[#BloombergLP-bslmt-ThreadUtil-createKey]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslmt.adoc[bslmt]::xref:BloombergLP/bslmt/ThreadUtil.adoc[ThreadUtil]::createKey
:relfileprefix: ../../../
:mrdocs:

Create a process‐wide key for thread‐local storage.

== Synopsis

Declared in `<bslmt_threadutil.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
static
int
createKey(
    xref:BloombergLP/bslmt/ThreadUtil/Key.adoc[Key]* key,
    xref:BloombergLP/bslmt/ThreadUtil/Destructor.adoc[Destructor] threadKeyCleanupFunction);
----

== Description

Load into the specified `key` a new process‐wide identifier that can be used to store (via `setSpecific`) and retrieve (via `getSpecific`) a pointer value local to each thread, and associate with the new key the specified `threadKeyCleanupFunction`, which will be called by each thread, if `threadKeyCleanupFunction` is non‐zero and the value associated with `key` for that thread is non‐zero, with the associated value as an argument, after the function passed to `create` has returned and before the thread terminates. Return 0 on success, and a non‐zero value otherwise. Note that multiple keys can be defined, which can result in multiple thread key cleanup functions being called for a given thread.

== Return Value

0 on success, and a non‐zero value otherwise

== Parameters

[cols="1,4"]
|===
| Name| Description
| *key*
| receives the new process‐wide thread‐local key
| *threadKeyCleanupFunction*
| optional destructor for key values
|===


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