RFR: 8367475: Incorrect lock usage in LambdaFormInvokers::regenerate_holder_classes

[David Holmes]

On Thu, 11 Sep 2025 17:22:20 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> The assert happens because we attempt to allocate Java objects while holding a mutex:
> 
> 
>     MutexLocker ml(Thread::current(), LambdaFormInvokers_lock);
>     list_lines = oopFactory::new_objArray_handle(vmClasses::String_klass(), len, CHECK);
>     for (int i = 0; i < len; i++) {
>       Handle h_line = java_lang_String::create_from_str(_lambdaform_lines->at(i), CHECK);
> 
> 
> It's possible for the allocations to trigger a call to Java when JVMTI is enabled.
> 
> The fix is to do the allocation outside of the mutex. However, we still use the mutex to make sure we have a consistent view of `_lambdaform_lines`, which may be modified by concurrent Java threads.

Seems reasonable. Thanks

Note that if you ever call a function with CHECK inside a mutex-locker scope you are potentially going to break the locking rule.

src/hotspot/share/cds/cdsConfig.cpp line 870:

> 868: bool CDSConfig::current_thread_is_dumper() {
> 869:   Thread* t = Thread::current();
> 870:   return t != nullptr && t == _dumper_thread;

Do you really need the null check here? How could an unattached thread be executing this?

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27231#pullrequestreview-3214398458
PR Review Comment: https://git.openjdk.org/jdk/pull/27231#discussion_r2342796930