Re: the state of the concurrency branch

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 01 Sep 2013 18:49:19 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: lekktu@gmail.com, monnier@iro.umontreal.ca, emacs-devel@gnu.org
> 
> >   Breakpoint 3, wrong_type_argument (predicate=55041794, value=8580880)
> >       at data.c:189
> >   189       xsignal2 (Qwrong_type_argument, predicate, value);
> >   (gdb) bt
> >   #0  wrong_type_argument (predicate=55041794, value=8580880) at data.c:189
> >   #1  0x0115b7de in find_symbol_value (symbol=8580880) at data.c:1147
> >   #2  0x01179dab in unbind_for_thread_switch () at eval.c:3495
> >   #3  0x011eb163 in post_acquire_global_lock (self=0x1501cd0 <primary_thread>)
> >       at thread.c:65
> >   #4  0x011eb252 in acquire_global_lock (self=0x1501cd0 <primary_thread>)
> >       at thread.c:90
> >   #5  0x011ebd53 in yield_callback (ignore=0x0) at thread.c:601
> >   #6  0x01155e4d in flush_stack_call_func (func=0x11ebd30 <yield_callback>,
> >       arg=0x0) at alloc.c:4777
> >   #7  0x011ebd6f in Fthread_yield () at thread.c:608
> >   #8  0x011770ac in eval_sub (form=56246638) at eval.c:2240
> >   #9  0x01172da3 in Fprogn (body=56246646) at eval.c:480
> >   #10 0x01174591 in Fwhile (args=56246630) at eval.c:1010
> >   #11 0x01176db9 in eval_sub (form=56246606) at eval.c:2191
> >   #12 0x01172da3 in Fprogn (body=56246654) at eval.c:480
> >   #13 0x01176db9 in eval_sub (form=56246526) at eval.c:2191
> >   #14 0x011768d3 in Feval (form=56246526, lexical=54986778) at eval.c:2062
> >   #15 0x011784b1 in Ffuncall (nargs=3, args=0x82f448) at eval.c:2876
> >   #16 0x011bd36c in exec_byte_code (bytestr=20123049, vector=20123069,
> >       maxdepth=16, args_template=54986778, nargs=0, args=0x0) at bytecode.c:902
> >   #17 0x01179016 in funcall_lambda (fun=20123021, nargs=1, arg_vector=0x82f618)
> >       at eval.c:3107
> >   #18 0x011786c3 in Ffuncall (nargs=2, args=0x82f614) at eval.c:2922
> >   #19 0x011bd36c in exec_byte_code (bytestr=20123489, vector=20123509,
> >       maxdepth=12, args_template=54986778, nargs=0, args=0x0) at bytecode.c:902
> >   #20 0x01179016 in funcall_lambda (fun=20123461, nargs=1, arg_vector=0x82f824)
> >       at eval.c:3107
> >   #21 0x011786c3 in Ffuncall (nargs=2, args=0x82f820) at eval.c:2922
> >   #22 0x01171e00 in Fcall_interactively (function=56891970,
> >       record_flag=54986778, keys=55033861) at callint.c:836
> >   #23 0x011784e7 in Ffuncall (nargs=4, args=0x82fa0c) at eval.c:2880
> >   #24 0x011bd36c in exec_byte_code (bytestr=19816129, vector=19816149,
> >       maxdepth=52, args_template=4100, nargs=1, args=0x82fbf0) at bytecode.c:902
> >   #25 0x01178c6b in funcall_lambda (fun=19816109, nargs=1, arg_vector=0x82fbec)
> >       at eval.c:3041
> >   #26 0x011786c3 in Ffuncall (nargs=2, args=0x82fbe8) at eval.c:2922
> >   #27 0x01177f76 in call1 (fn=55032674, arg1=56891970) at eval.c:2672
> >   #28 0x010e2f06 in command_loop_1 () at keyboard.c:1560
> >   #29 0x011750c4 in internal_condition_case (bfun=0x10e26a5 <command_loop_1>,
> >       handlers=55041242, hfun=0x10e1f31 <cmd_error>) at eval.c:1359
> >   #30 0x010e2374 in command_loop_2 (ignore=54986778) at keyboard.c:1161
> >   #31 0x01174938 in internal_catch (tag=55031122,
> >       func=0x10e2351 <command_loop_2>, arg=54986778) at eval.c:1133
> >   #32 0x010e232c in command_loop () at keyboard.c:1140
> >   #33 0x010e1ae3 in recursive_edit_1 () at keyboard.c:779
> >   #34 0x010e1c97 in Frecursive_edit () at keyboard.c:843
> >   #35 0x010dfee0 in main (argc=2, argv=0xa42880) at emacs.c:1564
> > 
> >   Lisp Backtrace:
> >   "thread-yield" (0x4e7fb08)
> >   "let" (0x4e7fd58)
> >   "threads-test-thread2" (0x3516f5c)
> >   (gdb) up 2
> >   #2  0x01179dab in unbind_for_thread_switch () at eval.c:3495
> >   3495              bind->let.saved_value = find_symbol_value (specpdl_symbol (bin
> >   d));
> >   (gdb) p bind
> >   $2 = (union specbinding *) 0x34dac64
> >   (gdb) p bind->let
> >   $3 = {
> >     kind = 72,  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> >     symbol = 8580880,
> >     old_value = 54986778,
> >     where = 1,
> >     saved_value = -1
> >   }
> > 
> > Isn't 72 a value that should never happen in bind->kind?  Any idea how
> > this could happen?
> 
> This part still happens sometimes, but at least now Emacs signals an
> error and doesn't crash.

Here's a recipe for reproducing this:

 emacs -Q

Insert this:

   (defvar threads-test-binding nil)

   (defun threads-test-thread2 ()
     (let ((threads-test-binding 23))
       (thread-yield))
     (setq threads-test-global 23))

   (progn
     (setq threads-test-global nil)
     (make-thread #'threads-test-thread2)
     (while (not threads-test-global)
       (thread-yield))
     (and (not threads-test-binding)
	  threads-test-global))

Mark the defvar and the defun, type "M-x eval-region RET".  Go to the
last closing parent of progn, type "C-x C-e", get the expected result
23.  All's well till now.

Go to the right paren of the defvar, type "C-x C-e" there.  Now go
again to the rightmost paren of progn, type "C-x C-e", and get the
wrong-type-argument error.