The C Standard, 7.26.5.6 \[[ISO/IEC 9899:2011](https://wiki.sei.cmu.edu/confluence/display/c/AA.+Bibliography#AA.Bibliography-ISO-IEC9899-2011)\], states that a thread shall not be joined once it was previously joined or detached. Similarly, subclause 7.26.5.3 states that a thread shall not be detached once it was previously joined or detached. Violating either of these subclauses results in [undefined behavior](https://wiki.sei.cmu.edu/confluence/display/c/BB.+Definitions#BB.Definitions-undefinedbehavior).

A consistent locking policy guarantees that multiple threads cannot simultaneously access or modify shared data. Atomic variables eliminate the need for locks by guaranteeing thread safety when certain operations are performed on them. The thread-safe operations on atomic variables are specified in the C Standard, subclauses 7.17.7 and 7.17.8 \[[ISO/IEC 9899:2011](https://wiki.sei.cmu.edu/confluence/display/c/AA.+Bibliography#AA.Bibliography-ISO%2FIEC9899-2011)\]. While atomic operations can be combined, combined operations do not provide the thread safety provided by individual atomic operations.