Mutex

In C, the basic threading tools are direct:

pthread_create(&tid, NULL, worker, ctx);
pthread_mutex_lock(&lock);
/* modify shared state */
pthread_mutex_unlock(&lock);

These tools can build reliable systems, but many rules are conventions:

• whether ctx points to data that may cross threads
• who owns that data
• whether multiple threads read and write it at the same time
• whether locking was forgotten
• which fields are protected by which lock
• whether resources outlive callbacks and thread exit paths

Rust does not make concurrency automatically simple. It moves some thread-safety requirements into types: