#include <iostream>#include <mutex>#include <shared_mutex>#include <string>#include <thread> std::string file="Original content.";// Simulates a filestd::mutex output_mutex;// mutex that protects output operations.std::shared_mutex file_mutex;// reader/writer mutex void read_content(int id){std::string content;{std::shared_lock lock(file_mutex,std::defer_lock);// Do not lock it first.        lock.lock();// Lock it here.        content= file;}std::lock_guard lock(output_mutex);std::cout<<"Contents read by reader #"<< id<<": "<< content<<'\n';} void write_content(){{std::lock_guard file_lock(file_mutex);        file="New content";}std::lock_guard output_lock(output_mutex);std::cout<<"New content saved.\n";} int main(){std::cout<<"Two readers reading from file.\n"<<"A writer competes with them.\n";std::thread reader1{read_content,1};std::thread reader2{read_content,2};std::thread writer{write_content};    reader1.join();    reader2.join();    writer.join();std::cout<<"The first few operations to file are done.\n";    reader1=std::thread{read_content,3};    reader1.join();}

Two readers reading from file.A writer competes with them.Contents read by reader #1: Original content.Contents read by reader #2: Original content.New content saved.The first few operations to file are done.Contents read by reader #3: New content