common-lisp,sbcl,cffi , cffi function call hangs
cffi function call hangs
I want to use stat(2) from Common Lisp.
I've defined the structs used by the
(cffi:defctype mode_t :unsigned-int)
(cffi:defctype ino_t :unsigned-int)
(cffi:defctype dev_t :int)
(cffi:defctype nlink_t :int)
(cffi:defctype uid_t :unsigned-int)
(cffi:defctype gid_t :unsigned-int)
(cffi:defctype off_t :int)
(cffi:defctype time_t :long)
(cffi:defctype blksize_t :unsigned-int)
(cffi:defctype blkcnt_t :int)
And the function itself:
(cffi:defcfun "stat" :int
(buf (:pointer (:struct stat))))
I'm trying to call it quite simply like this:
(cffi:with-foreign-object (buf '(:pointer (:struct stat)))
(stat "/home/florian/tmp/msg.txt" buf)
(cffi:with-foreign-slots ((st_mode) buf (:struct stat))
And Slime just hangs. No error, and the REPL input doesn't come back.
If you look into your
*inferior-lisp* buffer, you will see that SBCL has dropped into its low-level debugger due to some severe memory corruption.
The specific layout of
struct stat depends quite heavily on the architecture you have. On my 64-bit Ubuntu 14.04, the following seems to be 144 bytes in length, while your definition is only 52 bytes long - no wonder that trying to write into it causes memory corruption.
It is probably a Bad Idea to try writing
defcstruct forms for structs that the operating system is free to define in any way it wants. The code may run on your computer, but probably won't run on everybody else's system, if they are using a different OS or processor architecture - but if you really need to get it running on your system only, the easiest way is probably to write a short C program that dumps the sizes and offsets of all the fields on screen, then build up from there.
If you need to write code that runs on multiple different systems and that uses
stat, a good option is to write a simple proxy module in C yourself, with a well-defined, constant interface, that calls
stat on your behalf. This is the approach I have used on several occasions, keeping foreign stuff safe on the C side and only passing the really required data over the FFI.
For more robust CFFI definitions, there is also SWIG.
I see two different patterns for "output" functions in (common) lisp: (defun implicit () (format t "Life? Don't talk to me about life!")) (defun explicit (stream) (format stream "This will all end in tears.")) (defun test-im-vs-ex-plicit () (values (with-output-to-string (stream) (let ((*standard-output* stream)) (implicit))) (with-output-to-string (stream) (explicit stream)))) Is using...
Say if I define a metaclass that enhances standard slots with a validator slot, when I pass :validator (clavier:valid-email "The email is invalid") as an option, instead of storing the result of of the expression, which is a funcallable, it stores the expression itself. Am I'm missing a step when...
How can i compare characters with Common Lisp? I have google it and found out that there are some functions to do the comparison, like char=, char/=, char<, char>, char<=, and char>=. But, i can't use all of the functions just like: (char= 'a 'a) (char< 'a 'b) If i...
if strings are vectors of characters, and a vector's elements can be accessed using elt, and elt is setf-able - then why are strings immutable?
I have the following two classes: (defclass person () ()) (defmethod speak ((s person) string) (format t "-A" string)) (defmethod speak :before ((s person) string) (print "Hello! ")) (defmethod speak :after ((s person) string) (print "Have a nice day!")) (defclass speaker (person) ()) (defmethod speak ((i speaker) string) (print "Bonjour!"))...
I am trying to write a simple coin flip program in Common Lisp. This is the code I have (defun yn (let ht (random 1) (if (eq ht 1) (princ heads) (princ tails)) ) ) It seems simple enough, but I keep getting the error: "Invalid specialized parameter in method...
Ok, I must be missing something obvious. I'm getting stuck since yesterday to launch Emacs-live + slime. I'm using EMACS 24.3.1, installed Emacs-live and it worked well (if I start emacs-live without Slime it works), downloaded Slime-Pack from git and added this line to .emacs-live.el (live-append-packs '(~/.live-packs/slime-pack/)) I'm on a...
I have this macro, which rewrites define. If I remove the " ` " backtick it won't work. What is the explanation? (defmacro define ((name &rest r) body) `(defun ,name ,r ,body)) ...
How are tagbody and go implemented in Common Lisp? Is it some form of setjmp/longjmp or is there a more elegant way of handling this? I'm writing a lispy language implemented in C and would like to have something like this....
Hello why do i get *** - EVAL/APPLY: too many arguments given to F on function call with nested lists parameter. I cannot figure it out, since I passed a simple nested list. (defun f (L) (cond ((NULL l) nil) ((listp (car L)) (append (F(car L))) (F(cdr L) (car (F...
Both CL and Scheme define (and) to return t (or #t) with no arguments. I'm trying to understand the rationale for this. My naive assumption is that an empty set is false, and passing in zero arguments feels like passing in nothing that can be true. Edit: clojure follows the...
I have figured out how to make use of shared objects created from C code into Clisp using FFI:def-call-out but I am not able to figure out how to use FFI:Def-call-in. I don't know the process and actually I am confused if clisp will also create some .so file that...
I happened encounter a trouble with calling C printf function from SBCL via cffi. The problem is when I call printf function, I can't find the output text, just the return value of printf function show on the REPL. But when I quit SBCL, the output text appears on the...
I stumbled across a very weird bug (?) while I was developing an application in Allegro Common Lisp, v9.0 for Windows. I do not get the regular lisp errors, instead I get system errors encapsulated in a lisp condition. I managed to create a simple test-case to reproduce the error...
While trying to figure out CLIM, I ran into this example program. It's a simple maze game. The author claims to have tested it in LispWorks (and even has #+Genera in there, implying that this program would work on a real Lisp Machine), but I'm trying to get it working...
I have just started out programming in Common Lisp using GNU clisp-2.49 (compiled from source) as my implementation on OS X 10.10 Yosemite. I've written a simple "Hello World" program as follows: (EXT:SAVEINITMEM "test" :INIT-FUNCTION 'main :EXECUTABLE t) (defun main () (format t "Hello World!") (EXT:EXIT)) When I run: $...
Dear StackOverflow community, I started playing with SBCL Common Lisp and want to develop a small web application using Hunchentoot. For easy deployment I planned to save everything in a binary using sb-ext:save-lisp-and-die as I can live with the big output size. For the executable you need to supply a...
I want to write some data structures pointed to by FOO and BAR to a file, and to read the data structures back into the symbols FOO and BAR when I start a new session of Common Lisp. It would appear *PRINT-READABLY* allows objects to be printed in a fashion...
I am a beginner with lisp. I manipulate list of list: ((name1, second) (name2, second2)) The goal of my function is to get the second element of the list that have name as it first node. For example: my list is: ((name1, second1) (name2, second2)) getelement list name1 should return...
I am extremely new to lisp, had previous experience with functional programming (Haskell, SML). Why is this code returning 14, and not 10 (ie. 1 + 2y + 3 + 1)? (defvar x 1) (defun g (z) (+ x z)) (defun f (y) (+ (g 1) (let ((x (+ y...
I'm trying to multiply a list with n sublists with a list with n scalars. It's supposed to work like this: (kmult-matrix '((3 4 2 4) (2 5 6 9) (1 -2 8 10)) '(2 3 5)) => ((6 8 4 8) (6 15 18 27) (5 -10 40 50))...
I have a list of string like this called F: ("hello word i'am walid" "goodbye madame") => this list contain two elements of string and I have another list call S like this ("word" "madame") => this contain two words now I want to remove the elements of the list...
Honnestly, I'm not sure I fully understand what it means for a binding to be "dynamic" versus "lexical". But I understand that when I use defvar or defparameterto define a binding, 1. it declares a global variable 2. the binding is declared "special", so that it can be shadowed by...
As a result of musings around an exercism problem, I am trying to write a function that takes an input number and an arbitrary length list of divisors to test, along with the expected divisibility (i.e. remainder 0) as a boolean, returning true if all expectations are met (defaulting to...
(defun testthis (node index newvalue) (set-nth node index newvalue) node ) I would like to modify the nth element of a list in a function and then returns this list to save the modification performed. How can I do a such function in lisp?...
*Note: Despite having frequented StackOverflow for a long time, this is the first question that I have posted myself. Apologies if it's a bit verbose. Constructive criticism appreciated. When I define a struct in Common Lisp using defstruct, a predicate function is automatically generated that tests whether its argument is...
Set-macro-character has an optional argument called non-terminating-p. It seems to be used to indicate whether another character should be read after reading the macro character, but the reader algorithm seems to ignore this argument. Is there a difference whether I set it to true or false?
What's the best way to move a file in Lisp in an implementation-independent way? For example I have an image file: (setq oldpath #P"SERVER:PICTURES;TEMP;PHOTO.PNG") and I want to move it out of the TEMP directory into the PICTURES directory. This seems to work: (setq newpath (make-pathname :host (pathname-host oldpath) :directory...
I have a server running Hunchentoot (CentOS and SBCL). When a user submits a specific type of post request, a subprocess is launched (run-program) which can take up to four minutes to complete. If five people perform that specific type of request at the same time, the server runs out...
Hello guys I'm new In functional programming Really it is not Clear for me anyone can help me ? My Question just for getting the philosophy of writing on Functional programming language for example how I can write a program in Lisp language for reading the user inputs and compare...
Dear StackExchange members, I recently began toying around with Common Lisp and want to create a web interface for administrating a modded Minecraft server. I already tried out this solution but in this case the function just hangs and never returns. My code looks like this: (defvar *proc*) (defun create-minecraft-proc...
What is a common-lisp analogue of python's argparse library for parsing command-line arguments?
I am currently trying to wrap my head around packages, systems & co. I now have read Packages, systems, modules, libraries - WTF? a few times, and I think I'm still having difficulties to get it right. If I simply want to split a Lisp source file into two files,...
Solving the Euler project problems I get that I need to make operations with the digits of a long number normally as a string. I work in linux, emacs, slime with sbcl. For example, to get the sum of the digits of this power 2¹⁰⁰⁰, I work this way, 1)...
Recently I find a run-program hang issue of sbcl 1.2.7 (32bits, linux). The code as following (progn (with-open-file (s "test.out" :direction :output :if-exists :supersede) (loop repeat 900 do (write-line (make-string 76 :initial-element #\x) s))) (run-program "/bin/bash" (list "-c" "cat test.out") :output :stream)) That is when the "cat test.out" produce many...
I am new to Lisp. Deletion of an item in a list by a function gets reflected outside the function but insertion doesn't. How can I do the same for insertion? For example (defun test (a b) (delete 1 a) (delete 5 b) (append '(5) b) (member '5 b)) (setq...
Is it possible to use lisp's macro to do string interpolation? For instance, can I make a macro like this: (defmacro test (a) `",a") So that (test abc) returns "abc" as a string? I could probably cheat by quoting it and turning that quote into a string, but that doesn't...
I have defined the following simple macro: (defmacro define-class (class-name) `(defclass ,class-name ()())) And now I want to use it in the following function: (defun create-data (mode) (define-class mode)) After compiling the last function I get the following message, the variable MODE is defined but never used. And when I...
I currently have a list of objects, each containing a certain attribute. I would like to get the element of the list with the min attribute value. Is there a concise way of doing this? The python equivalent would be something like: min(d, key=d.get) Is there a way of getting...
I want to have a 2D array in Lisp . But each row can have different number of elements(At max 5). So I thought of maintaining another single list to store the current sizes of each row, and update them whenever required. So, my code goes like this : (setq...
I am trying to make a reader macro that would convert @this into "this". This is what I currently have: (defun string-reader (stream char) (declare (ignore char)) (format nil "\"~a\"" (read-line stream t nil t)) ) (set-macro-character #\@ #'string-reader ) The problem is that this requires that I put a...
I have a Go program which cannot be rewritten in Common Lisp for efficiency reasons. How can I run it via Common Lisp? Options so far: 1. CFFI Using the foreign function interface seems to me like the "correct" way to do this. However, the research I did lead directly...