or loading and unloading shared objects in memory. As such, using
caching allocators on systems that do not support
<code class="function">abi::__cxa_atexit</code> is not recommended.
- </p></div><div class="section" title="Implementation"><div class="titlepage"><div><div><h4 class="title"><a id="allocator.impl"/>Implementation</h4></div></div></div><div class="section" title="Interface Design"><div class="titlepage"><div><div><h5 class="title"><a id="id443701"/>Interface Design</h5></div></div></div><p>
+ </p></div><div class="section" title="Implementation"><div class="titlepage"><div><div><h4 class="title"><a id="allocator.impl"/>Implementation</h4></div></div></div><div class="section" title="Interface Design"><div class="titlepage"><div><div><h5 class="title"><a id="id542426"/>Interface Design</h5></div></div></div><p>
The only allocator interface that
is supported is the standard C++ interface. As such, all STL
containers have been adjusted, and all external allocators have
</p><p>
The base class that <code class="classname">allocator</code> is derived from
may not be user-configurable.
-</p></div><div class="section" title="Selecting Default Allocation Policy"><div class="titlepage"><div><div><h5 class="title"><a id="id443731"/>Selecting Default Allocation Policy</h5></div></div></div><p>
+</p></div><div class="section" title="Selecting Default Allocation Policy"><div class="titlepage"><div><div><h5 class="title"><a id="id542456"/>Selecting Default Allocation Policy</h5></div></div></div><p>
It's difficult to pick an allocation strategy that will provide
maximum utility, without excessively penalizing some behavior. In
fact, it's difficult just deciding which typical actions to measure
The current default choice for
<code class="classname">allocator</code> is
<code class="classname">__gnu_cxx::new_allocator</code>.
- </p></div><div class="section" title="Disabling Memory Caching"><div class="titlepage"><div><div><h5 class="title"><a id="id443842"/>Disabling Memory Caching</h5></div></div></div><p>
+ </p></div><div class="section" title="Disabling Memory Caching"><div class="titlepage"><div><div><h5 class="title"><a id="id542566"/>Disabling Memory Caching</h5></div></div></div><p>
In use, <code class="classname">allocator</code> may allocate and
deallocate using implementation-specified strategies and
heuristics. Because of this, every call to an allocator object's
A high-performance allocator that uses a bit-map to keep track
of the used and unused memory locations. It has its own
documentation, found <a class="link" href="bitmap_allocator.html" title="Chapter 21. The bitmap_allocator">here</a>.
- </p></li></ol></div></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h4 class="title"><a id="allocator.biblio"/>Bibliography</h4></div></div></div><div class="biblioentry"><a id="id444292"/><p><span class="citetitle"><em class="citetitle">
+ </p></li></ol></div></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h4 class="title"><a id="allocator.biblio"/>Bibliography</h4></div></div></div><div class="biblioentry"><a id="id543017"/><p><span class="citetitle"><em class="citetitle">
ISO/IEC 14882:1998 Programming languages - C++
</em>. </span>
isoc++_1998
- <span class="pagenums">20.4 Memory. </span></p></div><div class="biblioentry" title="The Standard Librarian: What Are Allocators Good For?"><a id="id444308"/><p><span class="title"><em>
+ <span class="pagenums">20.4 Memory. </span></p></div><div class="biblioentry" title="The Standard Librarian: What Are Allocators Good For?"><a id="id543032"/><p><span class="title"><em>
<a class="link" href="http://www.drdobbs.com/cpp/184403759">
The Standard Librarian: What Are Allocators Good For?
</a>
</em>. </span><span class="author"><span class="firstname">Matt</span> <span class="surname">Austern</span>. </span><span class="publisher"><span class="publishername">
C/C++ Users Journal
- . </span></span></p></div><div class="biblioentry" title="The Hoard Memory Allocator"><a id="id444339"/><p><span class="title"><em>
+ . </span></span></p></div><div class="biblioentry" title="The Hoard Memory Allocator"><a id="id543063"/><p><span class="title"><em>
<a class="link" href="http://www.cs.umass.edu/~emery/hoard">
The Hoard Memory Allocator
</a>
- </em>. </span><span class="author"><span class="firstname">Emery</span> <span class="surname">Berger</span>. </span></p></div><div class="biblioentry" title="Reconsidering Custom Memory Allocation"><a id="id444362"/><p><span class="title"><em>
+ </em>. </span><span class="author"><span class="firstname">Emery</span> <span class="surname">Berger</span>. </span></p></div><div class="biblioentry" title="Reconsidering Custom Memory Allocation"><a id="id543087"/><p><span class="title"><em>
<a class="link" href="http://www.cs.umass.edu/~emery/pubs/berger-oopsla2002.pdf">
Reconsidering Custom Memory Allocation
</a>
- </em>. </span><span class="author"><span class="firstname">Emery</span> <span class="surname">Berger</span>. </span><span class="author"><span class="firstname">Ben</span> <span class="surname">Zorn</span>. </span><span class="author"><span class="firstname">Kathryn</span> <span class="surname">McKinley</span>. </span><span class="copyright">Copyright © 2002 OOPSLA. </span></p></div><div class="biblioentry" title="Allocator Types"><a id="id444413"/><p><span class="title"><em>
+ </em>. </span><span class="author"><span class="firstname">Emery</span> <span class="surname">Berger</span>. </span><span class="author"><span class="firstname">Ben</span> <span class="surname">Zorn</span>. </span><span class="author"><span class="firstname">Kathryn</span> <span class="surname">McKinley</span>. </span><span class="copyright">Copyright © 2002 OOPSLA. </span></p></div><div class="biblioentry" title="Allocator Types"><a id="id543138"/><p><span class="title"><em>
<a class="link" href="http://www.angelikalanger.com/Articles/C++Report/Allocators/Allocators.html">
Allocator Types
</a>
</em>. </span><span class="author"><span class="firstname">Klaus</span> <span class="surname">Kreft</span>. </span><span class="author"><span class="firstname">Angelika</span> <span class="surname">Langer</span>. </span><span class="publisher"><span class="publishername">
C/C++ Users Journal
- . </span></span></p></div><div class="biblioentry"><a id="id444453"/><p><span class="citetitle"><em class="citetitle">The C++ Programming Language</em>. </span><span class="author"><span class="firstname">Bjarne</span> <span class="surname">Stroustrup</span>. </span><span class="copyright">Copyright © 2000 . </span><span class="pagenums">19.4 Allocators. </span><span class="publisher"><span class="publishername">
+ . </span></span></p></div><div class="biblioentry"><a id="id543177"/><p><span class="citetitle"><em class="citetitle">The C++ Programming Language</em>. </span><span class="author"><span class="firstname">Bjarne</span> <span class="surname">Stroustrup</span>. </span><span class="copyright">Copyright © 2000 . </span><span class="pagenums">19.4 Allocators. </span><span class="publisher"><span class="publishername">
Addison Wesley
- . </span></span></p></div><div class="biblioentry"><a id="id444490"/><p><span class="citetitle"><em class="citetitle">Yalloc: A Recycling C++ Allocator</em>. </span><span class="author"><span class="firstname">Felix</span> <span class="surname">Yen</span>. </span></p></div></div></div><div class="section" title="auto_ptr"><div class="titlepage"><div><div><h3 class="title"><a id="std.util.memory.auto_ptr"/>auto_ptr</h3></div></div></div><div class="section" title="Limitations"><div class="titlepage"><div><div><h4 class="title"><a id="auto_ptr.limitations"/>Limitations</h4></div></div></div><p>Explaining all of the fun and delicious things that can
+ . </span></span></p></div><div class="biblioentry"><a id="id543214"/><p><span class="citetitle"><em class="citetitle">Yalloc: A Recycling C++ Allocator</em>. </span><span class="author"><span class="firstname">Felix</span> <span class="surname">Yen</span>. </span></p></div></div></div><div class="section" title="auto_ptr"><div class="titlepage"><div><div><h3 class="title"><a id="std.util.memory.auto_ptr"/>auto_ptr</h3></div></div></div><div class="section" title="Limitations"><div class="titlepage"><div><div><h4 class="title"><a id="auto_ptr.limitations"/>Limitations</h4></div></div></div><p>Explaining all of the fun and delicious things that can
happen with misuse of the <code class="classname">auto_ptr</code> class
template (called <acronym class="acronym">AP</acronym> here) would take some
time. Suffice it to say that the use of <acronym class="acronym">AP</acronym>
Derived classes override those functions to destroy resources in a context
where the correct dynamic type is known. This is an application of the
technique known as type erasure.
- </p></div><div class="section" title="Implementation"><div class="titlepage"><div><div><h4 class="title"><a id="shared_ptr.impl"/>Implementation</h4></div></div></div><div class="section" title="Class Hierarchy"><div class="titlepage"><div><div><h5 class="title"><a id="id444841"/>Class Hierarchy</h5></div></div></div><p>
+ </p></div><div class="section" title="Implementation"><div class="titlepage"><div><div><h4 class="title"><a id="shared_ptr.impl"/>Implementation</h4></div></div></div><div class="section" title="Class Hierarchy"><div class="titlepage"><div><div><h5 class="title"><a id="id543565"/>Class Hierarchy</h5></div></div></div><p>
A <code class="classname">shared_ptr<T></code> contains a pointer of
type <span class="type">T*</span> and an object of type
<code class="classname">__shared_count</code>. The shared_count contains a
Unlike the other <code class="classname">_Sp_counted_*</code> classes, this one is parameterized on the
type of object, not the type of pointer; this is purely a convenience
that simplifies the implementation slightly.
- </p></dd></dl></div></div><div class="section" title="Thread Safety"><div class="titlepage"><div><div><h5 class="title"><a id="id445019"/>Thread Safety</h5></div></div></div><p>
+ </p></dd></dl></div></div><div class="section" title="Thread Safety"><div class="titlepage"><div><div><h5 class="title"><a id="id543744"/>Thread Safety</h5></div></div></div><p>
C++11-only features are: rvalue-ref/move support, allocator support,
aliasing constructor, make_shared & allocate_shared. Additionally,
the constructors taking <code class="classname">auto_ptr</code> parameters are
shared_ptr in libstdc++ the compiler and library are fixed, which
makes things much simpler: we have an atomic CAS or we don't, see Lock
Policy below for details.
-</p></div><div class="section" title="Selecting Lock Policy"><div class="titlepage"><div><div><h5 class="title"><a id="id445089"/>Selecting Lock Policy</h5></div></div></div><p>
+</p></div><div class="section" title="Selecting Lock Policy"><div class="titlepage"><div><div><h5 class="title"><a id="id543814"/>Selecting Lock Policy</h5></div></div></div><p>
</p><p>
There is a single <code class="classname">_Sp_counted_base</code> class,
which is a template parameterized on the enum
<code class="filename">ext/atomicity.h</code>, which detect if the program
is multi-threaded. If only one thread of execution exists in
the program then less expensive non-atomic operations are used.
- </p></div><div class="section" title="Dual C++11 and TR1 Implementation"><div class="titlepage"><div><div><h5 class="title"><a id="id445211"/>Dual C++11 and TR1 Implementation</h5></div></div></div><p>
+ </p></div><div class="section" title="Dual C++11 and TR1 Implementation"><div class="titlepage"><div><div><h5 class="title"><a id="id543936"/>Dual C++11 and TR1 Implementation</h5></div></div></div><p>
The interface of <code class="classname">tr1::shared_ptr</code> was extended for C++11
with support for rvalue-references and the other features from N2351.
The <code class="classname">_Sp_counted_base</code> base class is implemented in
C++11 and TR1 versions needs to diverge further then it might be necessary to
duplicate <code class="classname">_Sp_counted_base</code> and only make changes to
the C++11 version.
-</p></div><div class="section" title="Related functions and classes"><div class="titlepage"><div><div><h5 class="title"><a id="id445267"/>Related functions and classes</h5></div></div></div><div class="variablelist"><dl><dt><span class="term"><code class="code">dynamic_pointer_cast</code>, <code class="code">static_pointer_cast</code>,
+</p></div><div class="section" title="Related functions and classes"><div class="titlepage"><div><div><h5 class="title"><a id="id543992"/>Related functions and classes</h5></div></div></div><div class="variablelist"><dl><dt><span class="term"><code class="code">dynamic_pointer_cast</code>, <code class="code">static_pointer_cast</code>,
<code class="code">const_pointer_cast</code></span></dt><dd><p>
As noted in N2351, these functions can be implemented non-intrusively using
the alias constructor. However the aliasing constructor is only available
As well as the extra constructors, this implementation also needs some
members of _Sp_counted_deleter to be protected where they could otherwise
be private.
- </p></dd></dl></div></div></div><div class="section" title="Use"><div class="titlepage"><div><div><h4 class="title"><a id="shared_ptr.using"/>Use</h4></div></div></div><div class="section" title="Examples"><div class="titlepage"><div><div><h5 class="title"><a id="id445416"/>Examples</h5></div></div></div><p>
+ </p></dd></dl></div></div></div><div class="section" title="Use"><div class="titlepage"><div><div><h4 class="title"><a id="shared_ptr.using"/>Use</h4></div></div></div><div class="section" title="Examples"><div class="titlepage"><div><div><h5 class="title"><a id="id556361"/>Examples</h5></div></div></div><p>
Examples of use can be found in the testsuite, under
<code class="filename">testsuite/tr1/2_general_utilities/shared_ptr</code>,
<code class="filename">testsuite/20_util/shared_ptr</code>
and
<code class="filename">testsuite/20_util/weak_ptr</code>.
- </p></div><div class="section" title="Unresolved Issues"><div class="titlepage"><div><div><h5 class="title"><a id="id445446"/>Unresolved Issues</h5></div></div></div><p>
+ </p></div><div class="section" title="Unresolved Issues"><div class="titlepage"><div><div><h5 class="title"><a id="id556391"/>Unresolved Issues</h5></div></div></div><p>
The <span class="emphasis"><em><code class="classname">shared_ptr</code> atomic access</em></span>
clause in the C++11 standard is not implemented in GCC.
</p><p>
code to work with, Peter Dimov in particular for his help and
invaluable advice on thread safety. Phillip Jordan and Paolo
Carlini for the lock policy implementation.
- </p></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h4 class="title"><a id="shared_ptr.biblio"/>Bibliography</h4></div></div></div><div class="biblioentry" title="Improving shared_ptr for C++0x, Revision 2"><a id="id457760"/><p><span class="title"><em>
+ </p></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h4 class="title"><a id="shared_ptr.biblio"/>Bibliography</h4></div></div></div><div class="biblioentry" title="Improving shared_ptr for C++0x, Revision 2"><a id="id556484"/><p><span class="title"><em>
<a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2351.htm">
Improving shared_ptr for C++0x, Revision 2
</a>
</em>. </span><span class="subtitle">
N2351
- . </span></p></div><div class="biblioentry" title="C++ Standard Library Active Issues List"><a id="id457779"/><p><span class="title"><em>
+ . </span></p></div><div class="biblioentry" title="C++ Standard Library Active Issues List"><a id="id556504"/><p><span class="title"><em>
<a class="link" href="http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2456.html">
C++ Standard Library Active Issues List
</a>
</em>. </span><span class="subtitle">
N2456
- . </span></p></div><div class="biblioentry" title="Working Draft, Standard for Programming Language C++"><a id="id457798"/><p><span class="title"><em>
+ . </span></p></div><div class="biblioentry" title="Working Draft, Standard for Programming Language C++"><a id="id556523"/><p><span class="title"><em>
<a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2461.pdf">
Working Draft, Standard for Programming Language C++
</a>
</em>. </span><span class="subtitle">
N2461
- . </span></p></div><div class="biblioentry" title="Boost C++ Libraries documentation, shared_ptr"><a id="id457817"/><p><span class="title"><em>
+ . </span></p></div><div class="biblioentry" title="Boost C++ Libraries documentation, shared_ptr"><a id="id556542"/><p><span class="title"><em>
<a class="link" href="http://boost.org/libs/smart_ptr/shared_ptr.htm">
Boost C++ Libraries documentation, shared_ptr
</a>