Re: [boost] Request for interest in the new Synchro library

Subject: Re: [boost] Request for interest in the new Synchro library
From: Dmitry Goncharov (dgoncharov_at_[hidden])
Date: 2009-03-04 04:06:32

vicente.botet wrote:
>> What about the following adapter?
>>
>>
>> #ifndef BOOST_BINSEM_HPP
>> #define BOOST_BINSEM_HPP
>>
>> #include <boost/thread.hpp>
>>
>> namespace boost
>> {
>> template <typename Semaphore>
>> class binary_semaphore
>> {
>> public:
>>    explicit binary_semaphore(int v)
>>        : m_sem(v)
>>    {}
>>
>>    void wait()
>>    {
>>        m_sem.wait();
>>    }
>>
>>    void post()
>>    {
>>        // If cannot lock then some other thread is posting.
>>        // In this case just return.
>>        if (m_mutex.try_lock())
>>        {
>>            try
>>            {
>>                // The result of try_wait() is not important.
>>                m_sem.try_wait();
>>                m_sem.post();
>>            }
>>            catch (...)
>>            {
>>                m_mutex.unlock();
>>                throw;
>>            }
>>            m_mutex.unlock();
>>        }
>>    }
>>
>>    bool timed_wait(boost::posix_time::ptime const& t)
>>    {
>>        return m_sem.timed_wait(t);
>>    }
>>
>>    bool try_wait()
>>    {
>>        return m_sem.try_wait();
>>    }
>>
>> private:
>>    boost::mutex m_mutex;
>>    Semaphore m_sem;
>> };
>> }
>>
>> #endif
>>
>> This adapter makes a binary semaphore out of a regular one. The post() 
>> method is not as efficient as it should be. On the other hand the 
>> adapter is very simple.
>> There is also a test attached.
>>     
>
> Thanks for the proposal. I have another alternative using inheritance that avoid adding a new mutex.
>
> template <typename ScopeTag=multi_threaded_tag>
> class basic_binary_semaphore: public basic_semaphore<ScopeTag> {
> public:
>     BOOST_COPY_CONSTRUCTOR_DELETE(basic_binary_semaphore) /*< disable copy construction >*/
>     BOOST_COPY_ASSIGNEMENT_DELETE(basic_binary_semaphore) /*< disable copy asignement >*/
>
>     inline explict basic_binary_semaphore(int initialCount):basic_semaphore<ScopeTag>(initialCount>0?1:0) {};
>
>     inline void post()
>     {
>         scoped_lock lock(this->m_mut);
>         if(this->m_count == 0){
>             this->m_cond.notify_one();
>             ++(this->m_count);
>         }
>     }
> };
> typedef basic_binary_semaphore<> binary_semaphore;
>
> Attached the complete file. What do you think?
>
> Thanks,
> Vicente
>   
>   
Could not find basic_semaphore in boost. Is it one from your Synchro 
library?

Locking a mutex inside post() is inefficient. If one thread has the 
mutex locked then there is no need to wait until the mutex is unlocked. 
Use try_lock() and return if cannot lock.

In one of the previous posts i described why a 
binary_semaphore::timed_wait() was superior in my case than 
condition_variable::timed_wait(). Using a condition variable defeats the 
purpose of a binary_semaphore (at least in my usage scenario).

BR, Dmitry