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sfstack.c

/***********************************************************************
*                                                                      *
*               This software is part of the ast package               *
*          Copyright (c) 1985-2010 AT&T Intellectual Property          *
*                      and is licensed under the                       *
*                  Common Public License, Version 1.0                  *
*                    by AT&T Intellectual Property                     *
*                                                                      *
*                A copy of the License is available at                 *
*            http://www.opensource.org/licenses/cpl1.0.txt             *
*         (with md5 checksum 059e8cd6165cb4c31e351f2b69388fd9)         *
*                                                                      *
*              Information and Software Systems Research               *
*                            AT&T Research                             *
*                           Florham Park NJ                            *
*                                                                      *
*                 Glenn Fowler <gsf@research.att.com>                  *
*                  David Korn <dgk@research.att.com>                   *
*                   Phong Vo <kpv@research.att.com>                    *
*                                                                      *
***********************************************************************/
#include    "sfhdr.h"


/*    Push/pop streams
**
**    Written by Kiem-Phong Vo.
*/

#define STKMTXLOCK(f1,f2) \
      { if(f1) SFMTXLOCK(f1); \
        if(f2) SFMTXLOCK(f2); \
      }
#define STKMTXRETURN(f1,f2,rv) \
      { if(f1) SFMTXUNLOCK(f1); \
        if(f2) SFMTXUNLOCK(f2); \
        return(rv); \
      }

#if __STD_C
Sfio_t* sfstack(Sfio_t* f1, Sfio_t* f2)
#else
Sfio_t* sfstack(f1,f2)
Sfio_t*     f1;   /* base of stack  */
Sfio_t*     f2;   /* top of stack   */
#endif
{
      reg int           n;
      reg Sfio_t* rf;
      reg Sfrsrv_t*     rsrv;
      reg Void_t* mtx;

      STKMTXLOCK(f1,f2);

      if(f1 && (f1->mode&SF_RDWR) != f1->mode && _sfmode(f1,0,0) < 0)
            STKMTXRETURN(f1,f2, NIL(Sfio_t*));
      if(f2 && (f2->mode&SF_RDWR) != f2->mode && _sfmode(f2,0,0) < 0)
            STKMTXRETURN(f1,f2, NIL(Sfio_t*));
      if(!f1)
            STKMTXRETURN(f1,f2, f2);

      /* give access to other internal functions */
      _Sfstack = sfstack;

      if(f2 == SF_POPSTACK)
      {     if(!(f2 = f1->push))
                  STKMTXRETURN(f1,f2, NIL(Sfio_t*));
            f2->mode &= ~SF_PUSH;
      }
      else
      {     if(f2->push)
                  STKMTXRETURN(f1,f2, NIL(Sfio_t*));
            if(f1->pool && f1->pool != &_Sfpool && f1->pool != f2->pool &&
               f1 == f1->pool->sf[0])
            {     /* get something else to pool front since f1 will be locked */
                  for(n = 1; n < f1->pool->n_sf; ++n)
                  {     if(SFFROZEN(f1->pool->sf[n]) )
                              continue;
                        (*_Sfpmove)(f1->pool->sf[n],0);
                        break;
                  }
            }
      }

      if(f2->pool && f2->pool != &_Sfpool && f2 != f2->pool->sf[0])
            (*_Sfpmove)(f2,0);

      /* swap streams */
      sfswap(f1,f2);

      /* but the reserved buffer and mutex must remain the same */
      rsrv = f1->rsrv; f1->rsrv = f2->rsrv; f2->rsrv = rsrv;
      mtx = f1->mutex; f1->mutex = f2->mutex; f2->mutex = mtx;

      SFLOCK(f1,0);
      SFLOCK(f2,0);

      if(f2->push != f2)
      {     /* freeze the pushed stream */
            f2->mode |= SF_PUSH;
            f1->push = f2;
            rf = f1;
      }
      else
      {     /* unfreeze the just exposed stream */
            f1->mode &= ~SF_PUSH;
            f2->push = NIL(Sfio_t*);
            rf = f2;
      }

      SFOPEN(f1,0);
      SFOPEN(f2,0);

      STKMTXRETURN(f1,f2, rf);
}

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