Follow up on [JDK-7018422] - JavaAgent code always interpreted during initialization phase

[David Holmes]

Hi,

On 28/01/2021 10:51 am, Nhat Nguyen wrote:
> Hi,
> 
> I'm writing this email to follow up on JDK-7018422 [1] on jdk8u, where the JavaAgent code
> is always interpreted during the initialization phase on jdk8.

Just FYI for changes to 8u you need to raise the issue on 
jdk8u-dev at openjdk.java.net.

> For background, one of our tools is currently making use of a JavaAgent whose performance
> is important. As part of a performance investigation, I discovered that the CompilerBroker is
> not initialized by the time the premain method runs, therefore all compilation requests for
> the JavaAgent are discarded.
> 
> Fortunately, I found JDK-7018422 which describes the exact issue that we are experiencing.
> However, the ticket was closed as "Not an issue" because the initialization order is changed
> with the introduction of the module system.
> 
> So I would like to ask the mailing list for opinions on whether a fix for this issue can be
> considered for jdk8u. I have also attached a prototype fix [2] and would appreciate any
> suggestions and comments as well.

You have to be extremely careful changing the initialization order as 
there are many hidden inter-dependencies.

And as Serguei stated, that change may potentially allow JIT'ing to be 
possible, but that doesn't mean it will actually occur.

Cheers,
David
-----

> 
> [1]: https://bugs.openjdk.java.net/browse/JDK-7018422
> [2]:
> 
> ---
>   hotspot/src/share/vm/runtime/thread.cpp | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/hotspot/src/share/vm/runtime/thread.cpp b/hotspot/src/share/vm/runtime/thread.cpp
> index 330593acb3..3918f989cc 100644
> --- a/hotspot/src/share/vm/runtime/thread.cpp
> +++ b/hotspot/src/share/vm/runtime/thread.cpp
> @@ -3634,11 +3634,6 @@ jint Threads::create_vm(JavaVMInitArgs* args, bool* canTryAgain) {
>       create_vm_init_libraries();
>     }
>   
> -  // Notify JVMTI agents that VM initialization is complete - nop if no agents.
> -  JvmtiExport::post_vm_initialized();
> -
> -  JFR_ONLY(Jfr::on_vm_start();)
> -
>     if (CleanChunkPoolAsync) {
>       Chunk::start_chunk_pool_cleaner_task();
>     }
> @@ -3648,6 +3643,11 @@ jint Threads::create_vm(JavaVMInitArgs* args, bool* canTryAgain) {
>     CompileBroker::compilation_init();
>   #endif
>   
> +  // Notify JVMTI agents that VM initialization is complete - nop if no agents.
> +  JvmtiExport::post_vm_initialized();
> +
> +  JFR_ONLY(Jfr::on_vm_start();)
> +
>     if (EnableInvokeDynamic) {
>       // Pre-initialize some JSR292 core classes to avoid deadlock during class loading.
>       // It is done after compilers are initialized, because otherwise compilations of
> --
>