: '''unload''' ?''switches''? ''fileName'' ?''packageName''? ?''interp''?
http://www.purl.org/tcl/home/man/tcl8.5/TclCmd/unload.htm
New command in Tcl 8.5 that can remove functionality imported via [load] (in some cases). See TIP 100 [http://tip.tcl.tk/100] from [George Petasis] for where it came from.
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Hints for extension authors who want to have an unloadable extension:
* Be prepared for extra work when using a custom Tcl_Object type with non-NULL freeProc
* Be extremly careful in your use of TSD ([Thread] Specific Data)
* Be prepared for trouble if your extension involves the [VFS] layer
* ...
<<discussion>>
[JH]: Note that TIP 239 [http://tip.tcl.tk/239] will likely change the '''unload''' command before 8.5 is final.
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[RS] 2007-10-19: Here's a simple working example of building a [DLL] with [tcltcc], [load]ing, calling, [unload]ing it:
#!/usr/bin/env tclsh85
package require tcc 0.2
set d [tcc::dll]
$d ccode {static int fib(int n) {return n <= 2? 1 : fib(n-1) + fib(n-2);}}
$d cproc fiboy {int n} int {return fib(n);}
$d cproc hello {} char* {return "world";}
$d ccode {
DLL_EXPORT int Fiboy_Unload(Tcl_Interp* interp, int flags) {
Tcl_DeleteCommand(interp,"fiboy");
Tcl_DeleteCommand(interp,"hello");
printf("bye, world! flags: %d\n", flags);
return TCL_OK;
}
}
$d write -name fiboy -code {Tcl_Eval(interp,"puts {hello Fiboy!}");}
load fiboy[info sharedlibextension]
puts "[fiboy 20] [hello]"
unload fiboy[info sharedlibextension]
catch {puts "[fiboy 20] [hello]"} res
puts $res
which produces
hello Fiboy!
6765 world
bye, world! flags: 2
invalid command name "fiboy"
Only if a _Unload function is provided (_SafeUnload for safe interps) will [unload] succeed.
Be careful to delete all commands the DLL created, otherwise get a seg fault.
Another observation: on Win XP at least (ActiveTcl 8.5b1), the load/unload order matters. Given foo.dll and bar.dll, the sequence
load foo; load bar; unload foo; unload bar
segfaults, while
load foo; load bar; unload bar; unload foo
succeeds. Is that so? The man page does not mention such a condition. Example:
$ tclsh85
% load test.dll
DLL loaded
% load fiboy.dll
hello Fiboy!
% unload test.dll
DLL unloaded
% unload fiboy.dll
---------------------------------------- seg fault popup --------------------------
/etc/dk $
Then again, on [Windows 95], 8.5b1 built myself with mingw, I can unload a pair of DLLs in any of the two orders... Funny.
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[kbk] would like to revert [TIP]
[http://www.tcl.tk/cgi-bin/tct/tip/100.html%|%#100] because it doesn't really
work. There are too many calls that retain pointers into the loaded library,
e.g., `Tcl_RegisterObjType`, which can't be undone. (1)
** References **
1: [kbk], [Tcl Chatroom], 2014-11-24
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