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.