[clisp-list] Re: about ffi:close-foreign-library

[Hoehle, Joerg-C. <Joe...@t-...>]

Hi,

xu yong writes:
>(close-foreign-library "user32.dll")
>
>I got message which says ---#<INVALID FOREIGN POINTER...

This is normal: CLISP protects you from calling functions of a closed =
library. I.e. a valid library pointer becomes invalid after closing the =
library. The other pointers (such as foreign function objects) derived =
from this pointer become invalid at the same time, and clisp will =
complain about calling such a function. Try it out!


> MessageBox function resides in user32.dll.
>it would be very in-efficient because,I guess,
>the lib loading and unloading happen every time the lib=20
>function is called.

I wouldn't bother about opening a library such central as user32.dll =
several times. It's very likely to be already in use by the system =
(possibly even CLISP itself?) and therefore need not be reloaded from =
disk.

You're right to raise the question of the lifetime of a library in an =
application. Should it
 o be opened each time a tiny function uses it (which happens rarely?)
 o be opened at some larger level (i.e. when a group of functions is =
entered)?
 o be opened when my application starts?
 o be opened when clisp starts?
However, you are the one to make choice and provide an answer.

One note, though: Executing (Loading) a def-call-out form at top-level =
will cause the library to be opened. Therefore I guess that most =
clisp-users will only ever use foreign functions that have been opened =
when their application (or the clisp image) was loaded.
I suppose only few users control exactly the lifetime of a foreign =
function object (or rather its associated library). CMO/DCOM would use =
this.

Regards,
	J=F6rg H=F6hle.