winapi：线程结束时获取回调

Question

I have some c++ library code that creates some book-keeping data per thread that accesses it (based on thread-id). I would like to cleanup that data when a thread ends. Is there a way (if not portable, then using win-api) to get notified when a thread ends?

// simplified example:

std::mutex mutex_;
std::unordered_map<std::thread::id, int> thread_accesses_;

void LibFunction() {
  std::thread::id thread_id = std::this_thread::get_id();
  mutex_.lock();
  std::unordered_map<std::thread::id, int>::const_iterator it = thread_accesses_.find(thread_id);
  if(it == thread_accesses_.end()) {
    thread_accesses_[thread_id] = 0;
  } else {
    thread_accesses_[thread_id]++;
  }
  mutex_.unlock();
}

Answer 1

Thread-local storage is both C++ standard way and platform way.

C++ has thread_local keyword to declare thread-local variable. Then destructor of that variable is called for each thread for which it was constructed. Thread local variable is constructed for at least all threads that access the variable, and possibly for other threads.

Windows has thread-local storage as system mechanism. thread_local is implemented via this mechanism.

It is possible to have thread exit callbacks in Windows by other means:

• having thread-local data and TLS callbacks in module by other means
• Using DllMain callbacks
• Passing FlsCallback in FlsAlloc , fiber local storage is something superior to thread local storage, and in absence of fibers it behaves exactly like thread local storage

If cannot use thread_local , but want something simple and portable, consider also boost::thread_specific_ptr .