Hotspot源码解析-第七章

第七章

7.1 启动参数解析

7.1.1 arguments.cpp

7.1.1.1 Arguments::parse

jint Arguments::parse(const JavaVMInitArgs* args) {

  //  tail指向选项字符串的剩余部分，其实就是指向=后面的值
  const char* tail;

  // 如果 flag "-XX:Flags=flags-file" 被设置了，那么这就是第一个被处理的option选项
  const char* hotspotrc = ".hotspotrc";
  bool settings_file_specified = false;
  bool needs_hotspotrc_warning = false;

  ArgumentsExt::process_options(args);

  const char* flags_file;
  int index;
  for (index = 0; index < args->nOptions; index++) {
    const JavaVMOption *option = args->options + index;
      // 处理-XX:Flags
    if (match_option(option, "-XX:Flags=", &tail)) {
      flags_file = tail; // tail一直指向值，赋值flags_file
      settings_file_specified = true;
    }
    if (match_option(option, "-XX:+PrintVMOptions", &tail)) {
      PrintVMOptions = true;
    }
    if (match_option(option, "-XX:-PrintVMOptions", &tail)) {
      PrintVMOptions = false;
    }
    if (match_option(option, "-XX:+IgnoreUnrecognizedVMOptions", &tail)) {
      IgnoreUnrecognizedVMOptions = true;
    }
    if (match_option(option, "-XX:-IgnoreUnrecognizedVMOptions", &tail)) {
      IgnoreUnrecognizedVMOptions = false;
    }
    if (match_option(option, "-XX:+PrintFlagsInitial", &tail)) {
      CommandLineFlags::printFlags(tty, false);
      vm_exit(0);
    }
    if (match_option(option, "-XX:NativeMemoryTracking", &tail)) {
#if INCLUDE_NMT
      // The launcher did not setup nmt environment variable properly.
      if (!MemTracker::check_launcher_nmt_support(tail)) {
        warning("Native Memory Tracking did not setup properly, using wrong launcher?");
      }

      // Verify if nmt option is valid.
      if (MemTracker::verify_nmt_option()) {
        // Late initialization, still in single-threaded mode.
        if (MemTracker::tracking_level() >= NMT_summary) {
          MemTracker::init();
        }
      } else {
        vm_exit_during_initialization("Syntax error, expecting -XX:NativeMemoryTracking=[off|summary|detail]", NULL);
      }
#else
      jio_fprintf(defaultStream::error_stream(),
        "Native Memory Tracking is not supported in this VM\n");
      return JNI_ERR;
#endif
    }


#ifndef PRODUCT
    if (match_option(option, "-XX:+PrintFlagsWithComments", &tail)) {
      CommandLineFlags::printFlags(tty, true);
      vm_exit(0);
    }
#endif
  }

  if (IgnoreUnrecognizedVMOptions) {
    // uncast const to modify the flag args->ignoreUnrecognized
    *(jboolean*)(&args->ignoreUnrecognized) = true;
  }

  // Parse specified settings file
  if (settings_file_specified) {
    if (!process_settings_file(flags_file, true, args->ignoreUnrecognized)) {
      return JNI_EINVAL;
    }
  } else {
#ifdef ASSERT
    // Parse default .hotspotrc settings file
    if (!process_settings_file(".hotspotrc", false, args->ignoreUnrecognized)) {
      return JNI_EINVAL;
    }
#else
    struct stat buf;
    if (os::stat(hotspotrc, &buf) == 0) {
      needs_hotspotrc_warning = true;
    }
#endif
  }

  if (PrintVMOptions) {
    for (index = 0; index < args->nOptions; index++) {
      const JavaVMOption *option = args->options + index;
      if (match_option(option, "-XX:", &tail)) {
        logOption(tail);
      }
    }
  }

  // Parse JavaVMInitArgs structure passed in, as well as JAVA_TOOL_OPTIONS and _JAVA_OPTIONS
  jint result = parse_vm_init_args(args);
  if (result != JNI_OK) {
    return result;
  }

  // Call get_shared_archive_path() here, after possible SharedArchiveFile option got parsed.
  SharedArchivePath = get_shared_archive_path();
  if (SharedArchivePath == NULL) {
    return JNI_ENOMEM;
  }

  // Set up VerifySharedSpaces
  if (FLAG_IS_DEFAULT(VerifySharedSpaces) && SharedArchiveFile != NULL) {
    VerifySharedSpaces = true;
  }

  // Delay warning until here so that we've had a chance to process
  // the -XX:-PrintWarnings flag
  if (needs_hotspotrc_warning) {
    warning("%s file is present but has been ignored.  "
            "Run with -XX:Flags=%s to load the file.",
            hotspotrc, hotspotrc);
  }

#ifdef _ALLBSD_SOURCE  // UseLargePages is not yet supported on BSD.
  UNSUPPORTED_OPTION(UseLargePages, "-XX:+UseLargePages");
#endif

#if INCLUDE_ALL_GCS
  #if (defined JAVASE_EMBEDDED || defined ARM)
    UNSUPPORTED_OPTION(UseG1GC, "G1 GC");
  #endif
#endif

#ifndef PRODUCT
  if (TraceBytecodesAt != 0) {
    TraceBytecodes = true;
  }
  if (CountCompiledCalls) {
    if (UseCounterDecay) {
      warning("UseCounterDecay disabled because CountCalls is set");
      UseCounterDecay = false;
    }
  }
#endif // PRODUCT

  // JSR 292 is not supported before 1.7
  if (!JDK_Version::is_gte_jdk17x_version()) {
    if (EnableInvokeDynamic) {
      if (!FLAG_IS_DEFAULT(EnableInvokeDynamic)) {
        warning("JSR 292 is not supported before 1.7.  Disabling support.");
      }
      EnableInvokeDynamic = false;
    }
  }

  if (EnableInvokeDynamic && ScavengeRootsInCode == 0) {
    if (!FLAG_IS_DEFAULT(ScavengeRootsInCode)) {
      warning("forcing ScavengeRootsInCode non-zero because EnableInvokeDynamic is true");
    }
    ScavengeRootsInCode = 1;
  }

  if (PrintGCDetails) {
    // Turn on -verbose:gc options as well
    PrintGC = true;
  }

  if (!JDK_Version::is_gte_jdk18x_version()) {
    // To avoid changing the log format for 7 updates this flag is only
    // true by default in JDK8 and above.
    if (FLAG_IS_DEFAULT(PrintGCCause)) {
      FLAG_SET_DEFAULT(PrintGCCause, false);
    }
  }

  // Set object alignment values.
  set_object_alignment();

#if !INCLUDE_ALL_GCS
  force_serial_gc();
#endif // INCLUDE_ALL_GCS
#if !INCLUDE_CDS
  if (DumpSharedSpaces || RequireSharedSpaces) {
    jio_fprintf(defaultStream::error_stream(),
      "Shared spaces are not supported in this VM\n");
    return JNI_ERR;
  }
  if ((UseSharedSpaces && FLAG_IS_CMDLINE(UseSharedSpaces)) || PrintSharedSpaces) {
    warning("Shared spaces are not supported in this VM");
    FLAG_SET_DEFAULT(UseSharedSpaces, false);
    FLAG_SET_DEFAULT(PrintSharedSpaces, false);
  }
  no_shared_spaces("CDS Disabled");
#endif // INCLUDE_CDS

  return JNI_OK;
}

7.2 确定处理核数和指令集

7.2.1 os.cpp

7.2.1.1 init_before_ergo

void os::init_before_ergo() {
    // 通过系统调用api，拿到有效的cpu核数
  initialize_initial_active_processor_count();
  // 大页初始化，默认是没有实现
  large_page_init();

  // 确定平台特性，即所使用的平台架构指令集
  VM_Version::init_before_ergo();
}