atomic_exchange, atomic_exchange_explicit

 

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Threads thrd_create thrd_equal thrd_current    thrd_sleep thrd_yield thrd_exit thrd_detach thrd_join thrd_successthrd_timedoutthrd_busythrd_nomemthrd_error    Atomic operations atomic_init ATOMIC_VAR_INIT (until C23) ATOMIC_***_LOCK_FREE atomic_is_lock_free atomic_store atomic_load atomic_exchange atomic_compare_exchange atomic_fetch_add atomic_fetch_sub atomic_fetch_or atomic_fetch_xor atomic_fetch_and

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Defined in header <stdatomic.h>
C atomic_exchange( volatile A* obj, C desired );	(1)	(since C11)
C atomic_exchange_explicit( volatile A* obj, C desired, memory_order order );	(2)	(since C11)

Atomically replaces the value pointed by obj with desired and returns the value obj held previously. The operation is read-modify-write operation. The first version orders memory accesses according to memory_order_seq_cst, the second version orders memory accesses according to order.

This is a generic function defined for all atomic object types A. The argument is pointer to a volatile atomic type to accept addresses of both non-volatile and volatile (e.g. memory-mapped I/O) atomic objects, and volatile semantic is preserved when applying this operation to volatile atomic objects. C is the non-atomic type corresponding to A.

It is unspecified whether the name of a generic function is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual function (e.g. parenthesized like (atomic_exchange)(...)), or a program defines an external identifier with the name of a generic function, the behavior is undefined..

Parameters

obj	-	pointer to the atomic object to modify
desired	-	the value to replace the atomic object with
order	-	the memory synchronization ordering for this operation: all values are permitted

Return value

The value held previously be the atomic object pointed to by obj.

References

• C17 standard (ISO/IEC 9899:2018):

• 7.17.7.3 The atomic_exchange generic functions (p: 207)

• C11 standard (ISO/IEC 9899:2011):

• 7.17.7.3 The atomic_exchange generic functions (p: 283)

See also

atomic_compare_exchange_strongatomic_compare_exchange_strong_explicitatomic_compare_exchange_weakatomic_compare_exchange_weak_explicit (C11)	swaps a value with an atomic object if the old value is what is expected, otherwise reads the old value (function)
C++ documentation for atomic_exchange, atomic_exchange_explicit