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

This class template defines a fully thread‐safe container that provides a mapping from keys (of template parameter type `KEY`) to their associated mapped values (of template parameter type `VALUE`).

== Synopsis

Declared in `<bdlcc_stripedunorderedmap.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class KEY,
    class VALUE,
    class HASH = xref:bsl/hash-06.adoc[bsl::hash<KEY>],
    class EQUAL = xref:bsl/equal_to-0d.adoc[bsl::equal_to<KEY>]>
class StripedUnorderedMap;
----

== Description

The buckets of this hash map are guarded by `numStripes` reader‐writer locks, a value specified on construction. Partitioning the buckets among several locks allows greater overall concurrency than a `bsl::unordered_map` object guarded by a single lock.

The interface is inspired by, but not identical to that of `bsl::unordered_map`. Notably absent are iterators, which are of limited practicality in the typical use case because they are readily invalidated when the map population is open to modification by multiple threads.

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/StripedUnorderedMap/EraseIfValuePredicate.adoc[`EraseIfValuePredicate`] 
| An alias to a function meeting the following contract: ` /// Return `true` if the specified `value` is to be removed from /// the container, and `false` otherwise. Note that this /// functor can _not_ change the values associated with `value`. bool eraseIfValuePredicate(const VALUE& value); `
| xref:BloombergLP/bdlcc/StripedUnorderedMap/KVType.adoc[`KVType`] 
| Value type of a bulk insert entry.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/ReadOnlyVisitorFunction.adoc[`ReadOnlyVisitorFunction`] 
| An alias to a function meeting the following contract: ` /// Visit the specified `value` attribute associated with the /// specified `key`. Return `true` if this function may be /// called on additional elements, and `false` otherwise (i.e., /// if no other elements should be visited). Note that this /// functor can _not_ change the value associated with `key` /// and `value`. bool visitorFunction(const VALUE& value, const KEY& key); `
| xref:BloombergLP/bdlcc/StripedUnorderedMap/VisitorFunction.adoc[`VisitorFunction`] 
| An alias to a function meeting the following contract: ` /// Visit the specified `value` attribute associated with the /// specified `key`. Return `true` if this function may be /// called on additional elements, and `false` otherwise (i.e., /// if no other elements should be visited). Note that this /// functor can change the value associated with `key`. bool visitorFunction(VALUE *value, const KEY& key); `
|===


== Enums

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/StripedUnorderedMap/_04enum.adoc[`Unnamed enum`] 
| Default sizing constants for this map.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/StripedUnorderedMap/2constructor-03.adoc[`StripedUnorderedMap`]         [.small]#[constructor]#
| Create an empty `StripedUnorderedMap` object, a fully thread‐safe hash map where access is partitioned into "stripes" (a group of buckets protected a reader‐writer mutex). Optionally specify `numInitialBuckets` and `numStripes` which define the minimum number of buckets and the (fixed) number of stripes in this map. Optionally specify a `basicAllocator` used to supply memory. If `basicAllocator` is 0, the currently installed default allocator is used. The hash map has rehash enabled. Note that the number of stripes will not change after construction, but the number of buckets may (unless rehashing is disabled via `disableRehash`).
| xref:BloombergLP/bdlcc/StripedUnorderedMap/allocator.adoc[`allocator`] 
| Return the allocator used by this hash map to supply memory. Note that if no allocator was supplied at construction the default allocator installed at that time is used.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/bucketCount.adoc[`bucketCount`] 
| Return the number of buckets in the array of buckets maintained by this hash map. Note that unless rehash is disabled, the value returned may be obsolete by the time it is received.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/bucketIndex.adoc[`bucketIndex`] 
| Return the index of the bucket, in the array of buckets maintained by this hash map, where elements having the specified `key` are inserted. Note that unless rehash is disabled, the value returned may be obsolete at the time it is returned.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/bucketSize.adoc[`bucketSize`] 
| Return the number of elements contained in the bucket at the specified `index` in the array of buckets maintained by this hash map. The behavior is undefined unless `0 <= index < bucketCount()`. Note that unless rehash is disabled the value returned may be obsolete by the time it is returned.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/clear.adoc[`clear`] 
| Remove all elements from this hash map. If rehash is in progress, block until it completes.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/disableRehash.adoc[`disableRehash`] 
| Prevent future rehash until `enableRehash` is called.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/empty.adoc[`empty`] 
| Return `true` if this hash map contains no elements, and `false` otherwise.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/enableRehash.adoc[`enableRehash`] 
| Allow rehash. If conditions warrant, rehash will be started by the _next_ method call that observes the load factor is exceeded (see {Concurrent Rehash}). Note that calling `maxLoadFactor(maxLoadFactor())` (i.e., setting the maximum load factor to its current value) will trigger a rehash if needed but otherwise does not change the hash map.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/equalFunction.adoc[`equalFunction`] 
| Return (a copy of) the key‐equality functor used by this hash map. The returned function will return `true` if two `KEY` objects have the same value, and `false` otherwise.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/erase.adoc[`erase`] 
| Erase from this hash map the element having the specified `key`. Return 1 on success and 0 if `key` does not exist. Note that the returned value equals the number of elements removed.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/eraseBulk.adoc[`eraseBulk`] 
| Erase from this hash map elements in this hash map having any of the values in the keys contained between the specified `first` (inclusive) and `last` (exclusive) random‐access iterators. The iterators provide read access to a sequence of `KEY` objects. All erasures are done by the calling thread and the order of erasure is not specified. Return the number of elements removed. The behavior is undefined unless `first <= last`. Note that the map may not have an element for every value in `keys`.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/eraseIf.adoc[`eraseIf`] 
| Remove from this hash map the element, if any, having the specified `key`, where specified `predicate` holds true. Return the number of elements erased.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/getValue.adoc[`getValue`] 
| Load, into the specified `*value`, the value attribute of the element in this hash map having the specified `key`. Return 1 on success and 0 if `key` does not exist in this hash map. Note that the return value equals the number of values returned.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/hashFunction.adoc[`hashFunction`] 
| Return (a copy of) the unary hash functor used by this hash map. The return function will generate a hash value (of type `std::size_t`) for a `KEY` object.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/insert-08.adoc[`insert`] 
| `insert` overloads
| xref:BloombergLP/bdlcc/StripedUnorderedMap/insertBulk.adoc[`insertBulk`] 
| Insert into this hash map elements having the key‐value pairs obtained between the specified `first` (inclusive) and `last` (exclusive) random‐access iterators. The iterators provide read access to a sequence of `bsl::pair<KEY, VALUE>` objects. If an element having one of the keys already exists in this hash map, set the value attribute to the corresponding value from `data`. All insertions are done by the calling thread and the order of insertion is not specified. Return the number of elements inserted. The behavior is undefined unless `first <= last`.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/isRehashEnabled.adoc[`isRehashEnabled`] 
| Return `true` if rehash is enabled, or `false` otherwise.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/loadFactor.adoc[`loadFactor`] 
| Return the current quotient of the size of this hash map and the number of buckets. Note that the load factor is a measure of container "fullness"; that is, a high load factor typically implies many collisions (many elements landing in the same bucket) and that decreases performance. See {Rehash Control}.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/maxLoadFactor.adoc[`maxLoadFactor`] 
| Return the maximum load factor allowed for this hash map. If an insert operation would cause the load factor to exceed the `maxLoadFactor()` and rehashing is enabled, then that insert increases the number of buckets and rehashes the elements of the container into that larger set of buckets. See {Rehash Control}.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/numStripes.adoc[`numStripes`] 
| Return the number of stripes in the hash.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/rehash.adoc[`rehash`] 
| Recreate this hash map to one having at least the specified `numBuckets`. This operation is a no‐op if _any_ of the following are true: 1) rehash is disabled; 2) `numBuckets` less or equals the current number of buckets. See {Rehash}.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/setComputedValue.adoc[`setComputedValue`] 
| Invoke the specified `visitor` on the value associated with the specified `key`. The `visitor` will be passed the address of the value, and `key`. If `key` is not in the map, `value` will be default constructed. That is, `visitor` must be invocable with the `VisitorFunction` signature: ` bool visitor(VALUE *value, const Key& key); ` If no element in the map has `key`, insert `(key, VALUE())` and invoke `visitor` with `value` pointing to the default constructed value. Return 1 if `key` was found and `visitor` returned `true`, 0 if `key` was not found, and ‐1 if `key` was found and `visitor` returned `false`. `visitor`, when invoked, has exclusive access (i.e., write access) to the element. The behavior is undefined if hash map manipulators and `getValue*` methods are invoked from within `visitor`, as it may lead to a deadlock. Note that the return value equals the number of elements found having `key`. Also note that a return value of `0` implies that an element was inserted.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/setValue-0f.adoc[`setValue`] 
| `setValue` overloads
| xref:BloombergLP/bdlcc/StripedUnorderedMap/size.adoc[`size`] 
| Return the current number of elements in this hash map.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/update.adoc[`update`] 
| Call the specified `visitor` with the element (if one exists) in this hash map having the specified `key`. That is: ` bool visitor(&value, key); ` Return the number of elements updated or ‐1 if `visitor` returned `false`. `visitor` has exclusive access (i.e., write access) the element for during its invocation. The behavior is undefined if hash map manipulators and `getValue*` methods are invoked from within `visitor`, as it may lead to a deadlock.
| xref:BloombergLP/bdlcc/StripedUnorderedMap/visit-0c.adoc[`visit`] 
| `visit` overloads
| xref:BloombergLP/bdlcc/StripedUnorderedMap/visitReadOnly-04.adoc[`visitReadOnly`] 
| `visitReadOnly` overloads
|===



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