Here is the latest Caml Weekly News, for the week of March 02 to 09, 2010.
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/1eed3e0c978e47f2#Warren Harris asked and Sylvain Le Gall replied:
> I would like to determine what percentage of my application's cpu time > is spent in the garbage collector (for tuning purposes, but also just > to monitor the overhead). Is there any way to obtain this information > short of using gprof? Additional information provided by Gc.stat would > be ideal, or perhaps a Gc.alarm that was called at the beginning of > the gc cycle, but neither of these seem to exist. You can have a look at: http://ocamlviz.forge.ocamlcore.org This allow to instrument your code and watch GC activity. I think that with a little a little help on program side, you can be quite precise about GC without using gprof at all. This should also be more lightweight than gprof.Edgar Friendly then said:
I'd like to add my personal experience with ocamlviz - it's a great program, and has helped me a ton find unexpected performance. It has very good functions for starting and stopping timers that the gui can monitor in realtime, and associating these with counts of how many times your program reached a certain point can give good understanding of function call cost. It's memory profiler makes a very pretty graph of how much memory is in use by your program. I've also gotten started using its ability to watch the live value of ref values to monitor the state of the program easier than [eprintf]s, especially monitoring the state of many variables at once. It's very fast and the ability to debug over the network has come in handy more than once. This said, I've wanted to measure GC overhead with it, and found it lacking in that regard. If anyone finds a way to do this, I'm interested. I've not done much with its tree viewer, and the hashtbl monitor only indicated that the Hashtbl.t I was using had an amazingly horrible hash, and was filling only 3% of its buckets, and had thousands of entries in a few buckets. I tried to fix the hash, but ended up switching to a Map. Lastly, the ability to mark in memory certain values and have it count the total usage and/or count of those values seems interesting, but gets quite slow. I've not had much luck with it. Overall, good job. But is it going to die or stay maintained?Sylvain Le Gall replied:
Well, I hope it will stay maintained. At least source code, bugs and release on the forge will stay there for a long time (I can make promise on this part). And whenever current developpers become inactive, OCamlCore.org administrators can move ownership to other (with notice to current owner, of course): http://www.ocamlcore.org/philosophy/ (point 4) But anyway, this kind of tool is targeted at debugging on the first place. It is not a mandatory piece of a software/library. You can lie without it, when you have finished your job debugging/profiling your program. So I would say that long term maintainance should not bother user for now. It is actually something that is lightweight and that works. To my mind this is enough to consider using it. If a lot of people start using it, it is highly probable that it will stay maintained.Peter Hawkins suggested and Warren Harris replied:
> I would have recommended using oprofile on linux, which I greatly > prefer to GCC's built-in profiling support for profiling C programs. > It has a low and tunable overhead, and because it's a sampling > profiler it doesn't perturb the results anywhere near as much as > standard profiling instrumentation. > > Unfortunately last time I checked it had poor OCaml support (no > support for unwinding the OCaml call stack, so no context-sensitivity > in the profiles). That said, you probably don't need > context-sensitivity to determine the fraction of execution time spent > in the GC. Peter - gprof with ocaml works quite well: http://caml.inria.fr/pub/docs/manual-ocaml/manual031.htmlPeter Hawkins then replied:
I'm fully aware of gprof and ocaml's support of profiling. OCaml's profiling support works by adding calls to the _mcount library function at the entry point to every compiled function, which takes approximately 10 instructions on x86 (pushes and pops to save registers, and a call instruction). The _mcount function records function call counts, and is also responsible for producing the call graph. Separately, the profile library samples the program counter at some frequency, which lets us work out in which functions the program is spending its time. Using OCaml's profiling support has three problems: 1) programs compiled with profiling are slower, and 2) the profiling instrumentation itself distorts the resulting profile, and 3) the call graph accounting is inaccurate. Let's discuss each of these in turn: Problem (1) is simply that your program has extra overhead from all of those _mcount calls, which occur on every function invocation. You can't turn them off, and you can't make them happen less frequently. It's an all-or-nothing proposition. It would be unusual to include profiling instrumentation in a production system. Problem (2) is a little more subtle. Recall that the profiling instrumentation adds ~10 instructions to the start of each function, regardless of its size. For a large function, this may be a negligible overhead. For a small function, say one that was only 5 or 10 instructions in size to begin with, that is a substantial overhead. Since we determine how much time is spent in each function by sampling the program counter, small and frequently called functions will appear to take relatively longer than larger functions in the resulting profile. Small functions are common in OCaml code so we should see an appreciable amount of distortion. Problem (3) is a criticism of the _mcount mechanism in general. For each function f(), the profiler knows (a) how long we spent executing f() in total, and (b) how many times each of f()'s callers invoked f(). We do not know how much time f() spent executing on behalf of any given caller. If we assume that all of f()'s invocations took approximately the same amount of time, then we can use the caller counts to approximate the time spent executing f() on behalf of each caller. However, the assumption that f() always takes approximately the same amount of time is not necessarily a good one. I think it's an especially bad assumption in a functional program. These problems are avoided by using a sampling profiler like oprofile or shark, which samples an _uninstrumented_ binary at a particular frequency. Because the binary is unmodified, we can turn profiling on and off on a running system, avoiding point (1); furthermore we can adjust the sampling rate so profiling overhead is low enough to be tolerable. Since there is no instrumentation added to the program, the resulting profile does not suffer from the distortion of point (2). Some profilers (e.g. shark on Mac OS X) can deal with point (3) as well --- all we need to do is record a complete stack trace at sampling time. My point was that oprofile or one of its cousins (e.g. shark) is probably adequate for your needs. You can set the sampling rate low enough that your service can run more or less as normal. To determine GC overhead, you simply need to look at the total amount of time spent in the various GC functions of the runtime.Warren Harris then replied and David MENTRE said:
> Thanks, this is excellent info. I've been using both gprof and shark and > understand the tradeoffs. I really was looking for a way to just provide a > simple live "gc overhead" number that we could graph along with a bunch of > other server health stats for our zenoss monitors. So simply enable gprof on OCaml binaries and look at the total fraction of time spent in OCaml GC functions! http://caml.inria.fr/pub/ml-archives/caml-list/2003/01/e8ee9d44073ff9cb7d257fef86bc8f53.en.htmlOlivier Andrieu replied to the original post:
Here's what I use to measure GC overhead in my programs. There's a small modification to the runtime, so as to track the time spent in caml_minor_collection, and a helper ml module. It tracks and prints the time spent between calls to the start() and stop() function of the helper module, as well the number of collections, number of bytes allocated, etc. It is rather coarse-grained of course. I use it to profile the different parts of a compiler: parsing, typing, optimizations, code generation, etc. (Please see the archive link to download the attached files.)
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/098357ea26046912#Oleg announced:
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/0a7900499f7714ed#Joe asked:
Is there a good way to encode a parse tree in OCaml where the terms in the parse tree can be extended later? Essentially, it would be nice not to represent the trees for different grammars separately so that code for type checking, evaluation, or pretty printing can be reused. I'm including one possible solution below that seems to work reasonably well, but I'm interested in whether this can be done better. The two things that would be nice to improve upon the example are preventing statements such as "bad" where improper trees are created. It would also be nice to have the OCaml type system flag an error on the line with "`Junk". Though, it does give a warning now. Joe type base = [`Int of int];; type 'a basic= [base | `Add of 'a*'a | `Sub of 'a*'a ];; type 'a ext= ['a basic | `Mul of 'a*'a];; type basic'=('a basic as 'a) basic;; type ext'=('a ext as 'a) ext;; let (x:'a basic)=`Add (`Int 1,`Int 2);; let (y:'a ext)=`Mul (x,`Int 3);; let (z:'a basic)=`Add (`Int 3,x);; let w=`Add (`Mul (`Int 1,`Int 2),`Int 3);; let (bad:'a basic)=`Add (1,2);; let pp x= let rec pp (x:ext') = match x with | `Int x-> Printf.printf "%d" x | `Add (x,y) -> pp x; Printf.printf "+"; pp y | `Sub (x,y) -> pp x; Printf.printf "-"; pp y | `Mul (x,y) -> pp x; Printf.printf "*"; pp y | `Junk -> Printf.printf "BAD!" in pp (x :> ext');Printf.printf "\n" ;; let eval x= let rec eval (x:basic')= match x with | `Int x -> x | `Add (x,y) -> (eval x) + (eval y) | `Sub (x,y) -> (eval x) - (eval y) in eval (x:>basic') ;;Markus Mottl suggested:
> type basic'=('a basic as 'a) basic;; > type ext'=('a ext as 'a) ext;; This could also be written as: type basic' = basic' basic type ext' = ext' ext Cyclic types are acceptable to the compiler if the cycle is on polymorphic variants. > let (x:'a basic)=`Add (`Int 1,`Int 2);; > let (y:'a ext)=`Mul (x,`Int 3);; > let (z:'a basic)=`Add (`Int 3,x);; > let w=`Add (`Mul (`Int 1,`Int 2),`Int 3);; > let (bad:'a basic)=`Add (1,2);; When solving the problem with "bad", type constraints are your friend. Just define type 'basic" as e.g.: type 'a basic= [base | `Add of 'a*'a | `Sub of 'a*'a ] constraint 'a = [> base];; To fix the "Junk" problem, you may need to specify the type for one of the patterns, e.g.: match x with | (`Int x : ext')-> Printf.printf "%d" x ... But the function itself is not extensible. To achieve this, you'll have to define it in a similar way as we did for the type by introducing another parameter to "tie the recursive knot". E.g. (ignore incorrect printing of arithmetic expressions): let pp_base (`Int n) = Printf.printf "%d" n let pp_basic pp = function | #base as base -> pp_base base | `Add (l, r) -> pp l; Printf.printf "+"; pp r | `Sub (l, r) -> pp l; Printf.printf "-"; pp r let pp_ext pp = function | #basic as basic -> pp_basic pp basic | `Mul (l, r) -> pp l; Printf.printf "*"; pp r let rec pp_basic' basic' = pp_basic pp_basic' basic' let rec pp_ext' ext' = pp_ext pp_ext' ext' You will need to constrain a pattern with a type again if you want to make sure that the pattern match fails in the right place (match case) if unsupported tags are added. You could also turn warnings into errors, which should also fail on the "unused match case" then. IMHO, these features of polymorphic variants are the best thing since sliced bread, since they allow for elegant extensibility of e.g. recursive DSLs.
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/0624ae9e41bad6a5#Jeremy Bem announced:
I'm pleased to announce the initial release of NaCl/OCaml, a version of the native-code OCaml compiler whose output can be validated as safe to run over the web. Together with the "Native Client" plug-in under development at Google, this means that OCaml can now be used for client-side web programming! For more about Native Client, see http://code.google.com/p/nativeclient/. For NaCl/OCaml, including a ray tracer demo, see http://code.google.com/p/nacl-ocaml/. Feedback is welcome and appreciated. Please feel free to email me, report bugs at the project website, or email email@example.com .Daniel Bünzli asked and Jeremy Bem replied:
> Interesting contribution. > > Maybe this is more a question about native client but could you > elaborate on the kind of constraints nacl puts on the client code. > Which libraries can be used ? The standard library ? str.cmxa ? > unix.cmxa ? Third party pure caml modules ? C bindings ? etc. I hope to post more documentation, but in a nutshell: standard library: Yes, but file operations are typically unavailable at the NaCl level and will fail. Str (and Num): I haven't included these yet, but I intend to. Unix: Similar capabilities are provided by the "Service" library instead. This seemed slightly more in keeping with the NaCl underpinnings than hacking Unix into submission. Third party OCaml modules should be compilable and usable, just use "nacl-ocamlopt" in place of "ocamlopt". Of course complex libraries may present complications in practice (e.g. if they try to access the filesystem). C bindings: it should be possible to interface with C code as per the OCaml manual, again substituting "nacl-ocamlopt" for "ocamlopt". The NaCl-specific libraries that are included (such as "Multimedia") provide a template that can be emulated.Vincent Balat said:
Very interesting! We will try to make Eliom Client (the client side programming framework for Ocsigen) work on it. A summary of solutions to use Ocaml for client side programming: - OcamlJs (by Jake Donham): compiler OCaml -> JS - O'Browser (by Benjamin Canou): Ocaml virtual machine written in JS - NaCl/Ocaml: native code! (but requires Native client to be installed and only x86 for now) - and there may also be a compiler Ocaml bytecode -> JS soon ;-)
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/22e821c64a67a567#Yaron Minsky announced:
The following is the call for participation for CUFP, the Commerical Users of Functional Programming workshop that is co-located with ICFP. If you have experience using OCaml (or another functional language) in a practical application, consider submitting a proposal to give a talk about it at CUFP! Also, check out the new CUFP website: http://cufp.org Without further ado: CUFP 2010 Call For Participation ================================ Functional programming languages have been a hot topic of academic research for over 35 years, and have seen an ever larger practical impact in settings ranging from tech startups to financial firms to biomedical research labs. At the same time, a vigorous community of practically-minding functional programmers has come into existence. CUFP is designed to serve this community. The annual CUFP workshop is a place where people can see how others are using functional programming to solve real world problems; where practitioners meet and collaborate; where language designers and users can share ideas about the future of their favorite language; and where one can learn practical techniques and approaches for putting functional programming to work. Giving a CUFP Talk ------------------ If you have experience using functional languages in a practical setting, we invite you to submit a proposal to give a talk at the workshop. We're looking for two kinds of talks: **Experience reports** are typically 25 minutes long, and aim to inform participants about how functional programming plays out in real-world applications, focusing especially on lessons learned and insights gained. Experience reports don't need to be highly technical; reflections on the commercial, management, or software engineering aspects are, if anything, more important. You do not need to submit a paper! **Technical talks** are expected to be 30-45 minutes long, and should focus on teaching the audience something about a technical technique or methodology, from the point of view of someone who has seen it play out in practice. These talks could cover anything from techniques for building functional concurrent applications, to managing dynamic reconfigurations, to design recipes for using types effectively in large-scale applications. While these talks will often be based on a particular language, they should be accessible to a broad range of functional programmers. If you are interested in offering a talk, or nominating someone to do so, send an e-mail to francesco(at)erlang-consulting(dot)com or yminsky(at)janestreet(dot)com by 15 May 2010 with a short description of what you'd like to talk about or what you think your nominee should give a talk about. Such descriptions should be about one page long. There will be no published proceedings, as the meeting is intended to be more a discussion forum than a technical interchange. Program Committee ----------------- * Francesco Cesarini, Erlang Training and Consulting (Co-Chair) * Tim Dysinger, Sonian Networks * Alain Frisch, LexiFi * Nick Gerakines, Chegg * Adam Granicz, IntelliFactory * Amanda Laucher * Romain Lenglet, Google Japan * Yaron Misky, Jane Street (Co-Chair) * Mary Sheeran, Chalmers * Don Stewart, Galois * Dean Wampler, DRW Trading More information ---------------- For more information on CUFP, including videos of presentations from previous years, take a look at the CUFP website at http://cufp.org.
Thanks to Alp Mestan, we now include in the Caml Weekly News the links to the recent posts from the ocamlcore planet blog at http://planet.ocamlcore.org/. Liquidsoap-full 0.9.2-2 and ocaml-cry 0.1.2: http://blog.rastageeks.org/spip.php?article58 OCaml CSV 1.2: http://caml.inria.fr/cgi-bin/hump.cgi?contrib=447 OCamlEditor 1.2 released: http://forge.ocamlcore.org/forum/forum.php?forum_id=553 OCaml-FPDF: https://forge.ocamlcore.org/projects/ocamlfpdf/ ocaml batteries included 1.1.0 is in debian now: http://upsilon.cc/~zack/blog/posts/2010/03/ocaml_batteries_included_1.1.0_is_in_debian_now/ Reading Camlp4, part 5: filters: http://ambassadortothecomputers.blogspot.com/2010/03/reading-camlp4-part-5-filters.html
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