RUBY-1259 Wrappers for snapshotting VM values

In order to deal sanely across the various versions and implementations of Ruby
we support, this adds a layer that allows us to safely take snapshots of the VM
stats that we care about.

NewRelic::Agent::VM::Snapshot will have nil's for values that aren't supported
and represents the state of the VM at a given instant in time. It will be the
responsibility of the sampler to properly compare to prior snapshots and
calculate metrics based off these values.

lib/new_relic/agent/vm.rb

@@ -0,0 +1,32 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+require 'new_relic/language_support'
+require 'new_relic/agent/vm/mri_vm'
+require 'new_relic/agent/vm/jruby_vm'
+require 'new_relic/agent/vm/rubinius_vm'
+
+module NewRelic
+  module Agent
+    module VM
+      def self.snapshot
+        vm.snapshot
+      end
+
+      def self.vm
+        @vm ||= create_vm
+      end
+
+      def self.create_vm
+        if NewRelic::LanguageSupport.using_engine?('jruby')
+          JRubyVM.new
+        elsif NewRelic::LanguageSupport.using_engine?('rbx')
+          RubiniusVM.new
+        else
+          MriVM.new
+        end
+      end
+    end
+  end
+end

lib/new_relic/agent/vm/jruby_vm.rb

@@ -0,0 +1,17 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+require 'new_relic/agent/vm/vm_base'
+
+module NewRelic
+  module Agent
+    module VM
+      class JRubyVM < VMBase
+        def gather_stats(snap)
+          # TODO: Which can we gather here?
+        end
+      end
+    end
+  end
+end

lib/new_relic/agent/vm/mri_vm.rb

@@ -0,0 +1,68 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+require 'new_relic/agent/vm/vm_base'
+
+module NewRelic
+  module Agent
+    module VM
+      class MriVM < VMBase
+        def gather_stats(snap)
+          gather_gc_stats(snap)
+          gather_ruby_vm_stats(snap)
+          gather_thread_stats(snap)
+        end
+
+        def gather_gc_stats(snap)
+          if supports?(:gc_runs)
+            gc_stats = GC.stat
+            snap.gc_runs = gc_stats[:count]
+            snap.total_allocated_object = gc_stats[:total_allocated_object]
+            snap.major_gc_count = gc_stats[:major_gc_count]
+            snap.minor_gc_count = gc_stats[:minor_gc_count]
+            snap.heap_live = gc_stats[:heap_live_slot] || gc_stats[:heap_live_num]
+            snap.heap_free = gc_stats[:heap_free_slot] || gc_stats[:heap_free_num]
+          end
+        end
+
+        def gather_ruby_vm_stats(snap)
+          if supports?(:method_cache_invalidations)
+            vm_stats = RubyVM.stat
+            snap.method_cache_invalidations = vm_stats[:global_method_state]
+            snap.constant_cache_invalidations = vm_stats[:global_constant_state]
+          end
+        end
+
+        def gather_thread_stats(snap)
+          snap.thread_count = Thread.list.size
+        end
+
+        def supports?(key)
+          case key
+          when :gc_runs
+            RUBY_VERSION >= '1.9.2'
+          when :total_allocated_object
+            RUBY_VERSION >= '2.0.0'
+          when :major_gc_count
+            RUBY_VERSION >= '2.1.0'
+          when :minor_gc_count
+            RUBY_VERSION >= '2.1.0'
+          when :heap_live
+            RUBY_VERSION >= '1.9.2'
+          when :heap_free
+            RUBY_VERSION >= '1.9.2'
+          when :method_cache_invalidations
+            RUBY_VERSION >= '2.1.0'
+          when :constant_cache_invalidations
+            RUBY_VERSION >= '2.1.0'
+          when :thread_count
+            true
+          else
+            false
+          end
+        end
+      end
+    end
+  end
+end

lib/new_relic/agent/vm/rubinius_vm.rb

@@ -0,0 +1,17 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+require 'new_relic/agent/vm/vm_base'
+
+module NewRelic
+  module Agent
+    module VM
+      class RubiniusVM < VMBase
+        def gather_stats(snap)
+          # TODO: Which can we gather here?
+        end
+      end
+    end
+  end
+end

lib/new_relic/agent/vm/snapshot.rb

@@ -0,0 +1,16 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+module NewRelic
+  module Agent
+    module VM
+      class Snapshot
+        attr_accessor :gc_runs, :major_gc_count, :minor_gc_count,
+                      :total_allocated_object, :heap_live, :heap_free,
+                      :method_cache_invalidations, :constant_cache_invalidations,
+                      :thread_count
+      end
+    end
+  end
+end

lib/new_relic/agent/vm/vm_base.rb

@@ -0,0 +1,27 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+require 'new_relic/agent/vm/snapshot'
+
+module NewRelic
+  module Agent
+    module VM
+      class VMBase
+        def snapshot
+          snap = Snapshot.new
+          gather_stats(snap)
+          snap
+        end
+
+        def gather_stats(snap)
+          raise NotImplementedError("VM subclasses expected to implement gather_stats")
+        end
+
+        def supports?(key)
+          false
+        end
+      end
+    end
+  end
+end

test/new_relic/agent/vm/snapshot_test.rb

@@ -0,0 +1,11 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+require 'new_relic/agent/vm/snapshot'
+
+class NewRelic::Agent::VM::SnapshotTestCase < MiniTest::Unit::TestCase
+  def test_fail
+    #assert false
+  end
+end

test/new_relic/agent/vm_test.rb

@@ -0,0 +1,48 @@
+# encoding: utf-8
+# This file is distributed under New Relic's license terms.
+# See https://github.com/newrelic/rpm/blob/master/LICENSE for complete details.
+
+require File.expand_path(File.join(File.dirname(__FILE__),'..','..','test_helper'))
+require 'new_relic/agent/vm'
+
+class NewRelic::Agent::VMTestCase < MiniTest::Unit::TestCase
+  attr_reader :vm, :snapshot
+
+  def setup
+    @vm = NewRelic::Agent::VM.vm
+    @snapshot = NewRelic::Agent::VM.snapshot
+  end
+
+  def test_gets_snapshot
+    refute_nil snapshot
+  end
+
+  EXPECTED_SNAPSHOT_VALUES = [
+    :gc_runs,
+    :total_allocated_object,
+    :major_gc_count,
+    :minor_gc_count,
+    :heap_live,
+    :heap_free,
+    :method_cache_invalidations,
+    :constant_cache_invalidations,
+    :thread_count
+  ]
+
+  EXPECTED_SNAPSHOT_VALUES.each do |val|
+    define_method("test_snapshot_has_#{val}") do
+      assert_correct_value_for(val)
+    end
+  end
+
+  # A VM snapshot will either support a value and have something non-nil,
+  # or it will not support it in which case the method exists but must be nil!
+  def assert_correct_value_for(meth)
+    if vm.supports?(meth)
+      refute_nil snapshot.send(meth)
+    else
+      assert_nil snapshot.send(meth)
+    end
+  end
+end
+