[Caml-list] Shared memory parallel application: kernel threads
Hello,
I need to implement (meta) heuristic algorithms that
uses parallelism in order to (attempt to) solve a (hard)
machine learning problem that is inherently exponential.
The aim is to take maximum advantage of the multi-core
processors I have access to.
To that effect I have revisited many of the lively
discussions in threads related to concurrency, parallelism
and shared memory in this mailing list. I however still
have many doubts, some of which are very basic.
My initial objective is to make a very simple tests that
launches k jobs. Each of these jobs must access
a common data set that is read-only. Each of the k threads
in turn generates its own data. The data generated by the k
jobs are then placed in a queue for further processing.
The process continues by launching (or reusing) k/2 jobs.
Each job consumes two elements from the queue that where
previously generated (the common data set must still be
available). The process repeats itself until k=1. Note
that the queued data is not small nor can I determine
a fixed maximum size for it.
I have opted to use "kernel-level threads" that allow use
of the (multi-core) processors but still allow "easy"
access to shared memory".
I have done a cursory look at:
- Ocaml.Threads
- Ocaml.Unix (LinuxThreads)
- coThreads
- Ocamlnet2/3 (netshm, netcamlbox)
(An eThreads library exists in the forge but I did not examine this)
My first concern is to take advantage of the multi-cores so:
1. The thread library is not the answer
Chapter 24 - "The threads library is implemented by time-sharing on
a
single processor. It will not take advantage of multi-processor
machines." [1]
2. LinuxThreads seems to be what I need
"The main strength of this approach is that it can take full
advantage of multiprocessors." [2]
Issue 1
In the manual [3] I see only references to function for the creation
and use of processes. I see no calls that allow me to simply generate
and assign a function (job) to a thread (such as val create : ('a -> 'b)
-> 'a -> t in the Thread module). The unix library where LinuxThreads
is now integrated shows the same API. Am I missing something or
is their no way to launch "threaded functions" from the Unix module?
Naturally I assume that threads and processes are not the same thing.
Issue 2
If I cannot launch kernel-threads to allow for easy memory sharing, what
other options do I have besides netshm? The data I must share is defined
by a recursive variant and is not simple numerical data.
I would appreciate any comments.
TIA,
Hugo F.
[1] http://caml.inria.fr/pub/docs/manual-ocaml/manual038.html
[2] http://pauillac.inria.fr/~xleroy/linuxthreads/
[3] http://caml.inria.fr/pub/docs/manual-ocaml/libref/ThreadUnix.html
[4] http://caml.inria.fr/pub/docs/manual-ocaml/manual035.html
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Re: [Caml-list] Shared memory parallel application: kernel threads
On Fr, 2010-03-12 at 11:55 +, Hugo Ferreira wrote:
> Hello,
>
> I need to implement (meta) heuristic algorithms that
> uses parallelism in order to (attempt to) solve a (hard)
> machine learning problem that is inherently exponential.
> The aim is to take maximum advantage of the multi-core
> processors I have access to.
>
> To that effect I have revisited many of the lively
> discussions in threads related to concurrency, parallelism
> and shared memory in this mailing list. I however still
> have many doubts, some of which are very basic.
>
> My initial objective is to make a very simple tests that
> launches k jobs. Each of these jobs must access
> a common data set that is read-only. Each of the k threads
> in turn generates its own data. The data generated by the k
> jobs are then placed in a queue for further processing.
>
> The process continues by launching (or reusing) k/2 jobs.
> Each job consumes two elements from the queue that where
> previously generated (the common data set must still be
> available). The process repeats itself until k=1. Note
> that the queued data is not small nor can I determine
> a fixed maximum size for it.
>
> I have opted to use "kernel-level threads" that allow use
> of the (multi-core) processors but still allow "easy"
> access to shared memory".
>
> I have done a cursory look at:
> - Ocaml.Threads
> - Ocaml.Unix (LinuxThreads)
> - coThreads
> - Ocamlnet2/3 (netshm, netcamlbox)
> (An eThreads library exists in the forge but I did not examine this)
>
> My first concern is to take advantage of the multi-cores so:
>
> 1. The thread library is not the answer
> Chapter 24 - "The threads library is implemented by time-sharing on
> a
> single processor. It will not take advantage of multi-processor
> machines." [1]
>
> 2. LinuxThreads seems to be what I need
> "The main strength of this approach is that it can take full
> advantage of multiprocessors." [2]
I think you mix here several things up. LinuxThreads has nothing to do
with ocaml. It is an implementation of kernel threads for Linux on the C
level. It is considered as outdated as of today, and is usually replaced
by a better implementation (NPTL) that conforms more strictly to the
POSIX standard.
Ocaml uses for its multi-threading implementation the multi-threading
API the OS provides. This might be LinuxThreads or NPTL or something
else. So, on the lower half of the implementation the threads are kernel
threads, and multi-core-enabled. However, Ocaml prevents that more than
one of the kernel threads can run inside its runtime at any time. So
Ocaml code will always run only on one core (but you can call C code,
and this can then take full advantage of multi-cores).
This is the primary reason I am going with multi-processing in my
projects, and why Ocamlnet focuses on it.
The Netcamlbox module of Ocamlnet 3 might be interesting for you. Here
is an example program that mass-multiplies matrices on several cores:
https://godirepo.camlcity.org/svn/lib-ocamlnet2/trunk/code/examples/camlbox/manymult.ml
Netcamlbox can move complex values to shared memory, so you are not
restricted to bigarrays. The matrix example uses float array array as
representation. Recursive variants should also be fine.
For providing shared data to all workers, you can simply load it into
the master process before the children processes are forked off. Another
option is (especially when it is a lot of data, and you cannot afford to
have n copies) to create another camlbox in the master process before
forking, and to copy the shared data into it before forking. This avoids
that the data is copied at fork time.
One drawback of Netcamlbox is that it is unsafe, and violating the
programming rules is punished with crashes. (But this also applies, to
some extent, to multi-threading, only that the rules are different.)
Gerd
>
> Issue 1
>
> In the manual [3] I see only references to function for the creation
> and use of processes. I see no calls that allow me to simply generate
> and assign a function (job) to a thread (such as val create : ('a -> 'b)
> -> 'a -> t in the Thread module). The unix library where LinuxThreads
> is now integrated shows the same API. Am I missing something or
> is their no way to launch "threaded functions" from the Unix module?
> Naturally I assume that threads and processes are not the same thing.
>
> Issue 2
>
> If I cannot launch kernel-threads to allow for easy memory sharing, what
> other options do I have besides netshm? The data I must share is defined
> by a recursive variant and is not simple numerical data.
>
> I would appreciate any comments.
>
> TIA,
> Hugo F.
>
>
> [1] http://caml.inria.fr/pub/docs/manual-ocaml/manual038.html
> [2] http://pauillac.inria.fr/~xleroy/linuxthreads/
> [3] http://caml.inria.fr/pub/docs/manual-ocaml/libref/ThreadUnix.html
> [4] http://caml.inria.fr/pub/docs/manual-ocaml/manual035.html
>
>
>
>
Re: [Caml-list] [ANN] CCSS 1.0
> which I posit should rarely be an issue, precisely because > they live in different contexts. Example, a box whose height is a picture followed by three lines of text. > But anyway, I've implemented unit conversion, which you can find in SVN [1]. > In the next release this feature may be activated at user discretion. Great, thanks. Daniel ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
Re: [Caml-list] Shared memory parallel application: kernel threads
Hi,
Gerd Stolpmann wrote:
On Fr, 2010-03-12 at 11:55 +, Hugo Ferreira wrote:
Hello,
I need to implement (meta) heuristic algorithms that
uses parallelism in order to (attempt to) solve a (hard)
machine learning problem that is inherently exponential.
The aim is to take maximum advantage of the multi-core
processors I have access to.
snip
My first concern is to take advantage of the multi-cores so:
1. The thread library is not the answer
Chapter 24 - "The threads library is implemented by time-sharing on
a
single processor. It will not take advantage of multi-processor
machines." [1]
2. LinuxThreads seems to be what I need
"The main strength of this approach is that it can take full
advantage of multiprocessors." [2]
I think you mix here several things up. LinuxThreads has nothing to do
with ocaml. It is an implementation of kernel threads for Linux on the C
level. It is considered as outdated as of today, and is usually replaced
by a better implementation (NPTL) that conforms more strictly to the
POSIX standard.
Oops. Silly me.
Ocaml uses for its multi-threading implementation the multi-threading
API the OS provides. This might be LinuxThreads or NPTL or something
else. So, on the lower half of the implementation the threads are kernel
threads, and multi-core-enabled.
Ok.Should have read more carefully. As stated in the manual "Two
implementations of the threads library are available, depending on the
capabilities of the operating system:" So I have a recent glibc and
therefore "multi-core-enabled" threads.
However, Ocaml prevents that more than
one of the kernel threads can run inside its runtime at any time. So
Ocaml code will always run only on one core (but you can call C code,
and this can then take full advantage of multi-cores).
Ok. I was under the (wrong) impression that the native OS threads did
run simultaneously (multi-core) but were intermittently stopped due to
the GC. So threads won't help.
This is the primary reason I am going with multi-processing in my
projects, and why Ocamlnet focuses on it.
Understood.
The Netcamlbox module of Ocamlnet 3 might be interesting for you. Here
is an example program that mass-multiplies matrices on several cores:
https://godirepo.camlcity.org/svn/lib-ocamlnet2/trunk/code/examples/camlbox/manymult.ml
Netcamlbox can move complex values to shared memory, so you are not
restricted to bigarrays. The matrix example uses float array array as
representation. Recursive variants should also be fine.
For providing shared data to all workers, you can simply load it into
the master process before the children processes are forked off. Another
option is (especially when it is a lot of data, and you cannot afford to
have n copies) to create another camlbox in the master process before
forking, and to copy the shared data into it before forking. This avoids
that the data is copied at fork time.
The main data set is large, so I will opt for the latter.
One drawback of Netcamlbox is that it is unsafe, and violating the
programming rules is punished with crashes. (But this also applies, to
some extent, to multi-threading, only that the rules are different.)
Not an issue for me.
Going to read-up on and install ocamlnet3.
Thanks,
Hugo F.
Gerd
Issue 1
In the manual [3] I see only references to function for the creation
and use of processes. I see no calls that allow me to simply generate
and assign a function (job) to a thread (such as val create : ('a -> 'b)
-> 'a -> t in the Thread module). The unix library where LinuxThreads
is now integrated shows the same API. Am I missing something or
is their no way to launch "threaded functions" from the Unix module?
Naturally I assume that threads and processes are not the same thing.
Issue 2
If I cannot launch kernel-threads to allow for easy memory sharing, what
other options do I have besides netshm? The data I must share is defined
by a recursive variant and is not simple numerical data.
I would appreciate any comments.
TIA,
Hugo F.
[1] http://caml.inria.fr/pub/docs/manual-ocaml/manual038.html
[2] http://pauillac.inria.fr/~xleroy/linuxthreads/
[3] http://caml.inria.fr/pub/docs/manual-ocaml/libref/ThreadUnix.html
[4] http://caml.inria.fr/pub/docs/manual-ocaml/manual035.html
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[Caml-list] Re: Shared memory parallel application: kernel threads
On 12-03-2010, Hugo Ferreira wrote: > Hello, > > I have opted to use "kernel-level threads" that allow use > of the (multi-core) processors but still allow "easy" > access to shared memory". > > I have done a cursory look at: > - Ocaml.Threads > - Ocaml.Unix (LinuxThreads) > - coThreads > - Ocamlnet2/3 (netshm, netcamlbox) > (An eThreads library exists in the forge but I did not examine this) > I think you should also have a look at ocaml/mpi for communication: http://forge.ocamlcore.org/projects/ocamlmpi/ and ancient for accessing read-only memory: http://merjis.com/developers/ancient MPI can work on a single computer to take advantage of multi-core through multi-processus. Regards, Sylvain Le Gall ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
Re: [Caml-list] Re: Shared memory parallel application: kernel threads
Sylvain Le Gall wrote: On 12-03-2010, Hugo Ferreira wrote: Hello, I have opted to use "kernel-level threads" that allow use of the (multi-core) processors but still allow "easy" access to shared memory". I have done a cursory look at: - Ocaml.Threads - Ocaml.Unix (LinuxThreads) - coThreads - Ocamlnet2/3 (netshm, netcamlbox) (An eThreads library exists in the forge but I did not examine this) I think you should also have a look at ocaml/mpi for communication: http://forge.ocamlcore.org/projects/ocamlmpi/ and ancient for accessing read-only memory: http://merjis.com/developers/ancient MPI can work on a single computer to take advantage of multi-core through multi-processus. Indeed. I did not list these because I was specifically looking for a share memory solution amongst threads. Seeing as I am forced to use processes ancient is worth considering. Thanks, Hugo F. Regards, Sylvain Le Gall ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
[Caml-list] Strangeness with atexit and exception backtraces
I have been using the Bolt logging library[1] lately in my code, but have encountered a difficulty with debugging programs. Bolt uses an atexit handler to close all open log files when the program shuts down. However, if an uncought exception is encountered with this atexit handler in place, the program terminates with status 2 but neither the exception value nor its backtrace (with OCAMLRUNPARAM=b) are printed. If I disable the atexit handler, the error information is printed as I expect. I am currently working around this by modifying Bolt so that the atexit handler is disabled if OCaml starts up with stack traces enabled. I am wondering, though, if this is a known bug (or limitation)? Is there another workaround, or a fix on the horizon? Or should I go file the appropriate report in the OCaml bugtracker? Thanks, - Michael ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
Re: [Caml-list] [ANN] CCSS 1.0
Hi, In the meantime I've released version 1.1, which includes the requested unit conversion feature. It works as I described in a previous email, but is not activated by default. If you really need this feature, simply provide option '--convert' (short version '-c') upon command line invocation. For more information: http://ccss.forge.ocamlcore.org/ Hope you find it useful! Best regards, Dario Teixeira ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
[Caml-list] Last CfP: PPDP'10
== Call for Papers PPDP 2010 12th International ACM SIGPLAN Symposium on Principles and Practice of Declarative Programming Hagenberg, Austria, 26-28 July 2010 (co-located with LOPSTR 2010) http://www.risc.uni-linz.ac.at/conferences/ppdp2010/ == PPDP 2010 aims to bring together researchers from the declarative programming communities, including those working in the logic, constraint and functional programming paradigms, but also embracing a variety of other paradigms such as visual programming, executable specification languages, database languages, AI languages and knowledge representation languages used, for example, in the semantic web. The goal is to stimulate research in the use of logical formalisms and methods for specifying, performing, and analysing computations, including mechanisms for mobility, modularity, concurrency, object-orientation, security, and static analysis. Papers related to the use of declarative paradigms and tools in industry and education are especially solicited. The conference will take place in July 2010 in the Castle of Hagenberg, Austria, colocated with the 20th International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2010), organised by the Research Institute for Symbolic Computation (RISC) of the Johannes Kepler University Linz. Topics: * Logic, Constraint, and Functional Programming * Database, AI and Knowledge Representation Languages * Visual Programming * Executable Specification Languages * Applications of Declarative Programming * Methodologies: Program Design and Development * Declarative Aspects of Object-Oriented Programming * Concurrent Extensions to Declarative Languages * Declarative Mobile Computing * Integration of Paradigms * Proof Theoretic and Semantic Foundations * Type and Module Systems * Program Analysis and Verification * Program Transformation * Abstract Machines and Compilation * Programming Environments The list above is not exhaustive - submissions describing new and interesting ideas relating broadly to declarative programming are encouraged. Submission guidelines: Papers should be submitted via the Easychair submission website for PPDP 2010: http://www.easychair.org/conferences/?conf=ppdp2010 Papers should consist of the equivalent of 12 pages under the ACM formatting guidelines. These guidelines are available online, along with formatting templates or style files. Submitted papers will be judged on the basis of significance, relevance, correctness, originality, and clarity. They should include a clear identification of what has been accomplished and why it is significant. They must describe original, previously unpublished work that has not been simultaneously submitted for publication elsewhere. Authors who wish to provide additional material to the reviewers beyond the 12-page limit can do so in clearly marked appendices: reviewers are not required to read such appendices. No simultaneous submission to other publication outlets (either a conference or a journal) is allowed. Proceedings: The proceedings will be published by ACM Press. Authors of accepted papers will be required to sign a copyright form. Camera ready papers for accepted papers should be prepared and submitted according to the final instructions that will be sent by the publisher after notification of acceptance. Invited Speakers: Maria Paola Bonacina (Università degli Studi di Verona, Italy) Sumit Gulwani (Microsoft Research) Important Dates: # Submission: title and abstract: 15 March 2010 full paper: 21 March 2010 # Notification: 23 April 2010 # Final version: 12 May 2010 # Symposium: 26-28 July 2010 Programme Committee: Elvira Albert (Spain) Sergio Antoy (US) Frederic Blanqui (China) Michele Bugliesi (Italy) Giuseppe Castagna (France) Mariangiola Dezani (Italy) Francois Fages (France) Maribel Fernandez (UK), chair Joxan Jaffar (Singapore) Andy King (UK) Temur Kutsia (Austria) Francisco Lopez Fraguas (Spain) Ian Mackie (France) Henrik Nilsson (UK) Albert Rubio (Spain) Kazunori Ueda (Japan) Philip Wadler (UK) Symposium Chairs: Temur Kutsia and Wolfgang Schreiner (Austria) For more information, please contact the chairs: Maribel Fernandez King's College London, UK Email: maribel.fernan...@kcl.ac.uk Temur Kutsia and Wolfgang Schreiner Research Institute for Symbolic Computation Johannes Kepler University Linz Email: kut...@risc.uni-linz.ac.at ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: ht
[Caml-list] camelia on windows config problem
I've just been playing with using camelia on Windows, since some students in my class are using it. My problem is that I can't figure out how to configure Camelia to run a non-Cygwin Ocaml. My installation puts the executables in C:\Program Files\Objective Caml\bin, and I can redirect the configuration to look here. But when Camelia tries to run the ocaml toplevel, it complains that it cannot find pervasives.cmi. This is true when I also configure the libraries to be in C:\Program Files\Objective Caml\lib\. When I run ocaml from the terminal, it runs fine (i.e., it's able to find the .cmi file). Any camelia users with ideas about what is going on? Thanks in advance! -Mike ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
Re: [Caml-list] Re: Shared memory parallel application: kernel threads
Hi, If your program doesn't need usage-proved stability, you may be interested in the "OCaml for Multicore" project which provides an alternative runtime library (prototype quality) which allows threads to compute in parallel. http://www.algo-prog.info/ocmc/ If you choose to give it a try, we would enjoy your feedbacks. Cheers, -- Philippe Wang m...@philippewang.info ___ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
