X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=doc%2Fjava-agent.txt;h=a7612a6873e8835134650808316df0a79127dc75;hb=464c475658ae29039b3b9e769b5b02195688a94a;hp=3fc6c4931e495fa2195fc7480c78af4d35ecea8b;hpb=3707dfc52ecb7e3419029da002dd04671cd7478a;p=lttng-ust.git diff --git a/doc/java-agent.txt b/doc/java-agent.txt index 3fc6c493..a7612a68 100644 --- a/doc/java-agent.txt +++ b/doc/java-agent.txt @@ -1,17 +1,26 @@ +====================== + Using the Java agent +====================== + The agent can be built in three different configurations: 1) Java agent with JUL support: $ ./configure --enable-java-agent-jul -2) Java agent with Log4j support: +2) Java agent with Log4j 1.x support (deprecated): $ export CLASSPATH=$CLASSPATH:/path/to/log4j.jar $ ./configure --enable-java-agent-log4j -3) Java agent with JUL + Log4j support +3) Java agent with Log4j 2.x support: -$ export CLASSPATH=$CLASSPATH:/path/to/log4j.jar +$ export CLASSPATH=$CLASSPATH:/path/to/log4j-core.jar:/path/to/log4j-api.jar +$ ./configure --enable-java-agent-log4j2 + +4) Java agent with JUL + Log4j 1.x + Log4j 2.x support + +$ export CLASSPATH=$CLASSPATH:/path/to/log4j.jar:/path/to/log4j-core.jar:/path/to/log4j-api.jar $ ./configure --enable-java-agent-all To build the agent with log4j support, make sure that the log4j jar @@ -21,29 +30,100 @@ The configure script will automatically detect the appropriate Java binaries to use in order to build the Java agent. Enabling the JUL support will build a "lttng-ust-agent-jul.jar" file. Enabling -the log4j support will build a "lttng-ust-agent-log4j.jar". Both of these jars +the log4j 1.x support will build a "lttng-ust-agent-log4j.jar" and enabling +log4j 2.x support will build a "lttng-ust-agent-log4j2.jar". All of these jars depend on a third "lttng-ust-agent-common.jar", which will always be built. All these archives will be installed in the arch-agnostic "$prefix/share/java" path, e.g: "/usr/share/java". You need to make sure the .jar for the logging -API you want to use (either lttng-ust-agent-jul.jar or -log4j.jar) is on your +API you want to use (either "lttng-ust-agent-jul.jar", +"lttng-ust-agent-log4j.jar" or "lttng-ust-agent-log4j2.jar") is on your application's classpath. -Both logging libraries also require an architecture-specific shared object -(e.g: "liblttng-ust-jul-jni.so"), which is installed by the build system when -doing "make install". Make sure that your Java application can find this shared -object with the "java.library.path" property. +The logging libraries require an architecture-specific shared object, +"liblttng-ust-jul-jni.so" for JUL and "liblttng-ust-jul-log4j.so" for both +Log4j 1.x and 2.x, which are installed by the build system when doing "make +install". Make sure that your Java application can find this shared object, by +using the "java.library.path" property if necessary. + +In order to use UST tracing in your Java application, you simply need to +instantiate a LttngLogHandler or a LttngLogAppender (for JUL or Log4j, +respectively), then attach it to a JUL or Log4j Logger class. + +Refer to the code examples in "examples/java-jul/", "examples/java-log4j/" and +"examples/java-log4j2-*/". + +LTTng session daemon agents will be initialized as needed. If no session daemon +is available, the execution will continue and the agents will retry connecting +every 3 seconds. + + +============== + Object model +============== + +The object model of the Java agent implementation is as follows: + +--------- +Ownership +--------- +Log Handlers: LttngLogHandler, LttngLogAppender + n handlers/appenders, managed by the application. + Can be created programmatically, or via a configuration file, + Each one registers to a specific agent singleton (one per logging API) that is loaded on-demand + +Agent singletons: LttngJulAgent, LttngLog4jAgent + Keep track of all handlers/appenders registered to them. + Are disposed when last handler deregisters. + Each agent instantiates 2 TCP clients, one for the root session daemon, one for the user one. + One type of TCP client class for now. TCP client may become a singleton in the future. + +------- +Control +------- +Messages come from the session daemon through the socket connection. +Agent passes back-reference to itself to the TCP clients. +Clients use this reference to invoke callbacks, which modify the state of the agent (enabling/disabling events, etc.) + +--------- +Data path +--------- +Log messages are generated by the application and sent to the Logger objects, +which then send them to the Handlers. + +When a log event is received by a Handler (publish(LogRecord)), the handler +checks with the agent if it should log it or not, via +ILttngAgent#isEventEnabled() for example. + +Events that are logged call the native tracepoint through JNI, which generates +a UST event. There is one type of tracepoint per domain (Jul or Logj4). + +----------------------- +Filtering notifications +----------------------- +FilterChangeNotifier is the singleton notifier class. +Applications implement an IFilterChangeListener, and register it to the notifier. + +Whenever new event rules are enabled or disabled, the relevant agent informs the +notifier, which then sends notifications to all registered listeners by invoking +their callbacks. + +Upon registration, a new listener will receive notifications for all currently +active rules. -In order to enable the agent in your Java application, you simply have to add -this as early as you can in the runtime process. +The notifier keeps track of its own event rule refcounting, to handle the case +of multiple sessions or multiple agents enabling identical event rules. -import org.lttng.ust.agent.LTTngAgent; -[...] - private static LTTngAgent lttngAgent; - [...] - lttngAgent = LTTngAgent.getLTTngAgent(); +The FilterChangeNotifier does not have threads of its own. The listeners's +callbacks will be invoked by these threads: +* In the case of a notification being received while a listener is already + registered, the callback is executed by the TCP client's thread. This + effectively blocks the "lttng" command line until all callbacks are processed + (assuming no timeouts). +* In the case of a listener registering and receiving the currently-active + rules, the callbacks will be executed by the application's thread doing the + registerListener() call. -This will initialize automatically the singleton LTTngAgent, and will -return when the session daemon registration is done. If no session daemon is -available, the execution will continue and the agent will retry every -3 seconds. +The notifier is entirely synchronized. This ensure that if a rule is enabled +at the same time a listener is registered, that listener does not miss or +receive duplicate notifications.