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   <TITLE>libstdc++-v3 HOWTO:  Chapter 17</TITLE>
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<H1 CLASS="centered"><A NAME="top">Chapter 17:  Library Introduction</A></H1>

<P>Chapter 17 is actually a list of definitions and descriptions used
   in the following chapters of the Standard when describing the actual
   library.  Here, we use &quot;Introduction&quot; as an introduction
   to the <EM>GNU implementation of</EM> the ISO Standard C++ Library.
</P>


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<H1>Contents</H1>
<UL>
   <LI><A HREF="#2">The Standard C++ header files</A>
   <LI><A HREF="#3">Thread-safety</A>
   <LI><A HREF="#4"><TT>&lt;foo&gt;</TT> vs <TT>&lt;foo.h&gt;</TT></A>
   <LI><A HREF="porting-howto.html">Porting-howto</A>
</UL>

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<H2><A NAME="2">The Standard C++ header files</A></H2>
   <P>The Standard C++ Library specifies 50 header files that must be
      available to all hosted implementations.  Actually, the word
      &quot;files&quot; is a misnomer, since the contents of the headers
      don't necessarily have to be in any kind of external file.  The
      only rule is that when you <TT>#include</TT> a certain header, the
      contents of that header, as defined by the Standard, become
      available to you, no matter how.
   </P>
   <P>The names of the headers can be easily seen in
      <A HREF="headers_cc.txt"><TT>testsuite/17_intro/headers.cc</TT></A>,
      which is a small testbed we use to make certain that the headers
      all compile and run.
   </P>

<HR>
<H2><A NAME="3">Thread-safety</A></H2>
   <P>This is a thorny issue that gets brought up on the libstdc++-v3
      and gcc mailing lists on a regular basis (probably by a cron job).
      This entry will mention a very little bit about the general MT
      issues with libstdc++.  The latest status and quick notes will be
      in FAQ 5.6.  Some discussion about threadsafe containers will be
      in section 6.8 (the HOWTOs on containers).
   </P>
   <P>The libstdc++ code (all of it, not just the containers) has been
      designed so that thread-safety will be easily possible.  The first
      (!) problem is finding a <EM>fast</EM> method of implementation
      portable to all platforms.  A minor problem that pops up every so
      often is different interpretations of what &quot;thread-safe&quot;
      means for a library (not a general program).  We currently use the
      <A HREF="http://www.sgi.com/Technology/STL/thread_safety.html">same
      definition that SGI</A> uses for their STL subset.
   </P>
   <P>A recent journal article has described &quot;atomic integer
      operations,&quot; which would allow us to, well, perform updates
      on integers atomically, and without requiring an explicit mutex
      lock.  This appears promising, but the major difficulty is that
      these operations &quot;may not be available on all systems, and
      if they are, may have different interfaces.&quot; [quoting from
      mailing list messages]
   </P>
   <P>Here is a small link farm to threads (no pun) in the mail archives
      that discuss the threading problem.  Each link is to the first
      relevent message in the thread; from there you can use
      &quot;Thread Next&quot; to move down the thread.  This farm is in
      latest-to-oldest order.
      <UL>
        <LI>
      </UL>
      <BR>
      Here are discussions that took place before the current snapshot;
      they are still relevant and instructive.
      <BR>
      <UL>
        <LI>One way of preventing memory leaks by the old default memory
            allocator in multithreaded code is
            <A HREF="http://gcc.gnu.org/ml/gcc/1999-11n/msg00431.html">discussed here</A>.
        <LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q3/msg00167.html">This thread
            concerns strings</A>.
        <LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00339.html">So does this
            one</A>.  This initial message also refers to another
            thread in the GCC mailing list...
        <LI><A HREF="http://gcc.gnu.org/ml/gcc/1999-06n/msg00680.html">which is here</A>,
            and goes on for some time.  Ironically, the initial message
            in this thread also mentions another threading thread...
        <LI><A HREF="http://gcc.gnu.org/ml/gcc-bugs/1999-04n/msg00777.html">beginning here</A>,
            and talking about pthreads.  (Note that a much more recent
            message from the first thread in this list notes that
            <A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q3/msg00176.html">pthreads
            should not be used as a starting point</A> for making
            libstdc++ threadsafe.)
        <LI><A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00168.html">This
            message</A>,
            <A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00159.html">this one</A>,
            and <A HREF="http://gcc.gnu.org/ml/libstdc++/1999-q2/msg00156.html">this one</A>
            are the tops of related threads (all within the same time
            period) discussing threading and the IO library.  Much of it
            is dealing with the C library, but C++ is included as well.
      </UL>
   </P>
   <P>This section will be updated as new and interesting issues come
      to light.
   </P>
   <P>Return <A HREF="#top">to top of page</A> or
      <A HREF="../faq/index.html">to the FAQ</A>.
   </P>

<HR>
<H2><A NAME="4"><TT>&lt;foo&gt;</TT> vs <TT>&lt;foo.h&gt;</TT></A></H2>
   <P>The new-style headers are fully supported in libstdc++-v3.  The compiler
      itself fully supports namespaces.  However, at the moment, the compiler
      treats std:: as the global namespace by default.
   </P>
   <P>For those of you new to ISO C++98, no, that isn't a typo, the headers
      really have new names.  Marshall Cline's C++ FAQ Lite has a good
      explanation in
<A HREF="http://www.cerfnet.com/~mpcline/On-Line-C++-FAQ/coding-standards.html#[25.4]">item [25.4]</A>.
   </P>
   <P>Return <A HREF="#top">to top of page</A> or
      <A HREF="../faq/index.html">to the FAQ</A>.
   </P>


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<P CLASS="fineprint"><EM>
Comments and suggestions are welcome, and may be sent to
<A HREF="mailto:pme@sources.redhat.com">Phil Edwards</A> or
<A HREF="mailto:gdr@gcc.gnu.org">Gabriel Dos Reis</A>.
<BR> $Id: howto.html,v 1.6 2000/12/03 23:47:47 jsm28 Exp $
</EM></P>


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