上两篇中梳理了整个java启动过程中，jvm大致是如何运行的。即厘清了我们认为的jvm的启动过程。但那里面仅为一些大致的东西，比如参数解析，验证，dll加载等等。把最核心的loadJavaVM()交给了一个dll或者so库。也就是真正的jvm我们并没有接触到，我们仅看了一个包装者或者是上层应用的实现。即我们仅是在jdk的角度看了下虚拟机，这需要更深入一点。
1. 回顾jvm加载框架
虽然jvm的加载核心并不在jdk中，但它确实没有自己的简易入口。也就是说jvm想要启动，还得依靠jdk. 所以，让我们回顾下jdk是如何带动jvm的？
1.1. java启动框架自然是在 JLI_Launch 的入口查看了。
// share/bin/java.c /* * Entry point. */ int JLI_Launch(int argc, char ** argv, /* main argc, argc */ int jargc, const char** jargv, /* java args */ int appclassc, const char** appclassv, /* app classpath */ const char* fullversion, /* full version defined */ const char* dotversion, /* dot version defined */ const char* pname, /* program name */ const char* lname, /* launcher name */ jboolean javaargs, /* JAVA_ARGS */ jboolean cpwildcard, /* classpath wildcard*/ jboolean javaw, /* windows-only javaw */ jint ergo /* ergonomics class policy */ ) { int mode = LM_UNKNOWN; char *what = NULL; char *cpath = 0; char *main_class = NULL; int ret; InvocationFunctions ifn; jlong start, end; char jvmpath[MAXPATHLEN]; char jrepath[MAXPATHLEN]; char jvmcfg[MAXPATHLEN]; _fVersion = fullversion; _dVersion = dotversion; _launcher_name = lname; _program_name = pname; _is_java_args = javaargs; _wc_enabled = cpwildcard; _ergo_policy = ergo; // 初始化启动器 InitLauncher(javaw); // 打印状态 DumpState(); // 跟踪调用启动 if (JLI_IsTraceLauncher()) { int i; printf("Command line args:\n"); for (i = 0; i < argc ; i++) { printf("argv[%d] = %s\n", i, argv[i]); } AddOption("-Dsun.java.launcher.diag=true", NULL); } /* * Make sure the specified version of the JRE is running. * * There are three things to note about the SelectVersion() routine: * 1) If the version running isn't correct, this routine doesn't * return (either the correct version has been exec'd or an error * was issued). * 2) Argc and Argv in this scope are *not* altered by this routine. * It is the responsibility of subsequent code to ignore the * arguments handled by this routine. * 3) As a side-effect, the variable "main_class" is guaranteed to * be set (if it should ever be set). This isn't exactly the * poster child for structured programming, but it is a small * price to pay for not processing a jar file operand twice. * (Note: This side effect has been disabled. See comment on * bugid 5030265 below.) */ // 解析命令行参数，选择一jre版本 SelectVersion(argc, argv, &main_class); CreateExecutionEnvironment(&argc, &argv, jrepath, sizeof(jrepath), jvmpath, sizeof(jvmpath), jvmcfg, sizeof(jvmcfg)); if (!IsJavaArgs()) { // 设置一些特殊的环境变量 SetJvmEnvironment(argc,argv); } ifn.CreateJavaVM = 0; ifn.GetDefaultJavaVMInitArgs = 0; if (JLI_IsTraceLauncher()) { start = CounterGet(); } // 加载VM, 重中之重 if (!LoadJavaVM(jvmpath, &ifn)) { return(6); } if (JLI_IsTraceLauncher()) { end = CounterGet(); } JLI_TraceLauncher("%ld micro seconds to LoadJavaVM\n", (long)(jint)Counter2Micros(end-start)); ++argv; --argc; // 解析更多参数信息 if (IsJavaArgs()) { /* Preprocess wrapper arguments */ TranslateApplicationArgs(jargc, jargv, &argc, &argv); if (!AddApplicationOptions(appclassc, appclassv)) { return(1); } } else { /* Set default CLASSPATH */ cpath = getenv("CLASSPATH"); if (cpath == NULL) { cpath = "."; } SetClassPath(cpath); } /* Parse command line options; if the return value of * ParseArguments is false, the program should exit. */ // 解析参数 if (!ParseArguments(&argc, &argv, &mode, &what, &ret, jrepath)) { return(ret); } /* Override class path if -jar flag was specified */ if (mode == LM_JAR) { SetClassPath(what); /* Override class path */ } /* set the -Dsun.java.command pseudo property */ SetJavaCommandLineProp(what, argc, argv); /* Set the -Dsun.java.launcher pseudo property */ SetJavaLauncherProp(); /* set the -Dsun.java.launcher.* platform properties */ SetJavaLauncherPlatformProps(); // 进行jvm初始化操作，一般是新开一个线程，然后调用 JavaMain() 实现java代码的权力交接 return JVMInit(&ifn, threadStackSize, argc, argv, mode, what, ret); }