125 lines
3.5 KiB
C++
125 lines
3.5 KiB
C++
// include/atomic.hh
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// This file is part of libpbe; see http://svn.chezphil.org/libpbe/
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// (C) 2008 Philip Endecott
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 2 of the License, or
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// any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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#ifndef libpbe_atomic_hh
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#define libpbe_atomic_hh
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// This file provides some basic atomic operations using the gcc builtins.
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// It doesn't attempt to provide an N2427-compatiable interface.
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// Memory ordering sematics are those provided by the gcc builtins,
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// which basically means that they all provide full memory barriers (I think).
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// We have a special version for ARM:
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#ifdef __arm__
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#include "atomic_arm.hh"
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#else
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// gcc provides __sync atomic primatives from version 4.1. However,
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// they didn't bother to add the feature-test-macros until version 4.2 or 4.3.
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// Ideally we would ignore the gcc versions that have the primitives
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// but don't tell us about them, but unfortunately that covers a few systems
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// that we might be interested in. So for the time being we'll fake it:
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#if __GNUC__ == 4 && __GNUC_MINOR__ == 1
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// Maybe need to check for 4.2 too.
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// This assumes that all types <= 32 bits are atomic, which is a good
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// bet but not 100% certain.
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#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1
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#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
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#define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
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#endif
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#if defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_1) || defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_2) \
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|| defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
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#define PBE_HAVE_ATOMICS
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namespace pbe {
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// The N2427 proposed CAS is:
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// if ( *object == *expected )
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// *object = desired;
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// else
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// *expected = *object;
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// The boolean result of the comparison is returned.
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// Note that *expected is updated if the comparison fails. This seems
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// odd to me; it isn't what the gcc builtin does. I'm going to provide
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// something closer to gcc.
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template <typename T>
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// T must of course be a type that's atomic on the hardware in use.
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// I hope that some sort of error will occur if it isn't.
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bool atomic_compare_and_swap(volatile T& var, T expected, T newval) {
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// The return value indicates the result of the compare.
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return __sync_bool_compare_and_swap(&var, expected, newval);
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}
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template <typename T>
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T atomic_post_dec(volatile T& var, T amt = 1) {
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return __sync_fetch_and_sub(&var, amt);
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}
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template <typename T>
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T atomic_pre_inc(volatile T& var, T amt = 1) {
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return __sync_add_and_fetch(&var, amt);
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}
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template <typename T>
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void atomic_inc(volatile T& var, T amt = 1) {
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__sync_fetch_and_add(&var, amt);
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}
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template <typename T>
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void atomic_dec(volatile T& var, T amt = 1) {
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__sync_fetch_and_sub(&var, amt);
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}
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template <typename T>
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T atomic_swap(volatile T& var, T newval) {
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return __sync_lock_test_and_set(&var,newval); // misnamed
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}
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template <typename T>
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T atomic_read(volatile T& var) {
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return var;
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};
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template <typename T>
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void atomic_write(volatile T& var, T newval) {
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var = newval;
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};
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};
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#endif
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#endif
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#endif
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