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73 lines
2 KiB
C
73 lines
2 KiB
C
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/*
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* Provides atomic load and store functions using either native C11 atomic
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* types and operations if available, or otherwise using fallback
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* implementations (e.g. with GCC where stdatomic.h is not useable from
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* Objective-C).
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*
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* Adopted from FreeBSD's stdatomic.h.
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*/
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#ifndef _GSAtomic_h_
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#define _GSAtomic_h_
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#ifndef __has_extension
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#define __has_extension(x) 0
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#endif
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#if __has_extension(c_atomic) || __has_extension(cxx_atomic)
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/*
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* Use native C11 atomic operations. _Atomic() should be defined by the
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* compiler.
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*/
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#define atomic_load_explicit(object, order) \
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__c11_atomic_load(object, order)
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#define atomic_store_explicit(object, desired, order) \
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__c11_atomic_store(object, desired, order)
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#else
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/*
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* No native support for _Atomic(). Place object in structure to prevent
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* most forms of direct non-atomic access.
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*/
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#define _Atomic(T) struct { T volatile __val; }
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#if __has_builtin(__sync_swap)
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/* Clang provides a full-barrier atomic exchange - use it if available. */
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#define atomic_exchange_explicit(object, desired, order) \
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((void)(order), __sync_swap(&(object)->__val, desired))
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#else
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/*
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* __sync_lock_test_and_set() is only an acquire barrier in theory (although in
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* practice it is usually a full barrier) so we need an explicit barrier before
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* it.
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*/
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#define atomic_exchange_explicit(object, desired, order) \
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__extension__ ({ \
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__typeof__(object) __o = (object); \
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__typeof__(desired) __d = (desired); \
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(void)(order); \
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__sync_synchronize(); \
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__sync_lock_test_and_set(&(__o)->__val, __d); \
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})
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#endif
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#define atomic_load_explicit(object, order) \
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((void)(order), __sync_fetch_and_add(&(object)->__val, 0))
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#define atomic_store_explicit(object, desired, order) \
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((void)atomic_exchange_explicit(object, desired, order))
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#endif
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#ifndef __ATOMIC_SEQ_CST
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#define __ATOMIC_SEQ_CST 5
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#endif
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/*
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* Convenience functions.
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*/
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#define atomic_load(object) \
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atomic_load_explicit(object, __ATOMIC_SEQ_CST)
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#define atomic_store(object, desired) \
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atomic_store_explicit(object, desired, __ATOMIC_SEQ_CST)
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#endif // _GSAtomic_h_
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