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In order to facilitate the fine-tuning of how `libatomic_i.h' and `host-config.h' headers are used by different atomic functions, we define distinct identifier macros for each file which, in implementing atomic operations, imports these headers. The idea is that different parts of these headers could then be conditionally defined depending on the macros set by the file that `#include'd them. Given how it is possible that some file names are generic enough that using them as-is for macro names (e.g. flag.c -> FLAG) may potentially lead to name clashes with other macros, all file names first have LAT_ prepended to them such that, for example, flag.c is assigned the LAT_FLAG macro. Libatomic/ChangeLog: * cas_n.c (LAT_CAS_N): New. * exch_n.c (LAT_EXCH_N): Likewise. * fadd_n.c (LAT_FADD_N): Likewise. * fand_n.c (LAT_FAND_N): Likewise. * fence.c (LAT_FENCE): Likewise. * fenv.c (LAT_FENV): Likewise. * fior_n.c (LAT_FIOR_N): Likewise. * flag.c (LAT_FLAG): Likewise. * fnand_n.c (LAT_FNAND_N): Likewise. * fop_n.c (LAT_FOP_N): Likewise * fsub_n.c (LAT_FSUB_N): Likewise. * fxor_n.c (LAT_FXOR_N): Likewise. * gcas.c (LAT_GCAS): Likewise. * gexch.c (LAT_GEXCH): Likewise. * glfree.c (LAT_GLFREE): Likewise. * gload.c (LAT_GLOAD): Likewise. * gstore.c (LAT_GSTORE): Likewise. * load_n.c (LAT_LOAD_N): Likewise. * store_n.c (LAT_STORE_N): Likewise. * tas_n.c (LAT_TAS_N): Likewise.
85 lines
3.1 KiB
C
85 lines
3.1 KiB
C
/* Copyright (C) 2012-2024 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Atomic Library (libatomic).
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Libatomic is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#define LAT_GLFREE
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#include "libatomic_i.h"
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/* Accesses with a power-of-two size are not lock-free if we don't have an
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integer type of this size or if they are not naturally aligned. They
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are lock-free if such a naturally aligned access is always lock-free
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according to the compiler, which requires that both atomic loads and CAS
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are available.
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In all other cases, we fall through to LARGER (see below). */
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#define EXACT(N) \
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do { \
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if (!C2(HAVE_INT,N)) break; \
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if ((uintptr_t)ptr & (N - 1)) break; \
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if (__atomic_always_lock_free(N, 0)) return true; \
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if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break; \
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if (C2(FAST_ATOMIC_LDST_,N)) return true; \
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} while (0)
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/* We next check to see if an access of a larger size is lock-free. We use
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a similar check as in EXACT, except that we also check that the alignment
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of the access is so that the data to be accessed is completely covered
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by the larger access. */
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#define LARGER(N) \
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do { \
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uintptr_t r = (uintptr_t)ptr & (N - 1); \
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if (!C2(HAVE_INT,N)) break; \
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if (!C2(FAST_ATOMIC_LDST_,N)) break; \
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if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break; \
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if (r + n <= N) return true; \
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} while (0)
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/* Note that this can return that a size/alignment is not lock-free even if
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all the operations that we use to implement the respective accesses provide
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lock-free forward progress as specified in C++14: Users likely expect
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"lock-free" to also mean "fast", which is why we do not return true if, for
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example, we implement loads with this size/alignment using a CAS. */
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bool
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libat_is_lock_free (size_t n, void *ptr)
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{
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switch (n)
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{
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case 0: return true;
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case 1: EXACT(1); goto L4;
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case 2: EXACT(2); goto L4;
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case 4: EXACT(4); goto L8;
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case 8: EXACT(8); goto L16;
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case 16: EXACT(16); break;
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case 3: L4: LARGER(4); /* FALLTHRU */
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case 5 ... 7: L8: LARGER(8); /* FALLTHRU */
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case 9 ... 15: L16: LARGER(16); break;
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}
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return false;
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}
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EXPORT_ALIAS (is_lock_free);
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#undef LAT_GLFREE
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