include <condition_variable>
#include <iostream>
#include <mutex>
#include <string>
#include <thread>
 
std::mutex m;
std::condition_variable cv;
std::string data;
bool ready = false;
bool processed = false;
 
void worker_thread()
{
    // wait until main() sends data
    std::unique_lock lk(m);
    cv.wait(lk, []{ return ready; });
 
    // after the wait, we own the lock
    std::cout << "Worker thread is processing data\n";
    data += " after processing";
 
    // send data back to main()
    processed = true;
    std::cout << "Worker thread signals data processing completed\n";
 
    // manual unlocking is done before notifying, to avoid waking up
    // the waiting thread only to block again (see notify_one for details)
    lk.unlock();
    cv.notify_one();
}
 
int main()
{
    std::thread worker(worker_thread);
 
    data = "Example data";
    // send data to the worker thread
    {
        std::lock_guard lk(m);
        ready = true;
        std::cout << "main() signals data ready for processing\n";
    }
    cv.notify_one();
 
    // wait for the worker
    {
        std::unique_lock lk(m);
        cv.wait(lk, []{ return processed; });
    }
    std::cout << "Back in main(), data = " << data << '\n';
 
    worker.join();
}

--------------------

// waiting for timeout after 5 seconds
std::chrono::seconds timeoutPeriod = 5;
auto timePoint = std::chrono::system_clock::now() + timeoutPeriod;
std::unique_lock<std::mutex> uLock(myDataMutex);
while(!DataAreReadyForProcessing())
{
    if (myCondVar.wait_until(uLock, timePoint) //<##
        == std::cv_status::timeout)
    {
        // data conditions where not fulfilled within
        // the time period; e.g. do some error handling
        break;
    }
}

--

if (myCondVar.wait_for(uLock, timeoutPeriod,
    DataAreReadyForProcessing))
{
    // data conditions where fulfilled
    // regular processing
}
else // timeout occured, conditions are not fulfilled
{
    // e.g. do some error handling
}






-------------


static int rpmsg_sample_probe(struct rpmsg_device *rpdev)
{

	int ret;
	struct instance_data *idata;

	dev_info(&rpdev->dev, "new channel: 0x%x -> 0x%x!\n",
					rpdev->src, rpdev->dst);

	idata = devm_kzalloc(&rpdev->dev, sizeof(*idata), GFP_KERNEL);
	if (!idata)
		return -ENOMEM;

	dev_set_drvdata(&rpdev->dev, idata);

	/* send a message to our remote processor */
	ret = rpmsg_send(rpdev->ept, MSG, strlen(MSG));
	if (ret) {
		dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
		return ret;
	}

	return 0;