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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://sources.redhat.com/ml/libstdc++/1999-q3/msg00167.html">This thread
concerns strings</A>.
<LI><A HREF="http://sources.redhat.com/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://sources.redhat.com/ml/libstdc++/1999-q3/msg00176.html">pthreads
should not be used as a starting point</A> for making
libstdc++ threadsafe.)
<LI><A HREF="http://sources.redhat.com/ml/libstdc++/1999-q2/msg00168.html">This
message</A>,
<A HREF="http://sources.redhat.com/ml/libstdc++/1999-q2/msg00159.html">this one</A>,
and <A HREF="http://sources.redhat.com/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 1.4 2000/07/11 21:45:07 pme Exp $
</EM></P>
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