// intrinExample.cpp
// compile with: /EHsc /O2
// Simple example of using _Interlocked* intrinsics to
// do manual synchronization
//
// Add [-DSKIP_LOCKING] to the command line to disable
// the locking. This will cause the threads to execute out
// of sequence.

#define _CRT_RAND_S
 
#include "windows.h"
 
#include <iostream>
#include <queue>
#include <intrin.h>
 
using namespace std;
 
// --------------------------------------------------------------------
 
// if defined, will not do any locking on shared data
//#define SKIP_LOCKING
 
// A common way of locking using _InterlockedCompareExchange.
// Please refer to other sources for a discussion of the many issues
// involved. For example, this particular locking scheme performs well 
// when lock contention is low, as the while loop overhead is small and
// locks are acquired very quickly, but degrades as many callers want
// the lock and most threads are doing a lot of interlocked spinning.
// There are also no guarantees that a caller will ever acquire the
// lock.
namespace MyInterlockedIntrinsicLock
{
    typedef unsigned LOCK, *PLOCK;
 
#pragma intrinsic(_InterlockedCompareExchange, _InterlockedExchange)
 
    enum {LOCK_IS_FREE = 0, LOCK_IS_TAKEN = 1};
 
    void Lock(PLOCK pl) 
    {
#if !defined(SKIP_LOCKING)
        // If *pl == LOCK_IS_FREE, it is set to LOCK_IS_TAKEN
        // atomically, so only 1 caller gets the lock.
        // If *pl == LOCK_IS_TAKEN,
        // the result is LOCK_IS_TAKEN, and the while loop keeps spinning.
        while (_InterlockedCompareExchange((long *)pl,
                                           LOCK_IS_TAKEN, // exchange
                                           LOCK_IS_FREE)  // comparand
               == LOCK_IS_TAKEN)
        {
            // spin!
            // call __yield() here on the IPF architecture to improve
            // performance.
        }
        // This will also work.
        //while (_InterlockedExchange(pl, LOCK_IS_TAKEN) == 
        //                             LOCK_IS_TAKEN)
        //{
        //    // spin!
        //}
 
        // At this point, the lock is acquired.
#endif
    }
 
    void Unlock(PLOCK pl) {
#if !defined(SKIP_LOCKING)
        _InterlockedExchange((long *)pl, LOCK_IS_FREE);
#endif
    }
}
 
// ------------------------------------------------------------------
 
// Data shared by threads
 
queue<int> SharedQueue;
MyInterlockedIntrinsicLock::LOCK SharedLock;
int TicketNumber;
 
// ------------------------------------------------------------------
 
DWORD WINAPI
ProducerThread(
    LPVOID unused
    )
{
    unsigned int randValue;
    while (1) {
        // Acquire shared data. Enter critical section.
        MyInterlockedIntrinsicLock::Lock(&SharedLock);
 
        //cout << ">" << TicketNumber << endl;
        SharedQueue.push(TicketNumber++);
 
        // Release shared data. Leave critical section.
        MyInterlockedIntrinsicLock::Unlock(&SharedLock);

        rand_s(&randValue);
        Sleep(randValue % 20);
    }
 
    return 0;
}
 
DWORD WINAPI
ConsumerThread(
    LPVOID unused
    )
{
    while (1) {
        // Acquire shared data. Enter critical section
        MyInterlockedIntrinsicLock::Lock(&SharedLock);
 
        if (!SharedQueue.empty()) {
            int x = SharedQueue.front();
            cout << "<" << x << endl;
            SharedQueue.pop();
        }
 
        // Release shared data. Leave critical section
        MyInterlockedIntrinsicLock::Unlock(&SharedLock);

        unsigned int randValue;
        rand_s(&randValue);
        Sleep(randValue % 20);
    }
    return 0;
}
 
 
int main(
    void
    )
{
    const int timeoutTime = 500;
    int unused1, unused2;
    HANDLE threads[4];
 
    // The program creates 4 threads:
    // two producer threads adding to the queue
    // and two consumers taking data out and printing it.
    threads[0] = CreateThread(NULL,
                              0,
                              ProducerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);
 
    threads[1] = CreateThread(NULL,
                              0,
                              ConsumerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);
 
    threads[2] = CreateThread(NULL,
                              0,
                              ProducerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);
 
    threads[3] = CreateThread(NULL,
                              0,
                              ConsumerThread,
                              &unused1,
                              0,
                              (LPDWORD)&unused2);
 
    WaitForMultipleObjects(4, threads, TRUE, timeoutTime);
 
    return 0;
}

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