RFR: 8257967: JFR: Events for loaded agents [v16]

[Markus Grönlund]

On Wed, 12 Apr 2023 10:31:37 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> Markus Grönlund has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   renames
>
> src/hotspot/share/prims/jvmtiAgent.cpp line 323:
> 
>> 321:   assert(agent != nullptr, "invariant");
>> 322:   if (!agent->is_loaded()) {
>> 323:     if (!load_agent_from_executable(agent, on_load_symbols, num_symbol_entries)) {
> 
> It feels like I'm missing something.
> We already checked and found at line 322 that `agent->is_loaded() == false`.
> Also, we have the comment at line 265:
> 
> 265 // If this function returns true, then agent->is_static_lib().&& agent->is_loaded().
> 266 static bool load_agent_from_executable(Agent* agent, const char* on_load_symbols[], size_t num_symbol_entries) {
> 
> As the `agent->is_loaded() == false` then t he condition `agent->is_static_lib() && agent->is_loaded()` has to be `false` and can not be `true`. Then one of the if-checks at lines 322 and 323 is not needed and can be removed. Is it right? Otherwise, the comment at line 265 can be incorrect.

Good observation, Serguei.

It is because some paths call into lookup_On_load_Entry_point() twice.

It is primarily the attempted conversion of xrun agents, the first invocation comes from JvmtiAgent::convert_xrun_agent(). This will have the agent "loaded". If there is an Agent_OnLoad function, the agent is converted (i.e. xrun removed).

Then when the agent is to invoke the Agent_OnLoad function, there is a second invocation. Here a converted xrun library is already loaded, so I bypass attempting to load it again by checking the is_loaded() property.

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PR Review Comment: https://git.openjdk.org/jdk/pull/12923#discussion_r1163954754