cpp condition variable

Sure! Here is an explanation of using a condition variable in C++:

Step 1: Include the necessary header files

To use condition variables in C++, you need to include the <condition_variable> header file.

Step 2: Define the condition variable

Declare a condition variable object by using the std::condition_variable class. You can give it a name of your choice.

std::condition_variable cv;

Step 3: Create a mutex

To protect the shared data that the condition variable is associated with, you need to create a mutex (mutual exclusion) object. The mutex ensures that only one thread at a time can access the shared data.

std::mutex mtx;

Step 4: Define a shared variable

Create a shared variable that multiple threads will be waiting for or modifying. This variable should be protected by the mutex.

bool sharedVariable = false;

Step 5: Wait for a condition

In a thread that needs to wait for a certain condition to be met, you can use the std::unique_lock class along with the condition variable's wait() function. The wait() function releases the lock on the mutex and puts the thread to sleep until the condition is met.

std::unique_lock<std::mutex> lock(mtx);
cv.wait(lock, []{ return sharedVariable; });

The lambda function [] { return sharedVariable; } is used as a predicate to check if the condition is met. If the condition is not met, the thread will wait until another thread notifies it.

Step 6: Notify other threads

To notify waiting threads that the condition has changed, you can use the condition variable's notify_one() or notify_all() functions. The notify_one() function wakes up one waiting thread, while notify_all() wakes up all waiting threads.

sharedVariable = true;
cv.notify_one();

It's important to note that the condition variable should be used in conjunction with a mutex to ensure thread safety and avoid race conditions.

That's it! By following these steps, you can use a condition variable in C++ to synchronize threads based on certain conditions.