stdatomic.h

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/*
 * An implementation of C11 stdatomic.h directly borrowed from FreeBSD
 * (original copyright follows), with minor modifications for
 * portability to other systems. Works for recent Clang (that
 * implement the feature c_atomic) and GCC 4.7+; includes
 * compatibility for GCC below 4.7 but I wouldn't recommend it.
 *
 * Caveats and limitations:
 * - Only the ``_Atomic parentheses'' notation is implemented, while
 *   the ``_Atomic space'' one is not.
 * - _Atomic types must be typedef'ed, or programs using them will
 *   not type check correctly (incompatible anonymous structure
 *   types).
 * - Non-scalar _Atomic types would require runtime support for
 *   runtime locking, which, as far as I know, is not currently
 *   available on any system.
 */

/*-
 * Copyright (c) 2011 Ed Schouten <ed@FreeBSD.org>
 *                    David Chisnall <theraven@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 */

#ifndef _STDATOMIC_H_
#define _STDATOMIC_H_

#include <stddef.h>
#include <stdint.h>

#if !defined(__has_feature)
#define __has_feature(x) 0
#endif
#if !defined(__has_builtin)
#define __has_builtin(x) 0
#endif
#if !defined(__GNUC_PREREQ__)
#if defined(__GNUC__) && defined(__GNUC_MINOR__)
#define __GNUC_PREREQ__(maj, min)                                       \
        ((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
#else
#define __GNUC_PREREQ__(maj, min) 0
#endif
#endif

#if !defined(__CLANG_ATOMICS) && !defined(__GNUC_ATOMICS)
#if __has_feature(c_atomic)
#define __CLANG_ATOMICS
#elif __GNUC_PREREQ__(4, 7)
#define __GNUC_ATOMICS
#elif !defined(__GNUC__)
#error "stdatomic.h does not support your compiler"
#endif
#endif

/*
 * language independent type to represent a Boolean value
 */

typedef int __Bool;

/*
 * 7.17.1 Atomic lock-free macros.
 */

#ifdef __GCC_ATOMIC_BOOL_LOCK_FREE
#define ATOMIC_BOOL_LOCK_FREE           __GCC_ATOMIC_BOOL_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_CHAR_LOCK_FREE
#define ATOMIC_CHAR_LOCK_FREE           __GCC_ATOMIC_CHAR_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_CHAR16_T_LOCK_FREE
#define ATOMIC_CHAR16_T_LOCK_FREE       __GCC_ATOMIC_CHAR16_T_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_CHAR32_T_LOCK_FREE
#define ATOMIC_CHAR32_T_LOCK_FREE       __GCC_ATOMIC_CHAR32_T_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_WCHAR_T_LOCK_FREE
#define ATOMIC_WCHAR_T_LOCK_FREE        __GCC_ATOMIC_WCHAR_T_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_SHORT_LOCK_FREE
#define ATOMIC_SHORT_LOCK_FREE          __GCC_ATOMIC_SHORT_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_INT_LOCK_FREE
#define ATOMIC_INT_LOCK_FREE            __GCC_ATOMIC_INT_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_LONG_LOCK_FREE
#define ATOMIC_LONG_LOCK_FREE           __GCC_ATOMIC_LONG_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_LLONG_LOCK_FREE
#define ATOMIC_LLONG_LOCK_FREE          __GCC_ATOMIC_LLONG_LOCK_FREE
#endif
#ifdef __GCC_ATOMIC_POINTER_LOCK_FREE
#define ATOMIC_POINTER_LOCK_FREE        __GCC_ATOMIC_POINTER_LOCK_FREE
#endif

#if !defined(__CLANG_ATOMICS)
#define _Atomic(T)                      struct { volatile __typeof__(T) __val; }
#endif

/*
 * 7.17.2 Initialization.
 */

#if defined(__CLANG_ATOMICS)
#define ATOMIC_VAR_INIT(value)          (value)
#define atomic_init(obj, value)         __c11_atomic_init(obj, value)
#else
#define ATOMIC_VAR_INIT(value)          { .__val = (value) }
#define atomic_init(obj, value)         ((void)((obj)->__val = (value)))
#endif

/*
 * Clang and recent GCC both provide predefined macros for the memory
 * orderings.  If we are using a compiler that doesn't define them, use the
 * clang values - these will be ignored in the fallback path.
 */

#ifndef __ATOMIC_RELAXED
#define __ATOMIC_RELAXED                0
#endif
#ifndef __ATOMIC_CONSUME
#define __ATOMIC_CONSUME                1
#endif
#ifndef __ATOMIC_ACQUIRE
#define __ATOMIC_ACQUIRE                2
#endif
#ifndef __ATOMIC_RELEASE
#define __ATOMIC_RELEASE                3
#endif
#ifndef __ATOMIC_ACQ_REL
#define __ATOMIC_ACQ_REL                4
#endif
#ifndef __ATOMIC_SEQ_CST
#define __ATOMIC_SEQ_CST                5
#endif

/*
 * 7.17.3 Order and consistency.
 *
 * The memory_order_* constants that denote the barrier behaviour of the
 * atomic operations.
 */

typedef enum {
        memory_order_relaxed = __ATOMIC_RELAXED,
        memory_order_consume = __ATOMIC_CONSUME,
        memory_order_acquire = __ATOMIC_ACQUIRE,
        memory_order_release = __ATOMIC_RELEASE,
        memory_order_acq_rel = __ATOMIC_ACQ_REL,
        memory_order_seq_cst = __ATOMIC_SEQ_CST
} memory_order;

/*
 * 7.17.4 Fences.
 */

#define __unused

static __inline void
atomic_thread_fence(memory_order __order __unused)
{

#ifdef __CLANG_ATOMICS
        __c11_atomic_thread_fence(__order);
#elif defined(__GNUC_ATOMICS)
        __atomic_thread_fence(__order);
#else
        __sync_synchronize();
#endif
}

static __inline void
atomic_signal_fence(memory_order __order __unused)
{

#ifdef __CLANG_ATOMICS
        __c11_atomic_signal_fence(__order);
#elif defined(__GNUC_ATOMICS)
        __atomic_signal_fence(__order);
#else
        __asm volatile ("" ::: "memory");
#endif
}

#undef __unused

/*
 * 7.17.5 Lock-free property.
 */

#if defined(_KERNEL)
/* Atomics in kernelspace are always lock-free. */
#define atomic_is_lock_free(obj) \
        ((void)(obj), (__Bool)1)
#elif defined(__CLANG_ATOMICS)
#define atomic_is_lock_free(obj) \
        __atomic_is_lock_free(sizeof(*(obj)), obj)
#elif defined(__GNUC_ATOMICS)
#define atomic_is_lock_free(obj) \
        __atomic_is_lock_free(sizeof((obj)->__val), &(obj)->__val)
#else
#define atomic_is_lock_free(obj) \
        ((void)(obj), sizeof((obj)->__val) <= sizeof(void *))
#endif

/*
 * 7.17.6 Atomic integer types.
 */

typedef _Atomic(__Bool)                 atomic_bool;
typedef _Atomic(char)                   atomic_char;
typedef _Atomic(signed char)            atomic_schar;
typedef _Atomic(unsigned char)          atomic_uchar;
typedef _Atomic(short)                  atomic_short;
typedef _Atomic(unsigned short)         atomic_ushort;
typedef _Atomic(int)                    atomic_int;
typedef _Atomic(unsigned int)           atomic_uint;
typedef _Atomic(long)                   atomic_long;
typedef _Atomic(unsigned long)          atomic_ulong;
typedef _Atomic(long long)              atomic_llong;
typedef _Atomic(unsigned long long)     atomic_ullong;
#if 0
typedef _Atomic(char16_t)               atomic_char16_t;
typedef _Atomic(char32_t)               atomic_char32_t;
#endif
typedef _Atomic(wchar_t)                atomic_wchar_t;
typedef _Atomic(int_least8_t)           atomic_int_least8_t;
typedef _Atomic(uint_least8_t)          atomic_uint_least8_t;
typedef _Atomic(int_least16_t)          atomic_int_least16_t;
typedef _Atomic(uint_least16_t)         atomic_uint_least16_t;
typedef _Atomic(int_least32_t)          atomic_int_least32_t;
typedef _Atomic(uint_least32_t)         atomic_uint_least32_t;
typedef _Atomic(int_least64_t)          atomic_int_least64_t;
typedef _Atomic(uint_least64_t)         atomic_uint_least64_t;
typedef _Atomic(int_fast8_t)            atomic_int_fast8_t;
typedef _Atomic(uint_fast8_t)           atomic_uint_fast8_t;
typedef _Atomic(int_fast16_t)           atomic_int_fast16_t;
typedef _Atomic(uint_fast16_t)          atomic_uint_fast16_t;
typedef _Atomic(int_fast32_t)           atomic_int_fast32_t;
typedef _Atomic(uint_fast32_t)          atomic_uint_fast32_t;
typedef _Atomic(int_fast64_t)           atomic_int_fast64_t;
typedef _Atomic(uint_fast64_t)          atomic_uint_fast64_t;
typedef _Atomic(intptr_t)               atomic_intptr_t;
typedef _Atomic(uintptr_t)              atomic_uintptr_t;
typedef _Atomic(size_t)                 atomic_size_t;
typedef _Atomic(ptrdiff_t)              atomic_ptrdiff_t;
typedef _Atomic(intmax_t)               atomic_intmax_t;
typedef _Atomic(uintmax_t)              atomic_uintmax_t;

/*
 * 7.17.7 Operations on atomic types.
 */

/*
 * Compiler-specific operations.
 */

#if defined(__CLANG_ATOMICS)
#define atomic_compare_exchange_strong_explicit(object, expected,       \
    desired, success, failure)                                          \
        __c11_atomic_compare_exchange_strong(object, expected, desired, \
            success, failure)
#define atomic_compare_exchange_weak_explicit(object, expected,         \
    desired, success, failure)                                          \
        __c11_atomic_compare_exchange_weak(object, expected, desired,   \
            success, failure)
#define atomic_exchange_explicit(object, desired, order)                \
        __c11_atomic_exchange(object, desired, order)
#define atomic_fetch_add_explicit(object, operand, order)               \
        __c11_atomic_fetch_add(object, operand, order)
#define atomic_fetch_and_explicit(object, operand, order)               \
        __c11_atomic_fetch_and(object, operand, order)
#define atomic_fetch_or_explicit(object, operand, order)                \
        __c11_atomic_fetch_or(object, operand, order)
#define atomic_fetch_sub_explicit(object, operand, order)               \
        __c11_atomic_fetch_sub(object, operand, order)
#define atomic_fetch_xor_explicit(object, operand, order)               \
        __c11_atomic_fetch_xor(object, operand, order)
#define atomic_load_explicit(object, order)                             \
        __c11_atomic_load(object, order)
#define atomic_store_explicit(object, desired, order)                   \
        __c11_atomic_store(object, desired, order)
#elif defined(__GNUC_ATOMICS)
#define atomic_compare_exchange_strong_explicit(object, expected,       \
    desired, success, failure)                                          \
        __atomic_compare_exchange_n(&(object)->__val, expected,         \
            desired, 0, success, failure)
#define atomic_compare_exchange_weak_explicit(object, expected,         \
    desired, success, failure)                                          \
        __atomic_compare_exchange_n(&(object)->__val, expected,         \
            desired, 1, success, failure)
#define atomic_exchange_explicit(object, desired, order)                \
        __atomic_exchange_n(&(object)->__val, desired, order)
#define atomic_fetch_add_explicit(object, operand, order)               \
        __atomic_fetch_add(&(object)->__val, operand, order)
#define atomic_fetch_and_explicit(object, operand, order)               \
        __atomic_fetch_and(&(object)->__val, operand, order)
#define atomic_fetch_or_explicit(object, operand, order)                \
        __atomic_fetch_or(&(object)->__val, operand, order)
#define atomic_fetch_sub_explicit(object, operand, order)               \
        __atomic_fetch_sub(&(object)->__val, operand, order)
#define atomic_fetch_xor_explicit(object, operand, order)               \
        __atomic_fetch_xor(&(object)->__val, operand, order)
#define atomic_load_explicit(object, order)                             \
        __atomic_load_n(&(object)->__val, order)
#define atomic_store_explicit(object, desired, order)                   \
        __atomic_store_n(&(object)->__val, desired, order)
#else
#define __atomic_apply_stride(object, operand) \
        (((__typeof__((object)->__val))0) + (operand))
#define atomic_compare_exchange_strong_explicit(object, expected,       \
    desired, success, failure)  __extension__ ({                        \
        __typeof__(expected) __ep = (expected);                         \
        __typeof__(*__ep) __e = *__ep;                                  \
        (void)(success); (void)(failure);                               \
        (__Bool)((*__ep = __sync_val_compare_and_swap(&(object)->__val, \
            __e, desired)) == __e);                                     \
})
#define atomic_compare_exchange_weak_explicit(object, expected,         \
    desired, success, failure)                                          \
        atomic_compare_exchange_strong_explicit(object, expected,       \
                desired, success, failure)
#if __has_builtin(__sync_swap)
/* Clang provides a full-barrier atomic exchange - use it if available. */
#define atomic_exchange_explicit(object, desired, order)                \
        ((void)(order), __sync_swap(&(object)->__val, desired))
#else
/*
 * __sync_lock_test_and_set() is only an acquire barrier in theory (although in
 * practice it is usually a full barrier) so we need an explicit barrier before
 * it.
 */
#define atomic_exchange_explicit(object, desired, order)                \
__extension__ ({                                                        \
        __typeof__(object) __o = (object);                              \
        __typeof__(desired) __d = (desired);                            \
        (void)(order);                                                  \
        __sync_synchronize();                                           \
        __sync_lock_test_and_set(&(__o)->__val, __d);                   \
})
#endif
#define atomic_fetch_add_explicit(object, operand, order)               \
        ((void)(order), __sync_fetch_and_add(&(object)->__val,          \
            __atomic_apply_stride(object, operand)))
#define atomic_fetch_and_explicit(object, operand, order)               \
        ((void)(order), __sync_fetch_and_and(&(object)->__val, operand))
#define atomic_fetch_or_explicit(object, operand, order)                \
        ((void)(order), __sync_fetch_and_or(&(object)->__val, operand))
#define atomic_fetch_sub_explicit(object, operand, order)               \
        ((void)(order), __sync_fetch_and_sub(&(object)->__val,          \
            __atomic_apply_stride(object, operand)))
#define atomic_fetch_xor_explicit(object, operand, order)               \
        ((void)(order), __sync_fetch_and_xor(&(object)->__val, operand))
#define atomic_load_explicit(object, order)                             \
        ((void)(order), __sync_fetch_and_add(&(object)->__val, 0))
#define atomic_store_explicit(object, desired, order)                   \
        ((void)atomic_exchange_explicit(object, desired, order))
#endif

/*
 * Convenience functions.
 *
 * Don't provide these in kernel space. In kernel space, we should be
 * disciplined enough to always provide explicit barriers.
 */

#ifndef _KERNEL
#define atomic_compare_exchange_strong(object, expected, desired)       \
        atomic_compare_exchange_strong_explicit(object, expected,       \
            desired, memory_order_seq_cst, memory_order_seq_cst)
#define atomic_compare_exchange_weak(object, expected, desired)         \
        atomic_compare_exchange_weak_explicit(object, expected,         \
            desired, memory_order_seq_cst, memory_order_seq_cst)
#define atomic_exchange(object, desired)                                \
        atomic_exchange_explicit(object, desired, memory_order_seq_cst)
#define atomic_fetch_add(object, operand)                               \
        atomic_fetch_add_explicit(object, operand, memory_order_seq_cst)
#define atomic_fetch_and(object, operand)                               \
        atomic_fetch_and_explicit(object, operand, memory_order_seq_cst)
#define atomic_fetch_or(object, operand)                                \
        atomic_fetch_or_explicit(object, operand, memory_order_seq_cst)
#define atomic_fetch_sub(object, operand)                               \
        atomic_fetch_sub_explicit(object, operand, memory_order_seq_cst)
#define atomic_fetch_xor(object, operand)                               \
        atomic_fetch_xor_explicit(object, operand, memory_order_seq_cst)
#define atomic_load(object)                                             \
        atomic_load_explicit(object, memory_order_seq_cst)
#define atomic_store(object, desired)                                   \
        atomic_store_explicit(object, desired, memory_order_seq_cst)
#endif /* !_KERNEL */

/*
 * 7.17.8 Atomic flag type and operations.
 *
 * XXX: Assume atomic_bool can be used as an atomic_flag. Is there some
 * kind of compiler built-in type we could use?
 */

typedef struct {
        atomic_bool     __flag;
} atomic_flag;

#define ATOMIC_FLAG_INIT                { ATOMIC_VAR_INIT(0) }

static __inline __Bool
atomic_flag_test_and_set_explicit(volatile atomic_flag *__object,
    memory_order __order)
{
        return (atomic_exchange_explicit(&__object->__flag, 1, __order));
}

static __inline void
atomic_flag_clear_explicit(volatile atomic_flag *__object, memory_order __order)
{

        atomic_store_explicit(&__object->__flag, 0, __order);
}

#ifndef _KERNEL
static __inline __Bool
atomic_flag_test_and_set(volatile atomic_flag *__object)
{

        return (atomic_flag_test_and_set_explicit(__object,
            memory_order_seq_cst));
}

static __inline void
atomic_flag_clear(volatile atomic_flag *__object)
{

        atomic_flag_clear_explicit(__object, memory_order_seq_cst);
}
#endif /* !_KERNEL */

#endif /* !_STDATOMIC_H_ */