/*  Copyright  (c)  Günter Woigk   1990-2005
                    mailto:kio@little-bat.de

    This file is free software

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

    Redistribution and use in source and binary forms, with or without 
    modification, are permitted provided that the following conditions are met:

    • Redistributions of source code must retain the above copyright notice, 
      this list of conditions and the following disclaimer.
    • Redistributions in binary form must reproduce the above copyright notice, 
      this list of conditions and the following disclaimer in the documentation 
      and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
    AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 
    THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR 
    CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
    EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 
    OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
    WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
    OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
    ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/


#ifndef Sema_h
#define Sema_h

#include "kio/kio.h"
#include "Thread.h"
#include "BPObj.h"


class Var;



/* ---- Semaphors ----------------------------------------------------
        sema.flag   > 0     blocked
        sema.flag   <=0     free
*/
struct Sema : private BPObj
{
friend class Var;

        long        flag;       // >0 blocked; <=0 free
        Tid         wait;       // linked list of waiting threads
        Tid         owner;      // Tid of blocking thread

        Sema*       next;       // linked list of all Semas blocked by same owner
        Sema*       prev;

//      Var*        sema_var;   // representer in global tree; unlocked

        void        link_owner  ( Tid newowner );
        void        unlink_owner( );

                    Sema        ( const Sema& );    // prohibit
        Sema&       operator=   ( const Sema& );    // prohibit

public:
                    Sema        ( )             : flag(0),wait(0),owner(0),next(0),prev(0) { }
                    ~Sema       ( );            // destructor: unlink waiting tasks!

        bool        IsFree      ( ) const       { return flag<=0; }
        bool        IsBlocked   ( ) const       { return flag>0;  }
        long        BlockCount  ( ) const       { return flag; }
        bool        IsAvailable ( ) const       { return IsFree()    || owner==MyTid(); }
        bool        IsNotAvailable()const       { return IsBlocked() && owner!=MyTid(); }
        bool        IsMine      ( ) const       { return IsBlocked() && owner==MyTid(); }
        bool        IsNotMine   ( ) const       { return IsFree()    || owner!=MyTid(); }
        bool        IsWaiting   ( ) const       { return wait!=0; }
        Tid         Owner       ( ) const       { return owner; }

        void        Clear       ( );            // reset to initial state
        bool        Request     ( int n=1 );    // request semaphor
        bool        Request_WTO ( double timeout, int n=1 );    // request semaphor
        void        Release     ( int n=1 );    // release semaphor
};







#endif