91d3598475
Add cmpxchgi(), cmpxchgl() and cpu_relax() functions that we can use
as simple primitives to build spinlocks out of.
PR-URL: https://github.com/libuv/libuv/pull/197
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
[NB: This is a back-port of commit a3c3b37 from the v1.x branch.]
61 lines
2.1 KiB
C
61 lines
2.1 KiB
C
/* Copyright (c) 2013, Ben Noordhuis <info@bnoordhuis.nl>
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#ifndef UV_ATOMIC_OPS_H_
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#define UV_ATOMIC_OPS_H_
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#include "internal.h" /* UV_UNUSED */
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UV_UNUSED(static int cmpxchgi(int* ptr, int oldval, int newval));
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UV_UNUSED(static long cmpxchgl(long* ptr, long oldval, long newval));
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UV_UNUSED(static void cpu_relax(void));
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/* Prefer hand-rolled assembly over the gcc builtins because the latter also
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* issue full memory barriers.
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*/
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UV_UNUSED(static int cmpxchgi(int* ptr, int oldval, int newval)) {
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#if defined(__i386__) || defined(__x86_64__)
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int out;
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__asm__ __volatile__ ("lock; cmpxchg %2, %1;"
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: "=a" (out), "+m" (*(volatile int*) ptr)
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: "r" (newval), "0" (oldval)
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: "memory");
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return out;
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#else
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return __sync_val_compare_and_swap(ptr, oldval, newval);
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#endif
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}
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UV_UNUSED(static long cmpxchgl(long* ptr, long oldval, long newval)) {
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#if defined(__i386__) || defined(__x86_64__)
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long out;
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__asm__ __volatile__ ("lock; cmpxchg %2, %1;"
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: "=a" (out), "+m" (*(volatile long*) ptr)
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: "r" (newval), "0" (oldval)
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: "memory");
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return out;
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#else
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return __sync_val_compare_and_swap(ptr, oldval, newval);
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#endif
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}
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UV_UNUSED(static void cpu_relax(void)) {
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#if defined(__i386__) || defined(__x86_64__)
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__asm__ __volatile__ ("rep; nop"); /* a.k.a. PAUSE */
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#endif
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}
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#endif /* UV_ATOMIC_OPS_H_ */
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