libatomic/config/posix/lock.c

   1 /* Copyright (C) 2012-2020 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 }