Select and implement synchronization primitives that match your concurrency requirements and avoid unsafe patterns. Consider the number of consumers, thread safety requirements, and proper initialization order. Key guidelines: - Avoid environment variable modification (`std::env::set_var`, `std::env::remove_var`) in multi-threaded programs as it can cause data races with C/C++ code - Choose channel types based on usage patterns: use `broadcast` channels for multiple consumers, `mpsc` for single consumers - Use proper synchronization primitives like conditional variables instead of polling loops for thread coordination - Implement async flags and initialization correctly to prevent race conditions and out-of-order execution Example of correct async flag implementation: ```rust impl AsyncFlag { pub fn raise(&self) { self.0.add_permits(1); // Preserve semaphore state } pub async fn wait_raised(&self) { drop(self.0.acquire().await); // Proper waiting mechanism } } ``` Avoid unsafe patterns like direct environment modification in multi-threaded contexts, and ensure synchronization primitives maintain proper ordering and state consistency throughout their lifecycle.