The wait method for a std::condition_variable requires using a lambda function if the optional condition is specified.

Question

BlackTom AI · Accepted Answer

std::condition_variable::wait has an overload that accepts any Callable predicate (i.e., any object you can invoke that returns bool), so a lambda is not required. 1) Relevant knowledge points and concepts - std::condition_variable::wait has two common forms: wait(lock) and wait(lock, predicate). The predicate overload is a template: template void wait(unique_lock& lock, Predicate pred). - The predicate is invoked while the mutex is held to guard against spurious wakeups; wait(lock, pred) repeatedly evaluates pred and only returns when pred() is true. - "Callable" in C++ includes lambdas, function pointers, function objects (functors with operator()), std::function, and results of std::bind. 2) Step-by-step reasoning - The signature is template-based, so the compiler accepts any type Predicate for which pred() is well-formed and convertible to bool. - Because Predicate is a template parameter and not restricted to a specific type, the implementation does not require a lambda specifically. - When you call cv.wait(lock, pred), the condition variable uses pred() to decide whether to block or continue; the mechanism is identical regardless of predicate type. 3) Example (illustrative, no complex calculations) - Using a function pointer: bool ready() { return flag; } cv.wait(lock, ready); - Using a functor: struct IsReady { bool operator()() const { return flag; } }; cv.wait(lock, IsReady()); - Using std::bind or std::function also works. All these are valid because they are Callable. 4) Why the correct answer is correct - The statement asserts a requirement (must use a lambda). The language and template-based overload show there is no such requirement: any callable predicate is acceptable. 5) Why other options are incorrect - The only alternative was "True": that would be incorrect because it falsely claims a lambda is mandatory when it's only one convenient option among many. 6) Conclusion - Therefore the correct answer is False, which matches the provided answer.

The wait method for a std::condition_variable requires using a lambda function if the optional condition is specified.判断题

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