moduo之线程本地存储

简介

用于多线程私有数据操作

结构

ThreadLocal

构造函数

创建pthread_key，指定存储单元的释放处理函数

ThreadLocal()
{
  MCHECK(pthread_key_create(&pkey_, &ThreadLocal::destructor));
}

private:

  static void destructor(void *x)
  {
    T* obj = static_cast<T*>(x);
    typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];
    T_must_be_complete_type dummy; (void) dummy;
    delete obj;
  }

析构函数

删除pthread_key

~ThreadLocal()
{
  MCHECK(pthread_key_delete(pkey_));
}

设置/获取存储值

先看线程本地存储是否有设置，如果没有，分配内存，设置本地存储

T& value()
{
  T* perThreadValue = static_cast<T*>(pthread_getspecific(pkey_));
  if (!perThreadValue)
  {
    T* newObj = new T();
    MCHECK(pthread_setspecific(pkey_, newObj));
    perThreadValue = newObj;
  }
  return *perThreadValue;
}

ThreadLocalSingleton

单例

分配内存，通过Deleter在线程退出时，释放分配的内存

static T& instance()
  {
    if (!t_value_)
    {
      t_value_ = new T();
      deleter_.set(t_value_);
    }
    return *t_value_;
  }

获取存储地址

static T* pointer()
{
  return t_value_;
}

Deleter

具体调用pthread_key相关的类

Deleter()
{
  pthread_key_create(&pkey_, &ThreadLocalSingleton::destructor);
}

~Deleter()
{
  pthread_key_delete(pkey_);
}

void set(T* newObj)
{
  assert(pthread_getspecific(pkey_) == NULL);
  pthread_setspecific(pkey_, newObj);
}