Synchronization Primitives

Core building blocks

• std::mutex: exclusive lock.
• std::shared_mutex: many readers or one writer.
• std::condition_variable: wait for state changes.
• std::counting_semaphore: limit concurrent access to a pool.
• std::latch: one-shot rendezvous.
• std::barrier: repeated phase synchronization.

Reader-writer locking

std::shared_mutex mutex;

void read_value() {
    std::shared_lock lock(mutex);
}

void write_value() {
    std::unique_lock lock(mutex);
}

Semaphores

std::counting_semaphore<4> slots(4);

Use semaphores when access should be capped instead of fully serialized.

Coordination tools

• latch: workers finish setup before the next step begins.
• barrier: multiple threads repeat phased work together.

Practical guidance

• Prefer simple mutex-based designs before lock-free ideas.
• Protect invariants, not just individual variables.
• Keep waits predicate-based and cancellation-aware when possible.