(gdb) info threads
  Id   Target Id         Frame 
  2    Thread 0x7f399861a700 (LWP 18371) "ruby-timer-thr" 0x00007f39972d4c5d in poll () at ../sysdeps/unix/syscall-template.S:81
* 1    Thread 0x7f399860f740 (LWP 18369) "ruby" 0x00007f39972b31d7 in sched_yield () at ../sysdeps/unix/syscall-template.S:81

(gdb) backtrace
#0  0x00007f39972b31d7 in sched_yield () at ../sysdeps/unix/syscall-template.S:81
#1  0x00007f39982cf6f5 in native_stop_timer_thread () at thread_pthread.c:1664
#2  rb_thread_stop_timer_thread () at thread.c:3929
#3  0x00007f39981d63e6 in before_exec_non_async_signal_safe () at process.c:1175
#4  before_exec () at process.c:1181
#5  rb_f_exec (argc=<optimised out>, argv=<optimised out>) at process.c:2576
#6  0x00007f39982a3706 in vm_call_cfunc_with_frame (ci=<optimised out>, cc=<optimised out>, calling=<optimised out>, reg_cfp=0x7f399860d5d0, th=0x7f39988dc5d0) at vm_insnhelper.c:1642
#7  vm_call_cfunc (th=0x7f39988dc5d0, reg_cfp=0x7f399860d5d0, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:1737
#8  0x00007f39982b1683 in vm_call_method (th=0x7f39988dc5d0, cfp=0x7f399860d5d0, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:2176
#9  0x00007f39982abf69 in vm_exec_core (th=th@entry=0x7f39988dc5d0, initial=initial@entry=0) at insns.def:994
#10 0x00007f39982afcd1 in vm_exec (th=0x7f39988dc5d0) at vm.c:1650
#11 0x00007f39982b0473 in invoke_block (th=th@entry=0x7f39988dc5d0, iseq=iseq@entry=0x7f39996aa890, self=self@entry=139885363620920, cref=cref@entry=0x0, type=<optimised out>, opt_pc=0, 
    block=0x7f399dc34310) at vm.c:921
#12 0x00007f39982b081e in invoke_block_from_c_0 (th=0x7f39988dc5d0, block=0x7f399dc34310, self=139885363620920, argc=<optimised out>, argv=<optimised out>, blockptr=<optimised out>, cref=0x0, 
    splattable=0) at vm.c:971
#13 0x00007f39982b08f8 in invoke_block_from_c_unsplattable (cref=0x0, blockptr=0x0, argv=0x7ffca73d1710, argc=1, self=139885363620920, block=0x7f399dc34310, th=0x7f39988dc5d0) at vm.c:996
#14 vm_invoke_proc (th=th@entry=0x7f39988dc5d0, proc=proc@entry=0x7f399dc34310, self=139885363620920, argc=argc@entry=1, argv=0x7ffca73d1710, blockptr=0x0) at vm.c:1044
#15 0x00007f39982b10b7 in rb_vm_invoke_proc (blockptr=<optimised out>, argv=<optimised out>, argc=1, proc=0x7f399dc34310, th=0x7f39988dc5d0) at vm.c:1072
#16 vm_call_opt_call (th=0x7f39988dc5d0, cfp=0x7f399860d610, calling=0x7ffca73d18a0, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:1868
#17 0x00007f39982b1683 in vm_call_method (th=0x7f39988dc5d0, cfp=0x7f399860d610, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:2176
#18 0x00007f39982abf69 in vm_exec_core (th=th@entry=0x7f39988dc5d0, initial=initial@entry=0) at insns.def:994
#19 0x00007f39982afcd1 in vm_exec (th=0x7f39988dc5d0) at vm.c:1650
#20 0x00007f39982b0473 in invoke_block (th=th@entry=0x7f39988dc5d0, iseq=iseq@entry=0x7f39996a9dc8, self=self@entry=139885363620920, cref=cref@entry=0x0, type=<optimised out>, opt_pc=0, 
    block=<optimised out>) at vm.c:921
#21 0x00007f39982b2361 in invoke_block_from_c_0 (argc=<optimised out>, blockptr=<optimised out>, cref=<optimised out>, splattable=<optimised out>, argv=<optimised out>, self=<optimised out>, 
    block=<optimised out>, th=<optimised out>) at vm.c:971
#22 invoke_block_from_c_splattable (cref=<optimised out>, blockptr=<optimised out>, argv=<optimised out>, argc=<optimised out>, self=<optimised out>, block=<optimised out>, th=<optimised out>)
    at vm.c:988
#23 vm_yield (argc=<optimised out>, argv=<optimised out>, th=<optimised out>) at vm.c:1023
#24 rb_yield_0 (argv=<optimised out>, argc=<optimised out>) at vm_eval.c:1013
#25 rb_yield_1 (val=<optimised out>) at vm_eval.c:1019
#26 rb_yield (val=val@entry=52) at vm_eval.c:1029
#27 0x00007f399815c431 in rb_protect (proc=0x7f39982b20c0 <rb_yield>, data=data@entry=52, state=state@entry=0x7ffca73d206c) at eval.c:894
#28 0x00007f39981ce189 in rb_f_fork (obj=<optimised out>) at process.c:3721
#29 0x00007f39982a3706 in vm_call_cfunc_with_frame (ci=<optimised out>, cc=<optimised out>, calling=<optimised out>, reg_cfp=0x7f399860d690, th=0x7f39988dc5d0) at vm_insnhelper.c:1642
#30 vm_call_cfunc (th=0x7f39988dc5d0, reg_cfp=0x7f399860d690, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:1737
#31 0x00007f39982abe9e in vm_exec_core (th=th@entry=0x7f39988dc5d0, initial=initial@entry=0) at insns.def:963
#32 0x00007f39982afcd1 in vm_exec (th=0x7f39988dc5d0) at vm.c:1650
#33 0x00007f39982b0473 in invoke_block (th=th@entry=0x7f39988dc5d0, iseq=iseq@entry=0x7f399a0418b8, self=self@entry=139885373819120, cref=cref@entry=0x0, type=<optimised out>, opt_pc=0, 
    block=<optimised out>) at vm.c:921
#34 0x00007f39982b2719 in invoke_block_from_c_0 (argc=1, blockptr=0x0, cref=0x0, splattable=1, argv=0x7ffca73d2668, self=139885373819120, block=0x7f399860d830, th=0x7f39988dc5d0) at vm.c:971
#35 invoke_block_from_c_splattable (cref=0x0, blockptr=0x0, argv=0x7ffca73d2668, argc=1, self=139885373819120, block=<optimised out>, th=0x7f39988dc5d0) at vm.c:988
#36 vm_yield (argc=1, argv=0x7ffca73d2668, th=0x7f39988dc5d0) at vm.c:1023
#37 rb_yield_0 (argv=0x7ffca73d2668, argc=1) at vm_eval.c:1013
#38 catch_i (tag=<optimised out>, data=data@entry=0) at vm_eval.c:1921
#39 0x00007f39982a5f5e in rb_catch_protect (t=<optimised out>, func=func@entry=0x7f39982b2580 <catch_i>, data=data@entry=0, stateptr=stateptr@entry=0x7ffca73d2840) at vm_eval.c:2021
#40 0x00007f39982a60e1 in rb_catch_obj (data=0, func=0x7f39982b2580 <catch_i>, t=<optimised out>) at vm_eval.c:2000
#41 rb_f_catch (argc=<optimised out>, argv=<optimised out>) at vm_eval.c:1986
#42 0x00007f39982a3706 in vm_call_cfunc_with_frame (ci=<optimised out>, cc=<optimised out>, calling=<optimised out>, reg_cfp=0x7f399860d810, th=0x7f39988dc5d0) at vm_insnhelper.c:1642
#43 vm_call_cfunc (th=0x7f39988dc5d0, reg_cfp=0x7f399860d810, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:1737
#44 0x00007f39982abe9e in vm_exec_core (th=th@entry=0x7f39988dc5d0, initial=initial@entry=0) at insns.def:963
#45 0x00007f39982afcd1 in vm_exec (th=0x7f39988dc5d0) at vm.c:1650
#46 0x00007f39982b0473 in invoke_block (th=th@entry=0x7f39988dc5d0, iseq=iseq@entry=0x7f399a041250, self=self@entry=139885373819200, cref=cref@entry=0x0, type=<optimised out>, opt_pc=0, 
    block=0x7f399dff42f0) at vm.c:921
#47 0x00007f39982b081e in invoke_block_from_c_0 (th=0x7f39988dc5d0, block=0x7f399dff42f0, self=139885373819200, argc=<optimised out>, argv=<optimised out>, blockptr=<optimised out>, cref=0x0, 
    splattable=0) at vm.c:971
#48 0x00007f39982b08f8 in invoke_block_from_c_unsplattable (cref=0x0, blockptr=0x0, argv=0x7ffca73d3060, argc=1, self=139885373819200, block=0x7f399dff42f0, th=0x7f39988dc5d0) at vm.c:996
#49 vm_invoke_proc (th=th@entry=0x7f39988dc5d0, proc=proc@entry=0x7f399dff42f0, self=139885373819200, argc=argc@entry=1, argv=0x7ffca73d3060, blockptr=0x0) at vm.c:1044
#50 0x00007f39982b10b7 in rb_vm_invoke_proc (blockptr=<optimised out>, argv=<optimised out>, argc=1, proc=0x7f399dff42f0, th=0x7f39988dc5d0) at vm.c:1072
#51 vm_call_opt_call (th=0x7f39988dc5d0, cfp=0x7f399860dc90, calling=0x7ffca73d31f0, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:1868
#52 0x00007f39982b1683 in vm_call_method (th=0x7f39988dc5d0, cfp=0x7f399860dc90, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:2176
#53 0x00007f39982abf69 in vm_exec_core (th=th@entry=0x7f39988dc5d0, initial=initial@entry=0) at insns.def:994
#54 0x00007f39982afcd1 in vm_exec (th=0x7f39988dc5d0) at vm.c:1650
#55 0x00007f39982b0473 in invoke_block (th=th@entry=0x7f39988dc5d0, iseq=iseq@entry=0x7f3999ef7d90, self=self@entry=139885372464520, cref=cref@entry=0x0, type=<optimised out>, opt_pc=0, 
    block=<optimised out>) at vm.c:921
#56 0x00007f39982b2361 in invoke_block_from_c_0 (argc=<optimised out>, blockptr=<optimised out>, cref=<optimised out>, splattable=<optimised out>, argv=<optimised out>, self=<optimised out>, 
---Type <return> to continue, or q <return> to quit---
    block=<optimised out>, th=<optimised out>) at vm.c:971
#57 invoke_block_from_c_splattable (cref=<optimised out>, blockptr=<optimised out>, argv=<optimised out>, argc=<optimised out>, self=<optimised out>, block=<optimised out>, th=<optimised out>)
    at vm.c:988
#58 vm_yield (argc=<optimised out>, argv=<optimised out>, th=<optimised out>) at vm.c:1023
#59 rb_yield_0 (argv=<optimised out>, argc=<optimised out>) at vm_eval.c:1013
#60 rb_yield_1 (val=<optimised out>) at vm_eval.c:1019
#61 rb_yield (val=<optimised out>) at vm_eval.c:1029
#62 0x00007f39982d6ddd in rb_ary_each (ary=139885435792200) at array.c:1815
#63 0x00007f39982a3706 in vm_call_cfunc_with_frame (ci=<optimised out>, cc=<optimised out>, calling=<optimised out>, reg_cfp=0x7f399860de90, th=0x7f39988dc5d0) at vm_insnhelper.c:1642
#64 vm_call_cfunc (th=0x7f39988dc5d0, reg_cfp=0x7f399860de90, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:1737
#65 0x00007f39982abe9e in vm_exec_core (th=th@entry=0x7f39988dc5d0, initial=initial@entry=0) at insns.def:963
#66 0x00007f39982afcd1 in vm_exec (th=0x7f39988dc5d0) at vm.c:1650
#67 0x00007f39982b0473 in invoke_block (th=th@entry=0x7f39988dc5d0, iseq=iseq@entry=0x7f399a47bde8, self=self@entry=139885395942280, cref=cref@entry=0x0, type=<optimised out>, opt_pc=0, 
    block=<optimised out>) at vm.c:921
#68 0x00007f39982b28b1 in invoke_block_from_c_0 (argc=0, argv=0x0, blockptr=0x0, cref=0x0, splattable=1, self=139885395942280, block=0x7f399860df70, th=0x7f39988dc5d0) at vm.c:971
#69 invoke_block_from_c_splattable (cref=0x0, blockptr=0x0, argv=0x0, argc=0, self=139885395942280, block=<optimised out>, th=0x7f39988dc5d0) at vm.c:988
#70 vm_yield (argc=0, argv=0x0, th=0x7f39988dc5d0) at vm.c:1023
#71 rb_yield_0 (argv=0x0, argc=0) at vm_eval.c:1013
#72 loop_i () at vm_eval.c:1090
#73 0x00007f399815c172 in rb_rescue2 (b_proc=0x7f39982b2740 <loop_i>, data1=0, r_proc=0x7f399829ed00 <loop_stop>, data2=0) at eval.c:826
#74 0x00007f39982a3706 in vm_call_cfunc_with_frame (ci=<optimised out>, cc=<optimised out>, calling=<optimised out>, reg_cfp=0x7f399860df50, th=0x7f39988dc5d0) at vm_insnhelper.c:1642
#75 vm_call_cfunc (th=0x7f39988dc5d0, reg_cfp=0x7f399860df50, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:1737
#76 0x00007f39982b1683 in vm_call_method (th=0x7f39988dc5d0, cfp=0x7f399860df50, calling=<optimised out>, ci=<optimised out>, cc=<optimised out>) at vm_insnhelper.c:2176
#77 0x00007f39982abe9e in vm_exec_core (th=th@entry=0x7f39988dc5d0, initial=initial@entry=0) at insns.def:963
#78 0x00007f39982afcd1 in vm_exec (th=0x7f39988dc5d0) at vm.c:1650
#79 0x00007f39982b9cee in rb_iseq_eval_main (iseq=iseq@entry=0x7f3998e42e78) at vm.c:1893
#80 0x00007f3998157c24 in ruby_exec_internal (n=0x7f3998e42e78) at eval.c:245
#81 0x00007f399815b6ed in ruby_exec_node (n=0x7f3998e42e78) at eval.c:310
#82 ruby_run_node (n=<optimised out>) at eval.c:302
#83 0x00007f399815788b in main (argc=2, argv=0x7ffca73d4888) at main.c:36