How to define local local static variables of type thread?

Question

How to define local static variables (which support its value between function calls) that are not used for different threads?

I am looking for an answer in both C and C ++

Answer 1

on Windows using the Windows API: TlsAlloc () / TlsSetValue () / TlsGetValue ()

on Windows using the built-in compiler: use _declspec (thread)

on Linux (another POSIX ???): get_thread_area () and related

Answer 2

Just use static and __thread in your function.

Example:

int test(void) { static __thread a; return a++; } 

Answer 3

There is no model for streams or the same in the current C standard, so you cannot get an answer.

The utility provided by POSIX for this is pthread_[gs]etspecific .

The next version of the C standard adds streams and has the concept of local stream storage.

Answer 4

You can also use the addition of local C ++ 11 stream storage if you have access to C ++ 11.

Answer 5

You can create your own private stream storage as a single point for each stream identifier. Something like that:

 struct ThreadLocalStorage { ThreadLocalStorage() { // initialization here } int my_static_variable_1; // more variables }; class StorageManager { std::map<int, ThreadLocalStorage *> m_storages; ~StorageManager() { // storage cleanup std::map<int, ThreadLocalStorage *>::iterator it; for(it = m_storages.begin(); it != m_storages.end(); ++it) delete it->second; } ThreadLocalStorage * getStorage() { int thread_id = GetThreadId(); if(m_storages.find(thread_id) == m_storages.end()) { m_storages[thread_id] = new ThreadLocalStorage; } return m_storages[thread_id]; } public: static ThreadLocalStorage * threadLocalStorage() { static StorageManager instance; return instance.getStorage(); } }; 

GetThreadId (); It is a platform-specific function for determining the caller ID. Something like that:

 int GetThreadId() { int id; #ifdef linux id = (int)gettid(); #else // windows id = (int)GetCurrentThreadId(); #endif return id; } 

Now, as part of the stream function, you can use local storage:

 void threadFunction(void*) { StorageManager::threadLocalStorage()->my_static_variable_1 = 5; //every thread will have // his own instance of local storage. } 

Answer 6

You can create a data structure allocated from the heap for each thread.

Example:

 struct ThreadLocal { int var1; float var2; //etc.. }