[cgl_discussion] [Fwd: [ANNOUNCE] Native POSIX Thread Library 0.1]
bstevens at redhat.com
Fri Sep 20 14:46:33 PDT 2002
It is reasonable to expect it will be backported to 2.4.x soon.
Craig Thomas wrote:
>It says here that the build environment (to build the threaded
>library) must be 2.5, so I am assuming that it is implied that the
>library will be released on 2.5. This looks like something to consider,
>but will there be a need to have this back ported to 2.4.18?
>On Fri, 2002-09-20 at 09:25, Khalid Aziz wrote:
>>Here is another implementation of POSIX threads. Might be interesting
>>for POSIX threads project to look at. People have already started asking
>>for comparison with NGPT on lkml.
>>Ulrich Drepper wrote:
>>>-----BEGIN PGP SIGNED MESSAGE-----
>>>We are pleased to announce the first publically available source
>>>release of a new POSIX thread library for Linux. As part of the
>>>continuous effort to improve Linux's capabilities as a client, server,
>>>and computing platform Red Hat sponsored the development of this
>>>completely new implementation of a POSIX thread library, called Native
>>>POSIX Thread Library, NPTL.
>>>Unless major flaws in the design are found this code is intended to
>>>become the standard POSIX thread library on Linux system and it will
>>>be included in the GNU C library distribution.
>>>The work visible here is the result of close collaboration of kernel
>>>and runtime developers. The collaboration proceeded by developing the
>>>kernel changes while writing the appropriate parts of the thread
>>>library. Whenever something couldn't be implemented optimally some
>>>interface was changed to eliminate the issue. The result is this
>>>thread library which is, unlike previous attempts, a very thin layer
>>>on top of the kernel. This helps to achieve a maximum of performance
>>>for a minimal price.
>>>A white paper (still in its draft stage, though) describing the design
>>>is available at
>>>It provides a larger number of details on the design and insight into
>>>the design process. At this point we want to repeat only a few
>>>- - the new library is based on an 1-on-1 model. Earlier design
>>> documents stated that an M-on-N implementation was necessary to
>>> support a scalable thread library. This was especially true for
>>> the IA-32 and x86-64 platforms since the ABI with respect to threads
>>> forces the use of segment registers and the only way to use those
>>> registers was with the Local Descriptor Table (LDT) data structure
>>> of the processor.
>>> The kernel limitations the earlier designs were based on have been
>>> eliminated as part of this project, opening the road to a 1-on-1
>>> implementation which has many advantages such as
>>> + less complex implementation;
>>> + avoidance of two-level scheduling, enabling the kernel to make all
>>> scheduling decisions;
>>> + direct interaction between kernel and user-level code (e.g., when
>>> delivering signals);
>>> + and more and more.
>>> It is not generally accepted that a 1-on-1 model is superior but our
>>> tests showed the viability of this approach and by comparing it with
>>> the overhead added by existing M-on-N implementations we became
>>> convinced that 1-on-1 is the right approach.
>>> Initial confirmations were test runs with huge numbers of threads.
>>> Even on IA-32 with its limited address space and memory handling
>>> running 100,000 concurrent threads was no problem at all, creating
>>> and destroying the threads did not take more than two seconds. This
>>> all was made possible by the kernel work performed as part of this
>>> The only limiting factors on the number of threads today are
>>> resource availability (RAM and processor resources) and architecture
>>> limitations. Since every thread needs at least a stack and data
>>> structures describing the thread the number is capped. On 64-bit
>>> machines the architecture does not add any limitations anymore (at
>>> least for the moment) and with enough resources the number of
>>> threads can be grown arbitrarily.
>>> This does not mean that using hundreds of thousands of threads is a
>>> desirable design for the majority of applications. At least not
>>> unless the number of processors matches the number of threads. But
>>> it is important to note that the design on the library does not have
>>> a fixed limit.
>>> The kernel work to optimize for a high thread count is still
>>> ongoing. Some places in which the kernel iterates over process and
>>> threads remain and other places need to be cleaned up. But it has
>>> already been shown that given sufficient resources and a reasonable
>>> architecture an order of magnitude more threads can be created than
>>> in our tests on IA-32.
>>>- - The futex system call is used extensively in all synchronization
>>> primitives and other places which need some kind of
>>> synchronization. The futex mechanism is generic enough to support
>>> the standard POSIX synchronization mechanisms with very little
>>> The fact that this is possible is also essential for the selection
>>> of the 1-on-1 model since only with the kernel seeing all the
>>> waiters and knowing that they are blocked for synchronization
>>> purposes will allow the scheduler to make decisions as good as a
>>> thread library would be able to in an M-on-N model implementation.
>>> Futexes also allow the implementation of inter-process
>>> synchronization primitives, a sorely missed feature in the old
>>> LinuxThreads implementation (Hi jbj!).
>>>- - Substantial effort went into making the thread creation and
>>> destruction as fast as possible. Extensions to the clone(2) system
>>> call were introduced to eliminate the need for a helper thread in
>>> either creation or destruction. The exit process in the kernel was
>>> optimized (previously not a high priority). The library itself
>>> optimizes the memory allocation so that in many cases the creation
>>> of a new thread can be achieved with one single system call.
>>> On an old IA-32 dual 450MHz PII Xeon system 100,000 threads can be
>>> created and destroyed in 2.3 secs (with up to 50 threads running at
>>> any one time).
>>>- - Programs indirectly linked against the thread library had problems
>>> with the old implementation because of the way symbols are looked
>>> up. This should not be a problem anymore.
>>>The thread library is designed to be binary compatible with the old
>>>LinuxThreads implementation. This compatibility obviously has some
>>>limitations. In places where the LinuxThreads implementation diverged
>>>from the POSIX standard incompatibilities exist. Users of the old
>>>library have been warned from day one that this day will come and code
>>>which added work-arounds for the POSIX non-compliance better be
>>>prepared to remove that code. The visible changes of the library
>>>- - The signal handling changes from per-thread signal handling to the
>>> POSIX process signal handling. This change will require changes in
>>> programs which exploit the non-conformance of the old implementation.
>>> One consequence of this is that SIGSTOP works on the process. Job
>>> in the shell and stopping the whole process in a debugger work now.
>>>- - getpid() now returns the same value in all threads
>>>- - the exec functions are implemented correctly: the exec'ed process gets
>>> the PID of the process. The parent of the multi-threaded application
>>> is only notified when the exec'ed process terminates.
>>>- - thread handlers registered with pthread_atfork are not anymore run
>>> if vfork is used. This isn't required by the standard (which does
>>> not define vfork) and all which is allowed in the child is calling
>>> exit() or an exec function. A user of vfork better knows what s/he
>>>- - libpthread should now be much more resistant to linking problems: even
>>> if the application doesn't list libpthread as a direct dependency
>>> functions which are extended by libpthread should work correctly.
>>>- - no manager thread
>>>- - inter-process mutex, read-write lock, conditional variable, and barrier
>>> implementations are available
>>>- - the pthread_kill_other_threads_np function is not available. It was
>>> needed to work around the broken signal handling. If somebody shows
>>> some existing code which makes legitimate use of this function we
>>> might add it back.
>>>- - requires a kernel with the threading capabilities of Linux 2.5.36.
>>>The sources for the new library are for the time being available at
>>>The current sources contain support only for IA-32 but this will
>>>change very quickly. The thread library is built as part of glibc so
>>>the complete set of glibc sources is available as well. The current
>>>snapshot for glibc 2.3 (or glibc 2.3 when released) is necessary. You
>>>can find it at
>>>Final releases will be available on ftp.gnu.org and its mirrors.
>>>Building glibc with the new thread library is demanding on the
>>>- - The 2.5.36 kernel or above must be installed and used. To compile
>>> glibc it is necessary to create the symbolic link
>>> /lib/modules/$(uname -r)/build
>>> to point to the build directory.
>>>- - The general compiler requirement for glibc is at least gcc 3.2. For
>>> the new thread code it is even necessary to have working support for
>>> the __thread keyword.
>>> Similarly, binutils with functioning TLS support are needed.
>>> The (Null) beta release of the upcoming Red Hat Linux product is
>>> known to have the necessary tools available after updating from the
>>> latest binaries on the FTP site. This is no ploy to force everybody
>>> to use Red Hat Linux, it's just the only environment known to date
>>> which works. If alternatives are known they can be announced on the
>>> mailing list.
>>>- - To configure glibc it is necessary to run in the build directory
>>> (which always should be separate from the source directory):
>>> /path/to/glibc/configure --prefix=/usr --enable-add-ons=linuxthreads2 \
>>> --enable-kernel=current --with-tls
>>> The --enable-kernel parameter requires that the 2.5.36+ kernel is
>>> running. It is not strictly necessary but helps to avoid mistakes.
>>> It might also be a good idea to add --disable-profile, just to speed
>>> up the compilation.
>>> When configured as above the library must not be installed since it
>>> would overwrite the system's library. If you want to install the
>>> resulting library choose a different --prefix parameter value.
>>> Otherwise the new code can be used without installation. Running
>>> existing binaries is possible with
>>> elf/ld.so --library-path .:linuxthreads2:dlfcn:math <binary> <args>...
>>> Alternatively the binary could be build to find the dynamic linker
>>> and DSO by itself. This is a much easier way to debug the code
>>> since gdb can start the binary. Compiling is a bit more complicated
>>> in this case:
>>> gcc -nostdlib -nostartfiles -o <OUTPUT> csu/crt1.o csu/crti.o \
>>> $(gcc --print-file-name=crtbegin.o) <INPUTS> \
>>> -Wl,-rpath,$PWD,-dynamic-linker,$PWD/ld-linux.so.2 \
>>> linuxthreads2/libpthread.so.0 ./libc.so.6 ./libc_nonshared.a \
>>> elf/ld-linux.so.2 $(gcc --print-file-name=crtend.o) csu/crtn.o
>>> This command assumes that it is run in the build directory. Correct
>>> the paths if necessary. The compilation will use the system's
>>> headers which is a good test but might lead to strange effects if
>>> there are compatibility bugs left.
>>>Once all these prerequisites are met compiling glibc should be easy.
>>>But there are some tests which will flunk. For good reasons we aren't
>>>officially releasing the code yet. The bugs are either in the TLS
>>>code which is not enabled in the standard glibc build, or obviously in
>>>the thread library itself. To run the tests for the thread library
>>> make subdirs=linuxthreads2 check
>>>One word on the name 'linuxthreads2' of the directory. This is only a
>>>convenience thing so that the glibc configure scripts don't complain
>>>about missing thread support. It will we changed to reflect the real
>>>name of the library ASAP.
>>>What can you expect?
>>>This is a very early version of the code so the obvious answer is:
>>>some problems. The test suite for the new thread code should pass but
>>>beside that and some performance measurement tool we haven't run much
>>>code. Ideally we would get people to write many more of these small
>>>test programs which are included in the sources. Compiling big
>>>programs would mean not being able to locate problems easy. But I
>>>certainly won't object to people running and debugging bigger
>>>applications. Please report successes and failures to the mailing
>>>People who are interested in contributing must be aware that for any
>>>non-trivial change we need an assignment of the code to the FSF. The
>>>process is unfortunately necessary in today's world.
>>>People who are contaminated by having worked on proprietary thread
>>>library implementation should not participate in discussions on the
>>>mailing list unless they willfully disclose the information. Every
>>>bit of information is publically available from the mailing list
>>>Which brings us to the final point: the mailing list for *all*
>>>discussions related to this thread library implementation is
>>> phil-list at redhat.com
>>>to subscribe, unsubscribe, or review the archive.
>>>- ---------------. ,-. 1325 Chesapeake Terrace
>>>Ulrich Drepper \ ,-------------------' \ Sunnyvale, CA 94089 USA
>>>Red Hat `--' drepper at redhat.com `------------------------
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>>Khalid Aziz Linux Systems Division
>>khalid at fc.hp.com Fort Collins, CO
>>"The Linux kernel is subject to relentless development"
>> - Alessandro Rubini
>>cgl_discussion mailing list
>>cgl_discussion at lists.osdl.org
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