summaryrefslogtreecommitdiff
path: root/jni/ruby/lib/debug.rb
blob: fcbf849f0da3151221ad01c1fc60ae4fba130eab (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
# Copyright (C) 2000  Network Applied Communication Laboratory, Inc.
# Copyright (C) 2000  Information-technology Promotion Agency, Japan
# Copyright (C) 2000-2003  NAKAMURA, Hiroshi  <nahi@ruby-lang.org>

require 'continuation'

if $SAFE > 0
  STDERR.print "-r debug.rb is not available in safe mode\n"
  exit 1
end

require 'tracer'
require 'pp'

class Tracer # :nodoc:
  def Tracer.trace_func(*vars)
    Single.trace_func(*vars)
  end
end

SCRIPT_LINES__ = {} unless defined? SCRIPT_LINES__ # :nodoc:

##
# This library provides debugging functionality to Ruby.
#
# To add a debugger to your code, start by requiring +debug+ in your
# program:
#
#   def say(word)
#     require 'debug'
#     puts word
#   end
#
# This will cause Ruby to interrupt execution and show a prompt when the +say+
# method is run.
#
# Once you're inside the prompt, you can start debugging your program.
#
#   (rdb:1) p word
#   "hello"
#
# == Getting help
#
# You can get help at any time by pressing +h+.
#
#   (rdb:1) h
#   Debugger help v.-0.002b
#   Commands
#     b[reak] [file:|class:]<line|method>
#     b[reak] [class.]<line|method>
#                                set breakpoint to some position
#     wat[ch] <expression>       set watchpoint to some expression
#     cat[ch] (<exception>|off)  set catchpoint to an exception
#     b[reak]                    list breakpoints
#     cat[ch]                    show catchpoint
#     del[ete][ nnn]             delete some or all breakpoints
#     disp[lay] <expression>     add expression into display expression list
#     undisp[lay][ nnn]          delete one particular or all display expressions
#     c[ont]                     run until program ends or hit breakpoint
#     s[tep][ nnn]               step (into methods) one line or till line nnn
#     n[ext][ nnn]               go over one line or till line nnn
#     w[here]                    display frames
#     f[rame]                    alias for where
#     l[ist][ (-|nn-mm)]         list program, - lists backwards
#                                nn-mm lists given lines
#     up[ nn]                    move to higher frame
#     down[ nn]                  move to lower frame
#     fin[ish]                   return to outer frame
#     tr[ace] (on|off)           set trace mode of current thread
#     tr[ace] (on|off) all       set trace mode of all threads
#     q[uit]                     exit from debugger
#     v[ar] g[lobal]             show global variables
#     v[ar] l[ocal]              show local variables
#     v[ar] i[nstance] <object>  show instance variables of object
#     v[ar] c[onst] <object>     show constants of object
#     m[ethod] i[nstance] <obj>  show methods of object
#     m[ethod] <class|module>    show instance methods of class or module
#     th[read] l[ist]            list all threads
#     th[read] c[ur[rent]]       show current thread
#     th[read] [sw[itch]] <nnn>  switch thread context to nnn
#     th[read] stop <nnn>        stop thread nnn
#     th[read] resume <nnn>      resume thread nnn
#     p expression               evaluate expression and print its value
#     h[elp]                     print this help
#     <everything else>          evaluate
#
# == Usage
#
# The following is a list of common functionalities that the debugger
# provides.
#
# === Navigating through your code
#
# In general, a debugger is used to find bugs in your program, which
# often means pausing execution and inspecting variables at some point
# in time.
#
# Let's look at an example:
#
#   def my_method(foo)
#     require 'debug'
#     foo = get_foo if foo.nil?
#     raise if foo.nil?
#   end
#
# When you run this program, the debugger will kick in just before the
# +foo+ assignment.
#
#   (rdb:1) p foo
#   nil
#
# In this example, it'd be interesting to move to the next line and
# inspect the value of +foo+ again. You can do that by pressing +n+:
#
#   (rdb:1) n # goes to next line
#   (rdb:1) p foo
#   nil
#
# You now know that the original value of +foo+ was nil, and that it
# still was nil after calling +get_foo+.
#
# Other useful commands for navigating through your code are:
#
# +c+::
#   Runs the program until it either exists or encounters another breakpoint.
#   You usually press +c+ when you are finished debugging your program and
#   want to resume its execution.
# +s+::
#   Steps into method definition. In the previous example, +s+ would take you
#   inside the method definition of +get_foo+.
# +r+::
#   Restart the program.
# +q+::
#   Quit the program.
#
# === Inspecting variables
#
# You can use the debugger to easily inspect both local and global variables.
# We've seen how to inspect local variables before:
#
#   (rdb:1) p my_arg
#   42
#
# You can also pretty print the result of variables or expressions:
#
#   (rdb:1) pp %w{a very long long array containing many words}
#   ["a",
#    "very",
#    "long",
#    ...
#   ]
#
# You can list all local variables with +v l+:
#
#   (rdb:1) v l
#     foo => "hello"
#
# Similarly, you can show all global variables with +v g+:
#
#   (rdb:1) v g
#     all global variables
#
# Finally, you can omit +p+ if you simply want to evaluate a variable or
# expression
#
#   (rdb:1) 5**2
#   25
#
# === Going beyond basics
#
# Ruby Debug provides more advanced functionalities like switching
# between threads, setting breakpoints and watch expressions, and more.
# The full list of commands is available at any time by pressing +h+.
#
# == Staying out of trouble
#
# Make sure you remove every instance of +require 'debug'+ before
# shipping your code. Failing to do so may result in your program
# hanging unpredictably.
#
# Debug is not available in safe mode.

class DEBUGGER__
  MUTEX = Mutex.new # :nodoc:

  class Context # :nodoc:
    DEBUG_LAST_CMD = []

    begin
      require 'readline'
      def readline(prompt, hist)
        Readline::readline(prompt, hist)
      end
    rescue LoadError
      def readline(prompt, hist)
        STDOUT.print prompt
        STDOUT.flush
        line = STDIN.gets
        exit unless line
        line.chomp!
        line
      end
      USE_READLINE = false
    end

    def initialize
      if Thread.current == Thread.main
        @stop_next = 1
      else
        @stop_next = 0
      end
      @last_file = nil
      @file = nil
      @line = nil
      @no_step = nil
      @frames = []
      @finish_pos = 0
      @trace = false
      @catch = "StandardError"
      @suspend_next = false
    end

    def stop_next(n=1)
      @stop_next = n
    end

    def set_suspend
      @suspend_next = true
    end

    def clear_suspend
      @suspend_next = false
    end

    def suspend_all
      DEBUGGER__.suspend
    end

    def resume_all
      DEBUGGER__.resume
    end

    def check_suspend
      while MUTEX.synchronize {
          if @suspend_next
            DEBUGGER__.waiting.push Thread.current
            @suspend_next = false
            true
          end
        }
      end
    end

    def trace?
      @trace
    end

    def set_trace(arg)
      @trace = arg
    end

    def stdout
      DEBUGGER__.stdout
    end

    def break_points
      DEBUGGER__.break_points
    end

    def display
      DEBUGGER__.display
    end

    def context(th)
      DEBUGGER__.context(th)
    end

    def set_trace_all(arg)
      DEBUGGER__.set_trace(arg)
    end

    def set_last_thread(th)
      DEBUGGER__.set_last_thread(th)
    end

    def debug_eval(str, binding)
      begin
        eval(str, binding)
      rescue StandardError, ScriptError => e
        at = eval("caller(1)", binding)
        stdout.printf "%s:%s\n", at.shift, e.to_s.sub(/\(eval\):1:(in `.*?':)?/, '')
        for i in at
          stdout.printf "\tfrom %s\n", i
        end
        throw :debug_error
      end
    end

    def debug_silent_eval(str, binding)
      begin
        eval(str, binding)
      rescue StandardError, ScriptError
        nil
      end
    end

    def var_list(ary, binding)
      ary.sort!
      for v in ary
        stdout.printf "  %s => %s\n", v, eval(v.to_s, binding).inspect
      end
    end

    def debug_variable_info(input, binding)
      case input
      when /^\s*g(?:lobal)?\s*$/
        var_list(global_variables, binding)

      when /^\s*l(?:ocal)?\s*$/
        var_list(eval("local_variables", binding), binding)

      when /^\s*i(?:nstance)?\s+/
        obj = debug_eval($', binding)
        var_list(obj.instance_variables, obj.instance_eval{binding()})

      when /^\s*c(?:onst(?:ant)?)?\s+/
        obj = debug_eval($', binding)
        unless obj.kind_of? Module
          stdout.print "Should be Class/Module: ", $', "\n"
        else
          var_list(obj.constants, obj.module_eval{binding()})
        end
      end
    end

    def debug_method_info(input, binding)
      case input
      when /^i(:?nstance)?\s+/
        obj = debug_eval($', binding)

        len = 0
        for v in obj.methods.sort
          len += v.size + 1
          if len > 70
            len = v.size + 1
            stdout.print "\n"
          end
          stdout.print v, " "
        end
        stdout.print "\n"

      else
        obj = debug_eval(input, binding)
        unless obj.kind_of? Module
          stdout.print "Should be Class/Module: ", input, "\n"
        else
          len = 0
          for v in obj.instance_methods(false).sort
            len += v.size + 1
            if len > 70
              len = v.size + 1
              stdout.print "\n"
            end
            stdout.print v, " "
          end
          stdout.print "\n"
        end
      end
    end

    def thnum
      num = DEBUGGER__.instance_eval{@thread_list[Thread.current]}
      unless num
        DEBUGGER__.make_thread_list
        num = DEBUGGER__.instance_eval{@thread_list[Thread.current]}
      end
      num
    end

    def debug_command(file, line, id, binding)
      MUTEX.lock
      unless defined?($debugger_restart) and $debugger_restart
        callcc{|c| $debugger_restart = c}
      end
      set_last_thread(Thread.current)
      frame_pos = 0
      binding_file = file
      binding_line = line
      previous_line = nil
      if ENV['EMACS']
        stdout.printf "\032\032%s:%d:\n", binding_file, binding_line
      else
        stdout.printf "%s:%d:%s", binding_file, binding_line,
          line_at(binding_file, binding_line)
      end
      @frames[0] = [binding, file, line, id]
      display_expressions(binding)
      prompt = true
      while prompt and input = readline("(rdb:%d) "%thnum(), true)
        catch(:debug_error) do
          if input == ""
            next unless DEBUG_LAST_CMD[0]
            input = DEBUG_LAST_CMD[0]
            stdout.print input, "\n"
          else
            DEBUG_LAST_CMD[0] = input
          end

          case input
          when /^\s*tr(?:ace)?(?:\s+(on|off))?(?:\s+(all))?$/
            if defined?( $2 )
              if $1 == 'on'
                set_trace_all true
              else
                set_trace_all false
              end
            elsif defined?( $1 )
              if $1 == 'on'
                set_trace true
              else
                set_trace false
              end
            end
            if trace?
              stdout.print "Trace on.\n"
            else
              stdout.print "Trace off.\n"
            end

          when /^\s*b(?:reak)?\s+(?:(.+):)?([^.:]+)$/
            pos = $2
            if $1
              klass = debug_silent_eval($1, binding)
              file = $1
            end
            if pos =~ /^\d+$/
              pname = pos
              pos = pos.to_i
            else
              pname = pos = pos.intern.id2name
            end
            break_points.push [true, 0, klass || file, pos]
            stdout.printf "Set breakpoint %d at %s:%s\n", break_points.size, klass || file, pname

          when /^\s*b(?:reak)?\s+(.+)[#.]([^.:]+)$/
            pos = $2.intern.id2name
            klass = debug_eval($1, binding)
            break_points.push [true, 0, klass, pos]
            stdout.printf "Set breakpoint %d at %s.%s\n", break_points.size, klass, pos

          when /^\s*wat(?:ch)?\s+(.+)$/
            exp = $1
            break_points.push [true, 1, exp]
            stdout.printf "Set watchpoint %d:%s\n", break_points.size, exp

          when /^\s*b(?:reak)?$/
            if break_points.find{|b| b[1] == 0}
              n = 1
              stdout.print "Breakpoints:\n"
              break_points.each do |b|
                if b[0] and b[1] == 0
                  stdout.printf "  %d %s:%s\n", n, b[2], b[3]
                end
                n += 1
              end
            end
            if break_points.find{|b| b[1] == 1}
              n = 1
              stdout.print "\n"
              stdout.print "Watchpoints:\n"
              for b in break_points
                if b[0] and b[1] == 1
                  stdout.printf "  %d %s\n", n, b[2]
                end
                n += 1
              end
            end
            if break_points.size == 0
              stdout.print "No breakpoints\n"
            else
              stdout.print "\n"
            end

          when /^\s*del(?:ete)?(?:\s+(\d+))?$/
            pos = $1
            unless pos
              input = readline("Clear all breakpoints? (y/n) ", false)
              if input == "y"
                for b in break_points
                  b[0] = false
                end
              end
            else
              pos = pos.to_i
              if break_points[pos-1]
                break_points[pos-1][0] = false
              else
                stdout.printf "Breakpoint %d is not defined\n", pos
              end
            end

          when /^\s*disp(?:lay)?\s+(.+)$/
            exp = $1
            display.push [true, exp]
            stdout.printf "%d: ", display.size
            display_expression(exp, binding)

          when /^\s*disp(?:lay)?$/
            display_expressions(binding)

          when /^\s*undisp(?:lay)?(?:\s+(\d+))?$/
            pos = $1
            unless pos
              input = readline("Clear all expressions? (y/n) ", false)
              if input == "y"
                for d in display
                  d[0] = false
                end
              end
            else
              pos = pos.to_i
              if display[pos-1]
                display[pos-1][0] = false
              else
                stdout.printf "Display expression %d is not defined\n", pos
              end
            end

          when /^\s*c(?:ont)?$/
            prompt = false

          when /^\s*s(?:tep)?(?:\s+(\d+))?$/
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            @stop_next = lev
            prompt = false

          when /^\s*n(?:ext)?(?:\s+(\d+))?$/
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            @stop_next = lev
            @no_step = @frames.size - frame_pos
            prompt = false

          when /^\s*w(?:here)?$/, /^\s*f(?:rame)?$/
            display_frames(frame_pos)

          when /^\s*l(?:ist)?(?:\s+(.+))?$/
            if not $1
              b = previous_line ? previous_line + 10 : binding_line - 5
              e = b + 9
            elsif $1 == '-'
              b = previous_line ? previous_line - 10 : binding_line - 5
              e = b + 9
            else
              b, e = $1.split(/[-,]/)
              if e
                b = b.to_i
                e = e.to_i
              else
                b = b.to_i - 5
                e = b + 9
              end
            end
            previous_line = b
            display_list(b, e, binding_file, binding_line)

          when /^\s*up(?:\s+(\d+))?$/
            previous_line = nil
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            frame_pos += lev
            if frame_pos >= @frames.size
              frame_pos = @frames.size - 1
              stdout.print "At toplevel\n"
            end
            binding, binding_file, binding_line = @frames[frame_pos]
            stdout.print format_frame(frame_pos)

          when /^\s*down(?:\s+(\d+))?$/
            previous_line = nil
            if $1
              lev = $1.to_i
            else
              lev = 1
            end
            frame_pos -= lev
            if frame_pos < 0
              frame_pos = 0
              stdout.print "At stack bottom\n"
            end
            binding, binding_file, binding_line = @frames[frame_pos]
            stdout.print format_frame(frame_pos)

          when /^\s*fin(?:ish)?$/
            if frame_pos == @frames.size
              stdout.print "\"finish\" not meaningful in the outermost frame.\n"
            else
              @finish_pos = @frames.size - frame_pos
              frame_pos = 0
              prompt = false
            end

          when /^\s*cat(?:ch)?(?:\s+(.+))?$/
            if $1
              excn = $1
              if excn == 'off'
                @catch = nil
                stdout.print "Clear catchpoint.\n"
              else
                @catch = excn
                stdout.printf "Set catchpoint %s.\n", @catch
              end
            else
              if @catch
                stdout.printf "Catchpoint %s.\n", @catch
              else
                stdout.print "No catchpoint.\n"
              end
            end

          when /^\s*q(?:uit)?$/
            input = readline("Really quit? (y/n) ", false)
            if input == "y"
              exit!  # exit -> exit!: No graceful way to stop threads...
            end

          when /^\s*v(?:ar)?\s+/
            debug_variable_info($', binding)

          when /^\s*m(?:ethod)?\s+/
            debug_method_info($', binding)

          when /^\s*th(?:read)?\s+/
            if DEBUGGER__.debug_thread_info($', binding) == :cont
              prompt = false
            end

          when /^\s*pp\s+/
            PP.pp(debug_eval($', binding), stdout)

          when /^\s*p\s+/
            stdout.printf "%s\n", debug_eval($', binding).inspect

          when /^\s*r(?:estart)?$/
            $debugger_restart.call

          when /^\s*h(?:elp)?$/
            debug_print_help()

          else
            v = debug_eval(input, binding)
            stdout.printf "%s\n", v.inspect
          end
        end
      end
      MUTEX.unlock
      resume_all
    end

    def debug_print_help
      stdout.print <<EOHELP
Debugger help v.-0.002b
Commands
  b[reak] [file:|class:]<line|method>
  b[reak] [class.]<line|method>
                             set breakpoint to some position
  wat[ch] <expression>       set watchpoint to some expression
  cat[ch] (<exception>|off)  set catchpoint to an exception
  b[reak]                    list breakpoints
  cat[ch]                    show catchpoint
  del[ete][ nnn]             delete some or all breakpoints
  disp[lay] <expression>     add expression into display expression list
  undisp[lay][ nnn]          delete one particular or all display expressions
  c[ont]                     run until program ends or hit breakpoint
  s[tep][ nnn]               step (into methods) one line or till line nnn
  n[ext][ nnn]               go over one line or till line nnn
  w[here]                    display frames
  f[rame]                    alias for where
  l[ist][ (-|nn-mm)]         list program, - lists backwards
                             nn-mm lists given lines
  up[ nn]                    move to higher frame
  down[ nn]                  move to lower frame
  fin[ish]                   return to outer frame
  tr[ace] (on|off)           set trace mode of current thread
  tr[ace] (on|off) all       set trace mode of all threads
  q[uit]                     exit from debugger
  v[ar] g[lobal]             show global variables
  v[ar] l[ocal]              show local variables
  v[ar] i[nstance] <object>  show instance variables of object
  v[ar] c[onst] <object>     show constants of object
  m[ethod] i[nstance] <obj>  show methods of object
  m[ethod] <class|module>    show instance methods of class or module
  th[read] l[ist]            list all threads
  th[read] c[ur[rent]]       show current thread
  th[read] [sw[itch]] <nnn>  switch thread context to nnn
  th[read] stop <nnn>        stop thread nnn
  th[read] resume <nnn>      resume thread nnn
  pp expression              evaluate expression and pretty_print its value
  p expression               evaluate expression and print its value
  r[estart]                  restart program
  h[elp]                     print this help
  <everything else>          evaluate
EOHELP
    end

    def display_expressions(binding)
      n = 1
      for d in display
        if d[0]
          stdout.printf "%d: ", n
          display_expression(d[1], binding)
        end
        n += 1
      end
    end

    def display_expression(exp, binding)
      stdout.printf "%s = %s\n", exp, debug_silent_eval(exp, binding).to_s
    end

    def frame_set_pos(file, line)
      if @frames[0]
        @frames[0][1] = file
        @frames[0][2] = line
      end
    end

    def display_frames(pos)
      0.upto(@frames.size - 1) do |n|
        if n == pos
          stdout.print "--> "
        else
          stdout.print "    "
        end
        stdout.print format_frame(n)
      end
    end

    def format_frame(pos)
      _, file, line, id = @frames[pos]
      sprintf "#%d %s:%s%s\n", pos + 1, file, line,
        (id ? ":in `#{id.id2name}'" : "")
    end

    def script_lines(file, line)
      unless (lines = SCRIPT_LINES__[file]) and lines != true
        Tracer::Single.get_line(file, line) if File.exist?(file)
        lines = SCRIPT_LINES__[file]
        lines = nil if lines == true
      end
      lines
    end

    def display_list(b, e, file, line)
      if lines = script_lines(file, line)
        stdout.printf "[%d, %d] in %s\n", b, e, file
        b.upto(e) do |n|
          if n > 0 && lines[n-1]
            if n == line
              stdout.printf "=> %d  %s\n", n, lines[n-1].chomp
            else
              stdout.printf "   %d  %s\n", n, lines[n-1].chomp
            end
          end
        end
      else
        stdout.printf "No sourcefile available for %s\n", file
      end
    end

    def line_at(file, line)
      lines = script_lines(file, line)
      if lines and line = lines[line-1]
        return line
      end
      return "\n"
    end

    def debug_funcname(id)
      if id.nil?
        "toplevel"
      else
        id.id2name
      end
    end

    def check_break_points(file, klass, pos, binding, id)
      return false if break_points.empty?
      n = 1
      for b in break_points
        if b[0]           # valid
          if b[1] == 0    # breakpoint
            if (b[2] == file and b[3] == pos) or
                (klass and b[2] == klass and b[3] == pos)
              stdout.printf "Breakpoint %d, %s at %s:%s\n", n, debug_funcname(id), file, pos
              return true
            end
          elsif b[1] == 1 # watchpoint
            if debug_silent_eval(b[2], binding)
              stdout.printf "Watchpoint %d, %s at %s:%s\n", n, debug_funcname(id), file, pos
              return true
            end
          end
        end
        n += 1
      end
      return false
    end

    def excn_handle(file, line, id, binding)
      if $!.class <= SystemExit
        set_trace_func nil
        exit
      end

      if @catch and ($!.class.ancestors.find { |e| e.to_s == @catch })
        stdout.printf "%s:%d: `%s' (%s)\n", file, line, $!, $!.class
        fs = @frames.size
        tb = caller(0)[-fs..-1]
        if tb
          for i in tb
            stdout.printf "\tfrom %s\n", i
          end
        end
        suspend_all
        debug_command(file, line, id, binding)
      end
    end

    def trace_func(event, file, line, id, binding, klass)
      Tracer.trace_func(event, file, line, id, binding, klass) if trace?
      context(Thread.current).check_suspend
      @file = file
      @line = line
      case event
      when 'line'
        frame_set_pos(file, line)
        if !@no_step or @frames.size == @no_step
          @stop_next -= 1
          @stop_next = -1 if @stop_next < 0
        elsif @frames.size < @no_step
          @stop_next = 0          # break here before leaving...
        else
          # nothing to do. skipped.
        end
        if @stop_next == 0 or check_break_points(file, nil, line, binding, id)
          @no_step = nil
          suspend_all
          debug_command(file, line, id, binding)
        end

      when 'call'
        @frames.unshift [binding, file, line, id]
        if check_break_points(file, klass, id.id2name, binding, id)
          suspend_all
          debug_command(file, line, id, binding)
        end

      when 'c-call'
        frame_set_pos(file, line)

      when 'class'
        @frames.unshift [binding, file, line, id]

      when 'return', 'end'
        if @frames.size == @finish_pos
          @stop_next = 1
          @finish_pos = 0
        end
        @frames.shift

      when 'raise'
        excn_handle(file, line, id, binding)

      end
      @last_file = file
    end
  end

  trap("INT") { DEBUGGER__.interrupt }
  @last_thread = Thread::main
  @max_thread = 1
  @thread_list = {Thread::main => 1}
  @break_points = []
  @display = []
  @waiting = []
  @stdout = STDOUT

  class << DEBUGGER__
    # Returns the IO used as stdout. Defaults to STDOUT
    def stdout
      @stdout
    end

    # Sets the IO used as stdout. Defaults to STDOUT
    def stdout=(s)
      @stdout = s
    end

    # Returns the display expression list
    #
    # See DEBUGGER__ for more usage
    def display
      @display
    end

    # Returns the list of break points where execution will be stopped.
    #
    # See DEBUGGER__ for more usage
    def break_points
      @break_points
    end

    # Returns the list of waiting threads.
    #
    # When stepping through the traces of a function, thread gets suspended, to
    # be resumed later.
    def waiting
      @waiting
    end

    def set_trace( arg )
      MUTEX.synchronize do
        make_thread_list
        for th, in @thread_list
          context(th).set_trace arg
        end
      end
      arg
    end

    def set_last_thread(th)
      @last_thread = th
    end

    def suspend
      MUTEX.synchronize do
        make_thread_list
        for th, in @thread_list
          next if th == Thread.current
          context(th).set_suspend
        end
      end
      # Schedule other threads to suspend as soon as possible.
      Thread.pass
    end

    def resume
      MUTEX.synchronize do
        make_thread_list
        @thread_list.each do |th,|
          next if th == Thread.current
          context(th).clear_suspend
        end
        waiting.each do |th|
          th.run
        end
        waiting.clear
      end
      # Schedule other threads to restart as soon as possible.
      Thread.pass
    end

    def context(thread=Thread.current)
      c = thread[:__debugger_data__]
      unless c
        thread[:__debugger_data__] = c = Context.new
      end
      c
    end

    def interrupt
      context(@last_thread).stop_next
    end

    def get_thread(num)
      th = @thread_list.key(num)
      unless th
        @stdout.print "No thread ##{num}\n"
        throw :debug_error
      end
      th
    end

    def thread_list(num)
      th = get_thread(num)
      if th == Thread.current
        @stdout.print "+"
      else
        @stdout.print " "
      end
      @stdout.printf "%d ", num
      @stdout.print th.inspect, "\t"
      file = context(th).instance_eval{@file}
      if file
        @stdout.print file,":",context(th).instance_eval{@line}
      end
      @stdout.print "\n"
    end

    def thread_list_all
      for th in @thread_list.values.sort
        thread_list(th)
      end
    end

    def make_thread_list
      hash = {}
      for th in Thread::list
        if @thread_list.key? th
          hash[th] = @thread_list[th]
        else
          @max_thread += 1
          hash[th] = @max_thread
        end
      end
      @thread_list = hash
    end

    def debug_thread_info(input, binding)
      case input
      when /^l(?:ist)?/
        make_thread_list
        thread_list_all

      when /^c(?:ur(?:rent)?)?$/
        make_thread_list
        thread_list(@thread_list[Thread.current])

      when /^(?:sw(?:itch)?\s+)?(\d+)/
        make_thread_list
        th = get_thread($1.to_i)
        if th == Thread.current
          @stdout.print "It's the current thread.\n"
        else
          thread_list(@thread_list[th])
          context(th).stop_next
          th.run
          return :cont
        end

      when /^stop\s+(\d+)/
        make_thread_list
        th = get_thread($1.to_i)
        if th == Thread.current
          @stdout.print "It's the current thread.\n"
        elsif th.stop?
          @stdout.print "Already stopped.\n"
        else
          thread_list(@thread_list[th])
          context(th).suspend
        end

      when /^resume\s+(\d+)/
        make_thread_list
        th = get_thread($1.to_i)
        if th == Thread.current
          @stdout.print "It's the current thread.\n"
        elsif !th.stop?
          @stdout.print "Already running."
        else
          thread_list(@thread_list[th])
          th.run
        end
      end
    end
  end

  stdout.printf "Debug.rb\n"
  stdout.printf "Emacs support available.\n\n"
  RubyVM::InstructionSequence.compile_option = {
    trace_instruction: true
  }
  set_trace_func proc { |event, file, line, id, binding, klass, *rest|
    DEBUGGER__.context.trace_func event, file, line, id, binding, klass
  }
end