CPP Concurrency & Multithreading 3

Question 1

What is a data race in C++?

Accepted Answer

Two threads simultaneously accessing the same memory location where at least one access is a write and neither is synchronized

Answer

A data race is undefined behavior in C++ and occurs when two or more threads concurrently access the same memory location without synchronization, with at least one write.

Question 2

Which memory order provides the strongest synchronization guarantee in C++?

Accepted Answer

`std::memory_order_seq_cst`

Answer

`std::memory_order_seq_cst` (sequentially consistent) is the default and strongest ordering, ensuring a single total order of operations across all threads.

Question 3

What does `std::async` return?

Accepted Answer

`std::future`

Answer

`std::async` launches a callable asynchronously (or deferred) and returns a `std::future` object through which the result can be retrieved.

Question 4

What is the purpose of `std::promise` in C++ concurrency?

Accepted Answer

To provide a one-time channel for passing a value or exception from a producer thread to a consumer via an associated `std::future`

Answer

`std::promise` is one end of a future-promise pair: the promise sets a value or exception, and the associated `std::future` retrieves it, enabling one-time inter-thread communication.

Question 5

What is `std::call_once` used for?

Accepted Answer

Ensuring a function executes exactly once across all threads, even with concurrent calls

Answer

`std::call_once` with a `std::once_flag` guarantees that a callable is executed exactly once, even if multiple threads call it simultaneously — useful for thread-safe lazy initialization.

(CPP) C++ Programming Professional Certificate Practice Test

(CPP) C++ Programming Professional Certificate Practice Test

CPP Concurrency & Multithreading 3