1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML>
<HEAD>
<TITLE>pool_alloc - Boost Pool Standard Allocators</TITLE>
<LINK HREF="../pool.css" REL="stylesheet" TYPE="text/css">
</HEAD>
<BODY>
<IMG SRC="../../../../c++boost.gif" WIDTH=276 HEIGHT=86 ALT="C++ Boost">
<H1 ALIGN=CENTER>pool_alloc - Boost Pool Standard Allocators</H1>
<P>
<H2>Introduction</H2>
<P>
pool_alloc.hpp provides two template types that can be used for fast and efficient memory allocation. These types both satisfy the Standard Allocator requirements [20.1.5] and the additional requirements in [20.1.5/4], so they can be used with Standard or user-supplied containers. For information on other pool-based interfaces, see <A HREF="../interfaces.html">the other pool interfaces</A>.
<P>
<H2>Synopsis</H2>
<PRE CLASS="code">struct pool_allocator_tag { };
template <typename T,
typename UserAllocator = default_user_allocator_new_delete>
class pool_allocator
{
public:
typedef UserAllocator user_allocator;
typedef T value_type;
typedef value_type * pointer;
typedef const value_type * const_pointer;
typedef value_type & reference;
typedef const value_type & const_reference;
typedef typename pool<UserAllocator>::size_type size_type;
typedef typename pool<UserAllcoator>::difference_type difference_type;
template <typename U>
struct rebind
{ typedef pool_allocator<U, UserAllocator> other; };
public:
pool_allocator();
pool_allocator(const pool_allocator &);
// The following is not explicit, mimicking std::allocator [20.4.1]
template <typename U>
pool_allocator(const pool_allocator<U, UserAllocator> &);
pool_allocator & operator=(const pool_allocator &);
~pool_allocator();
static pointer address(reference r);
static const_pointer address(const_reference s);
static size_type max_size();
static void construct(pointer ptr, const value_type & t);
static void destroy(pointer ptr);
bool operator==(const pool_allocator &) const;
bool operator!=(const pool_allocator &) const;
static pointer allocate(size_type n);
static pointer allocate(size_type n, pointer);
static void deallocate(pointer ptr, size_type n);
};
struct fast_pool_allocator_tag { };
template <typename T
typename UserAllocator = default_user_allocator_new_delete>
class fast_pool_allocator
{
public:
typedef UserAllocator user_allocator;
typedef T value_type;
typedef value_type * pointer;
typedef const value_type * const_pointer;
typedef value_type & reference;
typedef const value_type & const_reference;
typedef typename pool<UserAllocator>::size_type size_type;
typedef typename pool<UserAllocator>::difference_type difference_type;
template <typename U>
struct rebind
{ typedef fast_pool_allocator<U, UserAllocator> other; };
public:
fast_pool_allocator();
fast_pool_allocator(const fast_pool_allocator &);
// The following is not explicit, mimicking std::allocator [20.4.1]
template <typename U>
fast_pool_allocator(const fast_pool_allocator<U, UserAllocator> &);
fast_pool_allocator & operator=(const fast_pool_allocator &);
~fast_pool_allocator();
static pointer address(reference r);
static const_pointer address(const_reference s);
static size_type max_size();
static void construct(pointer ptr, const value_type & t);
static void destroy(pointer ptr);
bool operator==(const fast_pool_allocator &) const;
bool operator!=(const fast_pool_allocator &) const;
static pointer allocate(size_type n);
static pointer allocate(size_type n, pointer);
static void deallocate(pointer ptr, size_type n);
static pointer allocate();
static void deallocate(pointer ptr);
};</PRE>
<P>
<H2>Template Parameters</H2>
<P>
<H3>T</H3>
<P>
The first template parameter is the type of object to allocate/deallocate.
<P>
<H3>UserAllocator</H3>
<P>
Defines the method that the underlying Pool will use to allocate memory from the system. See <A HREF="user_allocator.html">User Allocators</A> for details.
<P>
<H2>Semantics</H2>
<P>
Both of the pool allocators above satisfy all Standard Allocator requirements, as laid out in the Standard [20.1.5]. They also both satisfy the additional requirements found in [20.1.5/4]; this permits their usage with any Standard-compliant container.
<P>
In addition, the <SPAN CLASS="code">fast_pool_allocator</SPAN> also provides an additional allocation and an additional deallocation function:
<P>
<TABLE BORDER ALIGN=CENTER>
<CAPTION><EM>Symbol Table</EM></CAPTION>
<TR><TH>Symbol<TH>Meaning
<TR><TD CLASS="code">PoolAlloc<TD><SPAN CLASS="code">fast_pool_allocator<T, UserAllocator></SPAN>
<TR><TD CLASS="code">p<TD>value of type <SPAN CLASS="code">T *</SPAN>
</TABLE>
<P>
<TABLE BORDER ALIGN=CENTER>
<CAPTION><EM>Additional allocation/deallocation functions (<SPAN CLASS="code">fast_pool_allocator</SPAN> only)</EM></CAPTION>
<TR><TH>Expression<TH>Return Type<TH>Semantic Equivalence
<TR><TD CLASS="code">PoolAlloc::allocate()<TD CLASS="code">T *<TD CLASS="code">PoolAlloc::allocate(1)
<TR><TD CLASS="code">PoolAlloc::deallocate(p)<TD>void<TD CLASS="code">PoolAlloc::deallocate(p, 1)
</TABLE>
<P>
The typedef <SPAN CLASS="code">user_allocator</SPAN> publishes the value of the <SPAN CLASS="code">UserAllocator</SPAN> template parameter.
<P>
<H2>Notes</H2>
<P>
If the allocation functions run out of memory, they will throw <SPAN CLASS="code">std::bad_alloc</SPAN>.
<P>
The underlying Pool type used by the allocators is accessible through the <A HREF="singleton_pool.html">Singleton Pool Interface</A>. The identifying tag used for <SPAN CLASS="code">pool_allocator</SPAN> is <SPAN CLASS="code">pool_allocator_tag</SPAN>, and the tag used for <SPAN CLASS="code">fast_pool_allocator</SPAN> is <SPAN CLASS="code">fast_pool_allocator_tag</SPAN>. All template parameters of the allocators (including <A HREF="../implementation/pool_alloc.html">implementation-specific ones</A>) determine the type of the underlying Pool, with the exception of the first parameter <SPAN CLASS="code">T</SPAN>, whose size is used instead.
<P>
Since the size of <SPAN CLASS="code">T</SPAN> is used to determine the type of the underlying Pool, each allocator for different types of the same size <EM>will share</EM> the same underlying pool. The tag class prevents pools from being shared between <SPAN CLASS="code">pool_allocator</SPAN> and <SPAN CLASS="code">fast_pool_allocator</SPAN>. For example, on a system where sizeof(int) == sizeof(void *), <SPAN CLASS="code">pool_allocator<int></SPAN> and <SPAN CLASS="code">pool_allocator<void *></SPAN> will both allocate/deallocate from/to the same pool.
<P>
If there is only one thread running before <SPAN CLASS="code">main()</SPAN> starts and after <SPAN CLASS="code">main()</SPAN> ends, then both allocators are completely thread-safe.
<P>
<H2>The Fast Pool Allocator</H2>
<P>
<SPAN CLASS="code">pool_allocator</SPAN> is a more general-purpose solution, geared towards efficiently servicing requests for any number of contiguous chunks. <SPAN CLASS="code">fast_pool_allocator</SPAN> is also a general-purpose solution, but is geared towards efficiently servicing requests for one chunk at a time; it will work for contiguous chunks, but not as well as <SPAN CLASS="code">pool_allocator</SPAN>. If you are seriously concerned about performance, use <SPAN CLASS="code">fast_pool_allocator</SPAN> when dealing with containers such as <SPAN CLASS="code">std::list</SPAN>, and use <SPAN CLASS="code">pool_allocator</SPAN> when dealing with containers such as <SPAN CLASS="code">std::vector</SPAN>.
<P>
<H2>Symbols</H2>
<P>
<UL>
<LI>boost::pool_allocator</LI>
<LI>boost::pool_allocator_tag</LI>
<LI>boost::fast_pool_allocator</LI>
<LI>boost::fast_pool_allocator_tag</LI>
</UL>
<P>
<H2><A HREF="../implementation/pool_alloc.html">Implementation Details</A></H2>
<P>
<HR>
<P>
Copyright © 2000, 2001 Stephen Cleary (<A HREF="mailto:shammah@voyager.net">shammah@voyager.net</A>)
<P>
This file can be redistributed and/or modified under the terms found in <A HREF="../copyright.html">copyright.html</A>
<P>
This software and its documentation is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose.
</BODY>
</HTML>
|
