[#BloombergLP-bdlcc-FixedQueueIndexManager-reservePopIndex]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlcc.adoc[bdlcc]::xref:BloombergLP/bdlcc/FixedQueueIndexManager.adoc[FixedQueueIndexManager]::reservePopIndex
:relfileprefix: ../../../
:mrdocs:

Reserve the next available index from which to dequeue an element from an (externally managed) circular buffer; load the specified `index` with the reserved index and load the specified `generation` with the current generation of the circular buffer. Return 0 on success, and a non‐zero value if the queue is empty. If this method succeeds, other threads using this object may spin on the corresponding index state until `commitPopIndex` is called using the returned `index` and `generation` values; clients should call `commitPopIndex` quickly after this method returns, without performing any blocking operations. If this method fails the `generation` and `index` will be unmodified. The behavior is undefined if the current thread is already holding a reservation on either a push or pop index. Note that `generation` is necessary for invoking `commitPopIndex` but should not otherwise be used by the caller; the value reflects the of times the `index` in the circular buffer has been used.

== Synopsis

Declared in `<bdlcc_fixedqueueindexmanager.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
reservePopIndex(
    unsigned int* generation,
    unsigned int* index);
----


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