Tk Source Code

When an existing selection handler for a window is replaced by a different command, the original command is still invoked when an external program obtains the selection. It only works correctly when the original handler is removed before setting the new one.

The attached selection.tcl script shows the problem. Tcl/Tk will internally find the replaced command. But when pasting externally using the middle mouse button, it still reports "Using selproc version 1" instead of "Using selproc version 2".

See also [2443069fff].

I suppose you could call it a memory leak, although you could reclaim the lost memory by invoking Tk_DeleteSelHandler() enough times.

As mentioned, my proposed fix was based on the assumption that setting, updating, or clearing a STRING handler would do the same for UTF8_STRING. I don't think it's worth the effort to be extremely clever about it. That would probably just confuse users.

...install a new handler every time, without deleting any existing one

Isn't this a memory leak? Maybe I don't understand what you mean.

I have added more tests checking the behavior you have described on the tcl-core list. Test select-14.2.2 currently fails, because the current implementation always replaces a potentially existing handle for the UTF8-STRING target. We have to decide which one between the test and the implementation is correct.

If my interpretation of the code is correct, the change you proposed will install a new handler every time, without deleting any existing one. It will also still effectively replace any UTF8_STRING handler the user may have installed when a STRING handler is installed or updated.

If we accept that behavior, and we agree that the size for UTF8_STRING should always be 8 instead of 32, Tk_CreateSelHandler() can be simplified while fixing the problem at the same time. The function is basically doing the same thing twice: Once for the requested target, then again for UTF8_STRING if the requested target was STRING. That second part could simply be done by invoking itself once more.

I created checkin [793effdb8e] with the change described above.

The fix proposal I made in the discussion below at least lets the new test select-14.2 (added in [10121ce3]) pass whereas it failed previously. Moreoved no test from select.test test newly fails.

Discussed on the tcl-core mailing list.