The systhread_getdata function gets data that is associated with a specified key in the current thread.
void *systhread_getdata(int key);
A pointer to the data that was earlier used with the systhread_setkey function from the current thread, using the same value of key if the call succeeds. Returns NULL if the call did not succeed; for example, if the systhread_setkey function was never called with the specified key during this session.
int key is the value associated with the stored data by a systhread_setdata function. Keys are assigned by the systhread_newkey function.