[#BloombergLP-bdlcc-SingleConsumerQueue]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlcc.adoc[bdlcc]::SingleConsumerQueue
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:mrdocs:

This class provides a thread‐safe unbounded queue of values that assumes a single consumer thread.

== Synopsis

Declared in `<bdlcc_singleconsumerqueue.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class TYPE>
class SingleConsumerQueue;
----

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/SingleConsumerQueue/value_type.adoc[`value_type`] 
| The type for elements stored in this queue.
|===


== Enums

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/SingleConsumerQueue/_04enum.adoc[`Unnamed enum`] 
| Status codes returned by queue operations.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/SingleConsumerQueue/2constructor-03.adoc[`SingleConsumerQueue`]         [.small]#[constructor]#
| Constructors
| xref:BloombergLP/bdlcc/SingleConsumerQueue/allocator.adoc[`allocator`] 
| Return the allocator used by this object to supply memory.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/disablePopFront.adoc[`disablePopFront`] 
| Disable dequeueing from this queue. All subsequent invocations of `popFront` or `tryPopFront` will fail immediately. All blocked invocations of `popFront` and `waitUntilEmpty` will fail immediately. If the queue is already dequeue disabled, this method has no effect.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/disablePushBack.adoc[`disablePushBack`] 
| Disable enqueueing into this queue. All subsequent invocations of `pushBack` or `tryPushBack` will fail immediately. All blocked invocations of `pushBack` will fail immediately. If the queue is already enqueue disabled, this method has no effect.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/enablePopFront.adoc[`enablePopFront`] 
| Enable dequeueing. If the queue is not dequeue disabled, this call has no effect.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/enablePushBack.adoc[`enablePushBack`] 
| Enable queuing. If the queue is not enqueue disabled, this call has no effect.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/isEmpty.adoc[`isEmpty`] 
| Return `true` if this queue is empty (has no elements), or `false` otherwise.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/isFull.adoc[`isFull`] 
| Return `true` if this queue is full (has no available capacity), or `false` otherwise. Note that for unbounded queues, this method always returns `false`.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/isPopFrontDisabled.adoc[`isPopFrontDisabled`] 
| Return `true` if this queue is dequeue disabled, and `false` otherwise. Note that the queue is created in the "dequeue enabled" state.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/isPushBackDisabled.adoc[`isPushBackDisabled`] 
| Return `true` if this queue is enqueue disabled, and `false` otherwise. Note that the queue is created in the "enqueue enabled" state.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/numElements.adoc[`numElements`] 
| Returns the number of elements currently in this queue.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/popFront.adoc[`popFront`] 
| Remove the element from the front of this queue and load that element into the specified `value`. If the queue is empty, block until it is not empty. Return 0 on success, and a non‐zero value otherwise. Specifically, return `e_DISABLED` if `isPopFrontDisabled()`. On failure, `value` is not changed. Threads blocked due to the queue being empty will return `e_DISABLED` if `disablePopFront` is invoked. The behavior is undefined unless the invoker of this method is the single consumer.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/pushBack-0b2.adoc[`pushBack`] 
| `pushBack` overloads
| xref:BloombergLP/bdlcc/SingleConsumerQueue/removeAll.adoc[`removeAll`] 
| Remove all items currently in this queue. Note that this operation is not atomic; if other threads are concurrently pushing items into the queue the result of `numElements()` after this function returns is not guaranteed to be 0. The behavior is undefined unless the invoker of this method is the single consumer.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/tryPopFront.adoc[`tryPopFront`] 
| Attempt to remove the element from the front of this queue without blocking, and, if successful, load the specified `value` with the removed element. Return 0 on success, and a non‐zero value otherwise. Specifically, return `e_DISABLED` if `isPopFrontDisabled()`, and `e_EMPTY` if `!isPopFrontDisabled()` and the queue was empty. On failure, `value` is not changed. The behavior is undefined unless the invoker of this method is the single consumer.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/tryPushBack-03.adoc[`tryPushBack`] 
| `tryPushBack` overloads
| xref:BloombergLP/bdlcc/SingleConsumerQueue/waitUntilEmpty.adoc[`waitUntilEmpty`] 
| Block until all the elements in this queue are removed. Return 0 on success, and a non‐zero value otherwise. Specifically, return `e_DISABLED` if `!isEmpty() && isPopFrontDisabled()`. A blocked thread waiting for the queue to empty will return `e_DISABLED` if `disablePopFront` is invoked.
| xref:BloombergLP/bdlcc/SingleConsumerQueue/2conversion.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<SingleConsumerQueue, UsesBslmaAllocator>`] 
| Declare that this type uses a `bslma` allocator.
|===



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