Table of Contents

Development Tools for Ruby

TruffleRuby ships with tools automatically provided by GraalVM. Run --help:tools to see a full list of options.

The following program is used for illustration:

require 'chunky_png'

a = ChunkyPNG::Image.from_file('a.png')
b = ChunkyPNG::Image.from_file('b.png')
c = a.compose(b, 0, 0)
c.save('c.png')

VisualVM

You need to use the --jvm runtime configuration and install GraalVM to use VisualVM.

VisualVM is a GUI with many tools:

  • monitoring such as CPU usage, heap size, time spent in GC, etc (tab: Monitor)
  • capturing and exploring heap dumps (tab: Monitor)
  • a list of threads and their status, and thread dumps (tab: Threads)
  • CPU and memory sampling profilers at the Java level (tab: Sampler)
  • a CPU sampling profiler at the Ruby level (tab: Polyglot Sampler)

There is more documentation about VisualVM on the GraalVM website.

Profiling

CPU Tracer

The CPU tracer records the number of times methods, blocks, or statements that are run, and prints a histogram. Enable it with --cputracer:

-----------------------------------------------------------------------------------------------------------------------------------
Tracing Histogram. Counted a total of 41663 element executions.
  Total Count: Number of times the element was executed and percentage of total executions.
  Interpreted Count: Number of times the element was interpreted and percentage of total executions of this element.
  Compiled Count: Number of times the compiled element was executed and percentage of total executions of this element.
-----------------------------------------------------------------------------------------------------------------------------------
 Name                                               |          Total Count |    Interpreted Count |       Compiled Count | Location
-----------------------------------------------------------------------------------------------------------------------------------
 ChunkyPNG::Color#a                                 |          6474  15.5% |          6474 100.0% |             0   0.0% | chunky_png/color.rb~296-298:12189-12237
 block in ChunkyPNG::Canvas::PNGDecoding#decode_png_str_scanline_paeth |          5248  12.6% |          5248 100.0% |             0   0.0% | chunky_png/canvas/png_decoding.rb~476:25098-25131
 ChunkyPNG::Color#int8_mult                         |          3619   8.7% |          3619 100.0% |             0   0.0% | chunky_png/color.rb~344-347:13821-13900
 ChunkyPNG::Canvas#width                            |          3205   7.7% |          3205 100.0% |             0   0.0% | chunky_png/canvas.rb~50:1853-1874
 block in ChunkyPNG::Canvas::PNGEncoding#encode_png_str_scanline_up |          3072   7.4% |          3072 100.0% |             0   0.0% | chunky_png/canvas/png_encoding.rb~404:20111-20145
 ChunkyPNG::Canvas#get_pixel                        |          2048   4.9% |          2048 100.0% |             0   0.0% | chunky_png/canvas.rb~184-186:7144-7203
 ChunkyPNG::Color#opaque?                           |          1872   4.5% |          1872 100.0% |             0   0.0% | chunky_png/color.rb~304-306:12410-12468
 ChunkyPNG::Color#fully_transparent?                |          1500   3.6% |          1500 100.0% |             0   0.0% | chunky_png/color.rb~327-329:13138-13207
 block in ChunkyPNG::Canvas::PNGDecoding#decode_png_str_scanline_up |          1408   3.4% |          1408 100.0% |             0   0.0% | chunky_png/canvas/png_decoding.rb~453:24009-24042
 block in ChunkyPNG::Canvas::PNGDecoding#decode_png_str_scanline_sub |          1280   3.1% |          1280 100.0% |             0   0.0% | chunky_png/canvas/png_decoding.rb~443:23517-23550
 ChunkyPNG::Color#b                                 |          1037   2.5% |          1037 100.0% |             0   0.0% | chunky_png/color.rb~288-290:11969-12024
 ChunkyPNG::Color#r                                 |          1036   2.5% |          1036 100.0% |             0   0.0% | chunky_png/color.rb~272-274:11534-11590
 ChunkyPNG::Color#g                                 |          1035   2.5% |          1035 100.0% |             0   0.0% | chunky_png/color.rb~280-282:11752-11808
 ChunkyPNG::Color#compose_quick                     |          1024   2.5% |          1024 100.0% |             0   0.0% | chunky_png/color.rb~358-368:14300-14740
 ChunkyPNG::Canvas#set_pixel                        |          1024   2.5% |          1024 100.0% |             0   0.0% | chunky_png/canvas.rb~149-151:5706-5780
 block (2 levels) in ChunkyPNG::Canvas::Operations#compose! |          1024   2.5% |          1024 100.0% |             0   0.0% | chunky_png/canvas/operations.rb~58:2331-2367
 block in ChunkyPNG::Palette#opaque?                |           848   2.0% |           848 100.0% |             0   0.0% | chunky_png/palette.rb~89:3319-3361
 SortedSet#add                                      |           848   2.0% |           848 100.0% |             0   0.0% | lib/mri/set.rb~741-745:1000-1169
 ChunkyPNG::Color#rgba                              |           518   1.2% |           518 100.0% |             0   0.0% | chunky_png/color.rb~100-102:3905-3973
 block in ChunkyPNG::Canvas::PNGDecoding#decode_png_str_scanline_average |           256   0.6% |           256 100.0% |             0   0.0% | chunky_png/canvas/png_decoding.rb~464:24513-24546
 rb_str_new                                         |           199   0.5% |           199 100.0% |             0   0.0% | src/main/c/cext/ruby.c~837:23634-23684
 is_managed_rstring_ptr                             |           193   0.5% |           193 100.0% |             0   0.0% | src/main/c/cext/ruby.c~832:23499-23538
 is_rstring_ptr                                     |           193   0.5% |           193 100.0% |             0   0.0% | src/main/c/cext/ruby.c~828:23430-23461
 strlen                                             |           190   0.5% |           190 100.0% |             0   0.0% | string.c~56:0
 rb_str_new_cstr                                    |           190   0.5% |           190 100.0% |             0   0.0% | src/main/c/cext/ruby.c~858:24268-24310
 RB_NIL_P                                           |           138   0.3% |           138 100.0% |             0   0.0% | src/main/c/cext/ruby.c~413:11068-11094

Note how the C function strlen and the C preprocessor macro RB_NIL_P show up, being called by the zlib C extension.

CPU Sampler

The CPU tracer records the cumulative time spent executing methods, blocks, or statements, and prints a histogram. Enable it with --cpusampler:

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sampling Histogram. Recorded 3895 samples with period 1ms.
  Self Time: Time spent on the top of the stack.
  Total Time: Time spent somewhere on the stack.
  Opt %: Percent of time spent in compiled and therefore non-interpreted code.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Thread: Thread[main,5,main]
 Name                                                                                |      Total Time     |  Opt % ||       Self Time     |  Opt % | Location
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 <main>                                                                              |       3635ms  93.3% |   0.0% ||       1086ms  27.9% |   0.0% | test.rb~1-6:0-140
 <top (required)>                                                                    |       1068ms  27.4% |   0.0% ||        708ms  18.2% |   0.0% | chunky_png.rb~1-179:0-5528
 block in ChunkyPNG::Canvas::PNGEncoding#encode_png_str_scanline_up                  |        643ms  16.5% |   0.0% ||        643ms  16.5% |   0.0% | chunky_png/canvas/png_encoding.rb~404:20111-20145
 __sulong_dispose_context                                                            |        260ms   6.7% |   0.0% ||        257ms   6.6% |   0.0% | sulong_dispose_context.c~33:0
 block in ChunkyPNG::Canvas::PNGDecoding#decode_png_str_scanline_paeth               |         58ms   1.5% |   0.0% ||         58ms   1.5% |   0.0% | chunky_png/canvas/png_decoding.rb~476:25098-25131
 do_checksum                                                                         |         77ms   2.0% |   0.0% ||         47ms   1.2% |   0.0% | src/main/c/zlib/zlib.c~389:12721-12796
 ChunkyPNG::Palette#initialize                                                       |         52ms   1.3% |   0.0% ||         41ms   1.1% |   0.0% | chunky_png/palette.rb~21-24:954-1074
 block in Gem::Specification.load                                                    |         39ms   1.0% |   0.0% ||         39ms   1.0% |   0.0% | bigdecimal-1.4.1.gemspec~5:126-154
 rb_define_method                                                                    |         50ms   1.3% |   0.0% ||         36ms   0.9% |   0.0% | src/main/c/cext/ruby.c~2185:61849-61941
 rb_tr_init                                                                          |         44ms   1.1% |   0.0% ||         34ms   0.9% |   0.0% | src/main/c/cext/ruby.c~93:2351-2384
 <top (required)>                                                                    |         42ms   1.1% |   0.0% ||         33ms   0.8% |   0.0% | chunky_png/canvas.rb~1-372:0-13593
 __sulong_byte_array_to_native                                                       |         30ms   0.8% |   0.0% ||         30ms   0.8% |   0.0% | crt0.c~59:0
 rb_str_new                                                                          |         33ms   0.8% |   0.0% ||         29ms   0.7% |   0.0% | src/main/c/cext/ruby.c~837:23634-23684
 __sulong_init_context                                                               |         68ms   1.7% |   0.0% ||         26ms   0.7% |   0.0% | crt0.c~80:0
 Init_zlib                                                                           |        145ms   3.7% |   0.0% ||         24ms   0.6% |   0.0% | src/main/c/zlib/zlib.c~4465:112360-112374
 rb_zlib_crc32                                                                       |        101ms   2.6% |   0.0% ||         24ms   0.6% |   0.0% | src/main/c/zlib/zlib.c~473:14760-14808
 rb_data_typed_object_wrap                                                           |         21ms   0.5% |   0.0% ||         21ms   0.5% |   0.0% | src/main/c/cext/ruby.c~2834:79544-79639
 rb_tr_load_library                                                                  |         22ms   0.6% |   0.0% ||         20ms   0.5% |   0.0% | src/main/c/cext/ruby.c~2906:81858-81897
 ChunkyPNG::Canvas::PNGEncoding#encode_png_str_scanline_up                           |        662ms  17.0% |   0.0% ||         19ms   0.5% |   0.0% | chunky_png/canvas/png_encoding.rb~403-409:20027-20347
 rb_define_class_id_under                                                            |         18ms   0.5% |   0.0% ||         18ms   0.5% |   0.0% | src/main/c/cext/ruby.c~2165:61106-61178
 ChunkyPNG::Chunk.read                                                               |        137ms   3.5% |   0.0% ||         17ms   0.4% |   0.0% | chunky_png/chunk.rb~18-26:783-1054
 Datastream                                                                          |         15ms   0.4% |   0.0% ||         15ms   0.4% |   0.0% | chunky_png/datastream.rb~11:364-381
 ChunkyPNG::Color#compose_quick                                                      |         37ms   0.9% |   0.0% ||         14ms   0.4% |   0.0% | chunky_png/color.rb~358-368:14300-14740
 rb_deflate_s_deflate                                                                |         27ms   0.7% |   0.0% ||         13ms   0.3% |   0.0% | src/main/c/zlib/zlib.c~1622:44042-44097
 ChunkyPNG::Canvas::PNGDecoding#decode_png_str_scanline_paeth                        |         71ms   1.8% |   0.0% ||         13ms   0.3% |   0.0% | chunky_png/canvas/png_decoding.rb~475-488:25010-25650
 ChunkyPNG::Palette.from_canvas                                                      |         64ms   1.6% |   0.0% ||         12ms   0.3% |   0.0% | chunky_png/palette.rb~63-68:2377-2629
 __sulong_byte_arrays_to_native                                                      |         42ms   1.1% |   0.0% ||         12ms   0.3% |   0.0% | crt0.c~69:0
 ChunkyPNG::Chunk::ImageData.combine_chunks                                          |        167ms   4.3% |   0.0% ||         12ms   0.3% |   0.0% | chunky_png/chunk.rb~247-253:9766-9980
 rb_inflate_initialize                                                               |         19ms   0.5% |   0.0% ||         12ms   0.3% |   0.0% | src/main/c/zlib/zlib.c~1887:51522-51576
 strlen                                                                              |         12ms   0.3% |   0.0% ||         12ms   0.3% |   0.0% | string.c~56:0
 zstream_run                                                                         |         76ms   2.0% |   0.0% ||         12ms   0.3% |   0.0% | src/main/c/zlib/zlib.c~1024:27867-27929

By default you see this histogram, but you can also see a call tree with --cpusampler.Output=calltree.

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sampling CallTree. Recorded 3102 samples with period 1ms.
  Self Time: Time spent on the top of the stack.
  Total Time: Time spent somewhere on the stack.
  Opt %: Percent of time spent in compiled and therefore non-interpreted code.
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Thread: Thread[main,5,main]
 Name                                                                                        |      Total Time     |  Opt % ||       Self Time     |  Opt % | Location
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  ChunkyPNG::Canvas::PNGEncoding#save                                                        |        582ms  18.8% |   0.0% ||          5ms   0.2% |   0.0% | chunky_png/canvas/png_encoding.rb~42-44:1754-1871
   block in ChunkyPNG::Canvas::PNGEncoding#save                                              |        577ms  18.6% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/canvas/png_encoding.rb~43:1797-1861
    ChunkyPNG::Canvas::PNGEncoding#write                                                     |        577ms  18.6% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/canvas/png_encoding.rb~34-36:1430-1521
     ChunkyPNG::Image#to_datastream                                                          |        571ms  18.4% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/image.rb~61-65:2314-2447
      ChunkyPNG::Canvas::PNGEncoding#to_datastream                                           |        569ms  18.3% |   0.0% ||          1ms   0.0% |   0.0% | chunky_png/canvas/png_encoding.rb~74-89:3715-4561
       ChunkyPNG::Canvas::PNGEncoding#encode_png_pixelstream                                 |        489ms  15.8% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/canvas/png_encoding.rb~153-165:7702-8570
        ChunkyPNG::Canvas::PNGEncoding#encode_png_image_without_interlacing                  |        489ms  15.8% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/canvas/png_encoding.rb~172-176:8925-9195
         ChunkyPNG::Canvas::PNGEncoding#encode_png_image_pass_to_stream                      |        489ms  15.8% |   0.0% ||          3ms   0.1% |   0.0% | chunky_png/canvas/png_encoding.rb~203-231:10502-11685
          block in ChunkyPNG::Canvas::PNGEncoding#encode_png_image_pass_to_stream            |        481ms  15.5% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/canvas/png_encoding.rb~225:11418-11456
           ChunkyPNG::Canvas::PNGEncoding#encode_png_str_scanline_up                         |        481ms  15.5% |   0.0% ||         11ms   0.4% |   0.0% | chunky_png/canvas/png_encoding.rb~403-409:20027-20347
            block in ChunkyPNG::Canvas::PNGEncoding#encode_png_str_scanline_up               |        470ms  15.2% |   0.0% ||        470ms  15.2% |   0.0% | chunky_png/canvas/png_encoding.rb~404:20111-20145
          block in ChunkyPNG::Canvas::PNGEncoding#encode_png_image_pass_to_stream            |          5ms   0.2% |   0.0% ||          1ms   0.0% |   0.0% | chunky_png/canvas/png_encoding.rb~219:11252-11284
           ChunkyPNG::Canvas::PNGEncoding#encode_png_pixels_to_scanline_truecolor_8bit       |          4ms   0.1% |   0.0% ||          4ms   0.1% |   0.0% | chunky_png/canvas/png_encoding.rb~236-238:11896-12009
       ChunkyPNG::Canvas::PNGEncoding#determine_png_encoding                                 |         60ms   1.9% |   0.0% ||          2ms   0.1% |   0.0% | chunky_png/canvas/png_encoding.rb~102-145:5085-7303
        ChunkyPNG::Canvas#palette                                                            |         51ms   1.6% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/canvas.rb~268-270:10089-10154
         ChunkyPNG::Palette.from_canvas                                                      |         51ms   1.6% |   0.0% ||          9ms   0.3% |   0.0% | chunky_png/palette.rb~63-68:2377-2629
          ChunkyPNG::Palette#initialize                                                      |         42ms   1.4% |   0.0% ||         30ms   1.0% |   0.0% | chunky_png/palette.rb~21-24:954-1074
           SortedSet#initialize                                                              |         12ms   0.4% |   0.0% ||          0ms   0.0% |   0.0% | lib/mri/set.rb~726-729:725-819
            SortedSet#merge                                                                  |         12ms   0.4% |   0.0% ||          6ms   0.2% |   0.0% | lib/mri/set.rb~770-773:1759-1847
             SortedSet#add                                                                   |          6ms   0.2% |   0.0% ||          6ms   0.2% |   0.0% | lib/mri/set.rb~741-745:1000-1169
        ChunkyPNG::Palette#best_color_settings                                               |          7ms   0.2% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/palette.rb~195-211:7150-7613
         ChunkyPNG::Palette#opaque?                                                          |          3ms   0.1% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/palette.rb~88-90:3303-3369
          SortedSet#each                                                                     |          3ms   0.1% |   0.0% ||          2ms   0.1% |   0.0% | lib/mri/set.rb~775-779:1850-2004
           block in ChunkyPNG::Palette#opaque?                                               |          1ms   0.0% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/palette.rb~89:3319-3361
            ChunkyPNG::Color#opaque?                                                         |          1ms   0.0% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/color.rb~304-306:12410-12468
             ChunkyPNG::Color#a                                                              |          1ms   0.0% |   0.0% ||          1ms   0.0% |   0.0% | chunky_png/color.rb~296-298:12189-12237
         ChunkyPNG::Palette#black_and_white?                                                 |          3ms   0.1% |   0.0% ||          1ms   0.0% |   0.0% | chunky_png/palette.rb~104-106:3841-3940
          SortedSet#each                                                                     |          2ms   0.1% |   0.0% ||          1ms   0.0% |   0.0% | lib/mri/set.rb~775-779:1850-2004
           SortedSet#to_a                                                                    |          1ms   0.0% |   0.0% ||          1ms   0.0% |   0.0% | lib/mri/set.rb~781-784:2007-2116
         ChunkyPNG::Palette#grayscale?                                                       |          1ms   0.0% |   0.0% ||          0ms   0.0% |   0.0% | chunky_png/palette.rb~96-98:3570-3642
          SortedSet#each                                                                     |          1ms   0.0% |   0.0% ||          1ms   0.0% |   0.0% | lib/mri/set.rb~775-779:1850-2004
       ChunkyPNG::Chunk::ImageData.split_in_chunks                                           |         19ms   0.6% |   0.0% ||          7ms   0.2% |   0.0% | chunky_png/chunk.rb~255-259:9983-10267
        rb_deflate_s_deflate                                                                 |         12ms   0.4% |   0.0% ||          4ms   0.1% |   0.0% | src/main/c/zlib/zlib.c~1622:44042-44097
         rb_ensure                                                                           |          5ms   0.2% |   0.0% ||          1ms   0.0% |   0.0% | src/main/c/cext/ruby.c~2107:59266-59360
          deflate_run                                                                        |          4ms   0.1% |   0.0% ||          0ms   0.0% |   0.0% | src/main/c/zlib/zlib.c~1589:43218-43240
           zstream_run                                                                       |          4ms   0.1% |   0.0% ||          0ms   0.0% |   0.0% | src/main/c/zlib/zlib.c~1024:27867-27929
            zstream_append_input                                                             |          1ms   0.0% |   0.0% ||          0ms   0.0% |   0.0% | src/main/c/zlib/zlib.c~827:23738-23804
             rb_str_buf_cat                                                                  |          1ms   0.0% |   0.0% ||          0ms   0.0% |   0.0% | src/main/c/cext/ruby.c~981:27520-27591
              rb_str_cat                                                                     |          1ms   0.0% |   0.0% ||          0ms   0.0% |   0.0% | src/main/c/cext/ruby.c~882:24901-24968
               rb_enc_str_new                                                                |          1ms   0.0% |   0.0% ||          0ms   0.0% |   0.0% | src/main/c/cext/ruby.c~1301:37035-37101

Coverage

The coverage tool reports coverage by statement, line, and root. Root means the root of a function, i.e., how many methods and blocks were covered. Enable it with --coverage:

-------------------------------------------------------------------------------------------------------------------------------------
Code coverage histogram.
  Shows what percent of each element was covered during execution
-------------------------------------------------------------------------------------------------------------------------------------
 Path                                                                                            |  Statements |    Lines |    Roots
-------------------------------------------------------------------------------------------------------------------------------------
 chunky_png-1.3.11/lib/chunky_png.rb                                                             |     100.00% |  100.00% |  100.00%
 chunky_png-1.3.11/lib/chunky_png/canvas.rb                                                      |      58.40% |   69.41% |   35.90%
 chunky_png-1.3.11/lib/chunky_png/canvas/adam7_interlacing.rb                                    |      28.57% |   50.00% |   28.57%
 chunky_png-1.3.11/lib/chunky_png/canvas/data_url_exporting.rb                                   |      80.00% |   83.33% |   80.00%
 chunky_png-1.3.11/lib/chunky_png/canvas/data_url_importing.rb                                   |      57.14% |   70.00% |   80.00%
 chunky_png-1.3.11/lib/chunky_png/canvas/drawing.rb                                              |       8.28% |   44.02% |   13.33%
 chunky_png-1.3.11/lib/chunky_png/canvas/masking.rb                                              |      28.57% |   51.72% |   44.44%
 chunky_png-1.3.11/lib/chunky_png/canvas/operations.rb                                           |      42.42% |   65.07% |   21.95%
 chunky_png-1.3.11/lib/chunky_png/canvas/png_decoding.rb                                         |      52.84% |   68.27% |   26.98%
 chunky_png-1.3.11/lib/chunky_png/canvas/png_encoding.rb                                         |      44.44% |   62.07% |   40.43%
 chunky_png-1.3.11/lib/chunky_png/canvas/resampling.rb                                           |      17.46% |   48.51% |   25.00%
 chunky_png-1.3.11/lib/chunky_png/canvas/stream_exporting.rb                                     |      61.54% |   72.22% |   44.44%
 chunky_png-1.3.11/lib/chunky_png/canvas/stream_importing.rb                                     |      31.82% |   45.83% |   40.00%
 chunky_png-1.3.11/lib/chunky_png/chunk.rb                                                       |      82.84% |   86.32% |   68.42%
 chunky_png-1.3.11/lib/chunky_png/color.rb                                                       |      41.82% |   59.00% |   33.93%
 chunky_png-1.3.11/lib/chunky_png/compatibility.rb                                               |      75.00% |   66.67% |   75.00%
 chunky_png-1.3.11/lib/chunky_png/datastream.rb                                                  |      83.56% |   87.50% |   80.00%
 chunky_png-1.3.11/lib/chunky_png/dimension.rb                                                   |      42.11% |   62.07% |   23.08%
 chunky_png-1.3.11/lib/chunky_png/image.rb                                                       |      85.00% |   90.32% |   90.00%
 chunky_png-1.3.11/lib/chunky_png/palette.rb                                                     |      41.18% |   63.46% |   42.31%
 chunky_png-1.3.11/lib/chunky_png/point.rb                                                       |      42.86% |   62.96% |   25.00%
 chunky_png-1.3.11/lib/chunky_png/vector.rb                                                      |      40.98% |   63.10% |   10.34%
 chunky_png-1.3.11/lib/chunky_png/version.rb                                                     |     100.00% |  100.00% |  100.00%
-------------------------------------------------------------------------------------------------------------------------------------

Debugging

Debugging with VSCode

This is the best-supported debugger for TruffleRuby, see this documentation.

Chrome Inspector

GraalVM lets you debug Ruby programs, and any other language supported by GraalVM, using the Chrome DevTools Protocol to attach to debuggers such as Chrome Developer Tools.

Run with --inspect, open the given URL in Chrome, drag your file system into the sources list, and then set a breakpoint and resume execution. Having the debugger attached and simple breakpoints set should not reduce performance.

Chrome Developer Tools debugger session

NetBeans

You can also debug GraalVM languages using NetBeans. Run with --jvm --vm.agentlib:jdwp=transport=dt_socket,server=y,address=8000,suspend=y and attach to the process as if you were debugging a Java program. Then click Toggle pause in GraalVM script (the pause icon with a G superimposed) and break, and you will break into the Ruby code. You will see Ruby stack frames and local variables rather than Java stack frames and local variables.

NetBeans debugger session