atomic_exchange, atomic_exchange_explicit
| Defined in header <stdatomic.h>
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| 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
- C11 standard (ISO/IEC 9899:2011):
- 7.17.7.3 The atomic_exchange generic functions (p: 283)
See also
| swaps a value with the an atomic object if the old value is what is expected, otherwise reads the old value (function) |