C++: Using arrays with threads

The following C++ code demonstrates how to safely use an array that is written to by one thread and read from in another thread:

	//How to safely use an array that is written to by one thread and read from in another thread.
	//Requires C++11 or later.
	//Şamil Korkmaz, 10.03.2022, public domain.
	#include <chrono>
	#include <iostream>
	#include <thread>
	#include <mutex>
	std::mutex mx;
	std::condition_variable cv;
	const size_t arraySize = 1000;
	double arr[arraySize];
	void writeArray() {
	size_t counter = 0;
	while (1) {
	auto currentTime = std::chrono::steady_clock::now();
	auto nextTime = currentTime + std::chrono::milliseconds(1);
	//printf("writeArray, counter = %d\n", counter);
	{ //critical section
	std::unique_lock<std::mutex> lock(mx);
	for (size_t i = 0; i < arraySize; i++) {
	arr[i] = counter;
	}
	} //lock is automatically released here
	cv.notify_all(); //let other threads to get lock
	counter++;
	std::this_thread::sleep_until(nextTime);
	}
	}
	void readArray() {
	while (1) {
	auto currentTime = std::chrono::steady_clock::now();
	auto nextTime = currentTime + std::chrono::milliseconds(1);
	double arrStart;
	double arrEnd;
	{ //critical section
	std::unique_lock<std::mutex> lock(mx);
	cv.wait(lock); //wait for writeArray to finish
	arrStart = arr[0];
	arrEnd = arr[arraySize - 1];
	} //lock is automatically released here
	auto arrDiff = arrEnd - arrStart;
	printf("* readArray, arrStart = %1.0f, arrEnd = %1.0f, arrDiff = %1.1f\n", arrStart, arrEnd, arrDiff);
	if (arrDiff < 0) //happens when the end of array is lagging behing beginning of array. You trigger it by commenting out the lock line above
	{
	printf("End of array lagging behind beginning of array! arrDiff = %1.1f < 0\n", arrDiff);
	std::cout << "Press enter..." << std::endl;
	std::cin.get();
	exit(1);
	}
	std::this_thread::sleep_until(nextTime);
	}
	}
	int main() {
	std::thread worker1(writeArray);
	std::thread worker2(readArray);
	worker1.join();
	worker2.join();
	std::cout << "Press enter..." << std::endl;
	std::cin.get();
	}

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