single variable and QMutex

[drhex]

Yes, a statement such as

foo++;

foo++;

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can in the object code expand to several instructions. Pseudocode:

register = foo;
register += 1;
foo = register;

register = foo;
register += 1;
foo = register;

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If another thread is also executing the same instructions, it may have been interrupted right after the first pseudo-instruction above. The variable will then be incremented only once even when two threads tried to increment it...