《jdk8u源码分析》16.2.ContinueInNewThread

src/share/bin/java.c::ContinueInNewThread

int
ContinueInNewThread(InvocationFunctions* ifn, jlong threadStackSize,
                    int argc, char **argv,
                    int mode, char *what, int ret)
{

    /*
     * If user doesn't specify stack size, check if VM has a preference.
     * Note that HotSpot no longer supports JNI_VERSION_1_1 but it will
     * return its default stack size through the init args structure.
     */
    //如果用户未配置threadStackSize，获取默认值
    if (threadStackSize == 0) {
      struct JDK1_1InitArgs args1_1;
      memset((void*)&args1_1, 0, sizeof(args1_1));
      //#define JNI_VERSION_1_1 0x00010001
      args1_1.version = JNI_VERSION_1_1;
      ifn->GetDefaultJavaVMInitArgs(&args1_1);  /* ignore return value */
      if (args1_1.javaStackSize > 0) {
         threadStackSize = args1_1.javaStackSize;
      }
    }

    { /* Create a new thread to create JVM and invoke main method */
      JavaMainArgs args;
      int rslt;

      args.argc = argc;
      args.argv = argv;
      args.mode = mode;
      args.what = what;
      args.ifn = *ifn;
	  
	  //创建新线程执行main方法
      rslt = ContinueInNewThread0(JavaMain, threadStackSize, (void*)&args);
      /* If the caller has deemed there is an error we
       * simply return that, otherwise we return the value of
       * the callee
       */
      return (ret != 0) ? ret : rslt;
    }
}

src/share/javavm/export/jvm.h::JDK1_1InitArgs

/*
 * This structure is used by the launcher to get the default thread
 * stack size from the VM using JNI_GetDefaultJavaVMInitArgs() with a
 * version of 1.1.  As it is not supported otherwise, it has been removed
 * from jni.h
 */
typedef struct JDK1_1InitArgs {
    jint version;

    char **properties;
    jint checkSource;
    jint nativeStackSize;
    jint javaStackSize;
    jint minHeapSize;
    jint maxHeapSize;
    jint verifyMode;
    char *classpath;

    jint (JNICALL *vfprintf)(FILE *fp, const char *format, va_list args);
    void (JNICALL *exit)(jint code);
    void (JNICALL *abort)(void);

    jint enableClassGC;
    jint enableVerboseGC;
    jint disableAsyncGC;
    jint verbose;
    jboolean debugging;
    jint debugPort;
} JDK1_1InitArgs;

src/share/javavm/export/jni.h::JNI_VERSION_1_[1~8]

#define JNI_VERSION_1_1 0x00010001
#define JNI_VERSION_1_2 0x00010002
#define JNI_VERSION_1_4 0x00010004
#define JNI_VERSION_1_6 0x00010006
#define JNI_VERSION_1_8 0x00010008

src/share/bin/java.c::JavaMain

int JNICALL
JavaMain(void * _args)
{
    JavaMainArgs *args = (JavaMainArgs *)_args;
    int argc = args->argc;
    char **argv = args->argv;
    int mode = args->mode;
    char *what = args->what;
    InvocationFunctions ifn = args->ifn;

    JavaVM *vm = 0;
    JNIEnv *env = 0;
    jclass mainClass = NULL;
    jclass appClass = NULL; // actual application class being launched
    jmethodID mainID;
    jobjectArray mainArgs;
    int ret = 0;
    jlong start, end;

    RegisterThread();

    /* Initialize the virtual machine */
    start = CounterGet();
    //创建jvm
    if (!InitializeJVM(&vm, &env, &ifn)) {
    	//"Error: Could not create the Java Virtual Machine.\n" GEN_ERROR
        JLI_ReportErrorMessage(JVM_ERROR1);
        exit(1);
    }

	//根据指定类别打印设置信息
	//-XshowSettings:category[all | locale | properties | vm]
    if (showSettings != NULL) {
        ShowSettings(env, showSettings);
        CHECK_EXCEPTION_LEAVE(1);
    }

	//printVersion: -version //退出程序
	//showVersion: -showversion
    if (printVersion || showVersion) {
    	//输出版本信息，与java -version输出一致
        PrintJavaVersion(env, showVersion);
        CHECK_EXCEPTION_LEAVE(0);
        if (printVersion) {
            LEAVE();
        }
    }

	//printXUsage: -X //打印所有可用的 -X 选项
	//printUsage: -help | -h | -?
    /* If the user specified neither a class name nor a JAR file */
    if (printXUsage || printUsage || what == 0 || mode == LM_UNKNOWN) {
    	//输出可选项用例信息，与java -help输出一致
        PrintUsage(env, printXUsage);
        CHECK_EXCEPTION_LEAVE(1);
        LEAVE();
    }

	//释放读取自 jvm.cfg 的信息
    FreeKnownVMs();  /* after last possible PrintUsage() */

    if (JLI_IsTraceLauncher()) {
        end = CounterGet();
        JLI_TraceLauncher("%ld micro seconds to InitializeJVM\n",
               (long)(jint)Counter2Micros(end-start));
    }

    /* At this stage, argc/argv have the application's arguments */
    if (JLI_IsTraceLauncher()){
        int i;
        //Main class is 'com.johnjoe.study.Test'
        //App's argc is 1
  		//    argv[ 0] = '123456'
        printf("%s is '%s'\n", launchModeNames[mode], what);
        printf("App's argc is %d\n", argc);
        for (i=0; i < argc; i++) {
            printf("    argv[%2d] = '%s'\n", i, argv[i]);
        }
    }

    ret = 1;

    /*
     * Get the application's main class.
     *
     * See bugid 5030265.  The Main-Class name has already been parsed
     * from the manifest, but not parsed properly for UTF-8 support.
     * Hence the code here ignores the value previously extracted and
     * uses the pre-existing code to reextract the value.  This is
     * possibly an end of release cycle expedient.  However, it has
     * also been discovered that passing some character sets through
     * the environment has "strange" behavior on some variants of
     * Windows.  Hence, maybe the manifest parsing code local to the
     * launcher should never be enhanced.
     *
     * Hence, future work should either:
     *     1)   Correct the local parsing code and verify that the
     *          Main-Class attribute gets properly passed through
     *          all environments,
     *     2)   Remove the vestages of maintaining main_class through
     *          the environment (and remove these comments).
     *
     * This method also correctly handles launching existing JavaFX
     * applications that may or may not have a Main-Class manifest entry.
     */
    //加载校验主类，并尝试转换初始化字符串：([Ljava/lang/String;)V
    mainClass = LoadMainClass(env, mode, what);
    CHECK_EXCEPTION_NULL_LEAVE(mainClass);
    /*
     * In some cases when launching an application that needs a helper, e.g., a
     * JavaFX application with no main method, the mainClass will not be the
     * applications own main class but rather a helper class. To keep things
     * consistent in the UI we need to track and report the application main class.
     */
    //获取 LoadMainClass 中生成的主类Class对象
    appClass = GetApplicationClass(env);
    NULL_CHECK_RETURN_VALUE(appClass, -1);
    /*
     * PostJVMInit uses the class name as the application name for GUI purposes,
     * for example, on OSX this sets the application name in the menu bar for
     * both SWT and JavaFX. So we'll pass the actual application class here
     * instead of mainClass as that may be a launcher or helper class instead
     * of the application class.
     */
    //仅在MAC系统中增加环境变量：JAVA_MAIN_CLASS_${PID}=mainClass的getCanonicalName
    PostJVMInit(env, appClass, vm);
    /*
     * The LoadMainClass not only loads the main class, it will also ensure
     * that the main method's signature is correct, therefore further checking
     * is not required. The main method is invoked here so that extraneous java
     * stacks are not in the application stack trace.
     */
    mainID = (*env)->GetStaticMethodID(env, mainClass, "main",
                                       "([Ljava/lang/String;)V");
    CHECK_EXCEPTION_NULL_LEAVE(mainID);

	//转换参数
    /* Build platform specific argument array */
    mainArgs = CreateApplicationArgs(env, argv, argc);
    CHECK_EXCEPTION_NULL_LEAVE(mainArgs);

    //调用主类main方法
    /* Invoke main method. */
    (*env)->CallStaticVoidMethod(env, mainClass, mainID, mainArgs);

    /*
     * The launcher's exit code (in the absence of calls to
     * System.exit) will be non-zero if main threw an exception.
     */
    //系统退出：0-正常，1-异常
    ret = (*env)->ExceptionOccurred(env) == NULL ? 0 : 1;
    LEAVE();
}

src/share/bin/java.h::JavaMainArgs

typedef struct {
    int    argc;
    char **argv;
    int    mode;
    char  *what;
    InvocationFunctions ifn;
} JavaMainArgs;

src/share/javavm/export/jni.h

struct JNIInvokeInterface_ {
    void *reserved0;
    void *reserved1;
    void *reserved2;

    jint (JNICALL *DestroyJavaVM)(JavaVM *vm);

    jint (JNICALL *AttachCurrentThread)(JavaVM *vm, void **penv, void *args);

    jint (JNICALL *DetachCurrentThread)(JavaVM *vm);

    jint (JNICALL *GetEnv)(JavaVM *vm, void **penv, jint version);

    jint (JNICALL *AttachCurrentThreadAsDaemon)(JavaVM *vm, void **penv, void *args);
};

struct JavaVM_ {
    const struct JNIInvokeInterface_ *functions;
#ifdef __cplusplus

    jint DestroyJavaVM() {
        return functions->DestroyJavaVM(this);
    }
    jint AttachCurrentThread(void **penv, void *args) {
        return functions->AttachCurrentThread(this, penv, args);
    }
    jint DetachCurrentThread() {
        return functions->DetachCurrentThread(this);
    }

    jint GetEnv(void **penv, jint version) {
        return functions->GetEnv(this, penv, version);
    }
    jint AttachCurrentThreadAsDaemon(void **penv, void *args) {
        return functions->AttachCurrentThreadAsDaemon(this, penv, args);
    }
#endif
};

#ifdef __cplusplus
typedef JavaVM_ JavaVM;
#else
typedef const struct JNIInvokeInterface_ *JavaVM;
#endif