sample_spin_lock4.cpp

#include <chrono>
#include <thread>
#include <iostream> // std::cout
#include "spin_lock.hpp"  // SpinLock
 
std::chrono::milliseconds interval(100);
 
SpinLock mutex;
int job_shared = 0; // both threads can modify 'job_shared',
    // mutex will protect this variable
 
int job_exclusive = 0; // only one thread can modify 'job_exclusive'
    // no protection needed
 
// this thread can modify both 'job_shared' and 'job_exclusive'
void job_1() 
{
    std::this_thread::sleep_for(interval); // let 'job_2' take a lock
 
    while (true) {
        // try to lock mutex to modify 'job_shared'
        if (mutex.try_lock()) {
            std::cout << "job shared (" << job_shared << ")\n";
            mutex.unlock();
            return;
        } else {
            // can't get lock to modify 'job_shared'
            // but there is some other work to do
            ++job_exclusive;
            std::cout << "job exclusive (" << job_exclusive << ")\n";
            std::this_thread::sleep_for(interval);
        }
    }
}
 
// this thread can modify only 'job_shared'
void job_2() 
{
    mutex.lock();
    std::this_thread::sleep_for(5 * interval);
    ++job_shared;
    mutex.unlock();
}
 
int main() 
{
    std::thread thread_1(job_1);
    std::thread thread_2(job_2);
 
    thread_1.join();
    thread_2.join();
}

/*
Possible output:

job exclusive (1)
job exclusive (2)
job exclusive (3)
job exclusive (4)
job shared (1)
*/