[#BloombergLP-ball-AttributeContext]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/ball.adoc[ball]::AttributeContext
:relfileprefix: ../../
:mrdocs:

Mechanism for associating attributes with the current thread and evaluating logging rules.

== Synopsis

Declared in `<ball_attributecontext.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class AttributeContext;
----

== Description

This class provides a mechanism for associating attributes with the current thread, and evaluating the logging rules associated with a category using those stored attributes. `AttributeContext` contains class data members that must be initialized (using the `initialize` class method) with a `CategoryManager` object containing a `RuleSet` that represents the currently installed logging rules for the process. Clients can obtain the context for the current thread by calling the `getContext` class method. The `addAttributes` and `removeAttributes` methods are used to add and remove collections of attributes from the (thread‐local) context object. Finally, `AttributeContext` provides methods (used primarily by other components in the `ball` package') to determine the effect of the current logging rules on the logging thresholds of a category. The `hasRelevantActiveRules` method returns `true` if there are any relevant and active rules that might modify the logging thresholds of the supplied category. A rule is "relevant" if the rule's pattern matches the category's name, and a rule is "active" if all the attributes defined for the rule are satisfied by the current thread's attributes (i.e., `Rule::evaluate` returns `true` for the collection of attributes maintained for the current thread by the thread's `AttributeContext` object). The `determineThresholdLevels` method returns the logging threshold levels for a category, factoring in any active rules that apply to the category that might override the category's thresholds. The behavior for the `hasRelevantActiveRules` and `determineThresholdLevels` methods is undefined unless `initialize` has been called. Note that, in practice, `initialize` is called _internally_ when the logger manager singleton is initialized; clients ordinarily should not call `initialize` directly.

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/ball/AttributeContext/iterator.adoc[`iterator`] 
| Iterator over the attribute containers in an `AttributeContext`.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/ball/AttributeContext/addAttributes.adoc[`addAttributes`] 
| Add the specified `attributes` container to this context.
| xref:BloombergLP/ball/AttributeContext/clearCache.adoc[`clearCache`] 
| Clear this object's cache of evaluated rules.
| xref:BloombergLP/ball/AttributeContext/containers.adoc[`containers`] 
| Return the list of attribute containers maintained by this object.
| xref:BloombergLP/ball/AttributeContext/determineThresholdLevels.adoc[`determineThresholdLevels`] 
| Populate the specified `levels` with the threshold levels for the specified `category`.
| xref:BloombergLP/ball/AttributeContext/hasAttribute.adoc[`hasAttribute`] 
| Return whether an attribute with the specified `value` exists in this context.
| xref:BloombergLP/ball/AttributeContext/hasRelevantActiveRules.adoc[`hasRelevantActiveRules`] 
| Return `true` if there is at least one relevant and active rule for the specified `category`.
| xref:BloombergLP/ball/AttributeContext/print.adoc[`print`] 
| Format this object to the specified output stream.
| xref:BloombergLP/ball/AttributeContext/removeAttributes.adoc[`removeAttributes`] 
| Remove the specified `element` from this context's attribute containers.
|===


== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/ball/AttributeContext/getContext.adoc[`getContext`] 
| Return the address of the current thread's attribute context, creating one if needed.
| xref:BloombergLP/ball/AttributeContext/initialize.adoc[`initialize`] 
| Initialize the static data members of `AttributeContext` using the specified `categoryManager`.
| xref:BloombergLP/ball/AttributeContext/lookupContext.adoc[`lookupContext`] 
| Return the address of the current thread's attribute context, or 0 if none exists.
| xref:BloombergLP/ball/AttributeContext/reset.adoc[`reset`] 
| Reset the static data members of `AttributeContext` to their initial state.
| xref:BloombergLP/ball/AttributeContext/visitAttributes.adoc[`visitAttributes`] 
| Invoke the specified `visitor` for all attributes in all attribute containers maintained by this object.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:BloombergLP/ball/AttributeContextProctor.adoc[BloombergLP::ball::AttributeContextProctor]`
| Proctor that destroys the current thread's attribute context on destruction.
|===


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