1  /* Copyright (C) 2012-2023 Free Software Foundation, Inc.
       2     Contributed by Richard Henderson <rth@redhat.com>.
       3  
       4     This file is part of the GNU Atomic Library (libatomic).
       5  
       6     Libatomic is free software; you can redistribute it and/or modify it
       7     under the terms of the GNU General Public License as published by
       8     the Free Software Foundation; either version 3 of the License, or
       9     (at your option) any later version.
      10  
      11     Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
      12     WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
      13     FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
      14     more details.
      15  
      16     Under Section 7 of GPL version 3, you are granted additional
      17     permissions described in the GCC Runtime Library Exception, version
      18     3.1, as published by the Free Software Foundation.
      19  
      20     You should have received a copy of the GNU General Public License and
      21     a copy of the GCC Runtime Library Exception along with this program;
      22     see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      23     <http://www.gnu.org/licenses/>.  */
      24  
      25  #include "libatomic_i.h"
      26  #include <pthread.h>
      27  
      28  
      29  /* The target page size.  Must be no larger than the runtime page size,
      30     lest locking fail with virtual address aliasing (i.e. a page mmaped
      31     at two locations).  */
      32  #ifndef PAGE_SIZE
      33  #define PAGE_SIZE	4096
      34  #endif
      35  
      36  /* The target cacheline size.  This is an optimization; the padding that
      37     should be applied to the locks to keep them from interfering.  */
      38  #ifndef CACHLINE_SIZE
      39  #define CACHLINE_SIZE	64
      40  #endif
      41  
      42  /* The granularity at which locks are applied.  Almost certainly the
      43     cachline size is the right thing to use here.  */
      44  #ifndef WATCH_SIZE
      45  #define WATCH_SIZE	CACHLINE_SIZE
      46  #endif
      47  
      48  struct lock
      49  {
      50    pthread_mutex_t mutex;
      51    char pad[sizeof(pthread_mutex_t) < CACHLINE_SIZE
      52  	   ? CACHLINE_SIZE - sizeof(pthread_mutex_t)
      53  	   : 0];
      54  };
      55  
      56  #define NLOCKS		(PAGE_SIZE / WATCH_SIZE)
      57  static struct lock locks[NLOCKS] = {
      58    [0 ... NLOCKS-1].mutex = PTHREAD_MUTEX_INITIALIZER
      59  };
      60  
      61  static inline uintptr_t 
      62  addr_hash (void *ptr)
      63  {
      64    return ((uintptr_t)ptr / WATCH_SIZE) % NLOCKS;
      65  }
      66  
      67  void
      68  libat_lock_1 (void *ptr)
      69  {
      70    pthread_mutex_lock (&locks[addr_hash (ptr)].mutex);
      71  }
      72  
      73  void
      74  libat_unlock_1 (void *ptr)
      75  {
      76    pthread_mutex_unlock (&locks[addr_hash (ptr)].mutex);
      77  }
      78  
      79  void
      80  libat_lock_n (void *ptr, size_t n)
      81  {
      82    uintptr_t h = addr_hash (ptr);
      83    size_t i = 0;
      84  
      85    /* Don't lock more than all the locks we have.  */
      86    if (n > PAGE_SIZE)
      87      n = PAGE_SIZE;
      88  
      89    do
      90      {
      91        pthread_mutex_lock (&locks[h].mutex);
      92        if (++h == NLOCKS)
      93  	h = 0;
      94        i += WATCH_SIZE;
      95      }
      96    while (i < n);
      97  }
      98  
      99  void
     100  libat_unlock_n (void *ptr, size_t n)
     101  {
     102    uintptr_t h = addr_hash (ptr);
     103    size_t i = 0;
     104  
     105    if (n > PAGE_SIZE)
     106      n = PAGE_SIZE;
     107  
     108    do
     109      {
     110        pthread_mutex_unlock (&locks[h].mutex);
     111        if (++h == NLOCKS)
     112  	h = 0;
     113        i += WATCH_SIZE;
     114      }
     115    while (i < n);
     116  }