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Ulrich Drepper 1999-09-12 19:29:12 +00:00
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@ -1,3 +1,16 @@
1999-09-12 Ulrich Drepper <drepper@cygnus.com>
* resolv/nss_dns/dns-host.c (_nss_dns_gethostbyname2_r): if res_search
fails don't rely on errno value.
(getanswer_r): Sett *ERRNOP in error cases.
* sysdeps/posix/getaddrinfo.c (gaih_local): Test protocol and socktype.
(gaih_inet_serv): Return EIA_NODATA if name is known but has no
associated data. Test for matching numeric address and family.
(getaddrinfo): Remember EAI_NODATA result and return this in case
everything fails.
Reported by Arkadiusz Miskiewicz <misiek@misiek.eu.org>.
1999-09-07 Cristian Gafton <gafton@redhat.com>
* sysdeps/unix/sysv/linux/sys/raw.h: New file

157
linuxthreads/FAQ.html
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@ -73,13 +73,12 @@ platforms.<P>
<H4><A NAME="A.4">A.4: What is the status of LinuxThreads?</A></H4>
In short, it's not completely finished (hence the version numbers in
0.<I>x</I>), but what is done is pretty mature.
LinuxThreads implements almost all of Posix 1003.1c, as well as a few
extensions. The only part of LinuxThreads that does not conform yet
to Posix is signal handling (see section <A HREF="#J">J</A>). Apart
from the signal stuff, all the Posix 1003.1c base functionality is
provided and conforms to the standard (to the best of my knowledge).
from the signal stuff, all the Posix 1003.1c base functionality,
as well as a number of optional extensions, are provided and conform
to the standard (to the best of my knowledge).
The signal stuff is hard to get right, at least without special kernel
support, and while I'm definitely looking at ways to implement the
Posix behavior for signals, this might take a long time before it's
@ -90,11 +89,10 @@ completed.<P>
The basic functionality (thread creation and termination, mutexes,
conditions, semaphores) is very stable. Several industrial-strength
programs, such as the AOL multithreaded Web server, use LinuxThreads
and seem quite happy about it. There are some rough edges in
the LinuxThreads / C library interface, at least with libc 5, but most
of these rough edges are fixed in glibc 2, which should soon become
the standard C library for Linux distributions (see section <A
HREF="#C">C</A>). <P>
and seem quite happy about it. There used to be some rough edges in
the LinuxThreads / C library interface with libc 5, but glibc 2
fixes all of those problems and is now the standard C library on major
Linux distributions (see section <A HREF="#C">C</A>). <P>
<HR>
<P>
@ -139,12 +137,22 @@ HREF="news:comp.os.linux.development.kernel">comp.os.linux.development.kernel</A
The latter is especially appropriate for questions relative to the
interface between the kernel and LinuxThreads.<P>
Very specific LinuxThreads questions, and in particular everything
that looks like a potential bug in LinuxThreads, should be mailed
directly to me (<code>Xavier.Leroy@inria.fr</code>). Before mailing
me, make sure that your question is not answered in this FAQ.<P>
<H4><A NAME="B.4">B.4: How should I report a possible bug in
LinuxThreads?</A></H4>
<H4><A NAME="B.4">B.4: I'd like to read the POSIX 1003.1c standard. Is
If you're using glibc 2, the best way by far is to use the
<code>glibcbug</code> script to mail a bug report to the glibc
maintainers. <P>
If you're using an older libc, or don't have the <code>glibcbug</code>
script on your machine, then e-mail me directly
(<code>Xavier.Leroy@inria.fr</code>). <P>
In both cases, before sending the bug report, make sure that it is not
addressed already in this FAQ. Also, try to send a short program that
reproduces the weird behavior you observed. <P>
<H4><A NAME="B.5">B.5: I'd like to read the POSIX 1003.1c standard. Is
it available online?</A></H4>
Unfortunately, no. POSIX standards are copyrighted by IEEE, and
@ -183,8 +191,8 @@ integrated with glibc 2. The glibc 2 distribution contains the
sources of a specially adapted version of LinuxThreads.<P>
glibc 2 comes preinstalled as the default C library on several Linux
distributions, such as RedHat 5.0 and 5.1, and recent beta versions of
Debian. Those distributions include the version of LinuxThreads matching
distributions, such as RedHat 5 and up, and Debian 2.
Those distributions include the version of LinuxThreads matching
glibc 2.<P>
<H4><A NAME="C.2">C.2: My system has libc 5 preinstalled, not glibc
@ -199,14 +207,6 @@ libc 5.2.18 on the one hand, and libc 5.4.12 or later on the other hand.
Avoid 5.3.12 and 5.4.7: these have problems with the per-thread errno
variable. <P>
Unfortunately, many popular Linux distributions (e.g. RedHat 4.2) come
with libc 5.3.12 preinstalled -- the one that does not work with
LinuxThreads. Fortunately, you can often find pre-packaged binaries
of more recent versions of libc for these distributions. In the case
of RedHat 4, there is a RPM package for libc-5.4 in the "contrib"
area of RedHat FTP sites.
<P>
<H4><A NAME="C.3">C.3: So, should I switch to glibc 2, or stay with a
recent libc 5?</A></H4>
@ -219,7 +219,7 @@ Switching an already installed
system from libc 5 to glibc 2 is not completely straightforward.
See the <A HREF="http://sunsite.unc.edu/LDP/HOWTO/Glibc2-HOWTO.html">Glibc2
HOWTO</A> for more information. Much easier is (re-)installing a
Linux distribution based on glibc 2, such as RedHat 5.1.<P>
Linux distribution based on glibc 2, such as RedHat 6.<P>
<H4><A NAME="C.4">C.4: Where can I find glibc 2 and the version of
LinuxThreads that goes with it?</A></H4>
@ -237,6 +237,31 @@ For libc 5, see <A HREF="ftp://sunsite.unc.edu/pub/Linux/devel/GCC/"><code>ftp:/
For the libc 5 version of LinuxThreads, see
<A HREF="ftp://ftp.inria.fr/INRIA/Projects/cristal/Xavier.Leroy/linuxthreads/">ftp://ftp.inria.fr/INRIA/Projects/cristal/Xavier.Leroy/linuxthreads/</A>.<P>
<H4><A NAME="C.6">C.6: How can I recompile the glibc 2 version of the
LinuxThreads sources?</A></H4>
You must transfer the whole glibc sources, then drop the LinuxThreads
sources in the <code>linuxthreads/</code> subdirectory, then recompile
glibc as a whole. There are now too many inter-dependencies between
LinuxThreads and glibc 2 to allow separate re-compilation of LinuxThreads.
<P>
<H4><A NAME="C.7">C.7: What is the correspondence between LinuxThreads
version numbers, libc version numbers, and RedHat version
numbers?</A></H4>
Here is a summary. (Information on Linux distributions other than
RedHat are welcome.)<P>
<TABLE>
<TR><TD>LinuxThreads </TD> <TD>C library</TD> <TD>RedHat</TD></TR>
<TR><TD>0.7, 0.71 (for libc 5)</TD> <TD>libc 5.x</TD> <TD>RH 4.2</TD></TR>
<TR><TD>0.7, 0.71 (for glibc 2)</TD> <TD>glibc 2.0.x</TD> <TD>RH 5.x</TD></TR>
<TR><TD>0.8</TD> <TD>glibc 2.1.1</TD> <TD>RH 6.0</TD></TR>
<TR><TD>0.8</TD> <TD>glibc 2.1.2</TD> <TD>not yet released</TD></TR>
</TABLE>
<P>
<HR>
<P>
@ -271,11 +296,11 @@ descriptor opened on a pipe. When I link it with LinuxThreads,
You're using one of the buggy versions of libc (5.3.12, 5.4.7., etc).
See question <A HREF="#C.1">C.1</A> above.<P>
<H4><A NAME="D.4">D.4: My program crashes the first time it calls
<CODE>pthread_create()</CODE> !</A></H4>
<H4><A NAME="D.4">D.4: My program creates a lot of threads, and after
a while <CODE>pthread_create()</CODE> no longer returns!</A></H4>
You wouldn't be using glibc 2.0, by any chance? That's a known bug
with glibc 2.0. Please upgrade to 2.0.1 or later.<P>
This is known bug in the version of LinuxThreads that comes with glibc
2.1.1. An upgrade to 2.1.2 is recommended. <P>
<H4><A NAME="D.5">D.5: When I'm running a program that creates N
threads, <code>top</code> or <code>ps</code>
@ -359,6 +384,55 @@ stack-allocate some data structure, and
<code>pthread_cleanup_pop</code> to close that block. It's ugly, but
it's the standard way of implementing cleanup handlers.<P>
<H4><A NAME="D.9">D.9: I tried to use real-time threads and my program
loops like crazy and freezes the whole machine!</A></H4>
Versions of LinuxThreads prior to 0.8 are susceptible to ``livelocks''
(one thread loops, consuming 100% of the CPU time) in conjunction with
real-time scheduling. Since real-time threads and processes have
higher priority than normal Linux processes, all other processes on
the machine, including the shell, the X server, etc, cannot run and
the machine appears frozen.<P>
The problem is fixed in LinuxThreads 0.8.<P>
<H4><A NAME="D.10">D.10: My application needs to create thousands of
threads, or maybe even more. Can I do this with
LinuxThreads?</A></H4>
No. You're going to run into several hard limits:
<UL>
<LI>Each thread, from the kernel's standpoint, is one process. Stock
Linux kernels are limited to at most 512 processes for the super-user,
and half this number for regular users. This can be changed by
changing <code>NR_TASKS</code> in <code>include/linux/tasks.h</code>
and recompiling the kernel. On the x86 processors at least,
architectural constraints seem to limit <code>NR_TASKS</code> to 4090
at most.
<LI>LinuxThreads contains a table of all active threads. This table
has room for 1024 threads at most. To increase this limit, you must
change <code>PTHREAD_THREADS_MAX</code> in the LinuxThreads sources
and recompile.
<LI>By default, each thread reserves 2M of virtual memory space for
its stack. This space is just reserved; actual memory is allocated
for the stack on demand. But still, on a 32-bit processor, the total
virtual memory space available for the stacks is on the order of 1G,
meaning that more than 500 threads will have a hard time fitting in.
You can overcome this limitation by moving to a 64-bit platform, or by
allocating smaller stacks yourself using the <code>setstackaddr</code>
attribute.
<LI>Finally, the Linux kernel contains many algorithms that run in
time proportional to the number of process table entries. Increasing
this number drastically will slow down the kernel operations
noticeably.
</UL>
(Other POSIX threads libraries have similar limitations, by the way.)
For all those reasons, you'd better restructure your application so
that it doesn't need more than, say, 100 threads. For instance,
in the case of a multithreaded server, instead of creating a new
thread for each connection, maintain a fixed-size pool of worker
threads that pick incoming connection requests from a queue.<P>
<HR>
<P>
@ -519,7 +593,7 @@ be passed a C function as third argument.<P>
<H4><A NAME="F.3">F.3: I'm trying to use LinuxThreads in conjunction
with libg++, and I'm having all sorts of trouble.</A></H4>
From what I understand, thread support in libg++ is completely broken,
>From what I understand, thread support in libg++ is completely broken,
especially with respect to locking of iostreams. H.J.Lu wrote:
<BLOCKQUOTE>
If you want to use thread, I can only suggest egcs and glibc. You
@ -540,7 +614,14 @@ version of gdb 4.17 developed by Eric Paire and colleages at The Open
Group, Grenoble. The patches against gdb 4.17 are available at
<A HREF="http://www.gr.opengroup.org/java/jdk/linux/debug.htm"><code>http://www.gr.opengroup.org/java/jdk/linux/debug.htm</code></A>.
Precompiled binaries of the patched gdb are available in RedHat's RPM
format at <A HREF="http://odin.appliedtheory.com/"><code>http://odin.appliedtheory.com/</code></A>.
format at <A
HREF="http://odin.appliedtheory.com/"><code>http://odin.appliedtheory.com/</code></A>.<P>
Some Linux distributions provide an already-patched version of gdb;
others don't. For instance, the gdb in RedHat 5.2 is thread-aware,
but apparently not the one in RedHat 6.0. Just ask (politely) the
makers of your Linux distributions to please make sure that they apply
the correct patches to gdb.<P>
<H4><A NAME="G.2">G.2: Does it work with post-mortem debugging?</A></H4>
@ -668,11 +749,11 @@ signals available and the kernel reserves all of them but two:
<code>SIGUSR1</code> and <code>SIGUSR2</code>. So, LinuxThreads has
no choice but use those two signals.<P>
On recent kernels (late 2.1 kernels and the forthcoming 2.2 kernels),
more than 32 signals are provided in the form of realtime signals.
When run on one of those kernels, LinuxThreads uses two reserved
realtime signals for its internal operation, thus leaving
<code>SIGUSR1</code> and <code>SIGUSR2</code> free for user code.<P>
On recent kernels (2.2 and up), more than 32 signals are provided in
the form of realtime signals. When run on one of those kernels,
LinuxThreads uses two reserved realtime signals for its internal
operation, thus leaving <code>SIGUSR1</code> and <code>SIGUSR2</code>
free for user code. (This works only with glibc, not with libc 5.) <P>
<H4><A NAME="H.5">H.5: Is the stack of one thread visible from the
other threads? Can I pass a pointer into my stack to other threads?
@ -717,7 +798,7 @@ Windows client? </A></H4>
The best solution is to use X libraries that have been compiled with
multithreading options set. Linux distributions that come with glibc
2 as the main C library generally provide thread-safe X libraries.
At least, that seems to be the case for RedHat 5.<P>
At least, that seems to be the case for RedHat 5 and later.<P>
You can try to recompile yourself the X libraries with multithreading
options set. They contain optional support for multithreading; it's
@ -741,7 +822,7 @@ only. <P>
thread-safe X libraries that you could distribute?</A></H4>
No, I don't. Sorry. But consider installing a Linux distribution
that comes with thread-safe X libraries, such as RedHat 5.<P>
that comes with thread-safe X libraries, such as RedHat 6.<P>
<H4><A NAME="I.3">I.3: Can I use library FOO in a multithreaded
program?</A></H4>