What is the difference between a mutex lock and a condition variable in thread synchronization?

Mutex (mutual exclusion) is a synchronization primitive that provides exclusive access to a resource: at any given moment, only one thread can own the mutex and work with the protected data.

Condition Variable is a mechanism that allows a thread to wait for a certain condition to occur and, in the process, releases the mutex so that other threads can change the state, after which the waiting thread will be awakened.

Main differences:

• Mutex blocks access to a resource, preventing concurrent execution of a critical section.
• Condition Variable is used to organize waiting and notification between threads, allowing one thread to wait for an event and another to signal its occurrence.

Example of usage:

std::mutex mtx;
std::condition_variable cv;
bool ready = false;

// Consumer thread
std::unique_lock<std::mutex> lock(mtx);
cv.wait(lock, []{ return ready; }); // waits until ready == true
// continues work after waking up

// Producer thread
{
    std::lock_guard<std::mutex> guard(mtx);
    ready = true;
}
cv.notify_one(); // signals the consumer

Thus, the mutex controls access, and the condition variable coordinates thread interaction through waiting and notification.