Thread-local storage (TLS) is a computer programming method that uses static or global memory local to a thread
Thread-local storage (TLS) is a computer programming method that uses static or global memory local to a thread.
This is sometimes needed because normally all threads in a process share the same address space, which is sometimes undesirable. In other words, data in a static or global variable is normally always located at the same memory location, when referred to by threads from the same process. Variables on the call stack however are local to threads, because each thread has its own stack, residing in a different memory location.
Sometimes it is desirable that two threads referring to the same static or global variable are actually referring to different memory locations, thereby making the variable thread-local, a canonical example being the C error code variable error number.
If it is possible to make at least a memory address sized variable thread-local, it is in principle possible to make arbitrarily sized memory blocks thread-local, by allocating such a memory block and storing the memory address of that block in a thread-local variable.
