130 lines
4.6 KiB
Markdown
130 lines
4.6 KiB
Markdown
[allocator.members]
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# 20 Memory management library [[mem]](./#mem)
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## 20.2 Memory [[memory]](memory#allocator.members)
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### 20.2.10 The default allocator [[default.allocator]](default.allocator#allocator.members)
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#### 20.2.10.2 Members [allocator.members]
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L1994)
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Except for the destructor, member functions of the default allocator shall not introduce
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data races ([[intro.multithread]](intro.multithread "6.10.2 Multi-threaded executions and data races")) as a result of concurrent calls to those member
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functions from different threads[.](#1.sentence-1)
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Calls to these functions that allocate or deallocate a
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particular unit of storage shall occur in a single total order, and each such
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deallocation call shall happen before the next allocation (if any) in this order[.](#1.sentence-2)
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[ð](#lib:allocate,allocator)
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`constexpr T* allocate(size_t n);
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`
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2007)
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*Mandates*: T is not an incomplete type ([[basic.types.general]](basic.types.general#term.incomplete.type "6.9.1 General"))[.](#2.sentence-1)
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2011)
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*Returns*: A pointer to the initial element of an array of n T[.](#3.sentence-1)
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2015)
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*Throws*: bad_array_new_length ifnumeric_limits<size_t>::max() / sizeof(T) < n, orbad_alloc if the storage cannot be obtained[.](#4.sentence-1)
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2021)
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*Remarks*: The storage for the array
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is obtained by calling ::operator new ([[new.delete]](new.delete "17.6.3 Storage allocation and deallocation")),
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but it is unspecified when or how often this
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function is called[.](#5.sentence-1)
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This function starts the lifetime of the array object,
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but not that of any of the array elements[.](#5.sentence-2)
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[ð](#lib:allocate_at_least,allocator)
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`constexpr allocation_result<T*> allocate_at_least(size_t n);
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`
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[6](#6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2037)
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*Mandates*: T is not an incomplete type ([[basic.types.general]](basic.types.general#term.incomplete.type "6.9.1 General"))[.](#6.sentence-1)
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[7](#7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2041)
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*Returns*: allocation_result<T*>{ptr, count},
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where ptr is a pointer to
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the initial element of an array of count T andcount ⥠n[.](#7.sentence-1)
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[8](#8)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2048)
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*Throws*: bad_array_new_length if numeric_limits<size_t>::max() / sizeof(T) < n,
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or bad_alloc if the storage cannot be obtained[.](#8.sentence-1)
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[9](#9)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2054)
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*Remarks*: The storage for the array is obtained by calling ::operator new,
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but it is unspecified when or how often this function is called[.](#9.sentence-1)
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This function starts the lifetime of the array object,
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but not that of any of the array elements[.](#9.sentence-2)
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[ð](#lib:deallocate,allocator)
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`constexpr void deallocate(T* p, size_t n);
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`
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[10](#10)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2068)
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*Preconditions*:
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- [(10.1)](#10.1)
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If p is memory that was obtained by a call to allocate_at_least,
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let ret be the value returned andreq be the value passed as the first argument to that call[.](#10.1.sentence-1)
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p is equal to ret.ptr andn is a value such that req ⤠n ⤠ret.count[.](#10.1.sentence-2)
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- [(10.2)](#10.2)
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Otherwise, p is a pointer value obtained from allocate[.](#10.2.sentence-1)
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n equals the value passed as the first argument
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to the invocation of allocate which returned p[.](#10.2.sentence-2)
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[11](#11)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2083)
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*Effects*: Deallocates the storage referenced by p[.](#11.sentence-1)
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[12](#12)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L2087)
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*Remarks*: Uses::operator delete ([[new.delete]](new.delete "17.6.3 Storage allocation and deallocation")),
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but it is unspecified
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when this function is called[.](#12.sentence-1)
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