The Atomic Flag

The atomic flag, i.e. std::atomic_flag, has a very simple interface. Its clear method enables you to set its value to false; with the test_and_set method you can set the value back to true. There is no method to exclusively ask for the current value. To use std::atomic_flag it must be initialized to false with the constant ATOMIC_FLAG_INIT. std::atomic_flag has two outstanding properties.

std::atomic_flag is:

• the only lock-free atomic. A non-blocking algorithm is lock-free if there is guaranteed system-wide progress.
• the building block for higher level

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