[#BloombergLP-bsls-AtomicOperations_DefaultUint64-00-testAndSwapUint64AcqRel]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bsls.adoc[bsls]::xref:BloombergLP/bsls/AtomicOperations_DefaultUint64-00.adoc[AtomicOperations_DefaultUint64]::testAndSwapUint64AcqRel
:relfileprefix: ../../../
:mrdocs:

Conditionally swap `atomicUint` with acquire/release ordering.

== Synopsis

Declared in `<bsls_atomicoperations_default.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
static
xref:BloombergLP/bsls/Types/Uint64.adoc[Types::Uint64]
testAndSwapUint64AcqRel(
    AtomicTypes::Uint64* atomicUint,
    xref:BloombergLP/bsls/Types/Uint64.adoc[Types::Uint64] compareValue,
    xref:BloombergLP/bsls/Types/Uint64.adoc[Types::Uint64] swapValue);
----

== Description

Conditionally set the value of the specified `atomicUint` to the specified `swapValue` if and only if the value of `atomicUint` equals the value of the specified `compareValue`, and return the initial value of `atomicUint`, providing the acquire/release memory ordering guarantee. The whole operation is performed atomically.

== Return Value

initial value of `atomicUint` before the operation

== Parameters

[cols="1,4"]
|===
| Name| Description
| *atomicUint*
| atomic unsigned 64‐bit integer to test and possibly update
| *compareValue*
| expected current value of `atomicUint`
| *swapValue*
| value to store if the comparison succeeds
|===


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