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"></a>Implementation</h4></div></div></div><div class="section" title="Interface Design"><div class="titlepage"><div><div><h5 class="title"><a id="id494125"></a>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"></a>Implementation</h4></div></div></div><div class="section" title="Interface Design"><div class="titlepage"><div><div><h5 class="title"><a id="id596578"></a>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="id433040"></a>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="id621931"></a>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="id527578"></a>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="id623241"></a>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="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"></a>Bibliography</h4></div></div></div><div class="biblioentry" title="ISO/IEC 14882:1998 Programming languages - C++"><a id="id456326"></a><p><span class="title"><i>
+ </p></li></ol></div></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h4 class="title"><a id="allocator.biblio"></a>Bibliography</h4></div></div></div><div class="biblioentry" title="ISO/IEC 14882:1998 Programming languages - C++"><a id="id586118"></a><p><span class="title"><i>
ISO/IEC 14882:1998 Programming languages - C++
</i>. </span>
isoc++_1998
- <span class="pagenums">20.4 Memory. </span></p></div><div class="biblioentry"><a id="id461685"></a><p><span class="biblioid">
+ <span class="pagenums">20.4 Memory. </span></p></div><div class="biblioentry"><a id="id586133"></a><p><span class="biblioid">
<a class="ulink" href="http://www.drdobbs.com/cpp/184403759" target="_top">
<em class="citetitle">
The Standard Librarian: What Are Allocators Good For?
</a>
. </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"><a id="id519812"></a><p><span class="biblioid">
+ . </span></span></p></div><div class="biblioentry"><a id="id575589"></a><p><span class="biblioid">
<a class="ulink" href="http://www.cs.umass.edu/~emery/hoard/" target="_top">
<em class="citetitle">
The Hoard Memory Allocator
</em>
</a>
- . </span><span class="author"><span class="firstname">Emery</span> <span class="surname">Berger</span>. </span></p></div><div class="biblioentry"><a id="id499458"></a><p><span class="biblioid">
+ . </span><span class="author"><span class="firstname">Emery</span> <span class="surname">Berger</span>. </span></p></div><div class="biblioentry"><a id="id553897"></a><p><span class="biblioid">
<a class="ulink" href="http://www.cs.umass.edu/~emery/pubs/berger-oopsla2002.pdf" target="_top">
<em class="citetitle">
Reconsidering Custom Memory Allocation
</em>
</a>
- . </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"><a id="id503483"></a><p><span class="biblioid">
+ . </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"><a id="id543446"></a><p><span class="biblioid">
<a class="ulink" href="http://www.angelikalanger.com/Articles/C++Report/Allocators/Allocators.html" target="_top">
<em class="citetitle">
Allocator Types
</a>
. </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" title="The C++ Programming Language"><a id="id475167"></a><p><span class="title"><i>The C++ Programming Language</i>. </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" title="The C++ Programming Language"><a id="id602880"></a><p><span class="title"><i>The C++ Programming Language</i>. </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" title="Yalloc: A Recycling C++ Allocator"><a id="id529006"></a><p><span class="title"><i>Yalloc: A Recycling C++ Allocator</i>. </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"></a>auto_ptr</h3></div></div></div><div class="section" title="Limitations"><div class="titlepage"><div><div><h4 class="title"><a id="auto_ptr.limitations"></a>Limitations</h4></div></div></div><p>Explaining all of the fun and delicious things that can
+ . </span></span></p></div><div class="biblioentry" title="Yalloc: A Recycling C++ Allocator"><a id="id554889"></a><p><span class="title"><i>Yalloc: A Recycling C++ Allocator</i>. </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"></a>auto_ptr</h3></div></div></div><div class="section" title="Limitations"><div class="titlepage"><div><div><h4 class="title"><a id="auto_ptr.limitations"></a>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"></a>Implementation</h4></div></div></div><div class="section" title="Class Hierarchy"><div class="titlepage"><div><div><h5 class="title"><a id="id540433"></a>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"></a>Implementation</h4></div></div></div><div class="section" title="Class Hierarchy"><div class="titlepage"><div><div><h5 class="title"><a id="id545398"></a>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="id517308"></a>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="id552877"></a>Thread Safety</h5></div></div></div><p>
The interface of <code class="classname">tr1::shared_ptr</code> was extended for C++0x
with support for rvalue-references and the other features from
N2351. As with other libstdc++ headers shared by TR1 and C++0x,
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="id470416"></a>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="id620315"></a>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++0x and TR1 Implementation"><div class="titlepage"><div><div><h5 class="title"><a id="id455214"></a>Dual C++0x and TR1 Implementation</h5></div></div></div><p>
+ </p></div><div class="section" title="Dual C++0x and TR1 Implementation"><div class="titlepage"><div><div><h5 class="title"><a id="id642095"></a>Dual C++0x and TR1 Implementation</h5></div></div></div><p>
The classes derived from <code class="classname">_Sp_counted_base</code> (see Class Hierarchy
below) and <code class="classname">__shared_count</code> are implemented separately for C++0x
and TR1, in <code class="filename">bits/boost_sp_shared_count.h</code> and
change unless bug fixes require it. If the code that is common to both
C++0x and TR1 modes needs to diverge further then it might be necessary to
duplicate additional classes and only make changes to the C++0x versions.
-</p></div><div class="section" title="Related functions and classes"><div class="titlepage"><div><div><h5 class="title"><a id="id556462"></a>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="id628651"></a>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"></a>Use</h4></div></div></div><div class="section" title="Examples"><div class="titlepage"><div><div><h5 class="title"><a id="id441574"></a>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"></a>Use</h4></div></div></div><div class="section" title="Examples"><div class="titlepage"><div><div><h5 class="title"><a id="id595512"></a>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>.
- </p></div><div class="section" title="Unresolved Issues"><div class="titlepage"><div><div><h5 class="title"><a id="id441591"></a>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="id595527"></a>Unresolved Issues</h5></div></div></div><p>
The resolution to C++ Standard Library issue <a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#674" target="_top">674</a>,
"shared_ptr interface changes for consistency with N1856" will
need to be implemented after it is accepted into the working
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"></a>Bibliography</h4></div></div></div><div class="biblioentry"><a id="id453578"></a><p><span class="biblioid">
+ </p></div><div class="bibliography" title="Bibliography"><div class="titlepage"><div><div><h4 class="title"><a id="shared_ptr.biblio"></a>Bibliography</h4></div></div></div><div class="biblioentry"><a id="id605443"></a><p><span class="biblioid">
<a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2351.htm" target="_top">
<em class="citetitle">
Improving shared_ptr for C++0x, Revision 2
</a>
. </span><span class="subtitle">
N2351
- . </span></p></div><div class="biblioentry"><a id="id454142"></a><p><span class="biblioid">
+ . </span></p></div><div class="biblioentry"><a id="id557167"></a><p><span class="biblioid">
<a class="ulink" href="http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2456.html" target="_top">
<em class="citetitle">
C++ Standard Library Active Issues List
</a>
. </span><span class="subtitle">
N2456
- . </span></p></div><div class="biblioentry"><a id="id454164"></a><p><span class="biblioid">
+ . </span></p></div><div class="biblioentry"><a id="id560776"></a><p><span class="biblioid">
<a class="ulink" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2461.pdf" target="_top">
<em class="citetitle">
Working Draft, Standard for Programming Language C++
</a>
. </span><span class="subtitle">
N2461
- . </span></p></div><div class="biblioentry"><a id="id518017"></a><p><span class="biblioid">
+ . </span></p></div><div class="biblioentry"><a id="id560798"></a><p><span class="biblioid">
<a class="ulink" href="http://boost.org/libs/smart_ptr/shared_ptr.htm" target="_top">shared_ptr
<em class="citetitle">
Boost C++ Libraries documentation, shared_ptr