mirror of
git://gcc.gnu.org/git/gcc.git
synced 2024-12-25 04:19:01 +08:00
5e21803304
* config/threads-no.h: Remove file.
* config/threads-posix.h: Remove file.
* acconfig.h (_GLIBCPP_USE_THREADS): Remove.
(_GLIBCPP_SUPPORTS_WEAK): Add (required by namespace-clean gthr*.h).
(_GLIBCPP_HAVE_GTHR_DEFAULT): Likewise.
* config.h.in: Regenerate.
* acinclude.m4 (GLIBCPP_ENABLE_THREADS): Completely rework to
setup and use gthr*.h files. In particular, make gthr.h files
namespace-clean in the staging area (they don't have to be for
libgcc.a).
* aclocal.m4: Regenerate.
* configure: Regenerate.
* src/Makefile.am (build_headers): Remove bits/c++threads.h
and add bits/gthr.h bits/gthr-single.h bits/gthr-default.h.
* src/Makefile.in: Regenerate.
* include/bits/c++config: Cleanup threading configuration macros.
In particular, define __STL_GTHREADS macro which controls...
* include/bits/stl_threads.h: ...a brand new gthr.h-based
configuration here.
* config/c_io_stdio.h: Include staged gthr.h instead of local
thread configuration file. Always use __gthread_mutex_t
instead of __mutext_type (or int).
* include/bits/std_fstream.h: Likewise.
* docs/html/17_intro/howto.html: Remove placeholder comment in
case this configuration patch didn't make it. Add advice that
section only applies if configured with --enable-threads.
* docs/html/23_containers/howto.html: Reword to make clear
that _PTHREADS is no longer required for any port to be
correctly using STL with threads. Add advice that section
only applies if configured with --enable-threads.
Co-Authored-By: John David Anglin <dave@hiauly1.hia.nrc.ca>
From-SVN: r42998
192 lines
8.9 KiB
HTML
192 lines
8.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
|
|
<HTML>
|
|
<HEAD>
|
|
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
|
|
<META NAME="AUTHOR" CONTENT="pme@sources.redhat.com (Phil Edwards)">
|
|
<META NAME="KEYWORDS" CONTENT="HOWTO, libstdc++, gcc, g++, libg++, STL">
|
|
<META NAME="DESCRIPTION" CONTENT="HOWTO for libstdc++ chapter 17.">
|
|
<META NAME="GENERATOR" CONTENT="vi and eight fingers">
|
|
<TITLE>libstdc++-v3 HOWTO: Chapter 17</TITLE>
|
|
<LINK REL=StyleSheet HREF="../lib3styles.css">
|
|
<!-- $Id: howto.html,v 1.5 2001/05/31 02:45:03 ljrittle Exp $ -->
|
|
</HEAD>
|
|
<BODY>
|
|
|
|
<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 "Introduction" as an introduction
|
|
to the <EM>GNU implementation of</EM> the ISO Standard C++ Library.
|
|
</P>
|
|
|
|
|
|
<!-- ####################################################### -->
|
|
<HR>
|
|
<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><foo></TT> vs <TT><foo.h></TT></A>
|
|
<LI><A HREF="porting-howto.html">Porting-howto</A>
|
|
</UL>
|
|
|
|
<HR>
|
|
|
|
<!-- ####################################################### -->
|
|
|
|
<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
|
|
"files" 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 thread-safe containers will be
|
|
in section 6.8 (the HOWTOs on containers). This section only applies
|
|
when gcc and libstdc++-v3 were configured with --enable-threads.
|
|
</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 "thread-safe"
|
|
means for a library (not a general program). We currently use the
|
|
<A HREF="http://www.sgi.com/tech/stl/thread_safety.html">same
|
|
definition that SGI</A> uses for their STL subset.
|
|
<EM>Please see the many cautions given in HOWTOs on containers.</EM>
|
|
</P>
|
|
<P>
|
|
Here is another attempt at explaining the dangers of using the
|
|
STL with threading support without understanding some important
|
|
details. The STL implementation is currently configured to use
|
|
the high-speed caching memory allocator. If you absolutely
|
|
think you must change this on a global basis for your platform
|
|
to support multi-threading, then please consult all commentary
|
|
in include/bits/c++config and the HOWTOs on containers. Be
|
|
fully aware that you may change the external or internal ABI of
|
|
libstdc++-v3 when you provide -D__USE_MALLOC on the command line
|
|
or make a change to that configuration file.
|
|
</P>
|
|
<P>
|
|
If you don't like caches of objects being retained inside the
|
|
STL, then you might be tempted to define __USE_MALLOC either on
|
|
the command line or by rebuilding c++config.h. Please note,
|
|
once you define __USE_MALLOC, only the malloc allocator is
|
|
visible to application code (i.e. the typically higher-speed
|
|
allocator is not even available in this configuration). There
|
|
is a better way: It is possible to force the malloc-based
|
|
allocator on a per-case-basis for some application code even
|
|
when the above macro symbol is not defined. The author of this
|
|
comment believes that is a better way to tune an application for
|
|
high-speed using this implementation of the STL. Here is one
|
|
possible example displaying the forcing of the malloc-based
|
|
allocator over the typically higher-speed default allocator:
|
|
|
|
std::list <void*, std::malloc_alloc> my_malloc_based_list;
|
|
</P>
|
|
<P>A recent journal article has described "atomic integer
|
|
operations," 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 "may not be available on all systems, and
|
|
if they are, may have different interfaces." [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
|
|
"Thread Next" to move down the thread. This farm is in
|
|
latest-to-oldest order.
|
|
<UL>
|
|
<LI><A HREF="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00384.html">
|
|
inspired this most recent updating of issues with threading
|
|
and the SGI STL library. It also contains some example
|
|
POSIX-multithreaded STL code.</A>
|
|
<LI> <A HREF="http://gcc.gnu.org/ml/libstdc++/2001-05/msg00136.html">
|
|
an early analysis of why __USE_MALLOC should be disable for
|
|
the 3.0 release of libstdc++.</A>
|
|
</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><foo></TT> vs <TT><foo.h></TT></A></H2>
|
|
<P>The new-style headers are fully supported in libstdc++-v3. The compiler
|
|
itself fully supports namespaces, including <TT>std::</TT>.
|
|
</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>
|
|
|
|
|
|
|
|
<!-- ####################################################### -->
|
|
|
|
<HR>
|
|
<P CLASS="fineprint"><EM>
|
|
Comments and suggestions are welcome, and may be sent to
|
|
<A HREF="mailto:libstdc++@gcc.gnu.org">the mailing list</A>.
|
|
<BR> $Id: howto.html,v 1.5 2001/05/31 02:45:03 ljrittle Exp $
|
|
</EM></P>
|
|
|
|
|
|
</BODY>
|
|
</HTML>
|
|
|
|
|