[cffi-devel] CFFI and wait (2)

[Lorenzo Villani]

Hi,

I'm trying to use CFFI in order to wrap execve (2). The wrapper also
uses fork (2) and wait (2). While I have absolutely no problems with
execve or fork I'm stumbling on a problem with wait.

Wait takes a pointer to an int to store child process' status. The
problem is: after the call to wait the value stored in the pointer is
the same as before the call.

I am using CFFI  0.10.5 and GNU CLISP 2.47 on Fedora 13.

The code follows:

(defcfun ("fork" c-fork) :int)
(defcfun ("execve" c-execve) :int (filename :string) (args :pointer) (env 
:pointer))
(defcfun ("wait" c-wait) :int (status :pointer))

(defun execute-program (path argv env)
  (let ((child-pid (c-fork)))
    (if (= child-pid -1)
        (error "Unable to create child process")
        (if (= child-pid 0)
            ;; Child
            (progn
              ;; Remember: (nth 0 argv) must be the full path to the executable.
              (let ((c-argv (foreign-alloc :string :initial-contents (append 
(list path) argv)
                                           :null-terminated-p t))
                    (c-env (foreign-alloc :string :initial-contents env 
:null-terminated-p t)))
                (c-execve path c-argv c-env)
                (foreign-free c-argv)
                (foreign-free c-env)))
            ;; Parent code
            (progn
              (let ((wait-status (foreign-alloc :int)))
                (c-wait wait-status)
                ;; This test condition is a reimplementation of __WIFEXITED 
macro defined at
                ;; /usr/include/bits/waitstatus.h
                (if (= 0 (logand (mem-ref wait-status :int) #x7f))
                    ;; This test condition is a reimplementation of 
__WEXITSTATUS macro defined at
                    ;; /usr/include/bits/waitstatus.h
                    (when (/= 0 (ash (logand (mem-ref wait-status :int) #xff00) 
-8))
                        (error "Child returned an error"))
                    (error "Failed to execute child process"))
                (foreign-free wait-status)))))))


-- 
Lorenzo Villani <lvill...@binaryhelix.net>

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