Tk Source Code

Running this on ubuntu and other linux systems causes several types of failures as shown in the log below.

It does not crash every time, and so was run 1000 times in a bash script. It can also fail simply by doing a package require Tk, but far less frequently.

################
package require Thread

set script {
    proc putz {arg color } {
        if { ![info exist ::t_putz] } {
            set ::t_putz 1
            package require Tk
            
            text .ttttt
            pack .ttttt -side left -fill both -expand 1
            
            .ttttt tag configure normal             -foreground black
            .ttttt tag configure red                -foreground red -font {courier 10}
        }
        catch {
            .ttttt insert end $arg\n $color
            .ttttt see end
            update
        }
        
    }
    for {set n 0} {$n < 6 } {incr n} {
        putz "Testing $n"   normal
        putz "Testing $n"   red
    }
    thread::wait
    
}
proc wait { ms } {              
    after $ms set ::__sleep__tmp 1
    vwait ::__sleep__tmp
}
for {set n 0} {$n < 10 } {incr n} {
	thread::create $script
	wait 400
}


after 20000 exit
wait 2500
puts donex4 
exit
#####################

On windows this never fails.

Running this over and over using a bash script produced lines like this:


Xft: locking error too many file unlocks
Xft: locking error too many file unlocks
runalot.sh: line 19: 53611 Segmentation fault /usr/bin/tclsh crash.tcl
Xlib: charsets ISO8859-3:GR and ISO8859-3:GR have the same CT sequence
Xlib: charsets ISO8859-13:GR and ISO8859-13:GR have the same CT sequence

[xcb] Unknown request in queue while appending request
[xcb] Most likely this is a multi-threaded client and XInitThreads has
not been called
[xcb] Aborting, sorry about that.

tclsh: ../../src/xcb_io.c:151: append_pending_request: Assertion
`!xcb_xlib_unknown_req_pending' failed.
runalot.sh: line 24: 53671 Aborted /usr/bin/tclsh crash.tcl
runalot.sh: line 26: 53695 Segmentation fault /usr/bin/tclsh crash.tcl
runalot.sh: line 29: 53734 Segmentation fault /usr/bin/tclsh crash.tcl

A follow-up is the ongoing work in libXft regarding these threads

https://gitlab.freedesktop.org/xorg/lib/libxft/-/issues/4

https://gitlab.freedesktop.org/xorg/lib/libxft/-/issues/12

> Now, the usual fine question is, does it need TIP'ery ...

How about TIP #364? If we support building with --enable-threads, it should work, shouldn't it?

@chw, Thanks for you thorough analysis! diff applied now.

After playing with a modified copy of libXft which supports rendering
truetype color fonts (Noto Color Emoji for example) and adapting it as
a statically linked component in vanillawish (see the check-ins following

  https://www.androwish.org/home/info/395899767e37879a

) my final conclusion on libXft: no thread support at all (and the success
story is, that vanillawish renders color emojis. Progress!)

Thus it is crucial to serialize libXft calls as outlined in my initial patch
in order to make an X11/Xft based Tk working under all circumstances.

Now, the usual fine question is, does it need TIP'ery, or would some Tk
god use that diff, review it, and finally commit it?

I'm the submitter here, and I only really work on windows. I do however, test my code on linux if I intend to share, and for that I have a ubunutu in a vm, but I don't know enough linux to do anything more than just run the program. 

What I can add is that I can get it to fail more often if I remove the wait 400 between thread creates, and I can even reduce the script then to just a package require Tk (plus the thread::wait). 

I've run it in so many different ways I am forgetting just which ones I've done. Sometimes It will only crash 1 in a 1000 tries. It seems very much a timing problem, since with only 1 thread I don't think it crashes at all, but I can't be absolutely certain. And the crashes are all different, except that many do have something to do with malloc. I ran it with valgrind the memory leak detector and it reported errors, but I can't really say what the output was saying.

Here's the simplified test case from the OP from
https://groups.google.com/g/comp.lang.tcl/c/c1JEQQcEO_s

---snip---

package require Thread

set script {
    package require Tk
    thread::wait
}
proc wait { ms } {
    after $ms set ::__sleep__tmp 1
    vwait ::__sleep__tmp
}
for {set n 0} {$n < 5 } {incr n} {
    thread::create $script
}

after 20000 exit
wait 2500
puts donex4a
exit

Meanwhile, I believe, that Xft is not thread safe w.r.t. its management
of freetype font files (did some source code reading). Please try the
attached patch for core-8-6-branch tkUnixRFont.c which does some brute
force locking using a single mutex. Costs performance but hopefully
fixes these crashes.

What about running the same test with a Tk build using --disable-xft to
narrow the problem down? To see if Xft is the culprit.