🐛 Use monotonic time to calculate elapsed time

- See: https://blog.dnsimple.com/2018/03/elapsed-time-with-ruby-the-right-way/

Author: pboling

Gemfile

@@ -8,6 +8,9 @@ source "https://rubygems.org"
 # Uncomment this to use development version of html formatter from github
 # gem "simplecov-html", github: "simplecov-ruby/simplecov-html"
 
+# std lib gems removed from std lib
+gem "logger"
+
 gem "matrix"
 
 group :development do

Gemfile.lock

@@ -83,6 +83,7 @@ GEM
     json (2.9.1)
     json (2.9.1-java)
     language_server-protocol (3.17.0.3)
+    logger (1.6.6)
     matrix (0.4.2)
     method_source (1.1.0)
     mini_mime (1.1.5)
@@ -180,6 +181,7 @@ DEPENDENCIES
   benchmark-ips
   capybara
   cucumber
+  logger
   matrix
   minitest
   pry
@@ -192,4 +194,4 @@ DEPENDENCIES
   webrick
 
 BUNDLED WITH
-   2.7.0.dev
+   2.6.5

features/step_definitions/old_coverage_json_steps.rb

@@ -15,7 +15,7 @@
   in_current_directory do
     resultset_json = File.read(RESULTSET_JSON_PATH)
     resultset_hash = JSON.parse(resultset_json)
-    resultset_hash[COMMAND_NAME]["timestamp"] = Time.now.to_i
+    resultset_hash[COMMAND_NAME]["timestamp"] = SimpleCov::Timer.monotonic.truncate
     File.write(RESULTSET_JSON_PATH, JSON.pretty_generate(resultset_hash))
   end
 end

lib/simplecov.rb

@@ -267,7 +267,7 @@ def result_exit_status(result)
     #
     def final_result_process?
       # checking for ENV["TEST_ENV_NUMBER"] to determine if the tests are being run in parallel
-      !defined?(ParallelTests) || !ENV["TEST_ENV_NUMBER"] || ParallelTests.last_process?
+      !ENV["TEST_ENV_NUMBER"] || (defined?(ParallelTests) && ParallelTests.last_process?)
     end
 
     #
@@ -448,6 +448,7 @@ def probably_running_parallel_tests?
 require "forwardable"
 require_relative "simplecov/configuration"
 SimpleCov.extend SimpleCov::Configuration
+require_relative "simplecov/timer"
 require_relative "simplecov/coverage_statistics"
 require_relative "simplecov/exit_codes"
 require_relative "simplecov/profiles"

lib/simplecov/result.rb

@@ -51,9 +51,9 @@ def format!
       SimpleCov.formatter.new.format(self)
     end
 
-    # Defines when this result has been created. Defaults to Time.now
+    # Defines when this result has been created. Defaults to current truncated system monotonic uptime
     def created_at
-      @created_at ||= Time.now
+      @created_at ||= SimpleCov::Timer.monotonic.truncate
     end
 
     # The command name that launched this result.

lib/simplecov/result_merger.rb

@@ -87,7 +87,9 @@ def within_merge_timeout?(data)
       end
 
       def time_since_result_creation(data)
-        Time.now - Time.at(data.fetch("timestamp"))
+        timestamp = data.fetch("timestamp")
+        timer = SimpleCov::Timer.new(timestamp)
+        timer.elapsed_seconds
       end
 
       def create_result(command_names, coverage)

lib/simplecov/timer.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+# Use system uptime to calculate accurate and reliable elapsed time.
+#
+# Question:
+#   Why not just do:
+#     elapsed_time = Time.now - other_time
+# Answer:
+#   It is not accurate or reliable.
+#     https://blog.dnsimple.com/2018/03/elapsed-time-with-ruby-the-right-way/
+module SimpleCov
+  class Timer
+    attr_accessor :start_time
+
+    class << self
+      def monotonic
+        Process.clock_gettime(Process::CLOCK_MONOTONIC)
+      end
+    end
+
+    # Capture Time when instantiated
+    def initialize(start_time)
+      @start_time = start_time || self.class.monotonic
+    end
+
+    # Get Elapsed Time in Seconds
+    def elapsed_seconds
+      (self.class.monotonic - @start_time).truncate
+    end
+  end
+end

spec/result_merger_spec.rb

@@ -175,7 +175,7 @@
         data = {
           "some command name" => {
             "coverage" => content,
-            "timestamp" => Time.now.to_i
+            "timestamp" => SimpleCov::Timer.monotonic.truncate
           }
         }
         File.open(file_path, "w+") do |f|
@@ -286,7 +286,7 @@ def store_result(result, path:)
   end
 
   def outdated(result)
-    result.created_at = Time.now - 172_800
+    result.created_at = SimpleCov::Timer.monotonic.truncate - 172_800
     result
   end
 

spec/result_spec.rb

@@ -212,7 +212,7 @@
           source_fixture("sample.rb") => {"lines" => [nil, 1, 1, 1, nil, nil, 0, 0, nil, nil]}
         }
       end
-      let(:created_at) { Time.now.to_i }
+      let(:created_at) { SimpleCov::Timer.monotonic.truncate }
 
       it "can consume multiple commands" do
         input = {

spec/simplecov_spec.rb

@@ -299,7 +299,7 @@
       def create_mergeable_report(name, resultset, outdated: false)
         result = SimpleCov::Result.new(resultset)
         result.command_name = name
-        result.created_at = Time.now - 172_800 if outdated
+        result.created_at = SimpleCov::Timer.monotonic.truncate - 172_800 if outdated
         SimpleCov::ResultMerger.store_result(result)
         FileUtils.mv resultset_path, "#{resultset_path}#{name}.final"
       end