spin lock on x86

// spinlock.cpp : Defines the entry point for the console application.
//
// By Kyungmin Cho, bro@shinbiro.com
// 2006/07/28 http://neri.cafe24.com
//
#include "stdafx.h"
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <process.h>

typedef struct _spinlock
{
        int lock;
}spinlock;

void spin_lock_init( spinlock* s )
{
        s->lock = 1;        // unlocked.
}

int test_and_set( int* val, int newval )
{
        int prev;
        __asm
        {
                mov eax, newval
                mov ebx, val
                xchg eax, [ebx]                // 모든 코어에 대해 상호배재임. lock; prefix없어도 됨
                mov prev, eax
        }
        return prev;
}

void spin_lock( spinlock* s )
{
        int prev = 0;
        int* plock = &s->lock;
        do
        {
                // set s = 0 (lock)
                prev = test_and_set( &s->lock, 0 );
                if( s->lock == 0 && prev == 1 )
                        break;
        }while(1);
}

void spin_unlock( spinlock* s )
{
        test_and_set( &s->lock, 1 ); // unlock
}

// spin lock 획득 가능한가 한번 시도해보고 바로 리턴
int spin_lock_try( spinlock* s )
{
        int prev;
        prev = test_and_set( &s->lock, 0 );
        if( s->lock == 0 && prev == 1 )
                return 1;        // spin lock 획득!
        return 0; // 획득 실패
}

spinlock s;

void task1(void*)
{
        spin_lock( &s );

        printf("[task1] ok! \n");

        Sleep(1000);

        printf("[task1] somthing! \n");

        spin_unlock( &s );
}

void task2(void*)
{
        spin_lock( &s );

        printf("[task2] ok! \n");

        Sleep(1000);

        printf("[task2] somthing! \n");

        spin_unlock( &s );
}

int main(int argc, char* argv[])
{
        s.lock = 1;

        _beginthread( task1, 0, 0 );
        _beginthread( task2, 0, 0 );
        
        getch();
        return 0;
}