From ace77411ec9351384f5c7311a8c04784e8573706 Mon Sep 17 00:00:00 2001
From: Kye Wei <kye.wei@shopify.com>
Date: Thu, 12 Nov 2015 19:28:43 +0000
Subject: [PATCH 1/6] Proposed SysV structures and Mixin functionality

---
 lib/semian.rb                       |  7 +++-
 lib/semian/circuit_breaker.rb       | 12 ++++--
 lib/semian/simple_integer.rb        |  2 +-
 lib/semian/simple_sliding_window.rb |  4 +-
 lib/semian/simple_state.rb          |  2 +-
 lib/semian/sysv_integer.rb          | 12 ++++++
 lib/semian/sysv_shared_memory.rb    | 60 +++++++++++++++++++++++++++++
 lib/semian/sysv_sliding_window.rb   | 12 ++++++
 lib/semian/sysv_state.rb            | 59 ++++++++++++++++++++++++++++
 test/simple_state_test.rb           |  2 +-
 10 files changed, 163 insertions(+), 9 deletions(-)
 create mode 100644 lib/semian/sysv_integer.rb
 create mode 100644 lib/semian/sysv_shared_memory.rb
 create mode 100644 lib/semian/sysv_sliding_window.rb
 create mode 100644 lib/semian/sysv_state.rb

diff --git a/lib/semian.rb b/lib/semian.rb
index 9d4076e0..aa5efde3 100644
--- a/lib/semian.rb
+++ b/lib/semian.rb
@@ -124,7 +124,8 @@ def register(name, tickets:, permissions: 0660, timeout: 0, error_threshold:, er
       error_threshold: error_threshold,
       error_timeout: error_timeout,
       exceptions: Array(exceptions) + [::Semian::BaseError],
-      implementation: ::Semian::Simple,
+      permissions: permissions,
+      implementation: ::Semian::SysV,
     )
     resource = Resource.new(name, tickets: tickets, permissions: permissions, timeout: timeout)
     resources[name] = ProtectedResource.new(resource, circuit_breaker)
@@ -159,6 +160,10 @@ def resources
 require 'semian/simple_sliding_window'
 require 'semian/simple_integer'
 require 'semian/simple_state'
+require 'semian/sysv_shared_memory'
+require 'semian/sysv_sliding_window'
+require 'semian/sysv_integer'
+require 'semian/sysv_state'
 if Semian.semaphores_enabled?
   require 'semian/semian'
 else
diff --git a/lib/semian/circuit_breaker.rb b/lib/semian/circuit_breaker.rb
index f732ceb7..dfd89a19 100644
--- a/lib/semian/circuit_breaker.rb
+++ b/lib/semian/circuit_breaker.rb
@@ -2,16 +2,20 @@ module Semian
   class CircuitBreaker #:nodoc:
     extend Forwardable
 
-    def initialize(name, exceptions:, success_threshold:, error_threshold:, error_timeout:, implementation:)
+    def initialize(name, exceptions:, success_threshold:, error_threshold:, error_timeout:, permissions:, implementation:)
       @name = name.to_sym
       @success_count_threshold = success_threshold
       @error_count_threshold = error_threshold
       @error_timeout = error_timeout
       @exceptions = exceptions
 
-      @errors = implementation::SlidingWindow.new(max_size: @error_count_threshold)
-      @successes = implementation::Integer.new
-      @state = implementation::State.new
+      @errors = implementation::SlidingWindow.new(max_size: @error_count_threshold,
+                                                  name: "#{name}_sysv_sliding_window",
+                                                  permissions: permissions)
+      @successes = implementation::Integer.new(name: "#{name}_sysv_integer",
+                                               permissions: permissions)
+      @state = implementation::State.new(name: "#{name}_sysv_state",
+                                         permissions: permissions)
     end
 
     def acquire
diff --git a/lib/semian/simple_integer.rb b/lib/semian/simple_integer.rb
index aff73220..d2814aec 100644
--- a/lib/semian/simple_integer.rb
+++ b/lib/semian/simple_integer.rb
@@ -3,7 +3,7 @@ module Simple
     class Integer #:nodoc:
       attr_accessor :value
 
-      def initialize
+      def initialize(**_)
         reset
       end
 
diff --git a/lib/semian/simple_sliding_window.rb b/lib/semian/simple_sliding_window.rb
index 2507bfb8..e3de9978 100644
--- a/lib/semian/simple_sliding_window.rb
+++ b/lib/semian/simple_sliding_window.rb
@@ -1,3 +1,5 @@
+require 'forwardable'
+
 module Semian
   module Simple
     class SlidingWindow #:nodoc:
@@ -10,7 +12,7 @@ class SlidingWindow #:nodoc:
       # like this: if @max_size = 4, current time is 10, @window =[5,7,9,10].
       # Another push of (11) at 11 sec would make @window [7,9,10,11], shifting off 5.
 
-      def initialize(max_size:)
+      def initialize(max_size:, **_)
         @max_size = max_size
         @window = []
       end
diff --git a/lib/semian/simple_state.rb b/lib/semian/simple_state.rb
index d97f4960..e8880d48 100644
--- a/lib/semian/simple_state.rb
+++ b/lib/semian/simple_state.rb
@@ -1,7 +1,7 @@
 module Semian
   module Simple
     class State #:nodoc:
-      def initialize
+      def initialize(**_)
         reset
       end
 
diff --git a/lib/semian/sysv_integer.rb b/lib/semian/sysv_integer.rb
new file mode 100644
index 00000000..72554cc7
--- /dev/null
+++ b/lib/semian/sysv_integer.rb
@@ -0,0 +1,12 @@
+module Semian
+  module SysV
+    class Integer < Semian::Simple::Integer #:nodoc:
+      include SysVSharedMemory
+
+      def initialize(name:, permissions:)
+        data_layout = [:int]
+        super() unless acquire_memory_object(name, data_layout, permissions)
+      end
+    end
+  end
+end
diff --git a/lib/semian/sysv_shared_memory.rb b/lib/semian/sysv_shared_memory.rb
new file mode 100644
index 00000000..07b896ae
--- /dev/null
+++ b/lib/semian/sysv_shared_memory.rb
@@ -0,0 +1,60 @@
+module Semian
+  module SysVSharedMemory #:nodoc:
+    @type_size = {}
+    def self.sizeof(type)
+      size = (@type_size[type.to_sym] ||= (respond_to?(:_sizeof) ? _sizeof(type.to_sym) : 0))
+      raise TypeError.new("#{type} is not a valid C type") if size <= 0
+      size
+    end
+
+    def semid
+      -1
+    end
+
+    def shmid
+      -1
+    end
+
+    def synchronize(&proc)
+      if respond_to?(:_synchronize) && @using_shared_memory
+        return _synchronize(&proc)
+      else
+        yield if block_given?
+      end
+    end
+
+    alias_method :transaction, :synchronize
+
+    def destroy
+      if respond_to?(:_destroy) && @using_shared_memory
+        _destroy
+      else
+        super
+      end
+    end
+
+    private
+
+    def shared?
+      @using_shared_memory
+    end
+
+    def acquire_memory_object(name, data_layout, permissions)
+      return @using_shared_memory = false unless Semian.semaphores_enabled? && respond_to?(:_acquire)
+
+      byte_size = data_layout.inject(0) { |sum, type| sum + ::Semian::SysVSharedMemory.sizeof(type) }
+      raise TypeError.new("Given data layout is 0 bytes: #{data_layout.inspect}") if byte_size <= 0
+      # Calls C layer to acquire/create a memory block, calling #bind_init_fn in the process, see below
+      _acquire(name, byte_size, permissions)
+      @using_shared_memory = true
+    end
+
+    def bind_init_fn
+      # Concrete classes must implement this in a subclass in C to bind a callback function of type
+      # void (*object_init_fn)(size_t byte_size, void *dest, void *prev_data, size_t prev_data_byte_size);
+      # to location ptr->object_init_fn, where ptr is a semian_shm_object*
+      # It is called when memory needs to be initialized or resized, possibly using previous memory
+      raise NotImplementedError
+    end
+  end
+end
diff --git a/lib/semian/sysv_sliding_window.rb b/lib/semian/sysv_sliding_window.rb
new file mode 100644
index 00000000..85089553
--- /dev/null
+++ b/lib/semian/sysv_sliding_window.rb
@@ -0,0 +1,12 @@
+module Semian
+  module SysV
+    class SlidingWindow < Semian::Simple::SlidingWindow #:nodoc:
+      include SysVSharedMemory
+
+      def initialize(max_size:, name:, permissions:)
+        data_layout = [:int, :int].concat(Array.new(max_size, :long))
+        super(max_size: max_size) unless acquire_memory_object(name, data_layout, permissions)
+      end
+    end
+  end
+end
diff --git a/lib/semian/sysv_state.rb b/lib/semian/sysv_state.rb
new file mode 100644
index 00000000..0cd267c0
--- /dev/null
+++ b/lib/semian/sysv_state.rb
@@ -0,0 +1,59 @@
+require 'forwardable'
+
+module Semian
+  module SysV
+    class State < Semian::Simple::State #:nodoc:
+      include SysVSharedMemory
+      extend Forwardable
+
+      def_delegators :@integer, :semid, :shmid, :synchronize, :transaction,
+                     :shared?, :acquire_memory_object, :bind_init_fn
+      private :shared?, :acquire_memory_object, :bind_init_fn
+
+      def initialize(name:, permissions:)
+        @integer = Semian::SysV::Integer.new(name: name, permissions: permissions)
+        initialize_lookup([:closed, :open, :half_open])
+      end
+
+      def open
+        self.value = :open
+      end
+
+      def close
+        self.value = :closed
+      end
+
+      def half_open
+        self.value = :half_open
+      end
+
+      def reset
+        close
+      end
+
+      def destroy
+        reset
+        @integer.destroy
+      end
+
+      def value
+        @num_to_sym.fetch(@integer.value) { raise ArgumentError }
+      end
+
+      private
+
+      def value=(sym)
+        @integer.value = @sym_to_num.fetch(sym) { raise ArgumentError }
+      end
+
+      def initialize_lookup(symbol_list)
+        # Assume symbol_list[0] is mapped to 0
+        # Cannot just use #object_id since #object_id for symbols is different in every run
+        # For now, implement a C-style enum type backed by integers
+
+        @sym_to_num = Hash[symbol_list.each_with_index.to_a]
+        @num_to_sym = @sym_to_num.invert
+      end
+    end
+  end
+end
diff --git a/test/simple_state_test.rb b/test/simple_state_test.rb
index 6f629744..edab7c22 100644
--- a/test/simple_state_test.rb
+++ b/test/simple_state_test.rb
@@ -1,6 +1,6 @@
 require 'test_helper'
 
-class TestSimpleEnum < MiniTest::Unit::TestCase
+class TestSimpleState < MiniTest::Unit::TestCase
   CLASS = ::Semian::Simple::State
 
   def setup

From bcb187dd598a87db6efb9cb1b855ce8d1e4a13e5 Mon Sep 17 00:00:00 2001
From: Kye Wei <kye.wei@shopify.com>
Date: Fri, 13 Nov 2015 15:52:29 +0000
Subject: [PATCH 2/6] Stub tests that test fallback not-shared functionality

---
 lib/semian/sysv_shared_memory.rb | 19 +++++++++++++++--
 test/sysv_integer_test.rb        | 16 +++++++++++++++
 test/sysv_sliding_window_test.rb | 22 ++++++++++++++++++++
 test/sysv_state_test.rb          | 35 ++++++++++++++++++++++++++++++++
 4 files changed, 90 insertions(+), 2 deletions(-)
 create mode 100644 test/sysv_integer_test.rb
 create mode 100644 test/sysv_sliding_window_test.rb
 create mode 100644 test/sysv_state_test.rb

diff --git a/lib/semian/sysv_shared_memory.rb b/lib/semian/sysv_shared_memory.rb
index 07b896ae..d879a710 100644
--- a/lib/semian/sysv_shared_memory.rb
+++ b/lib/semian/sysv_shared_memory.rb
@@ -7,6 +7,21 @@ def self.sizeof(type)
       size
     end
 
+    def self.included(base)
+      def base.do_with_sync(*names)
+        names.each do |name|
+          new_name = "#{name}_inner".freeze.to_sym
+          alias_method new_name, name
+          private new_name
+          define_method(name) do |*args, &block|
+            synchronize do
+              method(new_name).call(*args, &block)
+            end
+          end
+        end
+      end
+    end
+
     def semid
       -1
     end
@@ -15,9 +30,9 @@ def shmid
       -1
     end
 
-    def synchronize(&proc)
+    def synchronize(&block)
       if respond_to?(:_synchronize) && @using_shared_memory
-        return _synchronize(&proc)
+        return _synchronize(&block)
       else
         yield if block_given?
       end
diff --git a/test/sysv_integer_test.rb b/test/sysv_integer_test.rb
new file mode 100644
index 00000000..8e1f72f5
--- /dev/null
+++ b/test/sysv_integer_test.rb
@@ -0,0 +1,16 @@
+require 'test_helper'
+
+class TestSysVInteger < MiniTest::Unit::TestCase
+  CLASS = ::Semian::SysV::Integer
+
+  def setup
+    @integer = CLASS.new(name: 'TestSysVInteger', permissions: 0660)
+    @integer.reset
+  end
+
+  def teardown
+    @integer.destroy
+  end
+
+  include TestSimpleInteger::IntegerTestCases
+end
diff --git a/test/sysv_sliding_window_test.rb b/test/sysv_sliding_window_test.rb
new file mode 100644
index 00000000..4543f5f5
--- /dev/null
+++ b/test/sysv_sliding_window_test.rb
@@ -0,0 +1,22 @@
+require 'test_helper'
+
+class TestSysVSlidingWindow < MiniTest::Unit::TestCase
+  CLASS = ::Semian::SysV::SlidingWindow
+
+  def setup
+    @sliding_window = CLASS.new(max_size: 6,
+                                name: 'TestSysVSlidingWindow',
+                                permissions: 0660)
+    @sliding_window.clear
+  end
+
+  def teardown
+    @sliding_window.destroy
+  end
+
+  include TestSimpleSlidingWindow::SlidingWindowTestCases
+
+  private
+
+  include TestSimpleSlidingWindow::SlidingWindowUtilityMethods
+end
diff --git a/test/sysv_state_test.rb b/test/sysv_state_test.rb
new file mode 100644
index 00000000..a8d7cad9
--- /dev/null
+++ b/test/sysv_state_test.rb
@@ -0,0 +1,35 @@
+require 'test_helper'
+
+class TestSysVState < MiniTest::Unit::TestCase
+  CLASS = ::Semian::SysV::State
+
+  def setup
+    @state = CLASS.new(name: 'TestSysVState',
+                       permissions: 0660)
+    @state.reset
+  end
+
+  def teardown
+    @state.destroy
+  end
+
+  include TestSimpleState::StateTestCases
+
+  def test_will_throw_error_when_invalid_symbol_given
+    # May occur if underlying integer gets into bad state
+    integer = @state.instance_eval "@integer"
+    integer.value = 100
+    assert_raises ArgumentError do
+      @state.value
+    end
+    assert_raises ArgumentError do
+      @state.open?
+    end
+    assert_raises ArgumentError do
+      @state.half_open?
+    end
+    assert_raises ArgumentError do
+      @state.closed?
+    end
+  end
+end

From 144e8eaa70677b0582b053544a28e6297152cdde Mon Sep 17 00:00:00 2001
From: Kye Wei <kye.wei@shopify.com>
Date: Mon, 16 Nov 2015 20:00:14 +0000
Subject: [PATCH 3/6] Naming and nit-pick

---
 lib/semian/simple_integer.rb        |  2 +-
 lib/semian/simple_sliding_window.rb |  2 +-
 lib/semian/simple_state.rb          |  2 +-
 lib/semian/sysv_shared_memory.rb    |  8 ++++----
 lib/semian/sysv_sliding_window.rb   |  2 +-
 lib/semian/sysv_state.rb            | 10 +++++-----
 6 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/lib/semian/simple_integer.rb b/lib/semian/simple_integer.rb
index d2814aec..cb4403e9 100644
--- a/lib/semian/simple_integer.rb
+++ b/lib/semian/simple_integer.rb
@@ -3,7 +3,7 @@ module Simple
     class Integer #:nodoc:
       attr_accessor :value
 
-      def initialize(**_)
+      def initialize(**)
         reset
       end
 
diff --git a/lib/semian/simple_sliding_window.rb b/lib/semian/simple_sliding_window.rb
index e3de9978..bfd57e54 100644
--- a/lib/semian/simple_sliding_window.rb
+++ b/lib/semian/simple_sliding_window.rb
@@ -12,7 +12,7 @@ class SlidingWindow #:nodoc:
       # like this: if @max_size = 4, current time is 10, @window =[5,7,9,10].
       # Another push of (11) at 11 sec would make @window [7,9,10,11], shifting off 5.
 
-      def initialize(max_size:, **_)
+      def initialize(max_size:, **)
         @max_size = max_size
         @window = []
       end
diff --git a/lib/semian/simple_state.rb b/lib/semian/simple_state.rb
index e8880d48..cefea9dd 100644
--- a/lib/semian/simple_state.rb
+++ b/lib/semian/simple_state.rb
@@ -1,7 +1,7 @@
 module Semian
   module Simple
     class State #:nodoc:
-      def initialize(**_)
+      def initialize(**)
         reset
       end
 
diff --git a/lib/semian/sysv_shared_memory.rb b/lib/semian/sysv_shared_memory.rb
index d879a710..8679af91 100644
--- a/lib/semian/sysv_shared_memory.rb
+++ b/lib/semian/sysv_shared_memory.rb
@@ -59,15 +59,15 @@ def acquire_memory_object(name, data_layout, permissions)
 
       byte_size = data_layout.inject(0) { |sum, type| sum + ::Semian::SysVSharedMemory.sizeof(type) }
       raise TypeError.new("Given data layout is 0 bytes: #{data_layout.inspect}") if byte_size <= 0
-      # Calls C layer to acquire/create a memory block, calling #bind_init_fn in the process, see below
+      # Calls C layer to acquire/create a memory block, calling #bind_initialize_memory_callback in the process, see below
       _acquire(name, byte_size, permissions)
       @using_shared_memory = true
     end
 
-    def bind_init_fn
+    def bind_initialize_memory_callback
       # Concrete classes must implement this in a subclass in C to bind a callback function of type
-      # void (*object_init_fn)(size_t byte_size, void *dest, void *prev_data, size_t prev_data_byte_size);
-      # to location ptr->object_init_fn, where ptr is a semian_shm_object*
+      # void (*initialize_memory)(size_t byte_size, void *dest, void *prev_data, size_t prev_data_byte_size);
+      # to location ptr->initialize_memory, where ptr is a semian_shm_object*
       # It is called when memory needs to be initialized or resized, possibly using previous memory
       raise NotImplementedError
     end
diff --git a/lib/semian/sysv_sliding_window.rb b/lib/semian/sysv_sliding_window.rb
index 85089553..4c54c022 100644
--- a/lib/semian/sysv_sliding_window.rb
+++ b/lib/semian/sysv_sliding_window.rb
@@ -4,7 +4,7 @@ class SlidingWindow < Semian::Simple::SlidingWindow #:nodoc:
       include SysVSharedMemory
 
       def initialize(max_size:, name:, permissions:)
-        data_layout = [:int, :int].concat(Array.new(max_size, :long))
+        data_layout = [:int, :int] + [:long] * max_size
         super(max_size: max_size) unless acquire_memory_object(name, data_layout, permissions)
       end
     end
diff --git a/lib/semian/sysv_state.rb b/lib/semian/sysv_state.rb
index 0cd267c0..8d228a3c 100644
--- a/lib/semian/sysv_state.rb
+++ b/lib/semian/sysv_state.rb
@@ -7,12 +7,12 @@ class State < Semian::Simple::State #:nodoc:
       extend Forwardable
 
       def_delegators :@integer, :semid, :shmid, :synchronize, :transaction,
-                     :shared?, :acquire_memory_object, :bind_init_fn
-      private :shared?, :acquire_memory_object, :bind_init_fn
+                     :shared?, :acquire_memory_object, :bind_initialize_memory_callback
+      private :shared?, :acquire_memory_object, :bind_initialize_memory_callback
 
       def initialize(name:, permissions:)
         @integer = Semian::SysV::Integer.new(name: name, permissions: permissions)
-        initialize_lookup([:closed, :open, :half_open])
+        initialize_lookup
       end
 
       def open
@@ -46,12 +46,12 @@ def value=(sym)
         @integer.value = @sym_to_num.fetch(sym) { raise ArgumentError }
       end
 
-      def initialize_lookup(symbol_list)
+      def initialize_lookup
         # Assume symbol_list[0] is mapped to 0
         # Cannot just use #object_id since #object_id for symbols is different in every run
         # For now, implement a C-style enum type backed by integers
 
-        @sym_to_num = Hash[symbol_list.each_with_index.to_a]
+        @sym_to_num = {closed: 0, open: 1, half_open: 2}
         @num_to_sym = @sym_to_num.invert
       end
     end

From 9d117e2fa662e948e7b3e6ef48cbed4bbca68668 Mon Sep 17 00:00:00 2001
From: Kye Wei <kye.wei@shopify.com>
Date: Tue, 17 Nov 2015 20:17:42 +0000
Subject: [PATCH 4/6] More nitpick

---
 lib/semian/circuit_breaker.rb |  6 +++---
 lib/semian/simple_state.rb    |  9 +++++----
 lib/semian/sysv_state.rb      | 18 +-----------------
 3 files changed, 9 insertions(+), 24 deletions(-)

diff --git a/lib/semian/circuit_breaker.rb b/lib/semian/circuit_breaker.rb
index dfd89a19..349dab98 100644
--- a/lib/semian/circuit_breaker.rb
+++ b/lib/semian/circuit_breaker.rb
@@ -10,11 +10,11 @@ def initialize(name, exceptions:, success_threshold:, error_threshold:, error_ti
       @exceptions = exceptions
 
       @errors = implementation::SlidingWindow.new(max_size: @error_count_threshold,
-                                                  name: "#{name}_sysv_sliding_window",
+                                                  name: "#{name}_sliding_window",
                                                   permissions: permissions)
-      @successes = implementation::Integer.new(name: "#{name}_sysv_integer",
+      @successes = implementation::Integer.new(name: "#{name}_integer",
                                                permissions: permissions)
-      @state = implementation::State.new(name: "#{name}_sysv_state",
+      @state = implementation::State.new(name: "#{name}_state",
                                          permissions: permissions)
     end
 
diff --git a/lib/semian/simple_state.rb b/lib/semian/simple_state.rb
index cefea9dd..eff76a98 100644
--- a/lib/semian/simple_state.rb
+++ b/lib/semian/simple_state.rb
@@ -5,7 +5,8 @@ def initialize(**)
         reset
       end
 
-      attr_reader :value
+      attr_accessor :value
+      private :value=
 
       def open?
         value == :open
@@ -20,15 +21,15 @@ def half_open?
       end
 
       def open
-        @value = :open
+        self.value = :open
       end
 
       def close
-        @value = :closed
+        self.value = :closed
       end
 
       def half_open
-        @value = :half_open
+        self.value = :half_open
       end
 
       def reset
diff --git a/lib/semian/sysv_state.rb b/lib/semian/sysv_state.rb
index 8d228a3c..c4225d1c 100644
--- a/lib/semian/sysv_state.rb
+++ b/lib/semian/sysv_state.rb
@@ -15,24 +15,8 @@ def initialize(name:, permissions:)
         initialize_lookup
       end
 
-      def open
-        self.value = :open
-      end
-
-      def close
-        self.value = :closed
-      end
-
-      def half_open
-        self.value = :half_open
-      end
-
-      def reset
-        close
-      end
-
       def destroy
-        reset
+        super
         @integer.destroy
       end
 

From 89075a2aa00d3fe6cbd87074e125171cb3304c6a Mon Sep 17 00:00:00 2001
From: Kye Wei <kye.wei@shopify.com>
Date: Fri, 20 Nov 2015 21:12:12 +0000
Subject: [PATCH 5/6] Made SysV override on boot-up

---
 lib/semian/sysv_shared_memory.rb | 39 ++++++--------------------------
 lib/semian/sysv_state.rb         | 28 +++++++----------------
 2 files changed, 15 insertions(+), 52 deletions(-)

diff --git a/lib/semian/sysv_shared_memory.rb b/lib/semian/sysv_shared_memory.rb
index 8679af91..58abe7ee 100644
--- a/lib/semian/sysv_shared_memory.rb
+++ b/lib/semian/sysv_shared_memory.rb
@@ -1,12 +1,5 @@
 module Semian
   module SysVSharedMemory #:nodoc:
-    @type_size = {}
-    def self.sizeof(type)
-      size = (@type_size[type.to_sym] ||= (respond_to?(:_sizeof) ? _sizeof(type.to_sym) : 0))
-      raise TypeError.new("#{type} is not a valid C type") if size <= 0
-      size
-    end
-
     def self.included(base)
       def base.do_with_sync(*names)
         names.each do |name|
@@ -30,38 +23,20 @@ def shmid
       -1
     end
 
-    def synchronize(&block)
-      if respond_to?(:_synchronize) && @using_shared_memory
-        return _synchronize(&block)
-      else
-        yield if block_given?
-      end
+    def synchronize
+      yield if block_given?
     end
 
-    alias_method :transaction, :synchronize
-
     def destroy
-      if respond_to?(:_destroy) && @using_shared_memory
-        _destroy
-      else
-        super
-      end
+      super
     end
 
     private
 
-    def shared?
-      @using_shared_memory
-    end
-
-    def acquire_memory_object(name, data_layout, permissions)
-      return @using_shared_memory = false unless Semian.semaphores_enabled? && respond_to?(:_acquire)
-
-      byte_size = data_layout.inject(0) { |sum, type| sum + ::Semian::SysVSharedMemory.sizeof(type) }
-      raise TypeError.new("Given data layout is 0 bytes: #{data_layout.inspect}") if byte_size <= 0
-      # Calls C layer to acquire/create a memory block, calling #bind_initialize_memory_callback in the process, see below
-      _acquire(name, byte_size, permissions)
-      @using_shared_memory = true
+    def acquire_memory_object(*)
+      # Concrete classes must call this method before accessing shared memory
+      # If SysV is enabled, a C method overrides this stub and returns true if acquiring succeeds
+      false
     end
 
     def bind_initialize_memory_callback
diff --git a/lib/semian/sysv_state.rb b/lib/semian/sysv_state.rb
index c4225d1c..fc338a9a 100644
--- a/lib/semian/sysv_state.rb
+++ b/lib/semian/sysv_state.rb
@@ -6,37 +6,25 @@ class State < Semian::Simple::State #:nodoc:
       include SysVSharedMemory
       extend Forwardable
 
-      def_delegators :@integer, :semid, :shmid, :synchronize, :transaction,
-                     :shared?, :acquire_memory_object, :bind_initialize_memory_callback
-      private :shared?, :acquire_memory_object, :bind_initialize_memory_callback
+      SYM_TO_NUM = {closed: 0, open: 1, half_open: 2}.freeze
+      NUM_TO_SYM = SYM_TO_NUM.invert.freeze
+
+      def_delegators :@integer, :semid, :shmid, :synchronize, :acquire_memory_object,
+                     :bind_initialize_memory_callback, :destroy
+      private :acquire_memory_object, :bind_initialize_memory_callback
 
       def initialize(name:, permissions:)
         @integer = Semian::SysV::Integer.new(name: name, permissions: permissions)
-        initialize_lookup
-      end
-
-      def destroy
-        super
-        @integer.destroy
       end
 
       def value
-        @num_to_sym.fetch(@integer.value) { raise ArgumentError }
+        NUM_TO_SYM.fetch(@integer.value) { raise ArgumentError }
       end
 
       private
 
       def value=(sym)
-        @integer.value = @sym_to_num.fetch(sym) { raise ArgumentError }
-      end
-
-      def initialize_lookup
-        # Assume symbol_list[0] is mapped to 0
-        # Cannot just use #object_id since #object_id for symbols is different in every run
-        # For now, implement a C-style enum type backed by integers
-
-        @sym_to_num = {closed: 0, open: 1, half_open: 2}
-        @num_to_sym = @sym_to_num.invert
+        @integer.value = SYM_TO_NUM.fetch(sym) { raise ArgumentError }
       end
     end
   end

From 8c6f6ddd5b515273f4b7324ff89a8fe11b01be65 Mon Sep 17 00:00:00 2001
From: Kye Wei <kye.wei@shopify.com>
Date: Mon, 23 Nov 2015 15:42:15 +0000
Subject: [PATCH 6/6] Small changes

---
 lib/semian.rb                    | 10 +++++-----
 test/sysv_integer_test.rb        |  4 ++--
 test/sysv_sliding_window_test.rb |  4 ++--
 test/sysv_state_test.rb          |  4 ++--
 4 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/lib/semian.rb b/lib/semian.rb
index aa5efde3..a8865131 100644
--- a/lib/semian.rb
+++ b/lib/semian.rb
@@ -125,7 +125,7 @@ def register(name, tickets:, permissions: 0660, timeout: 0, error_threshold:, er
       error_timeout: error_timeout,
       exceptions: Array(exceptions) + [::Semian::BaseError],
       permissions: permissions,
-      implementation: ::Semian::SysV,
+      implementation: Semian.semaphores_enabled? ? ::Semian::SysV : ::Semian::Simple,
     )
     resource = Resource.new(name, tickets: tickets, permissions: permissions, timeout: timeout)
     resources[name] = ProtectedResource.new(resource, circuit_breaker)
@@ -160,11 +160,11 @@ def resources
 require 'semian/simple_sliding_window'
 require 'semian/simple_integer'
 require 'semian/simple_state'
-require 'semian/sysv_shared_memory'
-require 'semian/sysv_sliding_window'
-require 'semian/sysv_integer'
-require 'semian/sysv_state'
 if Semian.semaphores_enabled?
+  require 'semian/sysv_shared_memory'
+  require 'semian/sysv_sliding_window'
+  require 'semian/sysv_integer'
+  require 'semian/sysv_state'
   require 'semian/semian'
 else
   Semian::MAX_TICKETS = 0
diff --git a/test/sysv_integer_test.rb b/test/sysv_integer_test.rb
index 8e1f72f5..afbdf5ea 100644
--- a/test/sysv_integer_test.rb
+++ b/test/sysv_integer_test.rb
@@ -1,10 +1,10 @@
 require 'test_helper'
 
 class TestSysVInteger < MiniTest::Unit::TestCase
-  CLASS = ::Semian::SysV::Integer
+  KLASS = ::Semian::SysV::Integer
 
   def setup
-    @integer = CLASS.new(name: 'TestSysVInteger', permissions: 0660)
+    @integer = KLASS.new(name: 'TestSysVInteger', permissions: 0660)
     @integer.reset
   end
 
diff --git a/test/sysv_sliding_window_test.rb b/test/sysv_sliding_window_test.rb
index 4543f5f5..ebedfb1f 100644
--- a/test/sysv_sliding_window_test.rb
+++ b/test/sysv_sliding_window_test.rb
@@ -1,10 +1,10 @@
 require 'test_helper'
 
 class TestSysVSlidingWindow < MiniTest::Unit::TestCase
-  CLASS = ::Semian::SysV::SlidingWindow
+  KLASS = ::Semian::SysV::SlidingWindow
 
   def setup
-    @sliding_window = CLASS.new(max_size: 6,
+    @sliding_window = KLASS.new(max_size: 6,
                                 name: 'TestSysVSlidingWindow',
                                 permissions: 0660)
     @sliding_window.clear
diff --git a/test/sysv_state_test.rb b/test/sysv_state_test.rb
index a8d7cad9..a2f8496e 100644
--- a/test/sysv_state_test.rb
+++ b/test/sysv_state_test.rb
@@ -1,10 +1,10 @@
 require 'test_helper'
 
 class TestSysVState < MiniTest::Unit::TestCase
-  CLASS = ::Semian::SysV::State
+  KLASS = ::Semian::SysV::State
 
   def setup
-    @state = CLASS.new(name: 'TestSysVState',
+    @state = KLASS.new(name: 'TestSysVState',
                        permissions: 0660)
     @state.reset
   end