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   9    <TITLE>libstdc++-v3 HOWTO:  Chapter 17</TITLE>
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  15 <H1 CLASS="centered"><A NAME="top">Chapter 17:  Library Introduction</A></H1>
  16
  17 <P>Chapter 17 is actually a list of definitions and descriptions used
  18    in the following chapters of the Standard when describing the actual
  19    library.  Here, we use &quot;Introduction&quot; as an introduction
  20    to the <EM>GNU implementation of</EM> the ISO Standard C++ Library.
  21 </P>
  22
  23
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  25 <HR>
  26 <H1>Contents</H1>
  27 <UL>
  28    <LI><A HREF="#2">The Standard C++ header files</A>
  29    <LI><A HREF="#3">Thread-safety</A>
  30    <LI><A HREF="#4"><TT>&lt;foo&gt;</TT> vs <TT>&lt;foo.h&gt;</TT></A>
  31    <LI><A HREF="porting-howto.html">Porting-howto</A>
  32 </UL>
  33
  34 <HR>
  35
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  37
  38 <H2><A NAME="2">The Standard C++ header files</A></H2>
  39    <P>The Standard C++ Library specifies 50 header files that must be
  40       available to all hosted implementations.  Actually, the word
  41       &quot;files&quot; is a misnomer, since the contents of the headers
  42       don't necessarily have to be in any kind of external file.  The
  43       only rule is that when you <TT>#include</TT> a certain header, the
  44       contents of that header, as defined by the Standard, become
  45       available to you, no matter how.
  46    </P>
  47    <P>The names of the headers can be easily seen in
  48       <A HREF="headers_cc.txt"><TT>testsuite/17_intro/headers.cc</TT></A>,
  49       which is a small testbed we use to make certain that the headers
  50       all compile and run.
  51    </P>
  52
  53 <HR>
  54 <H2><A NAME="3">Thread-safety</A></H2>
  55    <P>This is a thorny issue that gets brought up on the libstdc++-v3
  56       and gcc mailing lists on a regular basis (probably by a cron job).
  57       This entry will mention a very little bit about the general MT
  58       issues with libstdc++.  The latest status and quick notes will be
  59       in FAQ 5.6.  Some discussion about threadsafe containers will be
  60       in section 6.8 (the HOWTOs on containers).
  61    </P>
  62    <P>The libstdc++ code (all of it, not just the containers) has been
  63       designed so that thread-safety will be easily possible.  The first
  64       (!) problem is finding a <EM>fast</EM> method of implementation
  65       portable to all platforms.  A minor problem that pops up every so
  66       often is different interpretations of what &quot;thread-safe&quot;
  67       means for a library (not a general program).  We currently use the
  68       <A HREF="http://www.sgi.com/Technology/STL/thread_safety.html">same
  69       definition that SGI</A> uses for their STL subset.
  70    </P>
  71    <P>A recent journal article has described &quot;atomic integer
  72       operations,&quot; which would allow us to, well, perform updates
  73       on integers atomically, and without requiring an explicit mutex
  74       lock.  This appears promising, but the major difficulty is that
  75       these operations &quot;may not be available on all systems, and
  76       if they are, may have different interfaces.&quot; [quoting from
  77       mailing list messages]
  78    </P>
  79    <P>Here is a small link farm to threads (no pun) in the mail archives
  80       that discuss the threading problem.  Each link is to the first
  81       relevent message in the thread; from there you can use
  82       &quot;Thread Next&quot; to move down the thread.  This farm is in
  83       latest-to-oldest order.
  84       <UL>
  85         <LI>
  86       </UL>
  87       <BR>
  88       Here are discussions that took place before the current snapshot;
  89       they are still relevant and instructive.
  90       <BR>
  91       <UL>
  92         <LI>One way of preventing memory leaks by the old default memory
  93             allocator in multithreaded code is
  94             <A HREF="http://gcc.gnu.org/ml/gcc/1999-11n/msg00431.html">discussed here</A>.
  95         <LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q3/msg00167.html">This thread
  96             concerns strings</A>.
  97         <LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00339.html">So does this
  98             one</A>.  This initial message also refers to another
  99             thread in the GCC mailing list...
 100         <LI><A HREF="http://gcc.gnu.org/ml/gcc/1999-06n/msg00680.html">which is here</A>,
 101             and goes on for some time.  Ironically, the initial message
 102             in this thread also mentions another threading thread...
 103         <LI><A HREF="http://gcc.gnu.org/ml/gcc-bugs/1999-04n/msg00777.html">beginning here</A>,
 104             and talking about pthreads.  (Note that a much more recent
 105             message from the first thread in this list notes that
 106             <A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q3/msg00176.html">pthreads
 107             should not be used as a starting point</A> for making
 108             libstdc++ threadsafe.)
 109         <LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00168.html">This
 110             message</A>,
 111             <A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00159.html">this one</A>,
 112             and <A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00156.html">this one</A>
 113             are the tops of related threads (all within the same time
 114             period) discussing threading and the IO library.  Much of it
 115             is dealing with the C library, but C++ is included as well.
 116       </UL>
 117    </P>
 118    <P>This section will be updated as new and interesting issues come
 119       to light.
 120    </P>
 121    <P>Return <A HREF="#top">to top of page</A> or
 122       <A HREF="../faq/index.html">to the FAQ</A>.
 123    </P>
 124
 125 <HR>
 126 <H2><A NAME="4"><TT>&lt;foo&gt;</TT> vs <TT>&lt;foo.h&gt;</TT></A></H2>
 127    <P>The new-style headers are fully supported in libstdc++-v3.  The compiler
 128       itself fully supports namespaces.  However, at the moment, the compiler
 129       treats std:: as the global namespace by default.
 130    </P>
 131    <P>For those of you new to ISO C++98, no, that isn't a typo, the headers
 132       really have new names.  Marshall Cline's C++ FAQ Lite has a good
 133       explanation in
 134 <A HREF="http://www.cerfnet.com/~mpcline/On-Line-C++-FAQ/coding-standards.html#[25.4]">item [25.4]</A>.
 135    </P>
 136    <P>Return <A HREF="#top">to top of page</A> or
 137       <A HREF="../faq/index.html">to the FAQ</A>.
 138    </P>
 139
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 145 <P CLASS="fineprint"><EM>
 146 Comments and suggestions are welcome, and may be sent to
 147 <A HREF="mailto:pme@sources.redhat.com">Phil Edwards</A> or
 148 <A HREF="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</A>.
 149 <BR> $Id: howto.html,v 1.6 2000/12/03 23:47:47 jsm28 Exp $
 150 </EM></P>
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