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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Design</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><meta name="keywords" content=" C++ , library , debug " /><meta name="keywords" content=" ISO C++ , library " /><link rel="home" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="debug_mode.html" title="Chapter 17. Debug Mode" /><link rel="prev" href="bk01pt03ch17s03.html" title="Using" /><link rel="next" href="parallel_mode.html" title="Chapter 18. Parallel Mode" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Design</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt03ch17s03.html">Prev</a> </td><th width="60%" align="center">Chapter 17. Debug Mode</th><td width="20%" align="right"> <a accesskey="n" href="parallel_mode.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="Design"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.debug_mode.design"></a>Design</h2></div></div></div><p>
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</p><div class="sect2" title="Goals"><div class="titlepage"><div><div><h3 class="title"><a id="debug_mode.design.goals"></a>Goals</h3></div></div></div><p>
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</p><p> The libstdc++ debug mode replaces unsafe (but efficient) standard
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containers and iterators with semantically equivalent safe standard
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containers and iterators to aid in debugging user programs. The
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following goals directed the design of the libstdc++ debug mode:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Correctness</em></span>: the libstdc++ debug mode must not change
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the semantics of the standard library for all cases specified in
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the ANSI/ISO C++ standard. The essence of this constraint is that
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any valid C++ program should behave in the same manner regardless
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of whether it is compiled with debug mode or release mode. In
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particular, entities that are defined in namespace std in release
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mode should remain defined in namespace std in debug mode, so that
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legal specializations of namespace std entities will remain
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valid. A program that is not valid C++ (e.g., invokes undefined
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behavior) is not required to behave similarly, although the debug
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mode will abort with a diagnostic when it detects undefined
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behavior.</p></li><li class="listitem"><p><span class="emphasis"><em>Performance</em></span>: the additional of the libstdc++ debug mode
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must not affect the performance of the library when it is compiled
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in release mode. Performance of the libstdc++ debug mode is
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secondary (and, in fact, will be worse than the release
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mode).</p></li><li class="listitem"><p><span class="emphasis"><em>Usability</em></span>: the libstdc++ debug mode should be easy to
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use. It should be easily incorporated into the user's development
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environment (e.g., by requiring only a single new compiler switch)
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and should produce reasonable diagnostics when it detects a
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problem with the user program. Usability also involves detection
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of errors when using the debug mode incorrectly, e.g., by linking
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a release-compiled object against a debug-compiled object if in
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fact the resulting program will not run correctly.</p></li><li class="listitem"><p><span class="emphasis"><em>Minimize recompilation</em></span>: While it is expected that
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users recompile at least part of their program to use debug
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mode, the amount of recompilation affects the
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detect-compile-debug turnaround time. This indirectly affects the
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usefulness of the debug mode, because debugging some applications
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may require rebuilding a large amount of code, which may not be
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feasible when the suspect code may be very localized. There are
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several levels of conformance to this requirement, each with its
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own usability and implementation characteristics. In general, the
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higher-numbered conformance levels are more usable (i.e., require
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less recompilation) but are more complicated to implement than
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the lower-numbered conformance levels.
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</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p><span class="emphasis"><em>Full recompilation</em></span>: The user must recompile his or
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her entire application and all C++ libraries it depends on,
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including the C++ standard library that ships with the
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compiler. This must be done even if only a small part of the
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program can use debugging features.</p></li><li class="listitem"><p><span class="emphasis"><em>Full user recompilation</em></span>: The user must recompile
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his or her entire application and all C++ libraries it depends
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on, but not the C++ standard library itself. This must be done
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even if only a small part of the program can use debugging
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features. This can be achieved given a full recompilation
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system by compiling two versions of the standard library when
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the compiler is installed and linking against the appropriate
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one, e.g., a multilibs approach.</p></li><li class="listitem"><p><span class="emphasis"><em>Partial recompilation</em></span>: The user must recompile the
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parts of his or her application and the C++ libraries it
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depends on that will use the debugging facilities
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directly. This means that any code that uses the debuggable
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standard containers would need to be recompiled, but code
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that does not use them (but may, for instance, use IOStreams)
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would not have to be recompiled.</p></li><li class="listitem"><p><span class="emphasis"><em>Per-use recompilation</em></span>: The user must recompile the
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parts of his or her application and the C++ libraries it
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depends on where debugging should occur, and any other code
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that interacts with those containers. This means that a set of
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translation units that accesses a particular standard
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container instance may either be compiled in release mode (no
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checking) or debug mode (full checking), but must all be
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compiled in the same way; a translation unit that does not see
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that standard container instance need not be recompiled. This
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also means that a translation unit <span class="emphasis"><em>A</em></span> that contains a
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particular instantiation
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(say, <code class="code">std::vector<int></code>) compiled in release
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mode can be linked against a translation unit <span class="emphasis"><em>B</em></span> that
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contains the same instantiation compiled in debug mode (a
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feature not present with partial recompilation). While this
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behavior is technically a violation of the One Definition
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Rule, this ability tends to be very important in
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practice. The libstdc++ debug mode supports this level of
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recompilation. </p></li><li class="listitem"><p><span class="emphasis"><em>Per-unit recompilation</em></span>: The user must only
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recompile the translation units where checking should occur,
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regardless of where debuggable standard containers are
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used. This has also been dubbed "<code class="code">-g</code> mode",
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because the <code class="code">-g</code> compiler switch works in this way,
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emitting debugging information at a per--translation-unit
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granularity. We believe that this level of recompilation is in
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fact not possible if we intend to supply safe iterators, leave
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the program semantics unchanged, and not regress in
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performance under release mode because we cannot associate
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extra information with an iterator (to form a safe iterator)
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without either reserving that space in release mode
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(performance regression) or allocating extra memory associated
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with each iterator with <code class="code">new</code> (changes the program
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semantics).</p></li></ol></div><p>
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</p></li></ul></div></div><div class="sect2" title="Methods"><div class="titlepage"><div><div><h3 class="title"><a id="debug_mode.design.methods"></a>Methods</h3></div></div></div><p>
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</p><p>This section provides an overall view of the design of the
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libstdc++ debug mode and details the relationship between design
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decisions and the stated design goals.</p><div class="sect3" title="The Wrapper Model"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.wrappers"></a>The Wrapper Model</h4></div></div></div><p>The libstdc++ debug mode uses a wrapper model where the
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debugging versions of library components (e.g., iterators and
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containers) form a layer on top of the release versions of the
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library components. The debugging components first verify that the
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operation is correct (aborting with a diagnostic if an error is
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found) and will then forward to the underlying release-mode
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container that will perform the actual work. This design decision
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ensures that we cannot regress release-mode performance (because the
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release-mode containers are left untouched) and partially
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enables <a class="link" href="bk01pt03ch17s04.html#methods.coexistence.link" title="Link- and run-time coexistence of release- and debug-mode components">mixing debug and
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release code</a> at link time, although that will not be
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discussed at this time.</p><p>Two types of wrappers are used in the implementation of the debug
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mode: container wrappers and iterator wrappers. The two types of
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wrappers interact to maintain relationships between iterators and
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their associated containers, which are necessary to detect certain
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types of standard library usage errors such as dereferencing
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past-the-end iterators or inserting into a container using an
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iterator from a different container.</p><div class="sect4" title="Safe Iterators"><div class="titlepage"><div><div><h5 class="title"><a id="debug_mode.design.methods.safe_iter"></a>Safe Iterators</h5></div></div></div><p>Iterator wrappers provide a debugging layer over any iterator that
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is attached to a particular container, and will manage the
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information detailing the iterator's state (singular,
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dereferenceable, etc.) and tracking the container to which the
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iterator is attached. Because iterators have a well-defined, common
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interface the iterator wrapper is implemented with the iterator
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adaptor class template <code class="code">__gnu_debug::_Safe_iterator</code>,
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which takes two template parameters:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><code class="code">Iterator</code>: The underlying iterator type, which must
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be either the <code class="code">iterator</code> or <code class="code">const_iterator</code>
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typedef from the sequence type this iterator can reference.</p></li><li class="listitem"><p><code class="code">Sequence</code>: The type of sequence that this iterator
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references. This sequence must be a safe sequence (discussed below)
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whose <code class="code">iterator</code> or <code class="code">const_iterator</code> typedef
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is the type of the safe iterator.</p></li></ul></div></div><div class="sect4" title="Safe Sequences (Containers)"><div class="titlepage"><div><div><h5 class="title"><a id="debug_mode.design.methods.safe_seq"></a>Safe Sequences (Containers)</h5></div></div></div><p>Container wrappers provide a debugging layer over a particular
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container type. Because containers vary greatly in the member
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functions they support and the semantics of those member functions
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(especially in the area of iterator invalidation), container
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wrappers are tailored to the container they reference, e.g., the
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debugging version of <code class="code">std::list</code> duplicates the entire
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interface of <code class="code">std::list</code>, adding additional semantic
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checks and then forwarding operations to the
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real <code class="code">std::list</code> (a public base class of the debugging
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version) as appropriate. However, all safe containers inherit from
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the class template <code class="code">__gnu_debug::_Safe_sequence</code>,
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instantiated with the type of the safe container itself (an instance
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|
of the curiously recurring template pattern).</p><p>The iterators of a container wrapper will be
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|
<a class="link" href="bk01pt03ch17s04.html#debug_mode.design.methods.safe_iter" title="Safe Iterators">safe
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|
iterators</a> that reference sequences of this type and wrap the
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|
iterators provided by the release-mode base class. The debugging
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|
container will use only the safe iterators within its own interface
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(therefore requiring the user to use safe iterators, although this
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does not change correct user code) and will communicate with the
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release-mode base class with only the underlying, unsafe,
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release-mode iterators that the base class exports.</p><p> The debugging version of <code class="code">std::list</code> will have the
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following basic structure:</p><pre class="programlisting">
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|
template<typename _Tp, typename _Allocator = allocator<_Tp>
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class debug-list :
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public release-list<_Tp, _Allocator>,
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public __gnu_debug::_Safe_sequence<debug-list<_Tp, _Allocator> >
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{
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typedef release-list<_Tp, _Allocator> _Base;
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typedef debug-list<_Tp, _Allocator> _Self;
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public:
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typedef __gnu_debug::_Safe_iterator<typename _Base::iterator, _Self> iterator;
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typedef __gnu_debug::_Safe_iterator<typename _Base::const_iterator, _Self> const_iterator;
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// duplicate std::list interface with debugging semantics
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};
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</pre></div></div><div class="sect3" title="Precondition Checking"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.precond"></a>Precondition Checking</h4></div></div></div><p>The debug mode operates primarily by checking the preconditions of
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all standard library operations that it supports. Preconditions that
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are always checked (regardless of whether or not we are in debug
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mode) are checked via the <code class="code">__check_xxx</code> macros defined
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and documented in the source
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file <code class="code">include/debug/debug.h</code>. Preconditions that may or
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may not be checked, depending on the debug-mode
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macro <code class="code">_GLIBCXX_DEBUG</code>, are checked via
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the <code class="code">__requires_xxx</code> macros defined and documented in the
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same source file. Preconditions are validated using any additional
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information available at run-time, e.g., the containers that are
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associated with a particular iterator, the position of the iterator
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within those containers, the distance between two iterators that may
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form a valid range, etc. In the absence of suitable information,
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e.g., an input iterator that is not a safe iterator, these
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precondition checks will silently succeed.</p><p>The majority of precondition checks use the aforementioned macros,
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which have the secondary benefit of having prewritten debug
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messages that use information about the current status of the
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objects involved (e.g., whether an iterator is singular or what
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sequence it is attached to) along with some static information
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(e.g., the names of the function parameters corresponding to the
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objects involved). When not using these macros, the debug mode uses
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either the debug-mode assertion
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macro <code class="code">_GLIBCXX_DEBUG_ASSERT</code> , its pedantic
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cousin <code class="code">_GLIBCXX_DEBUG_PEDASSERT</code>, or the assertion
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check macro that supports more advance formulation of error
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messages, <code class="code">_GLIBCXX_DEBUG_VERIFY</code>. These macros are
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documented more thoroughly in the debug mode source code.</p></div><div class="sect3" title="Release- and debug-mode coexistence"><div class="titlepage"><div><div><h4 class="title"><a id="debug_mode.design.methods.coexistence"></a>Release- and debug-mode coexistence</h4></div></div></div><p>The libstdc++ debug mode is the first debug mode we know of that
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is able to provide the "Per-use recompilation" (4) guarantee, that
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allows release-compiled and debug-compiled code to be linked and
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executed together without causing unpredictable behavior. This
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guarantee minimizes the recompilation that users are required to
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perform, shortening the detect-compile-debug bug hunting cycle
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and making the debug mode easier to incorporate into development
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environments by minimizing dependencies.</p><p>Achieving link- and run-time coexistence is not a trivial
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implementation task. To achieve this goal we required a small
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extension to the GNU C++ compiler (since incorporated into the C++0x language specification, described in the GCC Manual for the C++ language as
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<a class="ulink" href="http://gcc.gnu.org/onlinedocs/gcc/Namespace-Association.html#Namespace-Association" target="_top">namespace
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association</a>), and a complex organization of debug- and
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release-modes. The end result is that we have achieved per-use
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recompilation but have had to give up some checking of the
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<code class="code">std::basic_string</code> class template (namely, safe
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iterators).
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</p><div class="sect4" title="Compile-time coexistence of release- and debug-mode components"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.compile"></a>Compile-time coexistence of release- and debug-mode components</h5></div></div></div><p>Both the release-mode components and the debug-mode
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components need to exist within a single translation unit so that
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the debug versions can wrap the release versions. However, only one
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of these components should be user-visible at any particular
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|
time with the standard name, e.g., <code class="code">std::list</code>. </p><p>In release mode, we define only the release-mode version of the
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component with its standard name and do not include the debugging
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component at all. The release mode version is defined within the
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|
namespace <code class="code">std</code>. Minus the namespace associations, this
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|
method leaves the behavior of release mode completely unchanged from
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|
its behavior prior to the introduction of the libstdc++ debug
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mode. Here's an example of what this ends up looking like, in
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|
C++.</p><pre class="programlisting">
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|
namespace std
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{
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template<typename _Tp, typename _Alloc = allocator<_Tp> >
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class list
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{
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// ...
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};
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} // namespace std
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</pre><p>In debug mode we include the release-mode container (which is now
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defined in the namespace <code class="code">__norm</code>) and also the
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|
debug-mode container. The debug-mode container is defined within the
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|
namespace <code class="code">__debug</code>, which is associated with namespace
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<code class="code">std</code> via the C++0x namespace association language feature. This
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|
method allows the debug and release versions of the same component to
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coexist at compile-time and link-time without causing an unreasonable
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maintenance burden, while minimizing confusion. Again, this boils down
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to C++ code as follows:</p><pre class="programlisting">
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|
namespace std
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{
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namespace __norm
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{
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template<typename _Tp, typename _Alloc = allocator<_Tp> >
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class list
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{
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// ...
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};
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} // namespace __gnu_norm
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|
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namespace __debug
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{
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template<typename _Tp, typename _Alloc = allocator<_Tp> >
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class list
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: public __norm::list<_Tp, _Alloc>,
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public __gnu_debug::_Safe_sequence<list<_Tp, _Alloc> >
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{
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// ...
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};
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} // namespace __norm
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// namespace __debug __attribute__ ((strong));
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inline namespace __debug { }
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}
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</pre></div><div class="sect4" title="Link- and run-time coexistence of release- and debug-mode components"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.link"></a>Link- and run-time coexistence of release- and
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|
debug-mode components</h5></div></div></div><p>Because each component has a distinct and separate release and
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|
debug implementation, there is no issue with link-time
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|
coexistence: the separate namespaces result in different mangled
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|
names, and thus unique linkage.</p><p>However, components that are defined and used within the C++
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|
standard library itself face additional constraints. For instance,
|
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|
some of the member functions of <code class="code"> std::moneypunct</code> return
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|
<code class="code">std::basic_string</code>. Normally, this is not a problem, but
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|
with a mixed mode standard library that could be using either
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|
debug-mode or release-mode <code class="code"> basic_string</code> objects, things
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|
get more complicated. As the return value of a function is not
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|
encoded into the mangled name, there is no way to specify a
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release-mode or a debug-mode string. In practice, this results in
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|
runtime errors. A simplified example of this problem is as follows.
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</p><p> Take this translation unit, compiled in debug-mode: </p><pre class="programlisting">
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|
// -D_GLIBCXX_DEBUG
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#include <string>
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|
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std::string test02();
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|
|
|||
|
std::string test01()
|
|||
|
{
|
|||
|
return test02();
|
|||
|
}
|
|||
|
|
|||
|
int main()
|
|||
|
{
|
|||
|
test01();
|
|||
|
return 0;
|
|||
|
}
|
|||
|
</pre><p> ... and linked to this translation unit, compiled in release mode:</p><pre class="programlisting">
|
|||
|
#include <string>
|
|||
|
|
|||
|
std::string
|
|||
|
test02()
|
|||
|
{
|
|||
|
return std::string("toast");
|
|||
|
}
|
|||
|
</pre><p> For this reason we cannot easily provide safe iterators for
|
|||
|
the <code class="code">std::basic_string</code> class template, as it is present
|
|||
|
throughout the C++ standard library. For instance, locale facets
|
|||
|
define typedefs that include <code class="code">basic_string</code>: in a mixed
|
|||
|
debug/release program, should that typedef be based on the
|
|||
|
debug-mode <code class="code">basic_string</code> or the
|
|||
|
release-mode <code class="code">basic_string</code>? While the answer could be
|
|||
|
"both", and the difference hidden via renaming a la the
|
|||
|
debug/release containers, we must note two things about locale
|
|||
|
facets:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>They exist as shared state: one can create a facet in one
|
|||
|
translation unit and access the facet via the same type name in a
|
|||
|
different translation unit. This means that we cannot have two
|
|||
|
different versions of locale facets, because the types would not be
|
|||
|
the same across debug/release-mode translation unit barriers.</p></li><li class="listitem"><p>They have virtual functions returning strings: these functions
|
|||
|
mangle in the same way regardless of the mangling of their return
|
|||
|
types (see above), and their precise signatures can be relied upon
|
|||
|
by users because they may be overridden in derived classes.</p></li></ol></div><p>With the design of libstdc++ debug mode, we cannot effectively hide
|
|||
|
the differences between debug and release-mode strings from the
|
|||
|
user. Failure to hide the differences may result in unpredictable
|
|||
|
behavior, and for this reason we have opted to only
|
|||
|
perform <code class="code">basic_string</code> changes that do not require ABI
|
|||
|
changes. The effect on users is expected to be minimal, as there are
|
|||
|
simple alternatives (e.g., <code class="code">__gnu_debug::basic_string</code>),
|
|||
|
and the usability benefit we gain from the ability to mix debug- and
|
|||
|
release-compiled translation units is enormous.</p></div><div class="sect4" title="Alternatives for Coexistence"><div class="titlepage"><div><div><h5 class="title"><a id="methods.coexistence.alt"></a>Alternatives for Coexistence</h5></div></div></div><p>The coexistence scheme above was chosen over many alternatives,
|
|||
|
including language-only solutions and solutions that also required
|
|||
|
extensions to the C++ front end. The following is a partial list of
|
|||
|
solutions, with justifications for our rejection of each.</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><span class="emphasis"><em>Completely separate debug/release libraries</em></span>: This is by
|
|||
|
far the simplest implementation option, where we do not allow any
|
|||
|
coexistence of debug- and release-compiled translation units in a
|
|||
|
program. This solution has an extreme negative affect on usability,
|
|||
|
because it is quite likely that some libraries an application
|
|||
|
depends on cannot be recompiled easily. This would not meet
|
|||
|
our <span class="emphasis"><em>usability</em></span> or <span class="emphasis"><em>minimize recompilation</em></span> criteria
|
|||
|
well.</p></li><li class="listitem"><p><span class="emphasis"><em>Add a <code class="code">Debug</code> boolean template parameter</em></span>:
|
|||
|
Partial specialization could be used to select the debug
|
|||
|
implementation when <code class="code">Debug == true</code>, and the state
|
|||
|
of <code class="code">_GLIBCXX_DEBUG</code> could decide whether the
|
|||
|
default <code class="code">Debug</code> argument is <code class="code">true</code>
|
|||
|
or <code class="code">false</code>. This option would break conformance with the
|
|||
|
C++ standard in both debug <span class="emphasis"><em>and</em></span> release modes. This would
|
|||
|
not meet our <span class="emphasis"><em>correctness</em></span> criteria. </p></li><li class="listitem"><p><span class="emphasis"><em>Packaging a debug flag in the allocators</em></span>: We could
|
|||
|
reuse the <code class="code">Allocator</code> template parameter of containers
|
|||
|
by adding a sentinel wrapper <code class="code">debug<></code> that
|
|||
|
signals the user's intention to use debugging, and pick up
|
|||
|
the <code class="code">debug<></code> allocator wrapper in a partial
|
|||
|
specialization. However, this has two drawbacks: first, there is a
|
|||
|
conformance issue because the default allocator would not be the
|
|||
|
standard-specified <code class="code">std::allocator<T></code>. Secondly
|
|||
|
(and more importantly), users that specify allocators instead of
|
|||
|
implicitly using the default allocator would not get debugging
|
|||
|
containers. Thus this solution fails the <span class="emphasis"><em>correctness</em></span>
|
|||
|
criteria.</p></li><li class="listitem"><p><span class="emphasis"><em>Define debug containers in another namespace, and employ
|
|||
|
a <code class="code">using</code> declaration (or directive)</em></span>: This is an
|
|||
|
enticing option, because it would eliminate the need for
|
|||
|
the <code class="code">link_name</code> extension by aliasing the
|
|||
|
templates. However, there is no true template aliasing mechanism
|
|||
|
in C++, because both <code class="code">using</code> directives and using
|
|||
|
declarations disallow specialization. This method fails
|
|||
|
the <span class="emphasis"><em>correctness</em></span> criteria.</p></li><li class="listitem"><p><span class="emphasis"><em> Use implementation-specific properties of anonymous
|
|||
|
namespaces. </em></span>
|
|||
|
See <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00004.html" target="_top"> this post
|
|||
|
</a>
|
|||
|
This method fails the <span class="emphasis"><em>correctness</em></span> criteria.</p></li><li class="listitem"><p><span class="emphasis"><em>Extension: allow reopening on namespaces</em></span>: This would
|
|||
|
allow the debug mode to effectively alias the
|
|||
|
namespace <code class="code">std</code> to an internal namespace, such
|
|||
|
as <code class="code">__gnu_std_debug</code>, so that it is completely
|
|||
|
separate from the release-mode <code class="code">std</code> namespace. While
|
|||
|
this will solve some renaming problems and ensure that
|
|||
|
debug- and release-compiled code cannot be mixed unsafely, it ensures that
|
|||
|
debug- and release-compiled code cannot be mixed at all. For
|
|||
|
instance, the program would have two <code class="code">std::cout</code>
|
|||
|
objects! This solution would fails the <span class="emphasis"><em>minimize
|
|||
|
recompilation</em></span> requirement, because we would only be able to
|
|||
|
support option (1) or (2).</p></li><li class="listitem"><p><span class="emphasis"><em>Extension: use link name</em></span>: This option involves
|
|||
|
complicated re-naming between debug-mode and release-mode
|
|||
|
components at compile time, and then a g++ extension called <span class="emphasis"><em>
|
|||
|
link name </em></span> to recover the original names at link time. There
|
|||
|
are two drawbacks to this approach. One, it's very verbose,
|
|||
|
relying on macro renaming at compile time and several levels of
|
|||
|
include ordering. Two, ODR issues remained with container member
|
|||
|
functions taking no arguments in mixed-mode settings resulting in
|
|||
|
equivalent link names, <code class="code"> vector::push_back() </code> being
|
|||
|
one example.
|
|||
|
See <a class="ulink" href="http://gcc.gnu.org/ml/libstdc++/2003-08/msg00177.html" target="_top">link
|
|||
|
name</a> </p></li></ul></div><p>Other options may exist for implementing the debug mode, many of
|
|||
|
which have probably been considered and others that may still be
|
|||
|
lurking. This list may be expanded over time to include other
|
|||
|
options that we could have implemented, but in all cases the full
|
|||
|
ramifications of the approach (as measured against the design goals
|
|||
|
for a libstdc++ debug mode) should be considered first. The DejaGNU
|
|||
|
testsuite includes some testcases that check for known problems with
|
|||
|
some solutions (e.g., the <code class="code">using</code> declaration solution
|
|||
|
that breaks user specialization), and additional testcases will be
|
|||
|
added as we are able to identify other typical problem cases. These
|
|||
|
test cases will serve as a benchmark by which we can compare debug
|
|||
|
mode implementations.</p></div></div></div><div class="sect2" title="Other Implementations"><div class="titlepage"><div><div><h3 class="title"><a id="debug_mode.design.other"></a>Other Implementations</h3></div></div></div><p>
|
|||
|
</p><p> There are several existing implementations of debug modes for C++
|
|||
|
standard library implementations, although none of them directly
|
|||
|
supports debugging for programs using libstdc++. The existing
|
|||
|
implementations include:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p><a class="ulink" href="http://www.mathcs.sjsu.edu/faculty/horstman/safestl.html" target="_top">SafeSTL</a>:
|
|||
|
SafeSTL was the original debugging version of the Standard Template
|
|||
|
Library (STL), implemented by Cay S. Horstmann on top of the
|
|||
|
Hewlett-Packard STL. Though it inspired much work in this area, it
|
|||
|
has not been kept up-to-date for use with modern compilers or C++
|
|||
|
standard library implementations.</p></li><li class="listitem"><p><a class="ulink" href="http://www.stlport.org/" target="_top">STLport</a>: STLport is a free
|
|||
|
implementation of the C++ standard library derived from the <a class="ulink" href="http://www.sgi.com/tech/stl/" target="_top">SGI implementation</a>, and
|
|||
|
ported to many other platforms. It includes a debug mode that uses a
|
|||
|
wrapper model (that in some ways inspired the libstdc++ debug mode
|
|||
|
design), although at the time of this writing the debug mode is
|
|||
|
somewhat incomplete and meets only the "Full user recompilation" (2)
|
|||
|
recompilation guarantee by requiring the user to link against a
|
|||
|
different library in debug mode vs. release mode.</p></li><li class="listitem"><p>Metrowerks CodeWarrior: The C++ standard library
|
|||
|
that ships with Metrowerks CodeWarrior includes a debug mode. It is
|
|||
|
a full debug-mode implementation (including debugging for
|
|||
|
CodeWarrior extensions) and is easy to use, although it meets only
|
|||
|
the "Full recompilation" (1) recompilation
|
|||
|
guarantee.</p></li></ul></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt03ch17s03.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="debug_mode.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="parallel_mode.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Using </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 18. Parallel Mode</td></tr></table></div></body></html>
|