[#BloombergLP-bslmt-Once-callOnce-02]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslmt.adoc[bslmt]::xref:BloombergLP/bslmt/Once.adoc[Once]::callOnce
:relfileprefix: ../../../
:mrdocs:

If no other thread has yet called `enter` or `callOnce`, then call the specified `function` and set this object to the state where pending and future calls to `enter` or `callOnce` will return `false` or do nothing, respectively. Otherwise, wait for the one‐time code to complete and return without calling `function` where `function` is a function or functor that can be called with no arguments. Note that one‐time code is considered not to have run if `function` terminates with an exception.

== Synopses

Declared in `<bslmt_once.h>`

If no other thread has yet called `enter` or `callOnce`, then call the specified `function` and set this object to the state where pending and future calls to `enter` or `callOnce` will return `false` or do nothing, respectively. Otherwise, wait for the one‐time code to complete and return without calling `function` where `function` is a function or functor that can be called with no arguments. Note that one‐time code is considered not to have run if `function` terminates with an exception.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class FUNC>
void
xref:BloombergLP/bslmt/Once/callOnce-0f.adoc[callOnce](FUNC& function);
----

[.small]#xref:BloombergLP/bslmt/Once/callOnce-0f.adoc[_» more..._]#

If no other thread has yet called `enter` or `callOnce`, then call the specified `function` and set this object to the state where pending and future calls to `enter` or `callOnce` will return `false` or do nothing, respectively. Otherwise, wait for the one‐time code to complete and return without calling `function` where `function` is a function or functor that can be called with no arguments. Note that one‐time code is considered not to have run if `function` terminates with an exception.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class FUNC>
void
xref:BloombergLP/bslmt/Once/callOnce-03.adoc[callOnce](FUNC const& function);
----

[.small]#xref:BloombergLP/bslmt/Once/callOnce-03.adoc[_» more..._]#


[.small]#Created with https://www.mrdocs.com[MrDocs]#