On Fri, 14 Apr 2023 22:22:13 GMT, Serguei Spitsyn <sspit...@openjdk.org> wrote:
>> Ok. the terminology here might be confusing. The concept of an agent being >> "initialized" is introduced and reported by JFR. For example, here is the >> JFR event type definition for a NativeAgent: >> ``` >> <Event name="NativeAgent" category="Java Virtual Machine, Diagnostics" >> label="Native Agent" description="A native programming language agent making >> use of the JVMTI interface used by development, profiling and monitoring >> tools" >> thread="false" startTime="false" period="endChunk" stackTrace="false"> >> <Field type="string" name="name" label="Name" /> >> <Field type="string" name="options" label="Options" /> >> <Field type="boolean" name="dynamic" label="Dynamic" description="If the >> library attached to the JVM dynamically during runtime, i.e. not at startup" >> /> >> <Field type="Ticks" name="initializationTime" label="Initialization >> Time" description="The time the JVM initialized the agent" /> >> <Field type="Tickspan" name="initializationDuration" >> label="Initialization Duration" description="The duration of executing the >> JVMTI VMInit event callback. If no VMInit callback is specified, the >> duration is 0. For a dynamically loaded agent, it is the duration of >> executing the call to Agent_OnAttach." /> >> <Field type="string" name="path" label="Path" description="The path of >> the library" /> >> </Event> >> >> As you can see, there are two fields: initializationTime and >> IntializationDuration. >> >> We report these to let users understand when an agent was initialized >> (VMInit or Agent_OnAttach), together with the duration it took to execute >> either. For JavaAgents, it measures the invocation and duration of the >> premain or agentmain methods. >> >> "Initialized" does not mean "loaded" (at this point, all agents are loaded), >> but rather it means the agent has received a timestamp set as a function of >> VMInit. This timestamp and duration are what we will report in JFR as part >> of the event. >> >> An "uninitialized" agent is an agent who has not yet been timestamped, as >> part of VMInit, for example. Since an agent can create multiple JvmtiEnvs, >> the function is called lookup_uninitialized_agent() because we can only have >> a single timestamp for an agent, but it can, in turn, have multiple >> JvmtiEnvs. When looking up an agent again, using a second JvmtiEnv created >> by it, the agent is already "initialized", so no agent is returned. >> >> We cannot have the timestamping logic as part of the call out to >> Agent_OnLoad, because that call happens very early during VM bootstrap, so >> the Ticks support structures are not yet in place. But, timing the >> Agent_OnLoad call would be rather meaningless because the agent cannot do >> much except construct a JvmtiEnv and setting capabilities and callbacks. >> >> VMInit is where most of the invocation logic, at least for JavaAgents >> happens, so the measurements are placed there. > > Thank you for explaining it. > Could you, please, add small comment explaining that it is for JFR purposes? Will do. Thank you, Serguei. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/12923#discussion_r1168407443
