(FACT-2753) Resolve facts sequentially.

acceptance/tests/options/parallel.rb

@@ -0,0 +1,11 @@
+test_name "--parallel argument does not generate any errors" do
+  tag 'risk:high'
+
+  agents.each do |agent|
+    step "--parallel should generate no errors" do
+      on(agent, facter("--parallel --debug"), :acceptable_exit_codes => 0) do |facter_output|
+        assert_match(/Resolving fact in parallel/, facter_output.stderr, "Resolving facts in parallel")
+      end
+    end
+  end
+end

facter.gemspec

@@ -33,6 +33,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'sys-filesystem', '~> 1.3'
   spec.add_development_dependency 'yard', '~> 0.9'
 
+  spec.add_runtime_dependency 'concurrent-ruby'
   spec.add_runtime_dependency 'hocon', '~> 1.3'
   spec.add_runtime_dependency 'thor', ['>= 1.0.1', '< 2.0']
 end

lib/facter.rb

@@ -104,6 +104,18 @@ def debugging(debug_bool)
       Facter::Options[:debug] = debug_bool
     end
 
+    def enable_parallel
+      Facter::Options[:parallel] = true
+    end
+
+    def disable_parallel
+      Facter::Options[:parallel] = false
+    end
+
+    def parallel?
+      Facter::Options[:parallel]
+    end
+
     # Returns a fact object by name.  If you use this, you still have to
     # call {Facter::Util::Fact#value `value`} on it to retrieve the actual
     # value.

lib/facter/framework/cli/cli.rb

@@ -108,6 +108,10 @@ class Cli < Thor
                  aliases: '-p',
                  desc: 'Load the Puppet libraries, thus allowing Facter to load Puppet-specific facts.'
 
+    class_option :parallel,
+                 type: :boolean,
+                 desc: 'Resolve facts in parallel'
+
     desc '--man', 'Manual', hide: true
     map ['--man'] => :man
     def man(*args)

lib/facter/framework/core/fact/internal/core_fact.rb

@@ -9,7 +9,7 @@ def initialize(searched_fact)
     def create
       fact_class = @searched_fact.fact_class
 
-      fact_class.new.call_the_resolver
+      fact_class&.new&.call_the_resolver
     end
   end
 end

lib/facter/framework/core/fact/internal/internal_fact_manager.rb

@@ -6,8 +6,16 @@ class InternalFactManager
 
     def resolve_facts(searched_facts)
       internal_searched_facts = filter_internal_facts(searched_facts)
-      threads = start_threads(internal_searched_facts)
-      resolved_facts = join_threads(threads, internal_searched_facts)
+
+      resolved_facts = if Options[:parallel]
+                         @@log.debug('Resolving fact in parallel')
+                         threads = start_threads(internal_searched_facts)
+                         join_threads(threads, internal_searched_facts)
+                         # thread_pool(internal_searched_facts)
+                       else
+                         @@log.debug('Resolving facts sequentially')
+                         resolve_sequentially(internal_searched_facts)
+                       end
 
       nil_resolved_facts = resolve_nil_facts(searched_facts)
 
@@ -29,20 +37,33 @@ def resolve_nil_facts(searched_facts)
       resolved_facts
     end
 
+    def resolve_sequentially(searched_facts)
+      resolved_facts = []
+
+      searched_facts
+        .uniq { |searched_fact| searched_fact.fact_class.name }
+        .each do |searched_fact|
+        begin
+          fact = CoreFact.new(searched_fact)
+          fact_value = fact.create
+          resolved_facts << fact_value unless fact_value.nil?
+        rescue StandardError => e
+          @@log.log_exception(e)
+        end
+      end
+
+      resolved_facts.flatten!
+      FactAugmenter.augment_resolved_facts(searched_facts, resolved_facts)
+    end
+
     def start_threads(searched_facts)
       threads = []
       # only resolve a fact once, even if multiple search facts depend on that fact
       searched_facts
         .uniq { |searched_fact| searched_fact.fact_class.name }
         .each do |searched_fact|
         threads << Thread.new do
-          begin
-            fact = CoreFact.new(searched_fact)
-            fact.create
-          rescue StandardError => e
-            @@log.log_exception(e)
-            nil
-          end
+          resolve_fact(searched_fact)
         end
       end
 
@@ -61,5 +82,32 @@ def join_threads(threads, searched_facts)
 
       FactAugmenter.augment_resolved_facts(searched_facts, resolved_facts)
     end
+
+    def thread_pool(searched_facts)
+      require 'concurrent'
+
+      pool = Concurrent::FixedThreadPool.new(12)
+      pr_futures = []
+
+      searched_facts
+        .uniq { |searched_fact| searched_fact.fact_class.name }
+        .each do |searched_fact|
+          pr_futures << Concurrent::Promises.future_on(pool) do
+            resolve_fact(searched_fact)
+          end
+        end
+
+      resolved_facts = Concurrent::Promises.zip(*pr_futures).value!.flatten.compact
+
+      FactAugmenter.augment_resolved_facts(searched_facts, resolved_facts)
+    end
+
+    def resolve_fact(searched_fact)
+      fact = CoreFact.new(searched_fact)
+      fact.create
+    rescue StandardError => e
+      @@log.log_exception(e)
+      nil
+    end
   end
 end

lib/facter/framework/core/options/option_store.rb

@@ -23,6 +23,7 @@ class OptionStore
     @block_list = {}
     @fact_groups = {}
     @color = false
+    @parallel = false
 
     class << self
       attr_reader :debug, :verbose, :log_level, :show_legacy, :ruby,
@@ -31,7 +32,7 @@ class << self
       attr_accessor :config, :user_query, :strict, :json, :haml, :external_facts,
                     :cache, :yaml, :puppet, :ttls, :block, :cli, :config_file_custom_dir,
                     :config_file_external_dir, :default_external_dir, :fact_groups,
-                    :block_list, :color, :trace
+                    :block_list, :color, :trace, :parallel
 
       attr_writer :external_dir
 
@@ -159,6 +160,7 @@ def reset_config
         @blocked_facts = []
         @fact_groups = {}
         @block_list = {}
+        @parallel = false
       end
 
       def fallback_external_dir

spec/framework/core/options/option_store_spec.rb

@@ -35,7 +35,8 @@
         config: nil,
         cache: true,
         color: false,
-        trace: false
+        trace: false,
+        parallel: false
       )
     end
   end