On Wed, 8 Mar 2023 18:56:55 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" >> initialization = 12:31:15.574 (2023-03-08) >> initializationTime = 172 ms >> initializationMethod = "premain" >> } >> // Dynamic load >> jdk.JavaAgent { >> startTime = 12:31:31.158 (2023-03-08) >> name = "JavaAgent.jar" >> options = "bar=baz" >> initialization = 12:31:31.037 (2023-03-08) >> initializationTime = 64,1 ms >> initializationMethod = "agentmain" >> } >> >> 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 event will also detail which initialization method was invoked by the >> JVM, "premain" for command line agents, and "agentmain" for agents loaded >> dynamically. >> >> "initialization" is the timestamp the JVM invoked the initialization method, >> and "initializationTime" is the duration of executing the initialization >> method. >> >> "startTime" represents the time the JFR framework issued the periodic event; >> hence "initialization" 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" >> path = >> "c:\ade\github\openjdk\jdk\build\windows-x86_64-server-slowdebug\jdk\bin\jdwp.dll" >> dynamic = false >> initialization = 12:31:36.142 (2023-03-08) >> initializationTime = 0,00184 ms >> } >> >> The layout of the event type is very similar to the jdk.JavaAgent event, but >> here the path to the native library is reported, and there is also a >> denotation if the agent was loaded via the command line (dynamic = false) or >> dynamically (dynamic = true). >> >> The initialization of a native agent is performed by invoking an >> agent-specified callback routine which is not detailed in the event (for >> now). The "initialization" is the time the JVM sent or would have sent the >> JVMTI VMInit event to a specified callback. "initializationTime" is the >> duration to execute that specific callback. If no callback is specified for >> the JVMTI VMInit event, the "initializationTime" will be 0. >> >> #### 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. >> >> To implement this capability, it was necessary to refactor the code used to >> represent agents, called 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 lists that maintain the agents (JVMTI) and libraries (JVMPI) >> are 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 two > additional commits since the last revision: > > - remove JVMPI > - cleanup No need to load any JFR classes. No change to startup logic. ------------- PR: https://git.openjdk.org/jdk/pull/12923
