OpenRtsp源码剖析之hashtable解析

            OpenRtsp源码剖析：hashtable

       这是主要保存数据value和key的结构体：         

    class TableEntry {           public:       TableEntry* fNext;       char const* key;       void* value;    }; 

      这是操作hashtable的类，里面包括一系列操作函数，下面只列出主要的数据成员：

      

     TableEntry** fBuckets; // pointer to bucket array     TableEntry* fStaticBuckets[SMALL_HASH_TABLE_SIZE];// used for small tables     unsigned fNumBuckets;  //桶的个数，初始化时等于SMALL_HASH_TABLE_SIZE     unsigned fNumEntries;   //数据entry的个数     unsigned fRebuildSize;  //当fNumEntries的个数大于等于它时就要重建rebuild，初始化时等于3*SMALL_HASH_TABLE_SIZE     int fKeyType;  //key的类型

        下面具体介绍几个主要的操作：

        主要的设计模型：

     添加成员部分源代码：  

   void* BasicHashTable::Add(char const* key, void* value) {   void* oldValue;   unsigned index;   TableEntry* entry = lookupKey(key, index);   if (entry != NULL) {      // There's already an item with this key      oldValue = entry->value;     } else {      // There's no existing entry; create a new one:      entry = insertNewEntry(index, key);      oldValue = NULL;     }   entry->value = value;   // If the table has become too large, rebuild it with more buckets:   if (fNumEntries >= fRebuildSize) rebuild();   return oldValue;  }

    

      对应的图：

     

       当添加到一定数量的时候重建：

       部分源代码：   

       

    void BasicHashTable::rebuild() {      // Remember the existing table size:    unsigned oldSize = fNumBuckets;    TableEntry** oldBuckets = fBuckets;    // Create the new sized table:    fNumBuckets *= 4;    fBuckets = new TableEntry*[fNumBuckets];    for (unsigned i = 0; i < fNumBuckets; ++i) {      fBuckets[i] = NULL;    }    fRebuildSize *= 4;    fDownShift -= 2;    fMask = (fMask<<2)|0x3;    // Rehash the existing entries into the new table:    for (TableEntry** oldChainPtr = oldBuckets; oldSize > 0;         --oldSize, ++oldChainPtr) {      for (TableEntry* hPtr = *oldChainPtr; hPtr != NULL;   hPtr = *oldChainPtr) {        *oldChainPtr = hPtr->fNext;        unsigned index = hashIndexFromKey(hPtr->key);        hPtr->fNext = fBuckets[index];        fBuckets[index] = hPtr;      }    }    // Free the old bucket array, if it was dynamically allocated:    if (oldBuckets != fStaticBuckets) delete[] oldBuckets;  }

      重建图 模型：