2012_03_15_tls_on_mac.md

实现 MacOS 下的 TLS

MacOS 下居然没有类似 win32/*nix 的 __declspec(thread)/__thread TLS

// there's no tls support in macos, modified from
// http://alex.tapmania.org/2011/03/simple-thread-local-storage-with-pthreads.html
//
// usage:
//   THREADLOCAL(int) val;
//   val = 10;
//
//   class MyFoo;
//   THREADLOCAL(MyFoo*) ptr;
//   if (!ptr) ptr = new MyFoo();
//   ptr->someFunc();
//   (*ptr).someFunc();

#include <assert.h>
#include <pthread.h>

class ThreadLocalStorageMacOSBase
{
private:
  pthread_key_t key_;

public:
  ThreadLocalStorageMacOSBase()
  {
    pthread_key_create(&key_, NULL);
  }
  ~ThreadLocalStorageMacOSBase()
  {
    pthread_key_delete(key_);
  }

  bool operator!()
  {
    return pthread_getspecific(key_) == NULL;
  }

protected:
  void* internalGet()
  {
    return pthread_getspecific(key_);
  }

  void internalSet(void *v)
  {
    pthread_setspecific(key_, v);
  }
};

// for int, object
class ThreadLocalStorageMacOS : public ThreadLocalStorageMacOSBase
{
public:
  ThreadLocalStorageMacOS& operator =(const T& val)
  {
    T *ptr = static_cast<T*>(internalGet());
    if (ptr == NULL)
    {
      ptr = new T;    // TODO: memory leak
      internalSet(ptr);
    }
    *ptr = val;
    return *this;
  }

  const T& get()
  {
    T *ptr = static_cast<T*>(internalGet());
    assert(ptr != NULL);
    return *ptr;
  }
};

// for pointer
template <typename T>
class ThreadLocalStorageMacOS<T*> : public ThreadLocalStorageMacOSBase
{
public:
  ThreadLocalStorageMacOS& operator =(T* val)
  {
    internalSet(val);
    return *this;
  }

  T& operator*()
  {
    return *(static_cast<T*>(internalGet()));
  }

  T* operator->()
  {
    return static_cast<T*>(internalGet());
  }
};

#define THREADLOCAL(type) ThreadLocalStorageMacOS<type>

介绍 D language 如何实现 MacOS 下的 TLS

• http://drdobbs.com/blogs/architecture-and-design/228701185

C++ 封装下 pthread_getspecific 来实现

• http://alex.tapmania.org/2011/03/simple-thread-local-storage-with-pthreads.html

讨论为啥 MacOS 下没有 TLS

• http://lifecs.likai.org/2010/05/mac-os-x-thread-local-storage.html