Hi,
I have seen a few posts saying its bad/illegal to do GUI calls from threads
other than main (where the widgets were created).
A few weeks ago I inherited some code that uses FLTK 1.1.7 and does exactly
that. I'm running on an ARM under linux.
Besides main, there are a couple other threads that call show, hide, and label.
Probably others too, but those are the most common.
It is a mostly working product but there are a few of outstanding problems:
- widgets that don't get redrawn unless another cycle of hide() and show() is
called.
- occasional garbage label text (that is also fixed with a hide/show cycle).
- a seemingly random segmentation fault that (from gdb's stack trace) always
comes from malloc. I've started using environment variable MALLOC_CHECK_=2
which causes malloc to do heap consistency checks but that didn't buy me much
-- its still in a malloc call which presumably is sometime after the actual
damage is done. The only trace I have captured in this scenario was during the
font loading which appears to be in a non-main thread. That's what got me
thinking about thread safety, and this posting.
Program terminated with signal 6, Aborted.
#0 0x40171c40 in kill () from /lib/libc.so.0
#1 0x4001701c in pthread_kill () from /lib/libpthread.so.0
#2 0x400175d0 in raise () from /lib/libpthread.so.0
#3 0x4016be44 in abort () from /lib/libc.so.0
#4 0x4016e380 in __malloc_consolidate () from /lib/libc.so.0
#5 0x4016d5f8 in malloc () from /lib/libc.so.0
#6 0x4004ea98 in XQueryFont (dpy=0x180588, font_ID=0) at QueryFont.c:58
#7 0x4004e8c8 in XLoadQueryFont (dpy=0x180588, name=0x9cac4 "fixed")
at QueryFont.c:8
#8 0x00082614 in Fl_FontSize::Fl_FontSize ()
#9 0x000828a8 in fl_font ()
#10 0x40025600 in __pthread_manager_thread () from /lib/libpthread.so.0
Backtrace stopped: frame did not save the PC
(gdb)
Today I put a mutex in each customized widget (and subclassed Fl_Window and
Fl_Box too, for this purpose) so I could ensure that the widget modifiers were
not happening at the same time as draw() calls. I don't have that protection
totally in place yet. But then I saw Lock() and Unlock() and am wondering if
those will do the same thing. And then I saw the forum posts that made me
think:
Do I need to re-architect the whole thing?
Any comments would be appreciated.
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