[#BloombergLP-bdlm-MetricsRegistry]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlm.adoc[bdlm]::MetricsRegistry
:relfileprefix: ../../
:mrdocs:

This class implements a mechanism that provides a registry of metrics that is transferable to implementations of the `bdlm::MetricsAdapter` protocol. This class is _usually_ a singleton.

== Synopsis

Declared in `<bdlm_metricsregistry.h>`

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

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlm/MetricsRegistry/Callback.adoc[`Callback`] 
| This `typedef` is an alias for a metrics registration callback.
| xref:BloombergLP/bdlm/MetricsRegistry/CallbackHandle.adoc[`CallbackHandle`] 
| This `typedef` is an alias for a metrics registration callback handle.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlm/MetricsRegistry/2constructor.adoc[`MetricsRegistry`]         [.small]#[constructor]#
| Create a `MetricsRegistry` object that stores the information necessary to forward the registration and unregistration of metrics to an adapter supplied with `setMetricsRegistry`. Optionally specify a `basicAllocator` used to supply memory. If `basicAllocator` is 0, the currently installed default allocator is used.
| xref:BloombergLP/bdlm/MetricsRegistry/2destructor.adoc[`~MetricsRegistry`] [.small]#[destructor]#
| Unregister all registered metrics and destroy this `MetricsRegistry` object.
| xref:BloombergLP/bdlm/MetricsRegistry/allocator.adoc[`allocator`] 
| Return the allocator used by this object to supply memory.
| xref:BloombergLP/bdlm/MetricsRegistry/disableMetricsCollection.adoc[`disableMetricsCollection`] 
| Disable metrics collection. If there is an associated metrics adapter, all the collection callbacks are unregistered from that adapter. The adapter remains associated with this registry. Collection callbacks registered with this registry are not registered with the associated adapter until metrics collections is enabled. Return 0 on success, and a non‐zero value otherwise. Metrics collection is enabled at construction of this registry.
| xref:BloombergLP/bdlm/MetricsRegistry/enableMetricsCollection.adoc[`enableMetricsCollection`] 
| Enable metrics collection. If there is an associated metrics adapter, all collection callbacks will be registered with the adapter. Return 0 on success, and non‐zero value otherwise. Metrics collection is enabled at construction of this registry.
| xref:BloombergLP/bdlm/MetricsRegistry/numRegisteredCollectionCallbacks.adoc[`numRegisteredCollectionCallbacks`] 
| Return the number of registered metrics collection callbacks.
| xref:BloombergLP/bdlm/MetricsRegistry/registerCollectionCallback.adoc[`registerCollectionCallback`] 
| Register the metric described by the specified `descriptor` and associate it with the specified `callback` to collect data from the metric, and load the specified `result` with a handle can be used later to unregister the metric. Return 0 on success, and a non‐zero value otherwise. After this operation completes, `result‐>isRegistered()` will be `true`. The metric and associated callback remain registered with this registry until either the handle is unregistered or destroyed. When a `MetricsAdapter` is associated with this registry using `setMetricsAdapter`, this object registers all the registered metrics and callbacks with that adapter, and similarly unregisters them if the `MetricAdapter` is later disassociated with this registry (either on this objects destruction, or due to a call to `removeMetricsAdapter` or `setMetricsAdapter`). Furthermore, metrics collection can be disable with `disableMetricsCollection` and enabled with `enableMetricsCollection`. In this way, a `MetricsRegistry` serves as an intermediary between users of `bdlm` that register metrics and the subsystem for collecting and publishing metrics being adapted by a concrete instance of `bdlm::MetricAdapter`.
| xref:BloombergLP/bdlm/MetricsRegistry/removeMetricsAdapter.adoc[`removeMetricsAdapter`] 
| If the specified `adapter` is the currently associated adapter, remove all registered metrics from it and disassociate with this registry. Return 0 on success, and a non‐zero value otherwise. Note that this operation takes an `adapter` to disambiguate multiple, potentially concurrent, calls to this method and `setMetricsAdapter`.
| xref:BloombergLP/bdlm/MetricsRegistry/setMetricsAdapter.adoc[`setMetricsAdapter`] 
| Configure this metrics registry to register all metrics collection callbacks with the specified `adapter` when the registry has metrics collection enabled. This operation first, if there is already an associated metrics adapter, unregisters all the collection callbacks from that adapter, then registers the collection callbacks with the new `adapter` if metrics collection is enabled. Return 0 on success, and a non‐zero value otherwise.
| xref:BloombergLP/bdlm/MetricsRegistry/2conversion.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<MetricsRegistry, UsesBslmaAllocator>`] 
| Declare that this type uses a `bslma` allocator.
|===


== Static Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlm/MetricsRegistry/defaultInstance.adoc[`defaultInstance`] 
| Return a non‐`const` reference to the metrics registry singleton.
|===



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