mpv/osdep/atomics.h

/*
 * This file is part of mpv.
 * Copyright (c) 2013 Stefano Pigozzi <stefano.pigozzi@gmail.com>
 *
 * mpv is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * mpv is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef MP_ATOMICS_H
#define MP_ATOMICS_H

#include <inttypes.h>
#include "config.h"

#if HAVE_STDATOMIC
#include <stdatomic.h>
#else

// Emulate the parts of C11 stdatomic.h needed by mpv.
// Still relies on gcc/clang atomic builtins.
// The t field is a hack to make the non-atomic fallback macro mess work.

typedef struct { volatile unsigned long v, t;       } atomic_ulong;
typedef struct { volatile int v, t;                 } atomic_int;
typedef struct { volatile unsigned int v, t;        } atomic_uint;
typedef struct { volatile _Bool v, t;               } atomic_bool;
typedef struct { volatile long long v, t;           } atomic_llong;
typedef struct { volatile uint_least32_t v, t;      } atomic_uint_least32_t;
typedef struct { volatile unsigned long long v, t;  } atomic_ullong;

#define ATOMIC_VAR_INIT(x) \
    {.v = (x)}

#define memory_order_relaxed 1
#define memory_order_seq_cst 2

#define atomic_load_explicit(p, e) atomic_load(p)

#if HAVE_ATOMIC_BUILTINS

#define atomic_load(p) \
    __atomic_load_n(&(p)->v, __ATOMIC_SEQ_CST)
#define atomic_store(p, val) \
    __atomic_store_n(&(p)->v, val, __ATOMIC_SEQ_CST)
#define atomic_fetch_add(a, b) \
    __atomic_fetch_add(&(a)->v, b, __ATOMIC_SEQ_CST)
#define atomic_fetch_and(a, b) \
    __atomic_fetch_and(&(a)->v, b, __ATOMIC_SEQ_CST)
#define atomic_fetch_or(a, b) \
    __atomic_fetch_or(&(a)->v, b, __ATOMIC_SEQ_CST)
#define atomic_compare_exchange_strong(a, b, c) \
    __atomic_compare_exchange_n(&(a)->v, b, c, 0, __ATOMIC_SEQ_CST, \
    __ATOMIC_SEQ_CST)

#elif HAVE_SYNC_BUILTINS

#define atomic_load(p) \
    __sync_fetch_and_add(&(p)->v, 0)
#define atomic_store(p, val) \
    (__sync_synchronize(), (p)->v = (val), __sync_synchronize())
#define atomic_fetch_add(a, b) \
    __sync_fetch_and_add(&(a)->v, b)
#define atomic_fetch_and(a, b) \
    __sync_fetch_and_and(&(a)->v, b)
#define atomic_fetch_or(a, b) \
    __sync_fetch_and_or(&(a)->v, b)
// Assumes __sync_val_compare_and_swap is "strong" (using the C11 meaning).
#define atomic_compare_exchange_strong(p, old, new) \
    ({ __typeof__((p)->v) val_ = __sync_val_compare_and_swap(&(p)->v, *(old), new); \
       bool ok_ = val_ == *(old);       \
       if (!ok_) *(old) = val_;         \
       ok_; })

#else

// This is extremely wrong. The build system actually disables code that has
// a serious dependency on working atomics, so this is barely ok.
#define atomic_load(p) ((p)->v)
#define atomic_store(p, val) ((p)->v = (val))
#define atomic_fetch_op_(a, b, op) \
    ((a)->t = (a)->v, (a)->v = (a)->v op (b), (a)->t)
#define atomic_fetch_add(a, b) atomic_fetch_op_(a, b, +)
#define atomic_fetch_and(a, b) atomic_fetch_op_(a, b, &)
#define atomic_fetch_or(a, b) atomic_fetch_op_(a, b, |)
#define atomic_compare_exchange_strong(p, old, new) \
    ((p)->v == *(old) ? ((p)->v = (new), 1) : (*(old) = (p)->v, 0))

#endif /* no atomics */

#endif /* else HAVE_STDATOMIC */

#endif