Gambit-list Avril 2007

gambit-list@iro.umontreal.ca

23 participants
47 discussions

Termite
by Marc Feeley 20 Avr '07

20 Avr '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 At yesterday's MSLUG meeting Dominique showed us how easy distribution can be done using Erlang. There was a question asking how Erlang and Termite compare. To give a quick idea, here is an example of how distribution can be done with Gambit-C/Termite. Assuming you have built the Gambit runtime to include Termite, you need to start a Termite instance on a machine (say "dynamo") and initialize it: dynamo% gsi -e '(node-init (make-node "dynamo" 7777))' - > This instance of termite is a "node" which is identified by the IP address "dynamo" and the IP port 7777. Note that a REPL is started, but we will not be using it. Now let's start a Termite instance on machine "neo" to get a REPL: neo% gsi -e '(node-init (make-node "neo" 8888))' - > This second node is identified by the IP address "neo" and the IP port 8888. We could have started two nodes on the same machine, as long as the IP ports are different. All the remaining REPL interaction is on neo. First, let's create a reference to the first node on "dynamo": > (define dynamo (make-node "dynamo" 7777)) Synchronous remote procedure call is done with the "on" function. It executes a thunk remotely and returns the result: > (on dynamo host-name) "dynamo.iro.umontreal.ca" Let's develop an asynchronous remote procedure call in stages. First a simple example of local process creation and communication: > (define s (self)) > (define p (spawn (lambda () (! s (expt 2 (?)))))) > (! p 10) > (?) 1024 The process p uses the "?" function to wait for and retrieve the next message in p's mailbox. The function "!" sends a message back to the primordial process (whose PID was saved in global variable s). This code can easily be extended to get a simple "power of 2" server: > (define p (spawn (lambda () (let loop () (! s (expt 2 (?))) (loop))))) > (! p 16) > (! p 32) > (?) 65536 > (?) 4294967296 Note that the results are retrieved asynchronously (i.e. the mailbox queues the messages received). Moreover the results are always sent back to the primordial process. To generalize, the request can be a pair containing, in the car, the PID of the process which the result should be sent to, and in the cdr, a function that is executed by the server to generate the result: > (define p (spawn (lambda () (let loop () (let ((x (?))) (! (car x) ((cdr x))) (loop)))))) > (! p (cons (self) host-name)) > (?) "neo.iro.umontreal.ca" In this example the server is running locally. By changing the "spawn" to a "remote-spawn" the server can be started on "dynamo": > (define p (remote-spawn dynamo (lambda () (let loop () (let ((x (?))) (! (car x) ((cdr x))) (loop)))))) > (! p (cons (self) host-name)) > (?) "dynamo.iro.umontreal.ca" Any serializable Scheme object can be passed in a message. This includes closures. Here is an example: > (! p (cons (self) (let ((a (host-name))) (lambda () (let ((b (host-name))) (lambda () (list a b (host-name)))))))) > (define f (?)) > (f) ("neo.iro.umontreal.ca" "dynamo.iro.umontreal.ca" "neo.iro.umontreal.ca") Note that the cdr of the pair sent to p is a closure which remembers the binding for a, which is "neo.iro.umontreal.ca" because that's where the first (host-name) was evaluated. When the server calls this closure, the second (host-name) is evaluated, giving "dynamo.iro.umontreal.ca". The binding of b is remembered in the closure created by the second lambda. This closure is sent back to the primordial process, which binds f to it. When this closure is called the third (host-name) is evaluated, resulting in "neo.iro.umontreal.ca". This example shows that the meaning of the global environment is node dependent. The global environment is not automatically kept consistent on all nodes, it is the programmer's responsibility to ensure this where needed. So for example: > (on dynamo (lambda () (with-exception-catcher (lambda (e) e) (lambda () (fact 10))))) #<unbound-global-exception #2> > (on dynamo (lambda () (load "test.scm"))) "/Users/feeley/test.scm" > (on dynamo (lambda () (with-exception-catcher (lambda (e) e) (lambda () (fact 10))))) 3628800 > (fact 10) *** ERROR IN (console)(a)24.2 -- Unbound variable: fact 1> Erlang's autoloading behavior is not built in to Termite. However it could be implemented on top of Gambit's exception handling system. The idea would be to extract from a fully qualified name (such as test#fact) the filename of the file to load, like this: (define (char-pos str c) (let loop ((i 0)) (if (< i (string-length str)) (if (char=? c (string-ref str i)) i (loop (+ i 1))) #f))) (define base-eh (current-exception-handler)) (current-exception-handler (lambda (e) (if (unbound-global-exception? e) (let* ((sym (unbound-global-exception-variable e)) (str (symbol->string sym)) (i (char-pos str #\#))) (if (not i) (base-eh e) (let ((mod (substring str 0 i))) (load (string-append mod)) (let ((val (##global-var-ref (##make-global-var sym)))) (if (##unbound? val) (base-eh e) val))))) (base-eh e)))) (namespace ("test#" fact)) (pp (fact 10)) The call (fact 10), due to the namespace declaration, is rewritten into (test#fact 10). When the interpreter evaluates the reference to test#fact the exception that is raised is caught by the exception handler which extracts the module name "test" and loads that file to access the definition of "fact". The file "test.scm" should contain: (namespace ("test#" fact)) (define (fact n) (if (= n 0) 1 (* n (fact (- n 1))))) Marc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (Darwin) iD8DBQFGKNrp//V9Zc2T/v4RAvEnAKCIvr+IXNxs+sEFkhWtBcEHB0YIsACeKUCn WRg15dYlEDtKTAGBHutqeV4= =uxwr -----END PGP SIGNATURE-----

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returning multiple values from a c-lambda?
by Phil Dawes 20 Avr '07

20 Avr '07

Hi Gambit List, Is there any way to return multiple values from a c-lambda? (other than e.g. creating a list and returning that) Cheers, Phil

2 1

Mention removal of latin1 char-encoding
by Bradley Lucier 19 Avr '07

19 Avr '07

Marc: After spending 15 minutes or so trying to interpret the cryptic and incomplete error message > (define g (pgm->f64 (read-pgm "circle-128.pgm"))) *** ERROR IN read-pgm, "../pgm.scm"@36.3 -- (Argument 1) STRING or port settings expected (call-with-input-file '(path: "circle-128.pgm" char-encoding: latin1 eol-encoding: lf) '#<procedure #2>) I discovered that you removed latin1 as a valid char-encoding. Perhaps you should mention this in the documentation. (I suppose a more helpful error message may work, too.) Brad

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Standard Windows version
by Tom Ayerst 18 Avr '07

18 Avr '07

Hi, Couple of quick questions (I probably should rtfm somewhere but I'm new to this). Which is the "standard" windows build that is offered on the Gambit-C? There seem to be several floating about. Will the currently offered Windows version work with Termite? i.e. Can I investigate termite on windows without resorting to a C compiler? Thanks Tom

3 4

New _num.scm
by Bradley Lucier 18 Avr '07

18 Avr '07

Marc: This _num.scm does a few things: 1. It uses the ##fixnum.+? and ##fixnum.-? functions in ##+, ##-, and ##negate. Together with my changes to gambit.h yesterday, this should allow you to remove -fwrapv from the command line. (But don't add more code that assumes that signed arithmetic wraps!) 2. It uses a new fft algorithm for bignum multiplication that is provably correct. (The mathematics behind it is correct, I obviously didn't prove that the code as implemented is correct.) The code is faster on some machines (my PowerPC Macs) and slower on others (my opteron box). It's also shorter and clearer than the old code. (There are many more comments, and I included alternate simple implementations of the fft's for which gsc does not generate any code.) The new code uses a number of tables, total size about 24KB, to calculate dynamically the table of sines and cosines needed for the fft. (BTW, can you write some code to cache the result of making the table? If one has already computed a bigger table of sines and cosines, you can use it where one would otherwise calculate a smaller table.) The .o file is about 7KB bigger, so I got rid of about 17KB of code while adding 24KB of data. I checked that all this machinery is omitted if (use-fast-bignum-algorithms) is defined to be #f at the head of _num.scm. Please look it over. It passes "make check" and I checked the fft bignum multiplication more thoroughly. Brad

1 1

Syntax-case, define-structure, and internal defines...
by TJ 17 Avr '07

17 Avr '07

I have a macro defined thus: (define-syntax define-only (lambda (exp) (syntax-case exp () ((_ (n ...) e ...) (with-syntax (((tmp ...) (generate-temporaries (syntax (n ...))))) (syntax (begin (define n #f) ... (let ((tmp #f) ...) ((lambda () e ... (set! tmp n) ...)) (set! n tmp) ...)))))))) Which, if it works, would enable me to do the following: (define-only (mkcounter inc! val) (define-structure counter v) ;; Invisible from the top-level. (define mkcounter (lambda () (make-counter 0))) (define inc! (lambda (c) (counter-v-set! c (+ 1 (counter-v c))))) (define val counter-v)) But which, unfortunately, gives me the following: *** ERROR -- invalid context for definition (define mkcounter (lambda () (make-counter 0))) I suspected that perhaps (define...)'s were not allowed after (define-structure...)'s. So I did this: (pp (lambda () (define-structure test a) 'done)) Which prints the following: (lambda () (letrec ((##type-1-test (##structure ##type-type (##make-uninterned-symbol "##type-1-test") 'test 8 #f '#(a 0 #f))) (make-test (lambda (p1) (##structure ##type-1-test p1))) (test? (lambda (obj) (##structure-direct-instance-of? obj (##type-id ##type-1-test)))) (test-a (lambda (obj) (##direct-structure-ref obj 1 ##type-1-test test-a))) (test-a-set! (lambda (obj val) (##direct-structure-set! obj val 1 ##type-1-test test-a-set!)))) 'done)) Which makes me wonder why my macro doesn't work. After all (define...)'s are allowed at the beginning of a letrec's body, no? TJ

2 2

Getting rid of the -fwrapv flag in gcc
by Bradley Lucier 15 Avr '07

15 Avr '07

Marc: I've been thinking about how to get the C code generated by gsc to conform to the ISO C standard. Beyond being just a "good thing", this would allow us to get rid of the -fwrapv and -fno-strict- aliasing flags in gcc, which would also enable some further compiler optimizations. (Well, getting rid of -fwrapv enables some optimizations and disables others.) I think the only places in the gambit back-end where we assume that signed arithmetic wraps on overflow are in the macros FIXADDP, FIXMULP, and FIXSUBP in gambit.h. I'm no expert on signed vs. unsigned arithmetic in C, but I think that simply casting the arguments of the possibly overflowing operations to unsigned, and then casting the result back to signed, will, in the end, give us the same result but will be standard-conforming. So I offer this (lightly tested, but it did pass "make check") patch for gambit.h that does precisely this. This should allow us to omit the -fwrapv flag for gcc. I don't have any performance figures for gsc compiled without -fwrapv, but the binary is a bit smaller: [brad:~/programs/gambc-4.0b22] lucier% ll gsc/gsc gsc-comp -rwxr-xr-x 1 lucier lucier 5544476 Apr 6 19:11 gsc-comp* -rwxr-xr-x 1 lucier lucier 5540296 Apr 15 17:58 gsc/gsc* The patch also has an extra guard to limit the use of __builtin_expect to versions of gcc >= 3.0. Brad

1 1

termite build error
by |/|/ Bendick 12 Avr '07

12 Avr '07

Hi, I'm trying to compile termite with the new b22 version but when I make I get this when it reaches _thread.scm. Vanilla b22 compiles fine. Any ideas? ../gsc-comp -:=".." -f -c -check _thread.scm /bin/sh: line 1: ../gsc-comp: No such file or directory make[1]: *** [_thread.c] Error 127 make: *** [all-recursive] Error 1 -- |/|/ Bendick

3 4

Build on mingw fails
by Mark Voortman 11 Avr '07

11 Avr '07

Hello, I'm trying to build the latest version on mingw, but it fails in the following way: gcc _gsi.o _gsi_.o ../lib/libgambc.a -lws2_32 -o gsi.exe ../lib/libgambc.a(os_tty.o):os_tty.c:(.text+0x74c): undefined reference to `___printf' collect2: ld returned 1 exit status make[1]: *** [gsi.exe] Error 1 make[1]: Leaving directory `/home/mark/gambc-4.0b22/gsi' make: *** [all-recursive] Error 1 Does anyone know how to fix this? Thanks, Mark

1 0

More char-size=1 woes
by TJ 11 Avr '07

11 Avr '07

The standalone executables created by a gsc with "--enable-char-size=1" do not seem to get a standard-output port. Shared object files work when (load)'ed into the gsc prompt though. ;; File (display "Hello world!") (newline) ;; End-file I compiled it with the very basic options: $ gsc -link test.scm $ gcc -o test -I (gambit-i-dir)/include/ -L (gambit-libdir)/lib/ test.c test_.c I also introduced a deliberate error to see if the runtime's exception handler was able to print anything to the stdout port. It wasn't. (+ 1 "b") By the way, is the Gambit bugzilla still being used? I only saw 4 bugs listed there, the latest dated September 2006, with none resolved. TJ

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Gambit-list Avril 2007