Could the JIT be started before JVMTI agents are loaded?

[Alan Bateman]

Volker Simonis wrote:
> Hi,
>
> we currently have some problems with long startup times due to JVMTI
> agents loaded with -javaagent. While investigating the problem we
> realized that the JIT compiler is only started AFTER the agent was
> loaded and initialized and therefore the whole agent initialization
> takes place in interpreted mode. Here is the corresponding code from
> thread.cpp:
>
>      3137   // Notify JVMTI agents that VM initialization is complete
> - nop if no agents.
>      3138   JvmtiExport::post_vm_initialized();
>      3139
>      3140   Chunk::start_chunk_pool_cleaner_task();
>      3141
>      3142   // initialize compiler(s)
>      3143   CompileBroker::compilation_init();
>
> Is there any particualr reason that the JIT gets initialized only
> after the agent initialization or could it be done just as well
> before? A short test where we placed
> "CompileBroker::compilation_init()" just before
> "JvmtiExport::post_vm_initialized()" succeeded with a considerable
> startup speedup, but we are not sure if this change would be valid in
> general.
>   
I agree it would be desirable to have the compiler enabled before the 
agent's premain is invoked. I haven't worked in this area for some time, 
and don't recall the reasoning for the ordering. One possible side 
effort is when you have multiple agents, say a java agent and native 
agent that enables CompieldMethodLoad. Depending on the ordering that 
they are initiated then the native agent might get compilation events 
before its VMInit is called (assuming the event is enabled early). I'm 
not saying this is a problem, just something to check into.

Robert, Dan - do you recall the reason for the ordering? (carried over 
from JVMDI perhaps?).

-Alan.