158 lines
6.8 KiB
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158 lines
6.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<META NAME="AUTHOR" CONTENT="pme@sources.redhat.com (Phil Edwards)">
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<META NAME="KEYWORDS" CONTENT="HOWTO, libstdc++, gcc, g++, libg++, STL">
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<META NAME="DESCRIPTION" CONTENT="HOWTO for libstdc++ chapter 17.">
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<META NAME="GENERATOR" CONTENT="vi and eight fingers">
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<TITLE>libstdc++-v3 HOWTO: Chapter 17</TITLE>
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<LINK REL="home" HREF="http://sources.redhat.com/libstdc++/docs/18_support/">
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<!-- $Id: howto.html,v 1.3 2000/05/03 16:11:02 pme Exp $ -->
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<BODY>
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<H1 CLASS="centered"><A NAME="top">Chapter 17: Library Introduction</A></H1>
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<P>Chapter 17 is actually a list of definitions and descriptions used
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in the following chapters of the Standard when describing the actual
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library. Here, we use "Introduction" as an introduction
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to the <EM>GNU implementation of</EM> the ISO Standard C++ Library.
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</P>
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<HR>
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<H1>Contents</H1>
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<UL>
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<LI><A HREF="#2">The Standard C++ header files</A>
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<LI><A HREF="#3">Thread-safety</A>
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<LI><A HREF="#4"><TT><foo></TT> vs <TT><foo.h></TT></A>
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<LI><A HREF="porting-howto.html">Porting-howto</A>
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</UL>
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<HR>
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<H2><A NAME="2">The Standard C++ header files</A></H2>
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<P>The Standard C++ Library specifies 50 header files that must be
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available to all hosted implementations. Actually, the word
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"files" is a misnomer, since the contents of the headers
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don't necessarily have to be in any kind of external file. The
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only rule is that when you <TT>#include</TT> a certain header, the
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contents of that header, as defined by the Standard, become
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available to you, no matter how.
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</P>
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<P>The names of the headers can be easily seen in
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<A HREF="headers_cc.txt"><TT>testsuite/17_intro/headers.cc</TT></A>,
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which is a small testbed we use to make certain that the headers
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all compile and run.
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</P>
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<HR>
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<H2><A NAME="3">Thread-safety</A></H2>
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<P>This is a thorny issue that gets brought up on the libstdc++-v3
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and gcc mailing lists on a regular basis (probably by a cron job).
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This entry will mention a very little bit about the general MT
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issues with libstdc++. The latest status and quick notes will be
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in FAQ 5.6. Some discussion about threadsafe containers will be
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in section 6.8 (the HOWTOs on containers).
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</P>
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<P>The libstdc++ code (all of it, not just the containers) has been
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designed so that thread-safety will be easily possible. The first
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(!) problem is finding a <EM>fast</EM> method of implementation
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portable to all platforms. A minor problem that pops up every so
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often is different interpretations of what "thread-safe"
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means for a library (not a general program). We currently use the
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<A HREF="http://www.sgi.com/Technology/STL/thread_safety.html">same
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definition that SGI</A> uses for their STL subset.
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</P>
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<P>A recent journal article has described "atomic integer
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operations," which would allow us to, well, perform updates
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on integers atomically, and without requiring an explicit mutex
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lock. This appears promising, but the major difficulty is that
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these operations "may not be available on all systems, and
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if they are, may have different interfaces." [quoting from
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mailing list messages]
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</P>
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<P>Here is a small link farm to threads (no pun) in the mail archives
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that discuss the threading problem. Each link is to the first
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relevent message in the thread; from there you can use
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"Thread Next" to move down the thread. This farm is in
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latest-to-oldest order.
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<UL>
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<LI>
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</UL>
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<BR>
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Here are discussions that took place before the current snapshot;
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they are still relevant and instructive.
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<BR>
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<UL>
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<LI>One way of preventing memory leaks by the old default memory
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allocator in multithreaded code is
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<A HREF="/ml/gcc/1999-11/msg00431.html">discussed here</A>.
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<LI><A HREF="/ml/libstdc++/1999-q3/msg00167.html">This thread
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concerns strings</A>.
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<LI><A HREF="/ml/libstdc++/1999-q2/msg00339.html">So does this
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one</A>. This initial message also refers to another
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thread in the GCC mailing list...
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<LI><A HREF="/ml/egcs/1999-06/msg00680.html">which is here</A>,
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and goes on for some time. Ironically, the initial message
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in this thread also mentions another threading thread...
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<LI><A HREF="/ml/egcs/1999-06/msg00771.html">beginning here</A>,
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and talking about pthreads. (Note that a much more recent
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message from the first thread in this list notes that
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<A HREF="/ml/libstdc++/1999-q3/msg00176.html">pthreads
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should not be used as a starting point</A> for making
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libstdc++ threadsafe.)
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<LI><A HREF="/ml/libstdc++/1999-q2/msg00168.html">This
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message</A>,
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<A HREF="/ml/libstdc++/1999-q2/msg00159.html">this one</A>,
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and <A HREF="/ml/libstdc++/1999-q2/msg00156.html">this one</A>
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are the tops of related threads (all within the same time
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period) discussing threading and the IO library. Much of it
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is dealing with the C library, but C++ is included as well.
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</UL>
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</P>
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<P>This section will be updated as new and interesting issues come
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to light.
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</P>
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<P>Return <A HREF="#top">to top of page</A> or
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<A HREF="../faq/index.html">to the FAQ</A>.
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</P>
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<HR>
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<H2><A NAME="4"><TT><foo></TT> vs <TT><foo.h></TT></A></H2>
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<P>The new-style headers are fully supported in libstdc++-v3. The compiler
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itself fully supports namespaces. However, at the moment, the compiler
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treats std:: as the global namespace by default.
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</P>
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<P>For those of you new to ISO C++98, no, that isn't a typo, the headers
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really have new names. Marshall Cline's C++ FAQ Lite has a good
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explanation in
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<A HREF="http://www.cerfnet.com/~mpcline/On-Line-C++-FAQ/coding-standards.html#[25.4]">item [25.4]</A>.
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</P>
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<P>Return <A HREF="#top">to top of page</A> or
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<A HREF="../faq/index.html">to the FAQ</A>.
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</P>
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<!-- ####################################################### -->
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<HR>
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<P CLASS="fineprint"><EM>
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Comments and suggestions are welcome, and may be sent to
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<A HREF="mailto:pme@sources.redhat.com">Phil Edwards</A> or
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<A HREF="mailto:gdr@egcs.cygnus.com">Gabriel Dos Reis</A>.
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<BR> $Id: howto.html,v 1.3 2000/05/03 16:11:02 pme Exp $
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</EM></P>
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