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my question is why use TLS mechanism instead of just local variables in a thread function? Can you please provide some fine example, or what's the advantage of TLS over local vars? Thank you, Mateusz
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With thread local storage (TLS), you can provide unique data for each thread that the process can access using a global index. One thread allocates the index, which can be used by the other threads to retrieve the unique data associated with the index.
In that scenario, accesses to thread-local variables can be almost as fast as access to other variables, the only difference being an extra pointer dereference. Unfortunately, many PC applications require something more complicated.
Thread Local Storage (TLS) is the method by which each thread in a given multithreaded process can allocate locations in which to store thread-specific data. Dynamically bound (run-time) thread-specific data is supported by way of the TLS API (TlsAlloc).
Threads share the data of the process to which it belongs to. This data sharing provides one of the benefits of multithreaded programming. However, in some circumstances, each thread might need its own copy of certain data. Such data is called thread-local storage (or TLS).
Here is good link from Intel on using Thread-local Storage to Reduce Synchronization : https://software.intel.com/en-us/articles/use-thread-local-storage-to-reduce-synchronization
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If you can use local variables then do so and you invariably can use locals. Only as a last resort should you use thread local storage which suffers from almost all the same disadvantages as global variables. Although you are looking for a reason to use thread local storage, in fact best practice is to search for ways to avoid it!
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