? ? ? ? ?ThreadLocal用來存儲線程私有數據的類。

// Use of this source code is governed by a BSD-style license // that can be found in the License file. // // Author: Shuo Chen (chenshuo at chenshuo dot com)#ifndef MUDUO_BASE_THREADLOCAL_H #define MUDUO_BASE_THREADLOCAL_H#include "muduo/base/Mutex.h" #include "muduo/base/noncopyable.h"#include <pthread.h>namespace muduo {template<typename T> class ThreadLocal : noncopyable //線程特定數據 {public:ThreadLocal(){MCHECK(pthread_key_create(&pkey_, &ThreadLocal::destructor));//構造函數中創建key，數據的銷毀由destructor來銷毀}~ThreadLocal(){MCHECK(pthread_key_delete(pkey_));//析構函數中銷毀key}T& value()//獲取線程特定數據{T* perThreadValue = static_cast<T*>(pthread_getspecific(pkey_));//通過key獲取線程特定數據if (!perThreadValue)//如果是空的，說明特定數據還沒有創建，那么就空構造一個{T* newObj = new T();MCHECK(pthread_setspecific(pkey_, newObj));//設置特定數據perThreadValue = newObj;//返回}return *perThreadValue;//返回對象引用，所以需要*}private:static void destructor(void *x){T* obj = static_cast<T*>(x);typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];//檢測是否是完全類型T_must_be_complete_type dummy; (void) dummy;delete obj;//如果是，我們就可以刪除它了}private:pthread_key_t pkey_;//key的類型是pthread_key_t類型 };} // namespace muduo#endif // MUDUO_BASE_THREADLOCAL_H

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