CODEWITHSUNDEEP
c++concurrencyatomic
Gordon Lee
Gordon Lee

Reputation: 15

Using compare_exchange_strong on atomic booleans (C++)

I'm new to concurrent programming and I'm trying to compile the following code:

private:
  std::atomic<bool> resizing_;

void Resize() { if (resizing_.compare_exchange_strong(false, true)... }

This throws error: no matching member function for call to 'compare_exchange_strong' and I'm not sure how I can fix this. I've tried using a bool* for the first argument but that didn't seem to help. I've tried to read the documentation on atomic<>s but it hasn't helped.

Any information on what I'm doing wrong would be really helpful!

Upvotes: 0

Views: 4466

Answers (1)

Dmitry Kuzminov
Dmitry Kuzminov

Reputation: 6584

The first parameter of the compare_exchange_strong method is a reference to the type. This method exchanges two values, but only if the comparison of the contained value and the expected value is true. Otherwise it replaces the expected with the contained value.

The idiom is like this:

std::atomic<int> value;

int expected = value;
do {
    int new_value = get_updated_value(expected);
} while(!value.compare_exchange_strong(expected, new_value));

Note that the expected is automatically updated whenever the comparison is false, and another new_value is evaluated each iteration.

Upvotes: 3

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