如何进行v8源码解析hashmap

hashmap是哈希表的实现。#ifndef V8_HASHMAP_H_#define V8_HASHMAP_H_namespace v8 { namespace internal {// Allocator defines the memory allocator interface// used by HashMap and implements a default allocator.class Allocator BASE_EMBEDDED { public:  virtual ~Allocator()  {}  virtual void* New(size_t size)  { return Malloced::New(size); }  virtual void Delete(void* p)  { Malloced::Delete(p); }};class HashMap { public:  static Allocator DefaultAllocator;  typedef bool (*MatchFun) (void* key1, void* key2);  // Dummy constructor.  This constructor doesn't set up the hash  // map properly so don't use it unless you have good reason.  HashMap();  // initial_capacity is the size of the initial hash map;  // it must be a power of 2 (and thus must not be 0).  HashMap(MatchFun match,          Allocator* allocator = &DefaultAllocator,          uint32_t initial_capacity = 8);  ~HashMap();  // HashMap entries are (key, value, hash) tripplets.  // Some clients may not need to use the value slot  // (e.g. implementers of sets, where the key is the value).  struct Entry {    void* key;    void* value;    uint32_t hash;  // the full hash value for key  };  // If an entry with matching key is found, Lookup()  // returns that entry. If no matching entry is found,  // but insert is set, a new entry is inserted with  // corresponding key, key hash, and NULL value.  // Otherwise, NULL is returned.  Entry* Lookup(void* key, uint32_t hash, bool insert);  // Empties the hash map (occupancy() == 0).  void Clear();  // The number of (non-empty) entries in the table.  uint32_t occupancy() const  { return occupancy_; }  // The capacity of the table. The implementation  // makes sure that occupancy is at most 80% of  // the table capacity.  uint32_t capacity() const  { return capacity_; }  // Iteration  //  // for (Entry* p = map.Start(); p != NULL; p = map.Next(p)) {  //   ...  // }  //  // If entries are inserted during iteration, the effect of  // calling Next() is undefined.  Entry* Start() const;  Entry* Next(Entry* p) const; private:  Allocator* allocator_;  MatchFun match_;  Entry* map_;  // 可分配的元素个数  uint32_t capacity_;  // 已分配的元素个数   uint32_t occupancy_;  // 数组末地址  Entry* map_end() const  { return map_ + capacity_; }  Entry* Probe(void* key, uint32_t hash);  void Initialize(uint32_t capacity);  void Resize();};} }  // namespace v8::internal#endif  // V8_HASHMAP_H_
   
     
 
    
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    // Copyright 2008 Google Inc. All Rights Reserved.// Redistribution and use in source and binary forms, with or without// modification, are permitted provided that the following conditions are// met:////     * Redistributions of source code must retain the above copyright//       notice, this list of conditions and the following disclaimer.//     * Redistributions in binary form must reproduce the above//       copyright notice, this list of conditions and the following//       disclaimer in the documentation and/or other materials provided//       with the distribution.//     * Neither the name of Google Inc. nor the names of its//       contributors may be used to endorse or promote products derived//       from this software without specific prior written permission.//// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.#include "v8.h"#include "hashmap.h"namespace v8 { namespace internal {/*  判断x是不是有且仅有一位是1.如果是则下面的式子成立。  假设x的第n位是1，x - 1后，n的左边位都是0，右边都是1，n变成0.  00001000 => 00000111,再和x与，n以及n的右边位是肯定为0的。右边就看  n的左边的位就可以了。*/static inline bool IsPowerOf2(uint32_t x) {  ASSERT(x != 0);  return (x & (x - 1)) == 0;}// 内存分配器Allocator HashMap::DefaultAllocator;// 默认构造函数HashMap::HashMap() {  allocator_ = NULL;  match_ = NULL;}// 初始化属性，分配内存HashMap::HashMap(MatchFun match,                 Allocator* allocator,                 uint32_t initial_capacity) {  allocator_ = allocator;  match_ = match;  Initialize(initial_capacity);}// 析构函数，释放内存HashMap::~HashMap() {  if (allocator_) {    allocator_->Delete(map_);  }}// 查找或插入一个元素HashMap::Entry* HashMap::Lookup(void* key, uint32_t hash, bool insert) {  // Find a matching entry.  // 找到key和hash对应的索引。  Entry* p = Probe(key, hash);  // 找到则返回  if (p->key != NULL) {    return p;  }  // No entry found; insert one if necessary.  // 没有找到判断是否需要插入  if (insert) {    p->key = key;    p->value = NULL;    p->hash = hash;    // 更新使用的元素个数    occupancy_++;    // Grow the map if we reached >= 80% occupancy.    // 分配的元素过多，重新分配内存，否则导致冲突频繁，影响效率    if (occupancy_ + occupancy_/4 >= capacity_) {      Resize();      // 重新查找对应的元素      p = Probe(key, hash);    }    return p;  }  // No entry found and none inserted.  return NULL;}// void HashMap::Clear() {  // Mark all entries as empty.  // 最后一个元素的末地址  const Entry* end = map_end();  // 遍历数组，清空key字段  for (Entry* p = map_; p < end; p++) {    p->key = NULL;  }  // 分配出去的元素个数为0  occupancy_ = 0;}// 用于迭代HashMap::Entry* HashMap::Start() const {  // Next函数的for执行了p++，所以这里要回退一个元素，见Next函数  return Next(map_ - 1);}HashMap::Entry* HashMap::Next(Entry* p) const {  // 最后一个元素的末地址  const Entry* end = map_end();  ASSERT(map_ - 1 <= p && p < end);  /*    遍历数组，返回遇到的第一个key非空的节点，    p++，所以初始化的时候，p指向第一个元素的第一个元素  */  for (p++; p < end; p++) {    if (p->key != NULL) {      return p;    }  }  return NULL;}// 根据key和hash找到哈希表中可用的索引，hash值由调用方提供HashMap::Entry* HashMap::Probe(void* key, uint32_t hash) {  ASSERT(key != NULL);  ASSERT(IsPowerOf2(capacity_));  // capacity_ - 1防止溢出，实现回环    Entry* p = map_ + (hash & (capacity_ - 1));  // 最后一个元素的末地址  const Entry* end = map_end();  ASSERT(map_ <= p && p < end);  // 至少有一个非NULL，使p->key != NULL成立  ASSERT(occupancy_ < capacity_);  // guarantees loop termination  /*    如果key等于空说明这个项还没被使用，则返回，    如果key非空，并且hash和key都匹配，则返回。    hash值不相等或者名字不match,则查找下一个可用的元素，即开放地址法  */  while (p->key != NULL && (hash != p->hash || !match_(key, p->key))) {    p++;    // 到底了，从头开始    if (p >= end) {      p = map_;    }  }  return p;}// 申请一个Entry* 数组void HashMap::Initialize(uint32_t capacity) {  ASSERT(IsPowerOf2(capacity));  map_ = reinterpret_cast<Entry*>(allocator_->New(capacity * sizeof(Entry)));  if (map_ == NULL) V8::FatalProcessOutOfMemory("HashMap::Initialize");  capacity_ = capacity;  // 初始化内存数据  Clear();}// 扩展void HashMap::Resize() {  // 先保存旧地址的指针  Entry* map = map_;  uint32_t n = occupancy_;  // 重新分配一个更大的数组  // Allocate larger map.  Initialize(capacity_ * 2);  // Rehash all current entries.  // 重新计算当前哈希表中的元素的位置，n的作用是迁移完n个可用退出循环了，不需要遍历到底  for (Entry* p = map; n > 0; p++) {    if (p->key != NULL) {      // 把旧的元素插入到新的数组中，因为map_更新了，里面是空的，所以会一直插入新的元素到map_      Lookup(p->key, p->hash, true)->value = p->value;      n--;    }  }  // 释放旧的地址  // Delete old map.  allocator_->Delete(map);}} }  // namespace v8::internalAI代码助手复制代码