Java虚拟机分析与优化 - Read.ppt

Java虚拟机分析与优化 Overview JVM Basics Overview of JVM/J9 and SUN/HP Memory Management / Garbage Collection Runtime Performance Tuning Debugging Tools JVM BasicsHighest Level Overview Java is a Write Once Run Anywhere (WORA) 3rd generation Object Oriented programming language that is executed on a virtual machine The Java Virtual Machine (JVM) runs applications written in Java after the Java code has been compiled to bytecode via the javac process. The JVM in conjunction with other components performs optimization on your compiled Java code to attempt to make it as fast as native code The JVM performs automatic memory management (Garbage Collection) to ensure that system wide memory leaks do not occur and to allow for easier development by allowing developers not to explicitly have to perform memory management. There are multiple implementations of the JVM which all “should” execute any application written for the Java specification level that JVM was developed for. JVM BasicsWhich JVM do I have? The different platforms that WebSphere Application Server runs on have different JVM implementations in some cases The IBM J9 JVM is the runtime environment on the following Operating Systems or Platforms AIX, Windows, Linux (x86), Linux (PPC), iSeries, zSeries The Sun JVM is the runtime environment on all platforms running the Solaris Operating System The HP JVM (which is a very simple Sun JVM port) is the runtime environment on all platforms running the HP-UX Operating System JVM BasicsThe Overall Java Application Stack JVM is built using OO design. Building Block components providing higher level function for simplified end user development and runtime JVM’s core runtimes are developed in C or C++ and execute a large majority of function in native code Garbage collector, MMU, JIT, etc IO subroutines, OS calls The J2SE/J2EE APIs all exist at the Java Code layer. Makes data structures available Gives users access to needed function Allow black box interacti