src/gmxlib/nonbonded/nb_kernel_f77_double/nb_kernel_f77sync.c

   1 /*
   2  *                This source code is part of
   3  *
   4  *                 G   R   O   M   A   C   S
   5  *
   6  * Copyright (c) 1991-2000, University of Groningen, The Netherlands.
   7  * Copyright (c) 2001-2009, The GROMACS Development Team
   8  *
   9  * Gromacs is a library for molecular simulation and trajectory analysis,
  10  * written by Erik Lindahl, David van der Spoel, Berk Hess, and others - for
  11  * a full list of developers and information, check out http://www.gromacs.org
  12  *
  13  * This program is free software; you can redistribute it and/or modify it under
  14  * the terms of the GNU Lesser General Public License as published by the Free
  15  * Software Foundation; either version 2 of the License, or (at your option) any
  16  * later version.
  17  * As a special exception, you may use this file as part of a free software
  18  * library without restriction.  Specifically, if other files instantiate
  19  * templates or use macros or inline functions from this file, or you compile
  20  * this file and link it with other files to produce an executable, this
  21  * file does not by itself cause the resulting executable to be covered by
  22  * the GNU Lesser General Public License.
  23  *
  24  * In plain-speak: do not worry about classes/macros/templates either - only
  25  * changes to the library have to be LGPL, not an application linking with it.
  26  *
  27  * To help fund GROMACS development, we humbly ask that you cite
  28  * the papers people have written on it - you can find them on the website!
  29  */
  30
  31
  32 #ifdef HAVE_CONFIG_H
  33 #include <config.h>
  34 #endif
  35
  36 #ifdef HAVE_PTHREAD_H
  37 #include <pthread.h>
  38 #endif
  39
  40 #include <stdio.h>
  41
  42 /*! \brief Lock innerloop mutex and read lists indices
  43  *
  44  *  \internal
  45  *
  46  *  This routine is only used when both Fortran innerloops
  47  *  and threads are enabled.
  48  *
  49  *  Since the Fortran77 standard does not include support
  50  *  for POSIX threads, we call this routine instead which
  51  *
  52  *    -  Locks the provided mutex
  53  *    -  Reads the counter from memory
  54  *    -  Advances the counter in successively smaller chunks
  55  *    -  Releases the mutex
  56  *
  57  *  In other words, it performs exactly the same action as
  58  *  we do natively in the nonbonded kernel outer loop
  59  *  when using C language for the kernels.
  60  *
  61  * Fortran does not know anything about a mutex, but since
  62  * arguments are passed by reference we mask it as a pointer
  63  * to an integer in the Fortran code.
  64  *
  65  * \param mtx       Pointer to the mutex to use, masked as int
  66  * \param count     Pointer to the outer loop counter
  67  * \param nri       Total umber of (outer loop) neighborlists
  68  * \param nthreads  Number of working threads
  69  * \param nn0       Returned value: Low index to use for outerloop
  70  * \param nn1       Returned value: High index to use for outerloop
  71  *
  72  * \warning There is one possible cause of problems. Some
  73  *          fortran compilers make all variables static by
  74  *          default, and that will obviously screw up
  75  *          multithreading in a major way. If your Fortran
  76  *          compiler does this you only have two alternatives:
  77  *          Either find the flag to turn it off, or compile
  78  *          Gromacs without any Fortran nonbonded kernels.
  79  */
  80 void
  81 F77_FUNC(f77kernelsync,F77KERNELSYNC)
  82      (int *       mtx,
  83       int *       count,
  84       int *       nri,
  85       int *       nthreads,
  86       int *       nn0,
  87       int *       nn1)
  88 {
  89   int n0,n1;
  90
  91
  92 #ifdef HAVE_PTHREADS_H
  93   pthread_mutex_lock((pthread_mutex_t *)mtx);
  94 #endif
  95   n0              = *count;
  96   /* Take successively smaller chunks */
  97   n1              = n0+((*nri)-n0)/(2*(*nthreads))+3;
  98   *count          = n1;
  99 #ifdef HAVE_PTHREADS_H
 100   pthread_mutex_unlock((pthread_mutex_t *)mtx);
 101 #endif
 102   *nn0            = n0;
 103   *nn1            = n1;
 104 }