[boost] Re: [Boost.Thread] mutex Win32 implementation changes

From: Michael Glassford (glassfordm_at_[hidden])
Date: 2004-07-15 15:49:45

Alexander Terekhov wrote:

> Michael Glassford wrote:
> [...]
> 
>>Do you have a full-fledged implementation for such a beast? 
> 
> 
> Trade secret.
> 
> 
>>I remember you posting sample code some time back, ...
> 
> 
> class swap_based_mutex_for_windows { // noncopyable
> 
>   atomic<int>      m_lock_status; // 0: free, 1/-1: locked/contention
>   auto_reset_event m_retry_event; 
> 
> public:
> 
>   // ctor/dtor [w/o lazy event init] 
> 
>   void lock() throw() {
>     if (m_lock_status.swap(1, msync::acq)) 
>       while (m_lock_status.swap(-1, msync::acq))
>         m_retry_event.wait();
>   } 
> 
>   bool trylock() throw() {
>     return !m_lock_status.swap(1, msync::acq) ? 
>       true : !m_lock_status.swap(-1, msync::acq);
>   }
> 
>   bool timedlock(absolute_timeout const & timeout) throw() {
>     if (m_lock_status.swap(1, msync::acq)) {
>       while (m_lock_status.swap(-1, msync::acq))
>         if (!m_retry_event.timedwait(timeout)) 
>           return false;
>     } 
>     return true;
>   }
> 
>   void unlock() throw() {
>     if (m_lock_status.swap(0, msync::rel) < 0) 
>       m_retry_event.set();
>   } 
> 
> };

Looking at this again, it's not entirely clear to me what the return 
value of atomic<int>::swap() is. Can you clarify?

Thanks,

Mike