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

Reserve a pop index for clearing cells up to a push reservation.

== Synopsis

Declared in `<bdlcc_fixedqueueindexmanager.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
reservePopIndexForClear(
    unsigned int* disposedGeneration,
    unsigned int* disposedIndex,
    unsigned int endGeneration,
    unsigned int endIndex);
----

== Description

If the next available index from which an element can be popped is before the specified `endGeneration` and `endIndex` then reserve that index for popping and load the specified `disposedGeneration` and `disposedIndex` with the generation and index of the reserved cell; otherwise this operation has no effect. Return 0 if an index was successfully reserved, and a non‐zero value if the current pop index is at `endIndex` and `endGeneration`. The behavior is undefined unless `endGeneration` and `endIndex` refer to a cell that has been acquired for writing. Note that this operation is used to facilitate removing all the elements in a circular buffer if an exception is thrown between reserving an index for pushing, and committing that index ‐‐ the intended usage is to call `reservePopIndexForClear` and then `commitPopIndex`, emptying all the cells up to the index that was reserved for writing, and then call `abortPushIndexReservation` on the reserved index.

== Return Value

0 if an index was reserved, non‐zero if at the end cell

== Parameters

[cols="1,4"]
|===
| Name| Description
| *disposedGeneration*
| receives the generation of the reserved cell
| *disposedIndex*
| receives the index of the reserved cell
| *endGeneration*
| generation of the push‐reserved end cell
| *endIndex*
| index of the push‐reserved end cell
|===


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