[Richard Suchenwirth] 2007-10-09 [Why does Tcl leak memory?] As explained on that page, Tk_Uids are created for [text] and [canvas] tags and never released. In a long running process, which on a [canvas] displays images and bounding boxes (polygons), I saw memory rise from 65MB to over 400 MB after some hours. Fixes as suggested by [dkf]:
   * reuse the displayed image: don't do each time
 $c create image 0 0 -image $im -anchor nw
 ...
 $c delete all
but create and display the image once, and reconfigure it with
 $im copy $im2 -shrink
   * reuse polygons by caching them in a global array g:
	if {![info exists g(of$n)]} {
	    set id [$w create poly $coords -fill {} -outline $color -tag "xx of$n"]
	    set g(of$n) $id
	} else {
	    set id $g(of$n)
	    $w coords $id $coords
	    $w itemconfigure $id -outline $color
	    $w raise $id
	}
and instead of deleting them, just move them "out of sight"
   foreach i [$w find withtag xx] {$w coords $i -100 -100 -99 -99}

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[George Peter Staplin] Dec 24, 2007 - Does anyone have an interest in replacing Tk_Uids with some sort of Tcl_Obj or Tcl_Obj-like structure with reference counts for the 8.6 release?  As I don't use the canvas widget much, the leaks don't bother me much, and I'm working on replacing Tk anyway with [NexTk].  Tk_Uids are definitely a design wart that should be fixed, if only for the legacy apps.  I don't think it would even require a TIP of any kind, because it's a serious bug/design fix.


[George Peter Staplin] Every color on a canvas results in a Tk_Uid, so if you use a lot of random colors, you'll see the memory usage increase for every unique color.

[KBK] My personal opinion is every use of '''Tk_Uid''' is a bug.  If someone had the energy to replace '''Tk_Uid''' with something else for colors, or fonts, or tags, or whatever, the changes could even be bundled in a patch release.  This is ''not'' a case where the TCT is obstructing the work; it's just a whale of a lot of work, and most of us have been concentrating on other things. It's also not a single project. Each use of '''Tk_Uid''' could be addressed separately.

John once told me that he considered '''Tk_Uid''' to be his single biggest mistake in the design of Tk.
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[Category performance]