如何查找 jdk 中的 native 实现

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class java_lang_String */

#ifndef _Included_java_lang_String
#define _Included_java_lang_String
#ifdef __cplusplus
extern "C" {
#endif
#undef java_lang_String_serialVersionUID
#define java_lang_String_serialVersionUID -6849794470754667710LL
/*
 * Class:     java_lang_String
 * Method:    intern
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_java_lang_String_intern
  (JNIEnv *, jobject);

#ifdef __cplusplus
}
#endif
#endif

inline oop JNIHandles::resolve_non_null(jobject handle) {
  assert(handle != NULL, "JNI handle should not be null");
  oop result = *(oop*)handle;
  assert(result != NULL, "Invalid value read from jni handle");
  assert(result != badJNIHandle, "Pointing to zapped jni handle area");
  // Don't let that private _deleted_handle object escape into the wild.
  assert(result != deleted_handle(), "Used a deleted global handle.");
  return result;
};

oop StringTable::intern(oop string, TRAPS)
{
  if (string == NULL) return NULL;
  ResourceMark rm(THREAD);
  int length;
  Handle h_string (THREAD, string);
  
  // 转为unicode string
  jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);
  
  // 调用intern的重载方法
  oop result = intern(h_string, chars, length, CHECK_NULL);
  
  return result;
}

oop StringTable::intern(Handle string_or_null, jchar* name,
                        int len, TRAPS) {
  // 计算hash值
  unsigned int hashValue = hash_string(name, len);
  
  // 将hash值转换为string table的index
  int index = the_table()->hash_to_index(hashValue);
  
  // 到bucket查找string
  oop found_string = the_table()->lookup(index, name, len, hashValue);

  // 找到了，直接返回
  if (found_string != NULL) {
    ensure_string_alive(found_string);
    return found_string;
  }

  debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
  assert(!Universe::heap()->is_in_reserved(name),
         "proposed name of symbol must be stable");

  Handle string;
  // 尝试尽可能重用string
  if (!string_or_null.is_null()) {
    string = string_or_null;
  } else {
    string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
  }

#if INCLUDE_ALL_GCS
  if (G1StringDedup::is_enabled()) {
    // Deduplicate the string before it is interned. Note that we should never
    // deduplicate a string after it has been interned. Doing so will counteract
    // compiler optimizations done on e.g. interned string literals.
    G1StringDedup::deduplicate(string());
  }
#endif

  // 因为the_table()可能在安全点发生变化，所以在获取它之前前，需要先获取StringTable_lock锁
  oop added_or_found;
  {
    MutexLocker ml(StringTable_lock, THREAD);
    // 将字符串添加到string table
    added_or_found = the_table()->basic_add(index, string, name, len,
                                  hashValue, CHECK_NULL);
  }

  ensure_string_alive(added_or_found);

  return added_or_found;
}

jobject JNIHandles::make_local(JNIEnv* env, oop obj) {
  if (obj == NULL) {
    return NULL;                // ignore null handles
  } else {
    JavaThread* thread = JavaThread::thread_from_jni_environment(env);
    
    // 确保obj指向的是堆上的保留区域（the reserved area of the heap）
    assert(Universe::heap()->is_in_reserved(obj), "sanity check");
    return thread->active_handles()->allocate_handle(obj);
  }
}

jobject JNIHandleBlock::allocate_handle(oop obj) {
  assert(Universe::heap()->is_in_reserved(obj), "sanity check");
  if (_top == 0) {
    // This is the first allocation or the initial block got zapped when
    // entering a native function. If we have any following blocks they are
    // not valid anymore.
    for (JNIHandleBlock* current = _next; current != NULL;
         current = current->_next) {
      assert(current->_last == NULL, "only first block should have _last set");
      assert(current->_free_list == NULL,
             "only first block should have _free_list set");
      current->_top = 0;
      if (ZapJNIHandleArea) current->zap();
    }
    // Clear initial block
    _free_list = NULL;
    _allocate_before_rebuild = 0;
    _last = this;
    if (ZapJNIHandleArea) zap();
  }

  // Try last block
  if (_last->_top < block_size_in_oops) {
    oop* handle = &(_last->_handles)[_last->_top++];
    *handle = obj;
    return (jobject) handle;
  }

  // Try free list
  if (_free_list != NULL) {
    oop* handle = _free_list;
    _free_list = (oop*) *_free_list;
    *handle = obj;
    return (jobject) handle;
  }
  // Check if unused block follow last
  if (_last->_next != NULL) {
    // update last and retry
    _last = _last->_next;
    return allocate_handle(obj);
  }

  // No space available, we have to rebuild free list or expand
  if (_allocate_before_rebuild == 0) {
      rebuild_free_list();        // updates _allocate_before_rebuild counter
  } else {
    // Append new block
    Thread* thread = Thread::current();
    Handle obj_handle(thread, obj);
    // This can block, so we need to preserve obj accross call.
    _last->_next = JNIHandleBlock::allocate_block(thread);
    _last = _last->_next;
    _allocate_before_rebuild--;
    obj = obj_handle();
  }
  return allocate_handle(obj);  // retry
}