gate.hxx

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#pragma once
 
#include <mutex>
#include <osl/conditn.hxx>
 
namespace framework{
 
/*-************************************************************************************************************
    @short          implement a gate to block multiple threads at the same time or unblock all
    @descr          A gate can be used as a negative-condition! You can open a "door" - wait() will not block ...
                    or you can close it - wait() blocks till open() is called again.
                    Then all currently waiting threads are running immediately - but new ones are blocked!
 
    @attention      To prevent us against wrong using, the default ctor, copy ctor and the =operator are marked private!
 
    @devstatus      ready to use
*//*-*************************************************************************************************************/
class Gate
{
 
    //  public methods
 
    public:
 
        /*-****************************************************************************************************
            @short      ctor
            @descr      These initialize the object right as an open gate.
        *//*-*****************************************************************************************************/
        Gate()
            :   m_bClosed   ( false )
        {
            open();
        }
 
        /*-****************************************************************************************************
            @short      dtor
            @descr      Is user forget it - we open the gate ...
                        blocked threads can running ... but I don't know
                        if it's right - we are destroyed yet!?
        *//*-*****************************************************************************************************/
        ~Gate()
        {
            open();
        }
        /*-****************************************************************************************************
            @short      copy-ctor
            @descr      Forbid copy construction
        *//*-*****************************************************************************************************/
        Gate(const Gate&) = delete;
        /*-****************************************************************************************************
            @short      copy-assignment
            @descr      Forbid copy assigning
        *//*-*****************************************************************************************************/
        Gate& operator=(const Gate&) = delete;
 
        /*-****************************************************************************************************
            @short      open the gate
            @descr      A wait() call will not block then.
 
            @seealso    method close()
        *//*-*****************************************************************************************************/
        void open()
        {
            // We must safe access to our internal member!
            std::unique_lock aLock( m_aAccessLock );
            // Set condition -> wait don't block any longer -> gate is open
            m_aPassage.set();
            // Check if operation was successful!
            // Check returns false if condition isn't set => m_bClosed will be true then => we must return false; opening failed
            m_bClosed = !m_aPassage.check();
        }
 
        /*-****************************************************************************************************
            @short      close the gate
            @descr      A wait() call will block then.
 
            @seealso    method open()
        *//*-*****************************************************************************************************/
        void close()
        {
            // We must safe access to our internal member!
            std::unique_lock aLock( m_aAccessLock );
            // Reset condition -> wait blocks now -> gate is closed
            m_aPassage.reset();
            // Check if operation was successful!
            // Check returns false if condition was reset => m_bClosed will be true then => we can return true; closing ok
            m_bClosed = !m_aPassage.check();
        }
 
        /*-****************************************************************************************************
            @short      must be called to pass the gate
            @descr      If gate "open"   => wait() will not block.
                        If gate "closed" => wait() will block till somewhere open it again.
 
            @seealso    method wait()
            @seealso    method open()
 
        *//*-*****************************************************************************************************/
        void wait()
        {
            // We must safe access to our internal member!
            std::unique_lock aLock( m_aAccessLock );
            // If gate not closed - caller can pass it.
            if( m_bClosed )
            {
                // Then we must release used access lock -
                // because next call will block...
                // and if we hold the access lock nobody else can use this object without a deadlock!
                aLock.unlock();
                // Wait for opening gate...
                m_aPassage.wait();
            }
        }
 
    //  private member
 
    private:
 
        std::mutex          m_aAccessLock;
        ::osl::Condition    m_aPassage;
        bool                m_bClosed;
 
};      //  class Gate
 
}       //  namespace framework
 
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