#include<atomic>
#include<cassert>#define SPIN_LOCK_UNLOCK 0
#define SPIN_LOCK_WRITE_LOCK -1using std::atomic;
using std::atomic_int;
using std::atomic_store_explicit;
using std::atomic_load_explicit;
using std::atomic_compare_exchange_weak_explicit;
using std::memory_order_relaxed;
using std::memory_order_acquire;
using std::memory_order_release;

typedef atomic<int> spinlock_t;void rwlock_init(spinlock_t &l)
{atomic_store_explicit(&l, SPIN_LOCK_UNLOCK, memory_order_relaxed);
}void read_lock(spinlock_t &l)
{int expected;int desired;while(true){expected = atomic_load_explicit(&l, memory_order_relaxed);if(expected >= 0){desired = 1 + expected;if(atomic_compare_exchange_weak_explicit(&l, &expected, desired, memory_order_relaxed, memory_order_relaxed))break; // success
        }}atomic_thread_fence(memory_order_acquire); // sync
}void read_unlock(spinlock_t &l)
{int expected;int desired;while(true){expected = atomic_load_explicit(&l, memory_order_relaxed);if(expected > 0){desired = expected - 1;atomic_thread_fence(memory_order_release); // syncif(atomic_compare_exchange_weak_explicit(&l, &expected, desired, memory_order_relaxed, memory_order_relaxed))break; // success
        }else{assert(false);}}
}void write_lock(spinlock_t &l)
{int expected;int desired;while(true){expected = atomic_load_explicit(&l, memory_order_relaxed);if(expected == SPIN_LOCK_UNLOCK){desired = SPIN_LOCK_WRITE_LOCK;if(atomic_compare_exchange_weak_explicit(&l, &expected, desired, memory_order_relaxed, memory_order_relaxed))break; // success
        }}atomic_thread_fence(memory_order_release); // sync
}void write_unlock(spinlock_t &l)
{int expected;int desired;while(true){expected = atomic_load_explicit(&l, memory_order_relaxed);if(expected == SPIN_LOCK_WRITE_LOCK){desired = SPIN_LOCK_UNLOCK;atomic_thread_fence(memory_order_release); // syncif(atomic_compare_exchange_weak_explicit(&l, &expected, desired, memory_order_relaxed, memory_order_relaxed))break; // success
        }else{assert(false);}}
}//#include<thread>
#include<boost/thread.hpp>
#include<iostream>spinlock_t g_lock;
long g_total;
const int count = 5000;void add_job()
{for(int i = 0; i < count; ++i){write_lock(g_lock);++g_total;std::cout << "Thread ++ " << boost::this_thread::get_id() << std::endl;write_unlock(g_lock);}
}void read_job()
{for(int i = 0; i < count; ++i){read_lock(g_lock);std::cout << g_total << std::endl;;read_unlock(g_lock);}
}int main()
{g_total = 0;rwlock_init(g_lock);boost::thread th1(add_job);boost::thread th2(add_job);boost::thread th3(read_job);boost::thread th4(read_job);boost::thread th5(read_job);th1.join();th2.join();th3.join();th4.join();th5.join();std::cout << "The total: " << g_total << std::endl;
}

g++  -std=c++11 -Wall -O2 spinlock.cpp -I/d/Sources/boost_1_55_0 -L /d/Sources/boost_1_55_0/stage/lib/ -lboost_thread-mgw48-mt-1_55 -lboost_system-mgw48-mt-1_55