boot_append_entries`?

Thanks Serguei.  I was trying to decide whether to move the lock there or add an assert that we are not multi-threaded when the lock isn't held.  But it's cleaner to just move the lock there, so I'll do that.

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PR: https://git.openjdk.java.net/jdk/pull/1935