《jdk8u源码分析》16.2.3.ShowSettings

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

/*
 * Prints all the Java settings, see the java implementation for more details.
 */
static void
ShowSettings(JNIEnv *env, char *optString)
{
    jmethodID showSettingsID;
    jstring joptString;
    //获取sun.launcher.LauncherHelper
    jclass cls = GetLauncherHelperClass(env);
    NULL_CHECK(cls);
    //调用LauncherHelper.showSettings静态方法：
    //e.g.: -XshowSettings:vm
    //VM settings:
    //	Max. Heap Size (Estimated): 7.08G
    //	Ergonomics Machine Class: client
    //	Using VM: Java HotSpot(TM) 64-Bit Server VM
    NULL_CHECK(showSettingsID = (*env)->GetStaticMethodID(env, cls,
            "showSettings", "(ZLjava/lang/String;JJJZ)V"));
    joptString = (*env)->NewStringUTF(env, optString);
    (*env)->CallStaticVoidMethod(env, cls, showSettingsID,
                                 USE_STDERR,//USE_STDERR ? System.err : System.out;
                                 joptString,//-XshowSettings:vm
                                 (jlong)initialHeapSize,
                                 (jlong)maxHeapSize,
                                 (jlong)threadStackSize,
                                 ServerClassMachine());
}

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

jclass
GetLauncherHelperClass(JNIEnv *env)
{
    if (helperClass == NULL) {
        NULL_CHECK0(helperClass = FindBootStrapClass(env,
                "sun/launcher/LauncherHelper"));
    }
    return helperClass;
}

src/solaris/bin/java_md_common.c::FindBootStrapClass

/*
 * The implementation for finding classes from the bootstrap
 * class loader, refer to java.h
 */
static FindClassFromBootLoader_t *findBootClass = NULL;

jclass
FindBootStrapClass(JNIEnv *env, const char* classname)
{
   if (findBootClass == NULL) {
       findBootClass = (FindClassFromBootLoader_t *)dlsym(RTLD_DEFAULT,
          "JVM_FindClassFromBootLoader");
       if (findBootClass == NULL) {
       	   //"Error: loading: %s"
           JLI_ReportErrorMessage(DLL_ERROR4,
               "JVM_FindClassFromBootLoader");
           return NULL;
       }
   }
   return findBootClass(env, classname);
}

src/windows/bin/java_md.c::FindBootStrapClass

/*
 * The implementation for finding classes from the bootstrap
 * class loader, refer to java.h
 */
static FindClassFromBootLoader_t *findBootClass = NULL;

jclass FindBootStrapClass(JNIEnv *env, const char *classname)
{
   HMODULE hJvm;

   //如果findBootClass为null重新加载jvm.dll
   if (findBootClass == NULL) {
       hJvm = GetModuleHandle(JVM_DLL);
       if (hJvm == NULL) return NULL;
       /* need to use the demangled entry point */
       findBootClass = (FindClassFromBootLoader_t *)GetProcAddress(hJvm,
            "JVM_FindClassFromBootLoader");
       if (findBootClass == NULL) {
       	  //"Error: loading: %s"
          JLI_ReportErrorMessage(DLL_ERROR4, "JVM_FindClassFromBootLoader");
          return NULL;
       }
   }
   return findBootClass(env, classname);
}