On Thu, 30 Mar 2023 19:20:11 GMT, Markus Grönlund <mgron...@openjdk.org> wrote:
>> Greetings, >> >> We are adding support to let JFR report on Agents. >> >> #### Design >> >> An Agent is a library that uses any instrumentation or profiling APIs. Most >> agents are started and initialized on the command line, but agents can also >> be loaded dynamically during runtime. Because command line agents initialize >> during the VM startup sequence, they add to the overall startup time latency >> in getting the VM ready. The events will report on the time the agent took >> to initialize. >> >> A JavaAgent is an agent written in the Java programming language, using the >> APIs in the package >> [java.lang.instrument](https://docs.oracle.com/en/java/javase/19/docs/api/java.instrument/java/lang/instrument/package-summary.html) >> >> A JavaAgent is sometimes called a JPLIS agent, where the acronym JPLIS >> stands for Java Programming Language Instrumentation Services. >> >> To report on JavaAgents, JFR will add the new event type jdk.JavaAgent and >> events will look similar to these two examples: >> >> // Command line >> jdk.JavaAgent { >> startTime = 12:31:19.789 (2023-03-08) >> name = "JavaAgent.jar" >> options = "foo=bar" >> dynamic = false >> initializationTime = 12:31:15.574 (2023-03-08) >> initializationDuration = 172 ms >> } >> >> // Dynamic load >> jdk.JavaAgent { >> startTime = 12:31:31.158 (2023-03-08) >> name = "JavaAgent.jar" >> options = "bar=baz" >> dynamic = true >> initializationTime = 12:31:31.037 (2023-03-08) >> initializationDuration = 64,1 ms >> } >> >> The jdk.JavaAgent event type is a JFR periodic event that iterates over >> running Java agents. >> >> For a JavaAgent event, the agent's name will be the specific .jar file >> containing the instrumentation code. The options will be the specific >> options passed to the .jar file as part of launching the agent, for example, >> on the command line: -javaagent: JavaAgent.jar=foo=bar. >> >> The "dynamic" field denotes if the agent was loaded via the command line >> (dynamic = false) or dynamically (dynamic = true) >> >> "initializationTime" is the timestamp the JVM invoked the initialization >> method, and "initializationDuration" is the duration of executing the >> initialization method. >> >> "startTime" represents the time the JFR framework issued the periodic event; >> hence "initializationTime" will be earlier than "startTime". >> >> An agent can also be written in a native programming language using the [JVM >> Tools Interface >> (JVMTI)](https://docs.oracle.com/en/java/javase/19/docs/specs/jvmti.html). >> This kind of agent, sometimes called a native agent, is a platform-specific >> binary, sometimes referred to as a library, but here it means a .so or .dll >> file. >> >> To report on native agents, JFR will add the new event type jdk.NativeAgent >> and events will look similar to this example: >> >> jdk.NativeAgent { >> startTime = 12:31:40.398 (2023-03-08) >> name = "jdwp" >> options = "transport=dt_socket,server=y,address=any,onjcmd=y" >> dynamic = false >> initializationTime = 12:31:36.142 (2023-03-08) >> initializationDuration = 0,00184 ms >> path = >> "c:\ade\github\openjdk\jdk\build\windows-x86_64-server-slowdebug\jdk\bin\jdwp.dll" >> } >> >> The layout of the event type is very similar to the jdk.JavaAgent event, but >> here the path to the native library is reported. >> >> The initialization of a native agent is performed by invoking an >> agent-specified callback routine. The "initializationTime" is when the JVM >> sent or would have sent the JVMTI VMInit event to a specified callback. >> "initializationDuration" is the duration to execute that specific callback. >> If no callback is specified for the JVMTI VMInit event, the >> "initializationDuration" will be 0. If the agent is loaded dynamically, >> "initializationDuration" is the time taken to execute the Agent_OnAttach >> callback. >> >> #### Implementation >> >> There has not existed a reification of a JavaAgent directly in the JVM, as >> these are built on top of the JDK native library, "instrument", using a >> many-to-one mapping. At the level of the JVM, the only representation of >> agents after startup is through JvmtiEnv's, which agents request from the >> JVM during startup and initialization — as such, mapping which JvmtiEnv >> belongs to what JavaAgent was not possible before. >> >> Using implementation details of how the JDK native library "instrument" >> interacts with the JVM, we can build this mapping to track what JvmtiEnv's >> "belong" to what JavaAgent. This mapping now lets us report the >> Java-relevant context (name, options) and measure the time it takes for the >> JavaAgent to initialize. >> >> When implementing this capability, it was necessary to refactor the code >> used to represent agents, AgentLibrary. The previous implementation was >> located primarily in arguments.cpp, and threads.cpp but also jvmtiExport.cpp. >> >> The refactoring isolates the relevant logic into two new modules, >> prims/agent.hpp and prims/agentList.hpp. Breaking out this code from their >> older places will help reduce the sizes of oversized arguments.cpp and >> threads.cpp. >> >> The previous two lists that maintained "agents" (JVMTI) and "libraries" >> (Xrun) were not thread-safe for concurrent iterations. A single list that >> allows for concurrent iterations is therefore introduced. >> >> Testing: jdk_jfr, tier 1 - 6 >> >> Thanks >> Markus > > Markus Grönlund has updated the pull request incrementally with one > additional commit since the last revision: > > restore misssing frees src/hotspot/share/jfr/metadata/metadata.xml line 1190: > 1188: <Field type="boolean" name="dynamic" label="Dynamic" > description="If the library attached to the JVM dynamically during runtime, > i.e. not at startup" /> > 1189: <Field type="Ticks" name="initializationTime" label="Initialization > Time" description="The time the JVM initialized the agent" /> > 1190: <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, the duration of executing the call to > Agent_OnAttach." /> Nit: In the last sentence I suggest s/the duration/it is the duration/ src/hotspot/share/prims/agent.cpp line 533: > 531: if (thread->is_pending_jni_exception_check()) { > 532: thread->clear_pending_jni_exception_check(); > 533: } Unsure why we pretend the agent checked this - don't we want -Xcheck:jni to report a bug in the agent? src/hotspot/share/prims/agent.cpp line 536: > 534: } > 535: > 536: // Agent_OnAttach may have used JNI Copied from above? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/12923#discussion_r1153965163 PR Review Comment: https://git.openjdk.org/jdk/pull/12923#discussion_r1153967066 PR Review Comment: https://git.openjdk.org/jdk/pull/12923#discussion_r1153966809
