Bootstrap support for running profiling tests with ruby_memcheck

The [`ruby_memcheck`](https://github.com/Shopify/ruby_memcheck) gem
provides a Ruby-specific user-friendly wrapper around valgrind.

In some cases, some of our tests were hanging or timing out due
to how valgrind runs code in a sequential manner. I've added a
new tag to be able to skip such tests.

I also explored using valgrind's `fair-sched` option
(see Shopify/ruby_memcheck#51) but ran
into issues with its output being incomplete, so decided to go
the skip route instead.

You can run the new job with `bundle exec rake spec:profiling:memcheck`.

Gemfile

@@ -83,6 +83,7 @@ group :check do
     gem 'steep', '~> 1.6.0', require: false
   end
   gem 'standard', require: false
+  gem 'ruby_memcheck', '>= 3' if RUBY_VERSION >= '3.4.0' && RUBY_PLATFORM != 'java'
 end
 
 group :dev do

Rakefile

@@ -6,6 +6,18 @@ require 'rspec/core/rake_task'
 require 'rake/extensiontask'
 require 'yard'
 require 'os'
+if Gem.loaded_specs.key? 'ruby_memcheck'
+  require 'ruby_memcheck'
+  require 'ruby_memcheck/rspec/rake_task'
+
+  RubyMemcheck.config(
+    # If there's an error, print the suppression for that error, to allow us to easily skip such an error if it's
+    # a false-positive / something in the VM we can't fix.
+    valgrind_generate_suppressions: true,
+    # This feature provides better quality data -- I couldn't get good output out of ruby_memcheck without it.
+    use_only_ruby_free_at_exit: true,
+  )
+end
 
 Dir.glob('tasks/*.rake').each { |r| import r }
 
@@ -314,6 +326,25 @@ namespace :spec do
       t.rspec_opts = [*args.to_a, '-t ractors'].join(' ')
     end
 
+    desc 'Run spec:profiling:main tests with memory leak checking'
+    if Gem.loaded_specs.key?('ruby_memcheck')
+      RubyMemcheck::RSpec::RakeTask.new(:memcheck) do |t, args|
+        t.pattern = 'spec/datadog/profiling/**/*_spec.rb,spec/datadog/profiling_spec.rb'
+        # Some of our specs use multi-threading + busy looping, or multiple processes, or are just really really slow.
+        # We skip running these when running under valgrind.
+        # (As a reminder, by default valgrind simulates a sequential/single-threaded execution).
+        #
+        # @ivoanjo: I previously tried https://github.com/Shopify/ruby_memcheck/issues/51 but in some cases valgrind
+        # would give incomplete output, causing a "FATAL: Premature end of data in tag valgrindoutput line 3" error in
+        # ruby_memcheck. I did not figure out why exactly.
+        t.rspec_opts = [*args.to_a, '-t ~ractors -t ~memcheck_valgrind_skip'].join(' ')
+      end
+    else
+      task :memcheck do
+        raise 'Memcheck requires the ruby_memcheck gem to be installed'
+      end
+    end
+
     # Make sure each profiling test suite has a dependency on compiled native extensions
     Rake::Task[:all].prerequisite_tasks.each { |t| t.enhance([:compile_native_extensions]) }
   end

spec/datadog/profiling/collectors/cpu_and_wall_time_worker_spec.rb

@@ -168,7 +168,7 @@
       # See native bits for more details.
       let(:options) { {**super(), skip_idle_samples_for_testing: true} }
 
-      it "triggers sampling and records the results" do
+      it "triggers sampling and records the results", :memcheck_valgrind_skip do
         start
 
         all_samples = loop_until do
@@ -182,6 +182,7 @@
       it(
         "keeps statistics on how many samples were triggered by the background thread, " \
         "as well as how many samples were requested from the VM",
+        :memcheck_valgrind_skip,
       ) do
         start
 
@@ -337,7 +338,7 @@
         background_thread.join
       end
 
-      it "is able to sample even when the main thread is sleeping" do
+      it "is able to sample even when the main thread is sleeping", :memcheck_valgrind_skip do
         background_thread
         ready_queue.pop
 
@@ -546,7 +547,7 @@
         # and we clamp it if it goes over the limit.
         # But the total amount of allocations recorded should match the number we observed, and thus we record the
         # remainder above the clamped value as a separate "Skipped Samples" step.
-        context "with a high allocation rate" do
+        context "with a high allocation rate", :memcheck_valgrind_skip do
           let(:options) { {**super(), dynamic_sampling_rate_overhead_target_percentage: 0.1} }
           let(:thread_that_allocates_as_fast_as_possible) { Thread.new { loop { BasicObject.new } } }
 

spec/datadog/profiling/native_extension_spec.rb

@@ -120,7 +120,7 @@
       it { is_expected.to be false }
     end
 
-    describe "correctness" do
+    describe "correctness", :memcheck_valgrind_skip do
       let(:ready_queue) { Queue.new }
       let(:background_thread) do
         Thread.new do

spec/datadog/profiling/validate_benchmarks_spec.rb

@@ -1,6 +1,6 @@
 require "datadog/profiling/spec_helper"
 
-RSpec.describe "Profiling benchmarks" do
+RSpec.describe "Profiling benchmarks", :memcheck_valgrind_skip do
   before { skip_if_profiling_not_supported(self) }
 
   around do |example|

suppressions/ruby-3.4.supp

@@ -0,0 +1,17 @@
+# This is a valgrind suppression configuration file.
+#
+# We use it together with the ruby_memcheck gem to find issues in the dd-trace-rb native extensions; in some cases
+# we need to ignore potential issues as they're not something we can fix (e.g. outside our code.)
+#
+# See https://valgrind.org/docs/manual/manual-core.html#manual-core.suppress for details.
+
+{
+  ruby-weak-map
+  Memcheck:Addr8
+  fun:wmap_cmp
+  fun:find_table_bin_ind
+  fun:st_general_foreach
+  fun:rb_st_foreach
+  ...
+}
+