I encountered the same problem. After installing the cwidget and aptitude debug packages, I got the following stack traces:
(gdb) thread apply all bt Thread 4 (Thread 0x7f3d3c885700 (LWP 8565)): #0 pthread_cond_timedwait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S:225 #1 0x00007f3d410528f4 in cwidget::threads::condition::timed_wait<cwidget::threads::mutex::lock> (until=..., l=<synthetic pointer>, this=0x7f3d412f8260 <cwidget::toplevel::timeout_thread::instance+96>) at ../../src/cwidget/generic/threads/threads.h:554 #2 cwidget::toplevel::timeout_thread::operator() (this=0x7f3d412f8200 <cwidget::toplevel::timeout_thread::instance>) at toplevel.cc:795 #3 cwidget::threads::bootstrap_proxy<cwidget::toplevel::timeout_thread>::operator() (this=<synthetic pointer>) at ../../src/cwidget/generic/threads/threads.h:1008 #4 cwidget::threads::thread::bootstrap<cwidget::threads::bootstrap_proxy<cwidget::toplevel::timeout_thread> > (p=<optimized out>) at ../../src/cwidget/generic/threads/threads.h:117 #5 0x00007f3d400aa464 in start_thread (arg=0x7f3d3c885700) at pthread_create.c:333 #6 0x00007f3d3f54c30d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109 Thread 3 (Thread 0x7f3d3d086700 (LWP 8564)): #0 do_sigwait (set=<optimized out>, set@entry=0x7f3d3d085e20, sig=sig@entry=0x7f3d3d085d9c) at ../sysdeps/unix/sysv/linux/sigwait.c:64 #1 0x00007f3d400b3cdd in __sigwait (set=set@entry=0x7f3d3d085e20, sig=sig@entry=0x7f3d3d085d9c) at ../sysdeps/unix/sysv/linux/sigwait.c:96 #2 0x00007f3d41049d13 in cwidget::toplevel::signal_thread::operator() (this=<optimized out>) at toplevel.cc:588 #3 0x00007f3d4105271e in cwidget::threads::thread::bootstrap<cwidget::toplevel::signal_thread> (p=<optimized out>) at ../../src/cwidget/generic/threads/threads.h:117 #4 0x00007f3d400aa464 in start_thread (arg=0x7f3d3d086700) at pthread_create.c:333 #5 0x00007f3d3f54c30d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109 Thread 2 (Thread 0x7f3d3d887700 (LWP 8563)): #0 0x00007f3d3f544f73 in select () at ../sysdeps/unix/syscall-template.S:84 #1 0x00007f3d41052a8f in cwidget::toplevel::input_thread::operator() (this=this@entry=0x7f3d412f8301 <cwidget::toplevel::input_thread::instance>) at toplevel.cc:484 #2 0x00007f3d41052bc1 in cwidget::threads::bootstrap_proxy<cwidget::toplevel::input_thread>::operator() (this=<synthetic pointer>) at ../../src/cwidget/generic/threads/threads.h:1008 #3 cwidget::threads::thread::bootstrap<cwidget::threads::bootstrap_proxy<cwidget::toplevel::input_thread> > (p=<optimized out>) at ../../src/cwidget/generic/threads/threads.h:117 #4 0x00007f3d400aa464 in start_thread (arg=0x7f3d3d887700) at pthread_create.c:333 #5 0x00007f3d3f54c30d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109 Thread 1 (Thread 0x7f3d41edb780 (LWP 8562)): #0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185 #1 0x00007f3d4104a663 in cwidget::threads::condition::wait<cwidget::threads::mutex::lock> (l=<synthetic pointer>, this=0x7f3d412f85d0 <cwidget::toplevel::eventq+80>) at ../../src/cwidget/generic/threads/threads.h:508 #2 cwidget::threads::condition::wait<cwidget::threads::mutex::lock, cwidget::threads::event_queue<cwidget::toplevel::event*>::not_empty> (p=..., l=<synthetic pointer>, this=0x7f3d412f85d0 <cwidget::toplevel::eventq+80>) at ../../src/cwidget/generic/threads/threads.h:527 #3 cwidget::threads::event_queue<cwidget::toplevel::event*>::get (this=0x7f3d412f8580 <cwidget::toplevel::eventq>) at ../../src/cwidget/generic/threads/event_queue.h:94 #4 cwidget::toplevel::mainloop (synch=synch@entry=0) at toplevel.cc:1167 #5 0x000055c03a9a689a in ui_main () at ../../src/ui.cc:3134 #6 0x000055c03a8c9825 in main (argc=<optimized out>, argv=<optimized out>) at ../../src/main.cc:1427
